Types of hydraulic pumps
There are generally three types of hydraulic pump structures found in mobile hydraulic applications. These include gears, pistons and blades. However, there are also clutch pumps, vacuum pumps, and dump truck pumps, such as Muncie Power Products' Dry Valve Pumps and Live PakTM.
A hydraulic pump is a component
of a hydraulic system that takes mechanical energy and converts it into fluid
energy in the form of an oil flow. This mechanical energy is taken from what is
called the main engine (rotational force) such as the PTO or directly from the
truck's engine.
With each hydraulic pump, the
pump will be of either a single-rotor or two-role design. As its name suggests,
the single-rotating pump is designed to operate in one direction of shaft
rotation. On the other hand, a bi-circulating pump has the ability to work in
any direction.
Gear pumps
For truck-mounted hydraulic
systems, the most common design in use is a gear pump. This design has fewer
moving parts, is easier to maintain, is more tolerant of pollution than other
designs, and is relatively inexpensive. Gear pumps are fixed displacement
pumps, also called positive displacement pumps. This means that the same volume
of flow is produced with each rotation of the pump shaft. Gear pumps are rated
for maximum pump pressure rating, displacement in cubic inches, and maximum
input speed.
Gear pumps are generally used in
open center hydraulic systems. Gear pumps trap oil in the areas between the
pump gear teeth and the pump body, move it around the circumference of the gear
bore, and then force it out through the outlet port when the gears are engaged.
Behind the copper alloy drive plates, or wear plates, a small amount of
pressurized oil pushes the plates firmly against the gear tips to improve pump
efficiency.
Piston pumps
When high operating pressures are
required, piston pumps are often used. Piston pumps traditionally withstand
higher pressures than gear pumps of similar displacement; however, there is a
higher initial cost associated with piston pumps, as well as lower resistance
to contamination and increased complexity.
The equipment designer and
service technician must understand this complexity to ensure that the piston
pump operates correctly with its additional moving parts, stricter filtration
requirements, and stricter tolerances. Piston pumps are often used with
truck-mounted cranes, but they are also found in other applications, such as
snow and ice control, where it may be desirable to vary the flow of the system
without changing the engine speed.
A cylinder block containing
pistons that move in and out is located inside a piston pump. It is the
movement of these pistons that pulls the oil from the supply port and then
pushes it through the port. The angle of the discontinuous plate, against which
the sliding end of the piston slides, determines the length of the stroke of
the piston. While the powder plate remains stationary, the cylinder block,
which includes the pistons, rotates with the pump's input shaft. The pump
displacement is then determined by the total volume of the pump cylinders.
Fixed and variable displacement designs are available.
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