CYLINDERS
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HYDRAULIC PUMPS
HYDRAULIC PUMP INFORMATION
Hydraulic pumps convert mechanical energy into fluid power energy. All hydraulic pumps are positive
displacement which means the outlet flow is sealed from the inlet flow. A small amount of fluid is de-
signed to leak internally to lubricate and cool the internal components of the pump. The only function
of the pump is to produce flow in a system. The amount of resistance and or load induced on the
system determines pressure. If a pump’s flow is directed back to the reservoir without restrictions, no
pressure will be developed. If a load or restriction is introduced to the pump’s flow, pressure will rise
to overcome the resistance. Hydraulic pumps can be grouped into two classes: fixed and variable
displacement.A fixed displacement pump will generate a constant flow at a given RPM. When designing a fixed
displacement system, low pressure flow returning to the reservoir is needed when the system is idle.
Some form of relief is always required with this type of pump.A variable displacement pump can change flow internally depending upon system pressure created
by an external signal. Flow from these pumps can be blocked provided the signal to the pump will
automatically limit the pressure below the lowest maximum pressure of any component in the system.HYDRAULIC PUMPS
Fixed displacement vane pumps use a set of vanes that are inserted into a rotor. The vanes extend
out to a cam ring that remains stationary. As the rotor and vanes turn, the area expands on the suc-
tion side of the pump, creating a vacuum. The vacuum draws the fluid into the pump. When the fluid
rotates to the pressure side of the pump, the area is reduced and forces the fluid out of the pump
through the pressure port.Fixed Vane Pumps
Gear pumps use two gears that mesh together to produce flow. The drive gear is connected to the
input shaft and the idler gear is turned by the drive gear. These fixed displacement pumps create
flow by rotating the gears together. As the gears rotate and separate, a vacuum is formed that draws
fluid into the suction port (this can vary from pump to pump). The fluid travels around the outside of
the gear to the pressure side of the pump. As the gears mesh together the fluid is forced out of the
pressure port. Due to their rugged construction and ability to handle higher levels of contaminants,
they are widely used in tougher applications.Gear Pumps
A variable displacement pressure compensated piston pump uses a set of pistons parallel to the in-
put shaft, which are inserted into a cylinder block. One end of the piston is attached to a swash plate
which can be set on an adjustable angle, perpendicular to the input shaft. As the shaft rotates and
turns the pistons and cylinder block around the shaft, the piston will reciprocate in the cylinder block
bore as it rides up and down on the slope of the swash plate. If the swash plate angle is set to zero,
fluid will not enter or exit the pump. As the angle of the swash plate increases, the piston travels a
longer stroke within the bore and displaces more fluid. The compensator mounted on the pump con-
trols the pressure at which the pump strokes to a near zero displacement.Pressure Compensated Piston Pump