Piston pump

Type of positive-displacement pump

If you want to learn more, please visit our website how do piston pumps work.

Piston pump compared to a plunger pump

A piston pump is a type of positive displacement pump where the high-pressure seal reciprocates with the piston.[1] Piston pumps can be used to move liquids or compress gases. They can operate over a wide range of pressures. High pressure operation can be achieved without adversely affecting flow rate. Piston pumps can also deal with viscous media and media containing solid particles.[2] This pump type functions through a piston cup, oscillation mechanism where down-strokes cause pressure differentials, filling of pump chambers, where up-stroke forces the pump fluid out for use. Piston pumps are often used in scenarios requiring high, consistent pressure and in water irrigation or delivery systems.[3]

Types

[

edit

]

The two main types of piston pump are the lift pump and the force pump.[4] Both types may be operated either by hand or by an engine.

Lift pump

Lift pump

[

edit

]

Force pump

In a lift pump, the upstroke of the piston draws water, through a valve, into the lower part of the cylinder. On the downstroke, water passes through valves set in the piston into the upper part of the cylinder. On the next upstroke, water is discharged from the upper part of the cylinder via a spout. This type of pump is limited by the height of water that can be supported by air pressure against a vacuum.

Force pump

[

edit

]

In a force pump, the upstroke of the piston draws water, through an inlet valve, into the cylinder. On the downstroke, the water is discharged, through an outlet valve, into the outlet pipe.

Piston pumps may be classified as either single-acting and single-effect (the fluid is pumped by a single face of the piston, and the active stroke is in only one direction) or double-acting and double-effect (the fluid is pumped by both faces of the piston, and the strokes in both directions are active).

• An animation of a single-acting piston force pump.

• An animation of a double-acting piston force pump with accumulators on both the inlet and outlet.

Calculation of delivery rate

[

edit

]

The calculation of a piston pump's theoretical delivery rate is relatively simple.

Single-acting pumps

[

edit

]

In a single acting pump, only one side of the piston is in contact with the fluid. As a result of this, only one stroke is a delivery stroke. The theoretical delivery rate can be calculated by using the following equation:[5]

Q = h × d 2 × π 4 × n {\displaystyle Q=h\times {\frac {d^{2}\times \pi }{4}}\times n}

Where Q is the delivery rate, d is the diameter of the piston, h is the stroke, and n is the rpm. If the pump has multiple cylinders, Q is multiplied by the number of cylinders.

Double-acting pumps

[

edit

]

In a double acting pump, both sides of the piston are in contact with the fluid. As a result of this, both strokes are delivery strokes. An approximation of the delivery rate is given by the following equation:[5]

Q = h × d 2 × π 4 × 2 n {\displaystyle Q=h\times {\frac {d^{2}\times \pi }{4}}\times 2n}

Contact us to discuss your requirements of piston pump for sale. Our experienced sales team can help you identify the options that best suit your needs.

However, this equation fails to take into consideration the volume taken up by the piston rod. The true delivery rate can be calculated accordingly:

Q = n h × ( 2 d 2 × π 4 − d 1 2 × π 4 ) = n h × π 4 ( 2 d 2 − d 1 2 ) {\displaystyle Q=nh\times \left(2{\frac {d^{2}\times \pi }{4}}-{\frac {d_{1}^{2}\times \pi }{4}}\right)=nh\times {\frac {\pi }{4}}\left(2d^{2}-d_{1}^{2}\right)}

Display of the delivery of a single-acting pump (left) and a double-acting pump (right) in relation to the movement of the crankshaft.

d1 is equal to the diameter of the piston rod.

Fluctuation in delivery rate

[

edit

]

The piston in a plunger and piston pump does not move at a constant velocity and as a result of this the pressure and delivery fluctuate over the duration of the stroke. The following diagram shows the relation between the angle of the crankshaft and the delivery rate of a single-acting and double-acting pump. The line shows the average delivery rate of the pump. These fluctuations in pressure and delivery can cause undesired effects such as water hammer and thus are generally mitigated by the installation of an air-filled accumulator. The delivery can be further smoothed out by the use of multiple cylinders that are offset from one another.

As a result the actual delivery rate is often smaller and can be found by the following equation:

Q s = Q × λ {\displaystyle Q_{s}=Q\times \lambda }

Qs is the actual delivery rate, Q is the theoretical rate, and λ is the loss coefficient.

Others

[

edit

]

See also

[

edit

]

References

[

edit

]

As mentioned earlier, piston pumps are devices designed to generate a constant flow of a liquid, through the reciprocating movement of one or more pistons within a cylinder. This reciprocating movement is the result of the application of an external mechanical force, often generated by an electric motor or an internal combustion engine.

Piston pumps operate following three fundamental phases:

• suction;
• compression;
• discharge. 

Let's examine each phase in detail:

Suction Phase

The suction phase is the first essential step in the operation of a piston pump. During this phase, the piston moves backward within the cylinder, moving away from the suction chamber. This piston movement creates a void inside the cylinder, reducing the pressure within it. This pressure reduction leads to the creation of a relative negative pressure, which is lower than that of the surrounding environment.

This negative pressure is what allows the liquid to be sucked from the feed pipe into the pump's suction chamber. In other words, the higher pressure in the surrounding environment pushes the fluid into the cylinder through the suction valves, utilizing the fundamental principle of flow from higher pressure points to lower pressure ones.

The effectiveness of the suction phase depends on several factors, including the power of the engine pushing the piston backward and the presence of well-designed suction valves that allow efficient fluid flow.

Compression Phase

The compression phase is the second crucial step in the operation of piston pumps. Once the liquid has been successfully sucked into the suction chamber, the piston begins its forward movement within the cylinder. This movement into the cylinder is the result of the energy provided by the engine or the power source associated with the pump.

As the piston moves forward, the fluid inside the cylinder is compressed. This means that the volume occupied by the fluid is reduced, generating an increase in pressure. The amount of pressure generated in this phase depends on several factors, including the power of the engine powering the pump, the speed of the piston, and the pump's specific configuration, such as the cylinder diameter and compression ratio.

Therefore, the ability to generate adequate pressure during this phase is closely linked to the overall power and efficiency of the piston pump.

It's also important to note that piston pumps can be designed to operate at different compression pressures, depending on the specific needs of the application.

Discharge Phase

The discharge phase is the third and final step in the operating cycle of piston pumps. During this phase, the piston continues its forward movement within the cylinder and pushes the compressed liquid through a discharge pipe. It's important to highlight that the pressure generated during the compression phase is crucial for the success of the discharge phase.

The pressure accumulated in the fluid during the compression phase is sufficient to overcome any resistance present in the piping system. This resistance can come from the length of the pipes, the diameter of the ducts, or the presence of regulating valves. The pressure generated in the cylinder by the piston's compression provides the necessary energy to overcome these resistances and make the fluid flow in the desired direction.

The compressed fluid, now at high pressure, can be directed to the desired destination point, where it will perform its specific task in the industrial application.

This final phase shows us how the careful design of the discharge pipes, pressure management, and flow control are essential to ensure the efficient and safe operation of piston pumps.

If you are looking for more details, kindly visit piston vacuum pump works.