Variable displacement pump

A variable displacement pump is a device that converts mechanical energy into hydraulic (fluid) energy . The displacement, or the amount of fluid pumped per revolution of the pump’s input shaft, can vary while the pump is running . Many variable displacement pumps are “reversible”, meaning they can act as a hydraulic motor and convert fluid energy into mechanical energy.


A common variable displacement pump used in vehicle technology is the axial piston pump . This pump consists of several pistons in cylinders arranged parallel to each other and rotating around a central shaft. At one end a swashplate is attached to the piston. As the pistons rotate, the angle of the plate causes them to move in and out of their cylinders. A rotary valve at the opposite end of the swapplateConnects each cylinder in turn to the fluid supply and distribution lines. By changing the angle of the swapplate, the stroke of the piston can be changed continuously. If the swashplate is perpendicular to the axis of rotation, no fluid will flow. If it is at a steep angle, a large amount of fluid will be pumped. Some pumps allow the swapplate to be moved in both directions from the zero position, pumping fluid in either direction without reversing the pump’s rotation.

An efficient variation is the bent axis pump. Turning the axle reduces the side load on the piston.

Piston pumps can be made variable-displacement by inserting inline springs with the pistons. Displacement is not controlled positively, but decreases as back-pressure increases.

Another variation is the variable displacement vane pump .

reciprocating pump:

A reciprocating displacement pump has a part called reciprocating and the water is raised with the help of the pump. Reciprocating pumps have their names associated with valves, exit valves and inlet valves. When there is suction in the liquid pump, the inlet valve is open but the exhaust valve is closed the other way. When the liquid is discharged, the exhaust valve is open but the inlet valve is closed.

Reciprocating positive displacement pumps consist of one simple or more than one (quad) cylinder. Most reciprocating positive displacement pumps have double or triple the number of cylinders.

Electricity can be generated manually which is driven by wind or steam or engine which can be driven by belt.

Variable displacement pump

With this reciprocating pump displacement pump heavy viscous liquid like oil, concrete can be lifted to the desired location. This reciprocating pump is also used where a low rate of flow is required for a high resistance fluid.

In a reciprocating pump, there is an increasing vacuum at the end of the suction and a decreasing vacuum at the end of the delivery. When the vacuum in the pump begins to expand, the fluid inside the vacuum begins to move, similarly when the vacuum in the pump begins to decrease, the fluid begins to discharge.

Working principle of reciprocating pump Then we can see that when the plunger moves to the right the amount of vacuum pump inside increases and in this position the fluid is sucked in. Now when the plunger moves to the left, the fluid inside the pump is pressurized and at that time the delivery valve is open and the fluid inside is released through the vacuum.

Reciprocating valves classified for the purpose of piston work in two categories. they are,

Single acting of reciprocating pump:

This type of pump has only one direction of motion. Means if suction is happening inside the pump then discharge and piston act in other direction of motion hence it is called single acting reciprocating pump.

Dual acting of reciprocating pump:

In this type of pump the motion of both the directions works at the same time. Means If there is suction inside the pump, the discharge and piston can act in the same direction, hence it is called double acting reciprocating pump.

Rotary Pump:

One of the most commonly used positive displacement pump types is the rotary positive displacement pump. Inside the rotary positive displacement pump a rotary is present for the liquid being lifted with the help of the pump. The liquid inside the rotary moves in a rotating motion and the liquid can move from the storage tank to the distribution pipe.

Linear Pump:

Linear pump is one of the most commonly used positive displacement pumps. With the help of tubing, waves of contraction are carried into the liquid. The individual reciprocating parts are continuously compressed into straight parts of flexible tubing for fluid movement. The liquid moves in a linear or straight direction. Linear pump can be located at any stationary location. This pump cannot be used in crowded areas. The main problems with this linear positive displacement pump are volume and noise. 

The most commonly used linear pumps are chain pumps and rope pumps. The application of this pump is in medical, environmental, decentralized waste water treatment, pond aeration and many others.