What are piston pumps?
A piston pump is a type of pump that uses a piston moving back and forth inside a cylinder to create pressure and move fluids (liquids or gases). It's a positive displacement pump, meaning that it can pump air, and it delivers a fixed amount of fluid with each stroke, regardless of the pressure acting against it. Due to its design, a piston pump can pump fluids that contain solids.
Piston Pump Parts
Piston
Fluid is drawn into each cylinder space by pistons. When a piston is closest to the inlet port, it begins to move in a linear direction back towards the swash plate. As it retracts, fluid is drawn into the cylinder space. The charged cylinder then rotates towards the discharge port, whilst the piston simultaneously begins moving away from the swash plate. Movement of the piston in the cylinder causes the fluid to be discharged from the cylinder and through the discharge port. Piston pumps may consist of one or multiple pistons depending upon the pump design.
Swash Plate
The amount of fluid pumped is dictated by the swash plate angle/pitch. Changing the pitch of the swash plate, changes the stroke of each piston, which changes the amount of fluid drawn into each cylinder, and consequently the amount of fluid pumped. Moving the swash plate to a neutral pitch will result in no fluid being pumped (because the length of each piston stroke is effectively zero). It is possible to reverse the direction of the fluid being pumped by changing the angle of the swash plate.
Cylinder Block
The cylinder block consists of a round cylinder with smaller bored cylinders penetrating through its entire length. Each of the smaller bored cylinders provides the necessary space for the pistons to move linearly back and forth (reciprocating motion). As the pistons move, they charge and discharge the cylinder space. The cylinder volume charged and discharged per stroke depends upon the length of each piston’s stroke.
Port Plate
Fluid is drawn into the cylinders, and discharged from the cylinders, via the port plate (sometimes called the ‘valve plate’).
Inlet/Outlet
Fluid enters or exits the pump through this port. The swash plate dictates in which direction the fluid will flow through the pump i.e. if the port is an inlet or outlet port.
Drive Shaft
The power to rotate the pump is provided via the drive shaft. Piston pumps are usually electrically or mechanically driven, although it is also possible to hydraulically operate the pump.
How does a piston pump work?
The basic working principle of a piston pump involves the reciprocating motion of a piston within a cylinder which alternately draws-in and discharges fluid, creating near continuous flow. During the suction stroke, the piston moves backward, decreasing the pressure in the cylinder, consequently drawing fluid into the cylinder through the inlet valve. During the discharge stroke, the piston moves forward, increasing the pressure within the cylinder, consequently opening the discharge valve and forcing the fluid out of the cylinder. Both the suction and discharge valves are spring-loaded to ensure they only open once specific pressures are reached.
Additional Resources
https://en.wikipedia.org/wiki/Piston_pump
https://www.panagonsystems.com/how-does-hydraulic-piston-pump-work
https://www.elprocus.com/piston-pump-working-and-different-types