Piston pump

Key takeaways

Piston pump belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Piston pump to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Piston pump from memory before moving on to harder problems.

Reference excerpt

A piston pump is a type of positive displacement pump where the high-pressure seal reciprocates with the piston. 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. 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.

Types

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

Lift 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 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).

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

Single-acting pumps 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:

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 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:

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

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)}

d1 is equal to the diameter of the piston rod.

Fluctuation in delivery rate

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. 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 Axial piston pump Radial piston pump

Illustrations

Piston pump: Piston pump diagram — Piston pump diagram

Worked examples

Example 1 — a first encounter with Piston pump

Start with the simplest possible case. Write down what Piston pump claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Piston pump before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Piston pump ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Piston pump

In research: Piston pump appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Piston pump in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Piston pump is common in secondary-school and first-year university syllabi. It links to neighbouring topics 13th-century inventions, Pumps, so understanding it makes those chapters shorter.
In everyday life: Look for Piston pump outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Piston pump in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Piston pump means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Piston pump out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Piston pump in simple terms?

A piston pump is a type of positive displacement pump where the high-pressure seal reciprocates with the piston. Piston pumps can be used to move liquids or compress gases.

Why does Piston pump matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Piston pump?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Piston pump.