Positive Displacement Pumps - Basic Principle
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Transcript of Positive Displacement Pumps - Basic Principle
POSITIVE DISPLACEMENT PUMPS
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
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.
Principle of Operation:Check valves in the suction and discharge ports allow flow
in only one direction.
Section Discharge
POSITIVE DISPLACEMENT PUMPS
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
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
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
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
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
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
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
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
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
Reciprocating pumps:Simplex and Duplex Pumps:
POSITIVE DISPLACEMENT PUMPS
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
Reciprocating pumps:Single-Acting and Double-Acting Pumps:
One possible arrangement for single-acting and double-acting pumps is shown :
POSITIVE DISPLACEMENT PUMPS
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
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
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
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.
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
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
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
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
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
Reciprocating pumps:Piston/Plunger Pump:
Disadvantages include the following:
• The necessity of slow speed operation
• The necessity of slow speed operation
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
POSITIVE DISPLACEMENT PUMPS
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
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
Reciprocating pumps:Diaphragm Pump:
•Is limited to low flow and head application due to the design of the
flexible diaphragm.
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 Blow case
pump
POSITIVE DISPLACEMENT PUMPS
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
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
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
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
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
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
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