capable of removing all contaminants larger than 10 to 25 microns (1 micron equals 0.00004 inch).
Another type is the cuno filter element. It has a stack of closely spaced disks shaped like spoked
wheels. The hydraulic fluid is filtered as it passes between the disks.
HAND-OPERATED HYDRAULIC PUMP
The heart of any hydraulic system is the pump which converts mechanical energy into hydraulic energy.
The source of mechanical energy may be an electric motor, the engine, or the operator's muscle.
Pumps powered by muscle are called hand pumps. They are used in emergencies as backups for power
pumps and for ground checks of the hydraulic system. The double-action hand pump produces fluid
flow with every stroke and is the only type used on Army aircraft.
Handle to the Right. The double-action hand pump, shown in Figure 1-4, consists of a cylinder
piston with built-in check valve, piston rod, operating handle, and a check valve built into the inlet port.
As the handle is moved to the right, the piston and rod also move to the right. On this stroke, the inlet
check valve opens as a result of the partial vacuum caused by the movement of the piston, allowing fluid
to be drawn into the left chamber. At the same time, the inner check valve closes. As the piston moves
to the right, the fluid in the right chamber is forced out into the system.
Figure 1-4. Double-Action Hand Pump.
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