Pumps & valvesPumps & valves

الدهشورى محمد احمد محمد الدهشورى عمرو محمد احمد محمد عمرو

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1- Pumps1- Pumps

A pump converts mechanical energy into A pump converts mechanical energy into hydraulic energy. hydraulic energy. The mechanical energy is delivered to the pump The mechanical energy is delivered to the pump form motor (electrical motor & diesel motor)form motor (electrical motor & diesel motor)

Classifications of pumpsClassifications of pumps

The classifications of pump in two typesThe classifications of pump in two types

1.1. Nonpostivie displacement pumpNonpostivie displacement pump

This type used for low pressure , high flow rateThis type used for low pressure , high flow rate

1.1. Positive displacement pumpPositive displacement pump

This type used for high pressure , low flow rateThis type used for high pressure , low flow rate

Nonpositive displacement pump

1-centrifugal pump

2-Axial flow pump

3 -Multiple flow pump

-Centrifugal pumps

Centrifugal pumps consist of a set of rotating Centrifugal pumps consist of a set of rotating vanes, enclosed within a housing or casing, vanes, enclosed within a housing or casing, used to impart energy to a fluid through used to impart energy to a fluid through centrifugal forcecentrifugal force. . The pump has two main The pump has two main partsparts: : a rotating element which includes an a rotating element which includes an impeller and a shaft, and a stationary element impeller and a shaft, and a stationary element made up of a casing made up of a casing ((volute or solidvolute or solid)), stuffing , stuffing box , and bearingsbox , and bearings

Fig 1 illustrates a crossFig 1 illustrates a cross--section of a typical section of a typical centrifugal pumpcentrifugal pump.. Fluid enters the inlet port at the center of the Fluid enters the inlet port at the center of the rotating impeller, or the suction eyerotating impeller, or the suction eye.. As the impeller spins in a counterAs the impeller spins in a counter--clockwise clockwise direction, it thrusts the fluid outward radially , direction, it thrusts the fluid outward radially , causing centrifugal accelerationcausing centrifugal acceleration. . As it does this, it creates a vacuum in its wake, As it does this, it creates a vacuum in its wake,

drawing even more fluid into the inletdrawing even more fluid into the inlet . .

Centrifugal acceleration creates energy Centrifugal acceleration creates energy proportional to the speed of the impellerproportional to the speed of the impeller. . The The faster the impeller rotates, the faster the fluid faster the impeller rotates, the faster the fluid movement and the stronger its forcemovement and the stronger its force. . This This energy is harnessed by introducingenergy is harnessed by introducing

Remember, a pump does not create pressure; it only provides flowRemember, a pump does not create pressure; it only provides flowPressure is a measure of the amount of resistance to that flowPressure is a measure of the amount of resistance to that flow

A centrifugal pump has two main A centrifugal pump has two main components, one moving and one components, one moving and one stationarystationary. . The moving component consists of an The moving component consists of an impeller and a shaftimpeller and a shaft. . The stationary component consists of a The stationary component consists of a casing, cover, and bearingscasing, cover, and bearings. . These are These are illustrated at the left, in Fig 2illustrated at the left, in Fig 2..

Moving ComponentsMoving Components:   :   Impellers & ShaftsImpellers & Shafts

ImpellerImpeller Impellers are the rotating Impellers are the rotating blades that actually move the blades that actually move the fluidfluid. . They are connected to They are connected to the drive shaft that rotates the drive shaft that rotates within the pump casingwithin the pump casing. . The The impeller is designed to impeller is designed to impart a whirling or motion impart a whirling or motion

to the liquid in the pumpto the liquid in the pump . .

StagesStages::The number of impellers determines the number of stages of the pumpThe number of impellers determines the number of stages of the pump..

Single-Stage pumpSingle-Stage pumphas just one impeller and is better for low head servicehas just one impeller and is better for low head service

TwoTwo--Stage pumpStage pump has two impellers mounted in series for medium head servicehas two impellers mounted in series for medium head service. .

MultiMulti--Stage pumpStage pumphas three or more impellers mounted in series for high head service such has three or more impellers mounted in series for high head service such as in deep well pumpsas in deep well pumps..

Single-Stage pumpSingle-Stage pump

TwoTwo--Stage pumpStage pump

MultiMulti--Stage pumpStage pump

22 - - Positive displacementPositive displacement

A - gear pumpsA - gear pumps

B- vane pumpsB- vane pumps

C – piston pumpsC – piston pumps

A- Gear pumpsA- Gear pumps A gear pump produces flow by carrying fluid in between the teeth of two meshing A gear pump produces flow by carrying fluid in between the teeth of two meshing

gearsgears. . One gear is driven by the drive shaft and turns the idler gearOne gear is driven by the drive shaft and turns the idler gear. . The chambers The chambers formed between adjacent gear teeth are enclosed by the pump housing and side formed between adjacent gear teeth are enclosed by the pump housing and side plates plates ((also called wear or pressure platesalso called wear or pressure plates((

A partial vacuum is created at the pump inlet as the gear teeth unmeshA partial vacuum is created at the pump inlet as the gear teeth unmesh. . Fluid flows Fluid flows in to fill the space and is carried around the outside of the gearsin to fill the space and is carried around the outside of the gears. . As the teeth mesh As the teeth mesh again at the outlet end, the fluid is forced outagain at the outlet end, the fluid is forced out..

Volumetric efficiencies of gear pumps run as high as 93% under optimum Volumetric efficiencies of gear pumps run as high as 93% under optimum conditionsconditions. . Running clearances between gear faces, gear tooth crests and the Running clearances between gear faces, gear tooth crests and the housing create an almost constant loss in any pumped volume at a fixed pressurehousing create an almost constant loss in any pumped volume at a fixed pressure . . This means that volumetric efficiency at low speeds and flows is poor, so that gear This means that volumetric efficiency at low speeds and flows is poor, so that gear pumps should be run close to their maximum rated speedspumps should be run close to their maximum rated speeds..

Although the loss through the running clearances, or Although the loss through the running clearances, or ""slip,slip," " increases with pressure, increases with pressure, this loss is nearly constant as speed and output changethis loss is nearly constant as speed and output change. . For one pump the loss For one pump the loss increases by about 1.5 gpm from zero to 2,000 psi regardless of speedincreases by about 1.5 gpm from zero to 2,000 psi regardless of speed. . Change in Change in slip with pressure change has little effect on performance when operated at higher slip with pressure change has little effect on performance when operated at higher speeds and outputsspeeds and outputs. . ExternalExternal--gear pumps are comparatively immune to gear pumps are comparatively immune to contaminants in the oil, which will increase wear rates and lower efficiency, but contaminants in the oil, which will increase wear rates and lower efficiency, but sudden seizure and failure are not likelysudden seizure and failure are not likely

A- Gear pumpsA- Gear pumps

The type of gear pumpsThe type of gear pumps

11--external gear pumpexternal gear pump

22--internal gear pumpinternal gear pump

33--lobe pumplobe pump

44--screw pumpscrew pump

1- The external gear pumps1- The external gear pumps

These pumps come with a straight spur, helical, or herringbone These pumps come with a straight spur, helical, or herringbone gearsgears. . Straight spur gears are easiest to cut and are the most Straight spur gears are easiest to cut and are the most widely usedwidely used. . Helical and herringbone gears run more quietly, Helical and herringbone gears run more quietly, but cost morebut cost more. .

• the type of external gear pumpthe type of external gear pump

1-Supr gear pump .1-Supr gear pump . 2-Helical gear pump . 2-Helical gear pump . 3-Herringbone gear pump .3-Herringbone gear pump .

11--Supr gear pumpSupr gear pump

The spur gear pump consists of two meshed The spur gear pump consists of two meshed gears which revolve in a housing. The drive gears which revolve in a housing. The drive gear in the illustration is turned by a drive gear in the illustration is turned by a drive shaft which is attached to the power source. shaft which is attached to the power source. The clearances between the gear teeth as they The clearances between the gear teeth as they mesh and between the teeth and the pump mesh and between the teeth and the pump housing are very small. housing are very small.

2-Helical gear pump2-Helical gear pump. .

The helical gear pump The helical gear pump ((figfig. . 4-44-4) ) is still another is still another modification of the spur gear pump. Because of the modification of the spur gear pump. Because of the helical gear design, the overlapping of successive helical gear design, the overlapping of successive discharges from spaces between the teeth is even discharges from spaces between the teeth is even greater than it is in the herringbone gear pump; greater than it is in the herringbone gear pump; therefore, the discharge flow is smoother. Since the therefore, the discharge flow is smoother. Since the discharge flow is smooth in the helical pump, the discharge flow is smooth in the helical pump, the gears can be designed with a small number of large gears can be designed with a small number of large teeth—thus allowing increased capacity without teeth—thus allowing increased capacity without sacrificing smoothness of flow.sacrificing smoothness of flow.

33--Herringbone gear pumpHerringbone gear pump. .

Herringbone Gear Pump discharge phase. Herringbone Gear Pump discharge phase. This overlapping and the relatively larger This overlapping and the relatively larger space at the center of the gears The space at the center of the gears The herringbone gear pump is a tend to herringbone gear pump is a tend to minimize pulsations and give a steadier minimize pulsations and give a steadier modification of the spur gear pump. The modification of the spur gear pump. The liquid flow than the spur gear pump.liquid flow than the spur gear pump.

2-The internal gear pump 2-The internal gear pump

InternalInternal--gear pumps, have an internal gear and an gear pumps, have an internal gear and an external gearexternal gear. . Because these pumps have one or two Because these pumps have one or two less teeth in the inner gear than the outer, relative less teeth in the inner gear than the outer, relative speeds of the inner and outer gears in these designs speeds of the inner and outer gears in these designs are loware low. . For example, if the number of teeth in the For example, if the number of teeth in the inner and outer gears were 10 and 11 respectively, the inner and outer gears were 10 and 11 respectively, the inner gear would turn 11 revolutions, while the outer inner gear would turn 11 revolutions, while the outer would turn 10would turn 10. . This low relative speed means a low This low relative speed means a low wear ratewear rate. . These pumps are small, compact unitsThese pumps are small, compact units..

InternalInternal--gear pumps has two kindgear pumps has two kind1-Crescent1-Crescent--seal pumpsseal pumps2-Gerotor pumps2-Gerotor pumps

11--CrescentCrescent--seal pumpsseal pumps

The crescent seal internalThe crescent seal internal--gear pump consists of an inner and outer gear gear pump consists of an inner and outer gear separated by a crescentseparated by a crescent--shaped sealshaped seal. . The two gears rotate in the same The two gears rotate in the same direction, with the inner gear rotating faster than the outerdirection, with the inner gear rotating faster than the outer. . The hydraulic The hydraulic oil is drawn into the pump at the point where the gear teeth begin to separate oil is drawn into the pump at the point where the gear teeth begin to separate and is carried to the outlet in the space between the crescent and the teeth of and is carried to the outlet in the space between the crescent and the teeth of both tearsboth tears. . The contact point of the gear teeth forms a seal, as does the small The contact point of the gear teeth forms a seal, as does the small tip clearance at the crescenttip clearance at the crescent. . Although in the past this pump was generally Although in the past this pump was generally used for low outputs, with pressures below 1,000 psi , a 2-stage, 4,000-psi used for low outputs, with pressures below 1,000 psi , a 2-stage, 4,000-psi model has recently become availablemodel has recently become available..

22--Gerotor pumpsGerotor pumps The gerotor internal-gear pump consists of a pair of gears The gerotor internal-gear pump consists of a pair of gears

which are always in sliding contact. The internal gear has one which are always in sliding contact. The internal gear has one more tooth than the gerotor gear. Both gears rotate in the same more tooth than the gerotor gear. Both gears rotate in the same direction. Oil is drawn into the chamber where the teeth are direction. Oil is drawn into the chamber where the teeth are separating, and is ejected when the teeth start to mesh again. separating, and is ejected when the teeth start to mesh again. The seal is provided by the sliding contact.The seal is provided by the sliding contact.

Generally, the internal-gear pump with toothcrest pressure Generally, the internal-gear pump with toothcrest pressure sealing has higher volumetric efficiency at low speeds than the sealing has higher volumetric efficiency at low speeds than the crescent type. Volumetric and overall efficiencies of these crescent type. Volumetric and overall efficiencies of these pumps are in the same general range as those of external-gear pumps are in the same general range as those of external-gear pumps. However, their sensitivity to dirt is somewhat higher.pumps. However, their sensitivity to dirt is somewhat higher.

33--lobe pumplobe pump

The lobe pump is a rotary, externalThe lobe pump is a rotary, external--gear gear pump ,the Figurepump ,the Figure. . It differs from the It differs from the conventional externalconventional external--gear pump in the way gear pump in the way the the ""gearsgears" " are drivenare driven. . In a gear pump, one In a gear pump, one gear drive the other; in a lobe pump, both gear drive the other; in a lobe pump, both lobes are driven through suitable drives gears lobes are driven through suitable drives gears outside of the pump casing chamberoutside of the pump casing chamber..

4-screw pump4-screw pump A screw pump is an axialA screw pump is an axial--flow gear pump, similar in operation to a rotary screw flow gear pump, similar in operation to a rotary screw

compressorcompressor. . Three types of screw pumps are the singleThree types of screw pumps are the single--screw, twoscrew, two--screw, and screw, and threethree--screwscrew. . In the singleIn the single--screw pump, a spiraled rotor rotates eccentrically in an screw pump, a spiraled rotor rotates eccentrically in an internal statorinternal stator. . The twoThe two--screw pump consists of two parallel intermeshing rotors screw pump consists of two parallel intermeshing rotors rotating in a housing machined to close tolerancesrotating in a housing machined to close tolerances. . The threeThe three--screw pump consists screw pump consists of a centralof a central--drive rotor with two meshing idler rotors; the rotors turn inside of a drive rotor with two meshing idler rotors; the rotors turn inside of a housing machined to close toleranceshousing machined to close tolerances..

Flow through a screw pump is axial and in the direction of the power rotor. The Flow through a screw pump is axial and in the direction of the power rotor. The inlet hydraulic fluid that surrounds the rotors is trapped as the rotors rotate. This inlet hydraulic fluid that surrounds the rotors is trapped as the rotors rotate. This fluid is pushed uniformly with the rotation of the rotors along the axis and is forced fluid is pushed uniformly with the rotation of the rotors along the axis and is forced out the other end.out the other end.

Note that the fluid delivered by screw pumps does not rotate, but moves linearly. Note that the fluid delivered by screw pumps does not rotate, but moves linearly. The rotors work like endless pistons which continuously move forward. There are The rotors work like endless pistons which continuously move forward. There are no pulsations even at higher speed. The absence of pulsations and the fact that there no pulsations even at higher speed. The absence of pulsations and the fact that there is no metal-to-metal contact results in very quiet operation.is no metal-to-metal contact results in very quiet operation.

Larger pumps are used as low-pressure, large-volume prefill pumps on large Larger pumps are used as low-pressure, large-volume prefill pumps on large presses. Other applications include hydraulic systems on submarines and other uses presses. Other applications include hydraulic systems on submarines and other uses where noise must be controlled.where noise must be controlled.

B- vane pumpsB- vane pumps In these pumps, a number of vanes slide in slots in a rotor In these pumps, a number of vanes slide in slots in a rotor

which rotates in a housing or ring. The housing may be which rotates in a housing or ring. The housing may be eccentric with the center of the rotor, or its shape may be oval, eccentric with the center of the rotor, or its shape may be oval, Figure 5. In some designs, centrifugal force holds the vanes in Figure 5. In some designs, centrifugal force holds the vanes in contact with the housing, while the vanes are forced in and out contact with the housing, while the vanes are forced in and out of the slots by the eccentricity of the housing. In one vane of the slots by the eccentricity of the housing. In one vane pump, light springs hold the vanes against the housing; in pump, light springs hold the vanes against the housing; in another pump design, pressurized pins urge the vanes outward.another pump design, pressurized pins urge the vanes outward.

During rotation, as the space or chamber enclosed by vanes, During rotation, as the space or chamber enclosed by vanes, rotor, and housing increases, a vacuum is created, and rotor, and housing increases, a vacuum is created, and atmospheric pressure forces oil into this space, which is the atmospheric pressure forces oil into this space, which is the inlet side of the pump. As the space or volume enclosed inlet side of the pump. As the space or volume enclosed reduces, the liquid is forced out through the discharge ports.reduces, the liquid is forced out through the discharge ports.

Unbalanced Vane PumpsUnbalanced Vane Pumps. . In the unbalanced design, (Figure 3-9), a cam ring's shape is a true circle that is on a different centerline from a rotor's. Pump displacement depends on how far a rotor and ring are eccentric. The advantage of a true-circle ring is that control can be applied to vary the eccentricity and thus vary the displacement. A disadvantage is that an unbalanced pressure at the outlet is effective against a small area of the rotor's edge, imposing side loads on the shaft. Thus there is a limit on a pump's size unless very large hearings and heavy supports are used.

Balanced Vane Pumps. In the balanced design (Figure 3-10), a pump has a stationary, elliptical cam ring and two sets of internal ports. A pumping chamber is formed between any two vanes twice in each revolution. The two inlets and outlets are 180 degrees apart. Back pressures against the edges of a rotor cancel each other. Recent design improvements that allow high operating speeds and pressures have made this pump the most universal in the mobile-equipment field.

C – piston pumpsC – piston pumps

Piston units operate at higher efficiencies than Piston units operate at higher efficiencies than gear and vane units and are used for highgear and vane units and are used for high--pressure applications with hydraulic oil or fire pressure applications with hydraulic oil or fire resistant fluidsresistant fluids. . Several types of piston pump Several types of piston pump are available that use different design are available that use different design approaches and these include those having approaches and these include those having axial and radial piston arrangementsaxial and radial piston arrangements..

This general type of pump includes a number of variations some of which This general type of pump includes a number of variations some of which are described below. are described below.

1-Radial Piston Pump 1-Radial Piston Pump 2-Swashplate Piston Pump 2-Swashplate Piston Pump 3-Wobble Plate Pump 3-Wobble Plate Pump 4-Bent Axis Piston Pump 4-Bent Axis Piston Pump

General General

The pumps are extensively used for power transfer applications in the off The pumps are extensively used for power transfer applications in the off shore , power transmission , agricultural, aerospace and construction shore , power transmission , agricultural, aerospace and construction industries,.. to list just a few. All of these pumps work on a similar industries,.. to list just a few. All of these pumps work on a similar principle.principle.

The pump includes a block with a number of symetrically arranged The pump includes a block with a number of symetrically arranged cylindrical pistons around a common centre line.   The pistons are caused cylindrical pistons around a common centre line.   The pistons are caused reciprocate in and out under the action of a Separate fixed or rotating plate reciprocate in and out under the action of a Separate fixed or rotating plate (axial Pistons) or and eccentric bearing ring (radial pump) or some other (axial Pistons) or and eccentric bearing ring (radial pump) or some other mechanical feature.   Each piston is interfaced with the inlet and outlet port mechanical feature.   Each piston is interfaced with the inlet and outlet port via a special valve arrangement such that as it moves out of its cylinder it via a special valve arrangement such that as it moves out of its cylinder it draws fluid in and as it moves back it pushes the fluid out.   The pumps are draws fluid in and as it moves back it pushes the fluid out.   The pumps are engineered to allow rotational speeds from less the 1 RPM to over engineered to allow rotational speeds from less the 1 RPM to over 25,000RPM25,000RPM

1 -Radial Piston Pumps.

Radial Piston pumps include a rotating cylinder Radial Piston pumps include a rotating cylinder containing equally spaced radial pistons arranged containing equally spaced radial pistons arranged radial around the cylinder centre lineradial around the cylinder centre line..  A springs   A springs pushes the pistons against the inner surface of an pushes the pistons against the inner surface of an encircling stationay ring mounted eccentric to the encircling stationay ring mounted eccentric to the cylindercylinder..The pistons draw in fluid during half a The pistons draw in fluid during half a revolution and drive fluid out during the other halfrevolution and drive fluid out during the other half. . The greater the ring eccentricity the longer the pistons The greater the ring eccentricity the longer the pistons stroke and the more fluid they transfer stroke and the more fluid they transfer

22--Swashplate Piston PumpSwashplate Piston Pump

Swashplate pumps have a rotating cylinder containing Swashplate pumps have a rotating cylinder containing parallel pistons arranged radially around the cylinder parallel pistons arranged radially around the cylinder centre linecentre line. . A spring pushes the pistons against a A spring pushes the pistons against a stationary swash plate located at one end of the stationary swash plate located at one end of the cylinder , which sits at an angle to the cylindercylinder , which sits at an angle to the cylinder..   The    The pistons draw in fluid during half a revolution and pistons draw in fluid during half a revolution and drive fluid out during the other halfdrive fluid out during the other half. . The greater the The greater the swashplate angle relative to the cylinder centre line swashplate angle relative to the cylinder centre line the further the longer the pistons stroke and the more the further the longer the pistons stroke and the more fluid they transferfluid they transfer. .

33--Wobble Plate PumpWobble Plate Pump This pump includes a stationary piston block This pump includes a stationary piston block

containing a number parallel pistons arranged radially containing a number parallel pistons arranged radially around the block centrearound the block centre((at least fiveat least five). ). The end of each The end of each piston is forced against a rotating wobble plate by piston is forced against a rotating wobble plate by springssprings. . The wobble plate is shaped with varying The wobble plate is shaped with varying thickness around its centre line and thus as it rotates it thickness around its centre line and thus as it rotates it causes the pistons to reciprocate at a fixed strokecauses the pistons to reciprocate at a fixed stroke..      The pistons draw in fluid from the cavity during half The pistons draw in fluid from the cavity during half a revolution and drive fluid out at the rear of the a revolution and drive fluid out at the rear of the pump during the other halfpump during the other half. .    The fluid flow is    The fluid flow is controlled using noncontrolled using non--return valves for each pistonreturn valves for each piston..

These pumps can generate pressures of up to 700 bar These pumps can generate pressures of up to 700 bar

44--Bent Axis Piston PumpBent Axis Piston Pump

Bent axis piston pumps have a rotating cylinder Bent axis piston pumps have a rotating cylinder containing parallel pistons arranged radially around containing parallel pistons arranged radially around the cylinder centre linethe cylinder centre line. . The cylinder is driven by an The cylinder is driven by an shaft which is arranged at an angle to the cylinder shaft which is arranged at an angle to the cylinder axisaxis. . the shaft includes a flange with a mechanical the shaft includes a flange with a mechanical connection to each pistonconnection to each piston. . As the shaft rotates the As the shaft rotates the pistons are made to reciprocate over a stroke based on pistons are made to reciprocate over a stroke based on the relative angle of the shaft and cylinderthe relative angle of the shaft and cylinder..

IntroductionIntroduction Valves are integral components in piping systems Valves are integral components in piping systems

they are the primary method of controlling the flow, they are the primary method of controlling the flow, pressure and direction of the fluidpressure and direction of the fluid..  Valves may be   Valves may be required to operate continuously erequired to operate continuously e..gg. . control valves, control valves, or they may be operated intermittently eor they may be operated intermittently e..gg. . isolation isolation valves, or they may be installed to operate rarely if valves, or they may be installed to operate rarely if ever eever e..gg. . safety valvessafety valves..   A valve can be an extremely    A valve can be an extremely simple, low cost item or it may be and extremely simple, low cost item or it may be and extremely complicated, expensive itemcomplicated, expensive item..   In piping design the    In piping design the valves probably require more engineering effort than valves probably require more engineering effort than any other piping componentany other piping component..

Types of valvesTypes of valves

A – direction control valve A – direction control valve B –pressure control valveB –pressure control valve C –flow control valveC –flow control valve

A – direction control valveA – direction control valve DirectionalDirectional--control valves also control flow directioncontrol valves also control flow direction. . However, they vary However, they vary

considerably in physical characteristics and operationconsiderably in physical characteristics and operation. . The valves may beThe valves may be

Poppet type, in which a piston or ball moves on and off a seatPoppet type, in which a piston or ball moves on and off a seat. . Rotary-spool type, in which a spool rotates about its axis. Rotary-spool type, in which a spool rotates about its axis. Sliding-spool type, in which a spool slides axially in a bore. In this type, a spool is Sliding-spool type, in which a spool slides axially in a bore. In this type, a spool is

often classified according to the flow conditions created when it is in the normal or often classified according to the flow conditions created when it is in the normal or neutral position. A closed-center spool blocks all valve ports from each other when neutral position. A closed-center spool blocks all valve ports from each other when in the normal position. In an open-center spool, all valve ports are open to each in the normal position. In an open-center spool, all valve ports are open to each other when the spool is in the normal position. other when the spool is in the normal position.

check valvecheck valve FigFig. . 11. . Basic check valve allows fluid Basic check valve allows fluid to flow in one direction, in this case to flow in one direction, in this case from bottom to topfrom bottom to top. . Shown are ISO Shown are ISO symbol and crosssymbol and cross--sectional photo of sectional photo of springspring--loaded check valveloaded check valve. . The The spring keeps fluid from flowing spring keeps fluid from flowing unless downstream pressure acting unless downstream pressure acting on the poppet overcomes spring on the poppet overcomes spring forceforce. .

Check ValvesCheck Valves. . Check valves are the most commonly used in fluidCheck valves are the most commonly used in fluid--powered powered systemssystems. . They allow flow in one direction and prevent flow in the They allow flow in one direction and prevent flow in the other directionother direction. . They may be installed independently in a line, or They may be installed independently in a line, or they may be incorporated as an integral part of a sequence, they may be incorporated as an integral part of a sequence, counterbalance, or pressurecounterbalance, or pressure--reducing valvereducing valve. . The valve element may The valve element may be a sleeve, cone, ball, poppet, piston, spool, or discbe a sleeve, cone, ball, poppet, piston, spool, or disc. . Force of the Force of the moving fluid opens a check valve; backflow, a spring, or gravity moving fluid opens a check valve; backflow, a spring, or gravity closes the valvecloses the valve. . Figures 5-14, 5-15 and 5-16 show various types of Figures 5-14, 5-15 and 5-16 show various types of check valvescheck valves. .

pilotpilot--operated check valveoperated check valve.. This valve consists of poppet 1 secured to piston 3This valve consists of poppet 1 secured to piston 3. . Poppet 1 is held against Poppet 1 is held against seat 4 by the action of spring 2 on piston 3seat 4 by the action of spring 2 on piston 3. . In diagram A, the valve is in the In diagram A, the valve is in the freefree--flow positionflow position. . Pressure at the inlet port, acting downward against poppet Pressure at the inlet port, acting downward against poppet 1, is sufficient to overcome the combined forces of spring 2 against piston 3 1, is sufficient to overcome the combined forces of spring 2 against piston 3 and the pressure, if any, at the outlet portand the pressure, if any, at the outlet port. (. (The pressure at the outlet port is The pressure at the outlet port is exerted over a greater effective area than that at the inlet because of the poppet exerted over a greater effective area than that at the inlet because of the poppet stemstem.) .) The drain post is open to the tank, and there is no pressure at the pilot The drain post is open to the tank, and there is no pressure at the pilot portport. . Diagram B shows the valve in a position to prevent reverse flow, with no Diagram B shows the valve in a position to prevent reverse flow, with no pressure at the pilot port and the drain opening to the tankpressure at the pilot port and the drain opening to the tank. . Diagram C shows the pilot operation of the valveDiagram C shows the pilot operation of the valve. . When sufficient pressure is When sufficient pressure is applied at the pilot port to overcome the thrust of spring 2 plus the net effect applied at the pilot port to overcome the thrust of spring 2 plus the net effect of pressure at the other ports, poppet 1 is unseated to allow reverse flowof pressure at the other ports, poppet 1 is unseated to allow reverse flow. . Pilot Pilot pressure must be equal to about 80 percent of that imposed at the outlet port to pressure must be equal to about 80 percent of that imposed at the outlet port to open the valve and allow reverse flowopen the valve and allow reverse flow..

a.a. Poppet ValvePoppet Valve shows a simple poppet valveshows a simple poppet valve. . It It

consists primarily of a movable consists primarily of a movable poppet that closes against a poppet that closes against a valve seatvalve seat. . Pressure from the Pressure from the inlet tends to hold the valve inlet tends to hold the valve tightly closedtightly closed. . A slight force A slight force applied to the poppet stem opens applied to the poppet stem opens the poppetthe poppet. . The action is similar The action is similar to the valves of an automobile to the valves of an automobile engineengine. . The poppet stem usually The poppet stem usually has anhas an OO--ring seal to prevent ring seal to prevent leakageleakage. . In some valves, the In some valves, the poppets are held in the seated poppets are held in the seated position by springsposition by springs. . The number The number of poppets in a valve depends on of poppets in a valve depends on the purpose of the valvethe purpose of the valve. .

TwoTwo--Way ValveWay Valve.. A twoA two--way valve is generally used to control the direction of fluid flow in a way valve is generally used to control the direction of fluid flow in a hydraulic circuit and is a slidinghydraulic circuit and is a sliding--spool typespool type. . Figure 5-21 shows a twoFigure 5-21 shows a two--way, way, slidingsliding--spool, directionalspool, directional--control valvecontrol valve. . As the spool moves back and forth, it As the spool moves back and forth, it either allows or prevents fluid flow through the valveeither allows or prevents fluid flow through the valve. . In either shifted In either shifted position in a twoposition in a two--way valve, a pressure port is open to one cylinder port, but way valve, a pressure port is open to one cylinder port, but the opposite cylinder port is not open to a tankthe opposite cylinder port is not open to a tank. . A tank port on this valve is A tank port on this valve is used primarily for drainingused primarily for draining

FourFour--Way ValvesWay Valves FourFour--way, directionalway, directional--control valves are used to control the control valves are used to control the direction of fluid flow in a hydraulic circuit, which controls the direction of fluid flow in a hydraulic circuit, which controls the direction of movement of a work cylinder or the rotation of a fluid direction of movement of a work cylinder or the rotation of a fluid motormotor. . These valves are usually the slidingThese valves are usually the sliding--spool typespool type. . A typical A typical fourfour--way, directionalway, directional--control valve has four portscontrol valve has four ports: :

•One pressure port is connected to a pressure lineOne pressure port is connected to a pressure line. . •One return or exhaust port is connected to a reservoir. One return or exhaust port is connected to a reservoir. •Two working ports are connected, by lines, to an actuating unit.Two working ports are connected, by lines, to an actuating unit.

With a direction control valve you determine the direction of the flow and therefore the direction With a direction control valve you determine the direction of the flow and therefore the direction of operation of a hydraulic motor or cylinder. In the animation we use a so called 4/3-direction of operation of a hydraulic motor or cylinder. In the animation we use a so called 4/3-direction control valve ; the 4/3 comes from: 4 line connections and 3 positions. control valve ; the 4/3 comes from: 4 line connections and 3 positions. The housing, commonly made of cast iron, with 4 line connections contains a spool of steel. This The housing, commonly made of cast iron, with 4 line connections contains a spool of steel. This spool, which is kept in the centre of the housing by two springs, can shift in the housing. In the spool, which is kept in the centre of the housing by two springs, can shift in the housing. In the drawn position, the middle position, the P-port is closed so the pump flow has to flow to the drawn position, the middle position, the P-port is closed so the pump flow has to flow to the reservoir through the pressure relief valve. This generates a lot of heat and should be avoided if reservoir through the pressure relief valve. This generates a lot of heat and should be avoided if possible. The A- en B-ports are closed as well so in this case a cylinder will be hydraulically locked possible. The A- en B-ports are closed as well so in this case a cylinder will be hydraulically locked in its position. By shifting the spool to the left the cylinder will make its outward stroke. The oil in its position. By shifting the spool to the left the cylinder will make its outward stroke. The oil flows from Port P to A to the cylinder and the oil from the roadside of the cylinder flows via port flows from Port P to A to the cylinder and the oil from the roadside of the cylinder flows via port B to T back to the reservoirB to T back to the reservoir

B – Pressure control valveB – Pressure control valve Pressure control valves are used to control and Pressure control valves are used to control and

regulate pressure in fluid power systemsregulate pressure in fluid power systems. . They are They are often globeoften globe--shaped and designed with flanged ends to shaped and designed with flanged ends to allow for ease of maintenanceallow for ease of maintenance. . The valve is smaller The valve is smaller than the line in which it is attachedthan the line in which it is attached. . This design This design feature prevents the valve from throttling, which feature prevents the valve from throttling, which would cause the seat to wear too quicklywould cause the seat to wear too quickly. . In hydraulic In hydraulic systems pressure regulators are used to unload the systems pressure regulators are used to unload the system and to maintain and regulate pressure at the system and to maintain and regulate pressure at the desired valuesdesired values..

Relief valvesRelief valvesMost fluid power systems are designed to Most fluid power systems are designed to operate within a preset pressure rangeoperate within a preset pressure range. . This range is a function of the forces the This range is a function of the forces the actuators in the system must generate to do actuators in the system must generate to do the required workthe required work. . Without controlling or Without controlling or limiting these forces, the fluid power limiting these forces, the fluid power components components ((and expensive equipmentand expensive equipment) ) could be damagedcould be damaged. . Relief valves avoid this Relief valves avoid this hazardhazard. . They are the safeguards which They are the safeguards which limit maximum pressure in a system by limit maximum pressure in a system by diverting excess oil when pressures get too diverting excess oil when pressures get too highhigh..

FigFig. . 11. . Simple, directSimple, direct--acting relief valve acting relief valve has no adjusting screw and therefore has no adjusting screw and therefore opens at a fixed, preopens at a fixed, pre--set pressure as set pressure as controlled by setting of compression controlled by setting of compression springspring. .

Because the usefulness of a fixed Because the usefulness of a fixed relief valve is limited to the single relief valve is limited to the single setting of its spring, most relief setting of its spring, most relief valves are adjustablevalves are adjustable. . This is This is commonly achieved with an commonly achieved with an adjusting screw acting on the adjusting screw acting on the spring, Figure 2spring, Figure 2. . By turning the By turning the screw in or out, the operator screw in or out, the operator compresses or decompresses the compresses or decompresses the spring respectivelyspring respectively. . The valve The valve can be set to open at any can be set to open at any pressure within a desired rangepressure within a desired range. . Aside from the adjustable Aside from the adjustable feature, this valve works just like feature, this valve works just like the fixed valve in Figure 1the fixed valve in Figure 1. .

FigFig. . 22. . Adjustable, directAdjustable, direct--acting acting relief valve blocks flow through the relief valve blocks flow through the valve until force of system pressure valve until force of system pressure on the poppet overcomes the on the poppet overcomes the adjustable spring force and adjustable spring force and downstream pressuredownstream pressure

PilotPilot--operated reliefoperated relief - - For applications requiring valves that must For applications requiring valves that must relieve large flows with small pressure differential, pilotrelieve large flows with small pressure differential, pilot--operated operated relief valves are often used, Figure 3relief valves are often used, Figure 3. . The pilotThe pilot--operated relief valve operated relief valve operates in two stagesoperates in two stages. . A pilot stage, which consists of a small, springA pilot stage, which consists of a small, spring--biased relief valve biased relief valve ((generally built into the main relief valvegenerally built into the main relief valve)), acts as a , acts as a trigger to control the main relief valvetrigger to control the main relief valve. . However, the pilot may also However, the pilot may also be located remotely and connected to the main valve with pipe or be located remotely and connected to the main valve with pipe or tubingtubing. .

FigFig. . 33. . PilotPilot--operated relief valve has operated relief valve has orifice through piston, which is held orifice through piston, which is held closed by force of light spring and closed by force of light spring and system pressure acting on larger piston system pressure acting on larger piston area at spring endarea at spring end. .

Types of Pressure Control ValvesTypes of Pressure Control Valves Pressure RegulatorsPressure Regulators-- Pressure regulators keep the output pressure at a set value. Pressure regulators keep the output pressure at a set value.

Pressure regulators control pressure in lines (usually adjustable) to remove Pressure regulators control pressure in lines (usually adjustable) to remove fluctuations and maintain consistent pressure. fluctuations and maintain consistent pressure.

Counter-Balance ValvesCounter-Balance Valves-- Counter-balance valves, also called load holding valves Counter-balance valves, also called load holding valves or over-center valves, are normally located between a directional control valve and or over-center valves, are normally located between a directional control valve and the outlet of a vertically mounted actuating cylinder that must support weight or be the outlet of a vertically mounted actuating cylinder that must support weight or be held in position for a period of time. The counter-balance valve serves as hydraulic held in position for a period of time. The counter-balance valve serves as hydraulic resistance to the actuating cylinder. resistance to the actuating cylinder.

Sequence ValvesSequence Valves-- Sequence valves control the sequence of operation between two Sequence valves control the sequence of operation between two branches of a circuit. They enable one unit to automatically set another unit into branches of a circuit. They enable one unit to automatically set another unit into motion. motion.

Uploading ValvesUploading Valves-- The main application of an unloading valve is to unload a The main application of an unloading valve is to unload a pump and save energy when the flow is not required. There are both hydraulic and pump and save energy when the flow is not required. There are both hydraulic and pneumatic applications. Pressure control valves can handle a wide range of media pneumatic applications. Pressure control valves can handle a wide range of media including air and gaseous materials; fuel, gas and oil; liquids, steam and hydraulic including air and gaseous materials; fuel, gas and oil; liquids, steam and hydraulic fluids. fluids.

PilotPilot--operated pressureoperated pressure reducing valvesreducing valves - - The spool The spool in a pilotin a pilot--operated, pressureoperated, pressure--reducing valve is balanced reducing valve is balanced hydraulically by downstream hydraulically by downstream pressure at both ends, Figure pressure at both ends, Figure 66. . A light spring holds the A light spring holds the valve openvalve open. . A small pilot A small pilot relief valve, usually built into relief valve, usually built into the main valve body, relieves the main valve body, relieves fluid to tank when reduced fluid to tank when reduced pressure reaches the pilot pressure reaches the pilot valve's spring settingvalve's spring setting. . This This fluid flow causes a pressure fluid flow causes a pressure drop across the spooldrop across the spool. . Pressure differential then Pressure differential then shifts the spool toward its shifts the spool toward its closed position against the closed position against the light spring forcelight spring force..

FigFig. . 66. . PilotPilot--operated, pressure operated, pressure reducing valve has reduced pressure reducing valve has reduced pressure on both ends of the spoolon both ends of the spool. . A light A light spring holds the spool openspring holds the spool open

Sequence valves Sequence valves are normally closed, 2-way are normally closed, 2-way valvesvalves. . They regulate the They regulate the sequence in which various sequence in which various functions in a circuit occur, functions in a circuit occur, Figure 7Figure 7. . They resemble They resemble directdirect--acting relief valves acting relief valves except that their spring except that their spring chambers are generally chambers are generally drained externally to drained externally to reservoir, instead of internally reservoir, instead of internally to the outlet port, as in a relief to the outlet port, as in a relief valvevalve

FigFig. . 77. . Sequence valve is a 2-way Sequence valve is a 2-way valve held closed by an adjustable valve held closed by an adjustable spring and opened by pressure at the spring and opened by pressure at the inlet port acting on the left of the inlet port acting on the left of the spoolspool. .

Counter-balance valvesCounter-balance valvesThese normallyThese normally--closed valves are closed valves are primarily used to maintain a set primarily used to maintain a set pressure in part of a circuit, pressure in part of a circuit, usually to counterbalance a usually to counterbalance a weight or external force or weight or external force or counteract a weight such as a counteract a weight such as a platen or a press and keep it platen or a press and keep it from freefrom free--fallingfalling. . The valve's The valve's primary port is connected to the primary port is connected to the cylinder's rod end, and the cylinder's rod end, and the secondary port to the directional secondary port to the directional control valve, Figure 8control valve, Figure 8. . The The pressure setting is slightly higher pressure setting is slightly higher than that required to keep the than that required to keep the load from freeload from free--fallingfalling..

FigFig. . 88. . Counter-balance valve Counter-balance valve stops flow from its inlet port to its stops flow from its inlet port to its outlet port until pressure at the outlet port until pressure at the inlet port overcomes adjusting inlet port overcomes adjusting spring forcespring force. . An integral check An integral check valve permits free flow through valve permits free flow through the valve in the opposite directionthe valve in the opposite direction

Unloading valvesThese valves are normally used to unload pumps. They direct pump output flow (often the output of one of the pumps in a multi-pump system) directly to reservoir at low pressure, after system pressure has been reached.The force exerted by the spring keeps the valve closed, Figure 9. When an external pilot signal acting on the opposite end of the valve spool exerts a force large enough to exceed that exerted by the spring, the valve spool shifts, diverting pump output to reservoir at low pressure.High-low circuits which use two pumps for traverse and speed, or clamping, depend on unloading valves to improve efficiency. Output from both pumps is needed only for fast traverse. During feed or clamping, output from the large pump is unloaded to reservoir at low pressure.Unloading valves for accumulator circuits - An unloading valve can be used in an accumulator circuit to unload the pump after the accumulator has been charged, Figure 10. The valve remains closed while the pump is charging the accumulator. After the accumulator is charged, the unloading valve opens, unloading the pump at low pressure while the accumulator supplies pressure fluid to the system. Every time pressure in the accumulator drops below a preset level (controlled by the setting of the spring) the charge/unload cycle repeats

Piloted unloading valvesPiloted unloading valves - - Unloading valves are also made with a pilot to Unloading valves are also made with a pilot to control the main valve, Figure 11control the main valve, Figure 11. . A port through the main valve plunger A port through the main valve plunger allows system pressure to act on both ends of the plungerallows system pressure to act on both ends of the plunger. . A light spring plus A light spring plus system pressure acting on the larger area at the spring end of the plunger system pressure acting on the larger area at the spring end of the plunger holds the valve closedholds the valve closed..

A builtA built--in check valve maintains system pressurein check valve maintains system pressure. . When system pressure When system pressure drops to a preset value, the pilot valve closesdrops to a preset value, the pilot valve closes. . Pump flow through the port in Pump flow through the port in the main valve spool closes the valvethe main valve spool closes the valve..

In most pumpIn most pump--unloading valves for accumulator circuits, only the opening unloading valves for accumulator circuits, only the opening pressure is adjustable and the closing pressure is a fixed percentage of itpressure is adjustable and the closing pressure is a fixed percentage of it . . However, a pilotHowever, a pilot--operated unloading valve can adjust both pressuresoperated unloading valve can adjust both pressures..

FigFig. . 99. . Unloading valve is springUnloading valve is spring--loaded to the loaded to the closed positionclosed position. . When system pressure, transmitted When system pressure, transmitted to the valve though the pilot port, is sufficient to to the valve though the pilot port, is sufficient to overcome force of the adjustable spring, the valve overcome force of the adjustable spring, the valve opensopens. . Pump delivery unloads to tank at low Pump delivery unloads to tank at low pressurepressure. .

Fig. 10. Unloading valve for accumulator circuit opens at a set unloading pressure and closes at a lower pressure. The valve opens when the system reaches a pressure determined by the adjustable spring and pump pressure on the right of the control piston. The valve closes at a lower pressure because force from system pressure on the left of the control spool must only overcome force of the adjusting spring.

FigFig. . 1111. . Piloted unloading valve has piston Piloted unloading valve has piston with pump pressure at both endswith pump pressure at both ends. . When When system pressure on the pilot piston overcomes system pressure on the pilot piston overcomes force of the pilot spring the pilot valve opensforce of the pilot spring the pilot valve opens. . Fluid from behind the main valve piston Fluid from behind the main valve piston drains to tank, which opens the valvedrains to tank, which opens the valve. . When When system pressure fails, the pilot valve closes, system pressure fails, the pilot valve closes, restoring equal pressure to both ends of main restoring equal pressure to both ends of main valve spoolvalve spool. .

C - flow control valveC - flow control valve

There are eight types of flowThere are eight types of flow--control valvescontrol valves::

OrificesOrifices - A simple orifice in the line, Figure 1(a), is - A simple orifice in the line, Figure 1(a), is the most elementary method for controlling flow. the most elementary method for controlling flow. (Note that this is also a basic pressure control device.) (Note that this is also a basic pressure control device.) When used to control flow, the orifice is placed in When used to control flow, the orifice is placed in series with the pump. An orifice can be a drilled hole series with the pump. An orifice can be a drilled hole in a fitting, in which case it is fixed; or it may be a in a fitting, in which case it is fixed; or it may be a calibrated needle valve, in which case it functions as calibrated needle valve, in which case it functions as a variable orifice, Figure 1(b). Both types are non-a variable orifice, Figure 1(b). Both types are non-compensated flow-control devices.compensated flow-control devices.

Fig. 1. Simple fixed orifice (a) and variable orifice (b) flow controls.

Flow regulators - This device, Figure 2, Flow regulators - This device, Figure 2, which is slightly more sophisticated than a which is slightly more sophisticated than a fixed orifice, consists of an orifice that fixed orifice, consists of an orifice that senses flow rate as a pressure drop across senses flow rate as a pressure drop across the orifice; a compensating piston adjusts the orifice; a compensating piston adjusts to variations in inlet and outlet pressures. to variations in inlet and outlet pressures. This compensating ability provides closer This compensating ability provides closer control of flow rate under varying control of flow rate under varying pressure conditions. Control accuracy pressure conditions. Control accuracy may be 5%, possibly less with specially may be 5%, possibly less with specially calibrated valves that operate around a calibrated valves that operate around a given flow-rate point.given flow-rate point.

FigFig. . 22. . Flow regulator adjusts Flow regulator adjusts to variations in inlet and to variations in inlet and output pressuresoutput pressures. .

Bypass flow regulatorsBypass flow regulators - - In this flow In this flow regulator, flow in excess of set flow rate regulator, flow in excess of set flow rate returns to reservoir through a bypass port, returns to reservoir through a bypass port, Figure 3Figure 3. . Flow rate is controlled by Flow rate is controlled by throttling fluid across a variable orifice throttling fluid across a variable orifice regulated by the compensator pistonregulated by the compensator piston. . The The bypass flow regulator is more efficient than bypass flow regulator is more efficient than a standard flow regulatora standard flow regulator..

Fig. 3. Bypass flow regulator returns excess flow from pump to tank.

Demand-compensated flow controls - Flow controls can also bypass excess system flow to a secondary circuit, Figure 4. Fluid is routed at a controlled flow rate to the primary circuit, and bypass fluid can be used for work functions in secondary circuits without affecting the primary one. There must be flow to the primary circuit for this type of valve to function - if the primary circuit is blocked, the valve will cut off flow to the secondary circuit.

Fig. 4. Demand-compensated flow control bypasses full pump output to tank during idle portion of work cycle.

PressurePressure--compensated, variable flow compensated, variable flow valvesvalves - - This flow control is equipped This flow control is equipped with an adjustable variable orifice with an adjustable variable orifice placed in series with a compensatorplaced in series with a compensator. . The compensator automatically adjusts The compensator automatically adjusts to varying inlet and load pressures, to varying inlet and load pressures, maintaining an essentially constant flow maintaining an essentially constant flow rate under these operating conditions to rate under these operating conditions to accuracies of 3% to 5%, Figure 5accuracies of 3% to 5%, Figure 5. . PressurePressure--compensated, variable flowcompensated, variable flow--control valves are available with control valves are available with integral reverseintegral reverse--flow check valves flow check valves ((which allow fluid to flow unrestricted which allow fluid to flow unrestricted in the opposite directionin the opposite direction) ) and integral and integral overload relief valves overload relief valves ((which route fluid which route fluid to tank when a maximum pressure is to tank when a maximum pressure is exceeded).exceeded).

Fig. 5. Pressure-compensated, variable flow-control valve adjusts to varying inlet and load pressures.

PressurePressure- - and temperatureand temperature--compensatedcompensated, , variable flow valves variable flow valves - - Because the viscosity of hydraulic oil Because the viscosity of hydraulic oil varies with temperature varies with temperature ((as do the as do the clearances between a valve's moving clearances between a valve's moving partsparts)), output of a flow, output of a flow--control valve control valve may tend to drift with temperature may tend to drift with temperature changeschanges. . To offset the effects of such To offset the effects of such temperature variations, temperature temperature variations, temperature compensators adjust the control compensators adjust the control orifice openings to correct the effects orifice openings to correct the effects of viscosity changes caused by of viscosity changes caused by temperature fluctuations of the fluid, temperature fluctuations of the fluid, Figure 6Figure 6. . This is done in combination This is done in combination with adjustments the control orifice with adjustments the control orifice for pressure changes as wellfor pressure changes as well. .

Fig. 6. Pressure- and temperature-compensated, variable flow-control valve adjusts the orifice size to offset changes in fluid viscosity.

Priority valves - A priority valve, Figure 7, is essentially a flow-control valve that supplies fluid at a set flow rate to the primary circuit, thus functioning as a pressure-compensated flow-control valve. Flow in excess of that required by the primary circuit bypasses to a secondary circuit at a pressure somewhat below that of the primary circuit. Should inlet or load pressure (or both) vary, the primary circuit has priority over the secondary - as far as supplying the design flow rate is concerned.

Fig. 7. Priority valve supplies fluid at a set rate to a primary circuit.

Deceleration valves - A deceleration valve, Figure 8, is a modified 2-way, spring-offset, cam actuated valve used for decelerating a load driven by a cylinder. A cam attached to the cylinder rod or load closes the valve gradually. This provides a variable orifice that gradually increases backpressure in the cylinder as the valve closes. Some deceleration valves are pressure-compensated.

Fig. 8. Deceleration valve slows load by being gradually closed by action of cam mounted on cylinder load.

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