The pump converts the mechanical energy of its primary motor into hydraulic energy by delivering a certain amount of hydraulic fluid at high pressure into the system.
In general, all pumps are divided into two categories, namely hydrodynamic or non-positive displacement and hydrostatic or positive displacement. Hydraulic systems generally employ positive displacement pumps only.
Positive Displacement Pumps:
These pumps provide a certain amount of fluid for each cycle of movement, that is, stroke or revolution. Its performance in terms of the volumetric flow depends solely on the speed of the primary motor and is independent of the output pressure despite the leaks.
These pumps are generally classified by their volumetric flow rate output at a given flow velocity and by their maximum operating pressure capacity, which is specified based on safety factors and life expectancy considerations.
A gear pump develops the flow by carrying fluid between the teeth of two meshing gears. One gear is driven by the transmission shaft and the other rotates, which is free. The pumping chambers formed between the gear teeth are enclosed by the pump housing and the side plates.
A low pressure region is created in the inlet when the teeth of the gears separate. As a result, the fluid flows and is transported by the gears. As the teeth re-engage in the outlet, a high pressure is created and the fluid is expelled.
In a vane pump, a rotor is coupled to the drive shaft and rotates inside a cam ring. The paddles are placed in the slots of the rotor and follow the inner surface of the ring as the rotor rotates.
The centrifugal force and the pressure under the blades keep them pressed against the ring. The pumping chambers are formed between the vanes and are surrounded by the rotor, the ring and the two side plates.
At the pump inlet, a low-pressure region is created as the gap between the rotor and the ring increases. The oil that enters here is trapped in the pumping chambers and then pushed towards the exit as the space decreases.
In piston pumps, a piston that moves alternately in a hole attracts the liquid as it retracts and ejects it in the advance stroke. Two basic types of piston pumps are radial and axial.
Radial Piston Pumps:
In a radial pump, the cylinder block rotates on a stationary cylinder and inside a circular reaction ring or rotor. As the block rotates, due to centrifugal force, load pressure or some form of mechanical action, the pistons remain pressed against the inner surface of the ring that is displaced from the center line of the cylinder block.
Because the ring is off center, when the pistons alternate in their holes, they absorb the fluid as they move outward and discharge it as they go.
Inline Piston Pumps:
In axial piston pumps, the cylinder block and drive shaft are coaxial and the pistons move parallel to the drive shaft. The simplest type of axial piston pump is the in-line design of the tilting plate.
The cylinder block in this pump is rotated by the primary motor connected to the drive shaft. The pistons mounted in the holes of the cylinder are connected to an angled oscillating plate. As the block rotates, the piston shoes follow the oscillating plate, causing the pistons to match, since the distance of the connection point changes cyclically as the oscillating plate rotates.
The fluid ports are placed on the valve plate so that the pistons pass through the inlet port as they are removed, so that the liquid enters the cylinder cavity, and pass the outlet when they are forced to return, sending liquid to the system.