How piston pumps work

Piston and plunger pumps are types of positive displacement reciprocating pumps that move and pressurise fluids by means of a reciprocating element — a piston or plunger — within a sealed cylinder.
They are designed for applications requiring high pressure, precise flow control, and excellent volumetric efficiency, making them ideal for oil and gas, chemical dosing, hydraulic systems, and high-pressure cleaning.

Working Principle

Both piston and plunger pumps operate on the same reciprocating displacement principle — alternating suction and discharge strokes move a fixed volume of fluid through the system each cycle.

1. Suction Stroke

As the piston or plunger moves backward, it increases the cylinder volume.
This creates a pressure drop, causing the suction valve to open.
Fluid is drawn into the cylinder from the suction line.

2. Discharge Stroke

When the piston or plunger moves forward, it reduces the cylinder volume.
The suction valve closes and the discharge valve opens under pressure.
The trapped liquid is forced out through the discharge port at high pressure.

Each cycle delivers a discrete, measured volume of fluid — meaning flow rate is directly proportional to speed and almost independent of discharge pressure.

Piston vs. Plunger Pump Design

Feature	Piston Pump	Plunger Pump
Reciprocating element	Piston with sealing rings or cups	Plunger with stationary packing seals
Seal location	Moves with the piston	Fixed in the cylinder head
Pressure capability	Medium (up to ~200 bar)	High (up to ~3,000 bar or more)
Applications	Hydraulic presses, irrigation, metering	High-pressure cleaning, oilfield injection, process dosing

Key difference: In a piston pump, the seal moves with the piston; in a plunger pump, the seal is stationary, allowing operation at much higher pressures and longer seal life.

Main Components

Power End: Converts rotary motion from a motor or engine into reciprocating motion using a crankshaft and connecting rod.
Fluid End: Contains the cylinder, valves, suction/discharge ports, and sealing arrangement.
Check Valves: One-way valves that control fluid direction — typically ball or spring-loaded disc types.
Packing/Seals: Maintain pressure integrity and prevent leakage around the piston or plunger.

Performance Characteristics

Flow Rate: Determined by stroke length, piston area, and speed.
Pressure: Determined by system resistance; can reach thousands of bar in plunger designs.
Efficiency: Volumetric efficiency typically >95%, even at high pressures.
Flow Uniformity: Can be improved with multiple plungers (triplex, quintuplex, etc.) for smoother delivery.