Displacement and Hydraulic Pumps: Working Principle, Types & Industrial Applications

In industrial fluid power systems, displacement and hydraulic pumps play a vital role in generating controlled pressure and flow. These pumps are widely used in manufacturing, construction, oil & gas, water jetting, and hydraulic power units where precision, reliability, and high pressure are required. This article explains the working principle, classification, and applications of positive displacement and hydraulic pumps, helping readers understand their importance in modern industries.

 

What Are Positive Displacement Pumps?

Pumps used in hydraulic systems are broadly classified into rotodynamic pumps and positive displacement pumps.

Positive displacement pumps operate by trapping a fixed volume of fluid in an enclosed cavity and then forcing (displacing) that fluid into the discharge pipe. Unlike centrifugal pumps, the flow rate of displacement pumps is directly proportional to speed and is almost independent of pressure.

In hydraulic systems, these pumps convert mechanical energy into hydraulic energy by moving fluid under pressure using internal mechanical components such as pistons, plungers, diaphragms, or gears.

Main Types of Positive Displacement Pumps

Positive displacement pumps include a wide range of designs used for specific industrial purposes:

• Piston Pumps
• Plunger Pumps
• High-Pressure Plunger Pumps
• Diaphragm Metering Pumps
• Membrane Pumps
• Screw Pumps
• Gear Pumps
• Rotary Gear Pumps
• Peristaltic Pumps
• Rotary Pumps
• Vane Pumps
• Hydraulic Ram Pumps
• Mud Pumps
• Submersible Pumps
• Hydraulic Power Units

Although the designs vary, pumps based on the same displacement principle share similar performance characteristics such as self-priming ability, high pressure generation, and accurate flow control.

Hydraulic (Plunger) Pumps Explained

A hydraulic plunger pump is a type of positive displacement pump in which fluid movement is generated by the reciprocating motion of a plunger or piston inside a fixed cylinder. The pump consists of:

• A closed working chamber
• Suction and discharge valves
• A plunger or piston driven by a crank mechanism or lever

Working Principle of a Hydraulic Plunger Pump

The operation of a hydraulic plunger pump occurs in cycles:

1. When the plunger moves backward, the volume of the working chamber increases.
2. Pressure inside the chamber drops, allowing fluid to enter through the suction valve.
3. When the plunger moves forward, the chamber volume decreases.
4. Fluid is forced out through the discharge valve at high pressure.

This continuous cycle allows the pump to deliver fluid in measured volumes, making it ideal for applications requiring controlled pressure rather than continuous flow.

Key Characteristics of Hydraulic Displacement Pumps

Hydraulic and plunger pumps exhibit several unique features:

• High pressure generation with relatively low flow rates
• Self-priming capability, eliminating the need for external priming
• Accurate volume control, suitable for metering applications
• Reliable performance under heavy-duty conditions

However, because the fluid is delivered in pulses, these pumps are less suitable for applications requiring perfectly smooth flow unless pulsation dampeners are used.

Industrial Applications of Displacement & Hydraulic Pumps

Due to their ability to generate very high pressure, hydraulic displacement pumps are widely used in:

• Water jetting and high-pressure cleaning systems
• Hydraulic power packs
• Construction equipment
• Oil & gas drilling and mud pumping
• Combustion engines and fuel injection systems
• Surface preparation and descaling
• Pressure testing and hydro-testing units

In water jet units, these pumps are especially effective for surface cleaning, coating removal, and industrial maintenance, where controlled high-pressure fluid is essential.

Conclusion

Displacement and hydraulic pumps form the backbone of many industrial fluid power systems. Their ability to deliver precise volumes at extremely high pressures, combined with self-priming and robust design, makes them indispensable across multiple industries.

Understanding the working principle and selection criteria of positive displacement pumps helps engineers, technicians, and buyers choose the right pump for their specific application.

👉 Keep reading our blog to learn more about piston pumps, plunger pumps, and advanced pumping equipment used in industrial applications.