Positive Displacement Pumps - Basic Principle

39
POSITIVE DISPLACEMENT PUMPS

Transcript of Positive Displacement Pumps - Basic Principle

Page 1: Positive Displacement Pumps - Basic Principle

POSITIVE DISPLACEMENT PUMPS

Page 2: Positive Displacement Pumps - Basic Principle

POSITIVE DISPLACEMENT PUMPS

Mixed flow

Axial flow

Centrifugal

Rotodynamic

Turbine

PUMP

Positive displacement

Diaphragm

Piston

Plunger

Reciprocating Rotary

Gear

Lobe

Sliding Vane

Screw

Positive displacement

Diaphragm

Piston

Plunger

Reciprocating Rotary

Gear

Lobe

Sliding Vane

Screw

Page 3: Positive Displacement Pumps - Basic Principle

Positive displacement pumps physically entrap a quantity of liquid at the suction of the pump and push that quantity out

the discharge of the pump.

A definite volume of liquid is delivered for each cycle of pump operation.

POSITIVE DISPLACEMENT PUMPS

The positive displacement pump delivers liquid in separate volumes with no delivery in between,

Positive displacement pumps can be grouped into three basic categories based on their design and operation. The three groups are reciprocating pumps, rotary pumps, and

diaphragm pumps.

Page 4: Positive Displacement Pumps - Basic Principle

Principle of Operation:Check valves in the suction and discharge ports allow flow

in only one direction.

Section Discharge

POSITIVE DISPLACEMENT PUMPS

Page 5: Positive Displacement Pumps - Basic Principle

Principle of Operation:

During the discharge stroke, the piston moves to the right,

seating the check valve in the suction line and opening

the check valve in the discharge line.

POSITIVE DISPLACEMENT PUMPS

Page 6: Positive Displacement Pumps - Basic Principle

Principle of Operation:

During the suction stroke, the piston moves to the left,

causing the check valve in the suction line between the

reservoir and the pump cylinder to open and admit

water from the reservoir.

POSITIVE DISPLACEMENT PUMPS

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Principle of Operation:

The volume of liquid moved by the pump in one cycle

(one suction stroke and one discharge stroke) is equal to

the change in the liquid volume of the cylinder as the

piston moves from its farthest left position to its farthest

right position.

POSITIVE DISPLACEMENT PUMPS

Page 8: Positive Displacement Pumps - Basic Principle

Mixed flow

Axial flow

Centrifugal

Rotodynamic

Turbine

PUMP

Positive displacement

Diaphragm

Piston

Plunger

Reciprocating Rotary

Gear

Lobe

Sliding Vane

Screw

Positive displacement

Diaphragm

Piston

Plunger

Reciprocating Rotary

Gear

Lobe

Sliding Vane

Screw

POSITIVE DISPLACEMENT PUMPS

Page 9: Positive Displacement Pumps - Basic Principle

Reciprocating pumps:Reciprocating positive displacement pumps are generally

categorized in four ways:

1. Direct-acting or Indirect-acting. 2. Simplex or Duplex .

3. Single-acting or Double-acting . 4. Power pumps.

POSITIVE DISPLACEMENT PUMPS

Page 10: Positive Displacement Pumps - Basic Principle

Reciprocating pumps:Direct-Acting and Indirect-Acting Pumps:

Direct-acting pumps have a plunger on the liquid (pump) end

that is directly driven by the pump rod (also the piston rod or

extension thereof) and carries the piston of the power end.

POSITIVE DISPLACEMENT PUMPS

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Reciprocating pumps:Direct-Acting and Indirect-Acting Pumps:

Indirect-acting pumps are driven by means of a beam or linkage connected to and actuated by the power piston rod of a separate reciprocating engine.

POSITIVE DISPLACEMENT PUMPS

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Reciprocating pumps:Simplex and Duplex Pumps:

A simplex pump, sometimes referred to as a single pump, is a pump having a single liquid (pump) cylinder.

A duplex pump is the equivalent of two simplex pumps placed side by side on the same foundation.

POSITIVE DISPLACEMENT PUMPS

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Reciprocating pumps:Simplex and Duplex Pumps:

The driving of the pistons of a duplex pump is arranged in such a manner that when one piston is on its upstroke the

other piston is on its down stroke, and vice versa. This arrangement doubles the capacity of the duplex pump

compared to a simplex pump of comparable design.

POSITIVE DISPLACEMENT PUMPS

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Reciprocating pumps:Simplex and Duplex Pumps:

POSITIVE DISPLACEMENT PUMPS

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Reciprocating pumps:Single-Acting and Double-Acting Pumps:

A single-acting pump is one that takes a suction, filling the pump cylinder on the stroke in only one direction, called the suction stroke, and then forces the liquid out of the cylinder

on the return stroke, called the discharge stroke. A double-acting pump is one that, as it fills one end of the

liquid cylinder, is discharging liquid from the other end of the cylinder.

On the return stroke, the end of the cylinder just emptied is filled, and the end just filled is emptied.

POSITIVE DISPLACEMENT PUMPS

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Reciprocating pumps:Single-Acting and Double-Acting Pumps:

One possible arrangement for single-acting and double-acting pumps is shown :

POSITIVE DISPLACEMENT PUMPS

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Reciprocating pumps:Power Pumps:

Power pumps convert rotary motion to low speed reciprocating motion by reduction gearing, a crankshaft,

connecting rods and crossheads. Plungers or pistons are driven by the crosshead drives. Rod

and piston construction, similar to duplex double-acting steam pumps, is used by the liquid ends of the low

pressure, higher capacity units.

POSITIVE DISPLACEMENT PUMPS

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Reciprocating pumps:Power Pumps:

The higher pressure units are normally single-acting plungers, and usually employ three (triplex) plungers. Three

or more plungers substantially reduce flow pulsations relative to simplex and even duplex pumps.

Power pumps typically have high efficiency and are capable of developing very high pressures. They can be driven by

either electric motors or turbines.

POSITIVE DISPLACEMENT PUMPS

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Reciprocating pumps:Power Pumps:

They are relatively expensive pumps and can rarely be justified on the basis of efficiency over centrifugal pumps.

However, they are frequently justified over steam reciprocating pumps where continuous duty service is

needed due to the high steam requirements of direct-acting steam pumps.

POSITIVE DISPLACEMENT PUMPS

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Reciprocating pumps:Power Pumps:

In general, the effective flow rate of reciprocating pumps decreases as the viscosity of the fluid being pumped

increases because the speed of the pump must be reduced.

POSITIVE DISPLACEMENT PUMPS

In contrast to centrifugal pumps, the differential pressure generated by reciprocating pumps is independent of fluid

density. It is dependent entirely on the amount of force exerted on the piston.

Page 21: Positive Displacement Pumps - Basic Principle
Page 22: Positive Displacement Pumps - Basic Principle

Mixed flow

Axial flow

Centrifugal

Rotodynamic

Turbine

PUMP

Positive displacement

Diaphragm

Piston

Plunger

Reciprocating Rotary

Gear

Lobe

Sliding Vane

Screw

Positive displacement

Diaphragm

Piston

Plunger

Reciprocating Rotary

Gear

Lobe

Sliding Vane

Screw

POSITIVE DISPLACEMENT PUMPS

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Reciprocating pumps:Piston/Plunger Pump:

A tight-fitting piston in a closed cylinder or a loose-fitting plunger acting as a displacer are familiar versions of the

common reciprocating pump.

POSITIVE DISPLACEMENT PUMPS

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Reciprocating pumps:Piston/Plunger Pump:

Piston/plunger pumps have the following characteristics:

• Capable of almost any pressure, and of large flow

capacity.

• Capable of almost any pressure, and of large flow

capacity.

POSITIVE DISPLACEMENT PUMPS

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Reciprocating pumps:Piston/Plunger Pump:

Piston/plunger pumps have the following characteristics:

• NPSH requirements for these pumps are more complex than for rotary or kinetic pumps due

to the pulsed nature of the suction.

• Are expensive in large sizes.• Easily controlled by stroke adjustment or variable speed.

POSITIVE DISPLACEMENT PUMPS

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Reciprocating pumps:Piston/Plunger Pump:

Advantages include the following:

• The ability to develop high pressures in a single stage.

• High reliability.

• The ability to develop high pressures in a single stage.

POSITIVE DISPLACEMENT PUMPS

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Reciprocating pumps:Piston/Plunger Pump:

Disadvantages include the following:

• The necessity of slow speed operation

• The necessity of slow speed operation

POSITIVE DISPLACEMENT PUMPS

Page 28: Positive Displacement Pumps - Basic Principle

Mixed flow

Axial flow

Centrifugal

Rotodynamic

Turbine

PUMP

Positive displacement

Diaphragm

Piston

Plunger

Reciprocating Rotary

Gear

Lobe

Sliding Vane

Screw

Positive displacement

Diaphragm

Piston

Plunger

Reciprocating Rotary

Gear

Lobe

Sliding Vane

Screw

POSITIVE DISPLACEMENT PUMPS

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Reciprocating pumps:Diaphragm Pump:

Fluid is transferred by the pressure of a diaphragm that flexes to form a cavity that is filled by liquid.

A diaphragm pump has the following characteristics:•Transfers virtually any liquid.

•Designs can handle high temperatures.

•Designs can handle high temperatures.

POSITIVE DISPLACEMENT PUMPS

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Reciprocating pumps:Diaphragm Pump:

•Is infinitely adjustable in capacity and discharge pressure by

regulating the movement of the diaphragm.

•Can be flexed by either an air supply or a reciprocating plunger.

•Is used for pumping chemicals, glue, ink, solvents, fat, grease, and

dirty water.

POSITIVE DISPLACEMENT PUMPS

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Reciprocating pumps:Diaphragm Pump:

•Is limited to low flow and head application due to the design of the

flexible diaphragm.

POSITIVE DISPLACEMENT PUMPS

Page 32: Positive Displacement Pumps - Basic Principle

Mixed flow

Axial flow

Centrifugal

Rotodynamic

Turbine

PUMP

Positive displacement

Diaphragm

Piston

Plunger

Reciprocating Rotary

Gear

Lobe

Sliding Vane

Screw

Positive displacement

Diaphragm

Piston

Plunger

Reciprocating Rotary

Gear

Lobe

Sliding Vane

Screw Blow case

pump

POSITIVE DISPLACEMENT PUMPS

Page 33: Positive Displacement Pumps - Basic Principle

Reciprocating pumps:Blow case pump:

This is a special configuration of a positive displacement

pump .

It consists of two pressure chambers that are alternately

filled with liquid.

When a chamber is filled, air or steam is forced into the

chamber.

POSITIVE DISPLACEMENT PUMPS

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Reciprocating pumps:Blow case pump:

This causes the contents to be discharged into the system.

The two chambers alternate in this action, resulting in a fairly

constant discharge.

It is popular for pumping hot condensate. Why?

because there is no heat loss, and flashing liquid can be transferred.

POSITIVE DISPLACEMENT PUMPS

Page 35: Positive Displacement Pumps - Basic Principle

Mixed flow

Axial flow

Centrifugal

Rotodynamic

Turbine

PUMP

Positive displacement

Diaphragm

Piston

Plunger

Reciprocating Rotary

Gear

Lobe

Sliding Vane

Screw

Positive displacement

Diaphragm

Piston

Plunger

Reciprocating Rotary

Gear

Lobe

Sliding Vane

Screw Blow case

pump

Open-screw pump

POSITIVE DISPLACEMENT PUMPS

Page 36: Positive Displacement Pumps - Basic Principle

Reciprocating pumps:Open-screw pump:

This is an example of a pump configuration that does not

conform to the classical forms discussed in the preceding

sections.

An open-screw pump consists of a U-shaped channel into which a rotating screw fits

tightly (minimal clearance).

POSITIVE DISPLACEMENT PUMPS

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Reciprocating pumps:Open-screw pump:

Modern forms of this pump are usually quite large.

This pump is used extensively in waste water plants for

moving contaminated water, and in irrigation channels for

lifting large volumes of water.

POSITIVE DISPLACEMENT PUMPS

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Reciprocating pumps:Open-screw pump:

The large sizes with closely fitted screws are reasonably

efficient.

An open-screw pump is well suited for this purpose as there

is little chance of down time.

POSITIVE DISPLACEMENT PUMPS

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Reciprocating pumps:Open-screw pump:

All bearings are thus outside of the liquid and there is no liquid

leakage.

One version surrounds the screw within a large tube and

the whole assembly is then rotated.

POSITIVE DISPLACEMENT PUMPS