The plunger pump

Construction, functional principle and use

Plunger pumps can be found as reliable high-pressure pumps in many industrial applications, for example in cleaning applications or in process technology in the chemical industry. Displacement pumps are suitable for small or large flow rates and achieve different pressure levels. They convey all liquid media such as water, oils or liquid gases over a wide temperature range. Even abrasive media such as detergent slurries or carbon mashes can easily be pumped via various pressure levels with the oscillating plunger pumps.

The plunger pump

The plunger pump is a special version of the piston pump. The term plunger comes from the English language and means piston rod or plunger.


In contrast to a piston pump, the piston does not reach the cylinder wall. The piston rod itself represents the piston. On the outside, it has no seals closing with the cylinder wall. The pump operates according to the displacement principle.

The functional principle of the plunger pump

In contrast to a piston pump, the plunger pump does not move with the piston, but has a fixed seal in the stuffing box. A retracting plunger creates a suction effect in the liquid end and opens the suction valve. The medium flows into the liquid end. The plunger then moves forward. The plunger displaces the available volume through its own volume and increases the pressure of the fluid to be pumped. The suction valve closes and the pressure valve opens the way into the process area for the pressurized fluid.


The forward and backward movement of the plunger repeats itself continuously and opens or closes the valves. Depending on the application, the cycles are repeated up to several hundred times per minute. To prevent an intermittent flow of fluid, so-called suction side and discharge sided pulsation dampers are used, which ensure uniform flow and reduced pulsations. Several plungers can be used in a single pump in combination to increase the flow rate and for a more even flow rate. They feed the common process area via the same pressure pipe. The number of plungers in the pump varies depending on the design and application.

The plungers are driven hydraulically or by a crankshaft with connecting rods and crosshead extensions. If there are several plungers, the angular positions on the crankshaft can be distributed in such a way that the pressure peaks in the pump are staggered.

Functionality of the plunger pump

3D Animation

The construction of the plunger pump

Basically, the plunger pump consists of two main components: the power end and the liquid end.


The power end converts the rotating movement of a drive motor into an oscillating forward and backward movement of the plunger. Crankshaft, connecting rods and cross heads are used for this purpose. The plungers are coupled to the cross heads and enter the liquid end of the pump via the stuffing boxes. Drive motors can be electric motors, but also internal combustion engines. Hydraulic drives are also possible. The power end is made of a robust cast material to be prepared for the tough continuous use under extreme conditions.

The liquid end consists of the stuffing boxes and the valve chamber in which the pressure increase of the medium takes place. The various components of the liquid end come into contact with the liquid media and must therefore be designed to meet the requirements. Stuffing box housing, valve block and valves are made of materials that are adapted to the application and the fluid to be pumped. These can be, for example, simple casting materials, high-alloy stainless steels such as superduplex or even titanium.


Depending on the process to be operated, the sealing solutions permanently installed in the liquid end can be equipped with auxiliary systems such as sealing systems, injections or flushing.

Applications for high-pressure plunger pumps

Plunger pumps can be used in a wide variety of applications. Wherever liquid media has to be pumped at high pressure, they provide suitable solutions. Applications range from pumps for cleaning processes of the lowest performance classes with a few kilograms to pumping systems for the process industry with performance requirements of several megawatts and a weight of 40 tons. Pressure stages of up to 3,000 bar can be achieved with the high-pressure pumps.


Thanks to sophisticated design, optimized material selection, flexible speed control and high precision in production, plunger pumps can be used 24 hours a day and approx. 8,000 hours a year without interruption. All media can be pumped in a liquid state. These can be water or oil at normal temperatures, but also hot oils and liquid gases such as carbon dioxide and ammoniac. Due to their functional principle, plunger pumps are also ideally suited for media with abrasives such as detergent slurries or coal mashes.

Typical applications for plunger pumps are:

  • Cleaning applications
  • Coal liquefaction
  • Process technology for the chemical and pharmaceutical industries
  • Pressure testing
  • Urea production
  • Surface preparation
  • Oil and gas production

Plunger pumps operate according to the displacement principle and are ideally suited for reliable continuous operation. They can be used for various liquid media and achieve pressures of up to 3,000 bar. URACA has a lot of know-how in the development and production of plunger pumps.


If you have any questions or are looking for a suitable pump for your application, contact the URACA experts now.