at a given speed and (2) variable delivery when running
at a given speed.
Pumps may further be divided into types, based
upon the design used to create force (fluid flow).
Practically all hydraulic pumps fall within three
classifications of designrotary, reciprocating, and
centrifugal. The centrifugal style pumps find little use
in CESE hydraulic systems used in the Naval
Construction Force and will not be covered here. Pumps
may be driven by air pressure, electric motors, gas
turbine engines, or the conventional internal combustion
engines (gasoline and diesel).
All rotary pumps operate by means of rotating parts,
that trap the fluid at the inlet (suction) port and force it
through the discharge port into the hydraulic system.
Gears, lobes, and vanes are commonly used as elements
in rotary pumps. Rotary pumps operate on the positive
displacement principle and are of the fixed displacement
There are numerous types of rotary pumps and
various methods of classification. They may be
classified as to shaft positioneither vertically or
horizontally mounted; the type of drive-electric motor,
internal combustion engine, and so forth;
manufacturers name; or service application; however,
classification of rotary pumps is generally made
according to the type of rotating element. A few of the
most common types of rotary pumps are covered in the
GEAR PUMP. Gear pumps are classified by their
method of meshing together. This style pump is simple
in design and finds wide use in low-pressure hydraulic
systems. A gear pump delivers a constant volume of
fluid at any given rpm (fig. 10-3).
The pump shown is known as a spur tooth and
consists of two meshed gears that revolve alongside
each other in one housing. The drive gear in the
illustration is turned by a drive shaft that engages the
power source. The clearances between the gear teeth, as
they mesh, and the pump housing are very small.
Figure 10-3.-Typical gear type of hydraulic pump.