(2) The pump provides hydraulic
vides the operator with an indication of
pressure being applied. The HIGH PRES-
pressure as commanded by the PRESSURE
SURE BYPASS valve provides a path for
The two pressure
of hydraulic fluid when
command lines to the pump carry 28 vdc
either the load valve is closed or when
which positions the pressure adjustment
hoses to the aircraft (or dual manifold)
mechanism inside the pump. When output
Restrictions in the
connector pin G is at 28 vdc (pin H is
are not connected.
the return) the pump mechanism operates
HIGH PRESSURE BYPASS valve line and in
to increase pressure. When the applied
the dual manifold bypass line provide a
voltage is reversed on the pump input
back-pressure of 500 psi when the bypass
leads, the mechanism operates to de-
This back-pressure is
valve is open.
crease pressure. The PRESSURE switch is
required for proper pump operation.
spring loaded to its unconnected center
position. So the pump pressure mechan-
(6) Application of hydraulic power
to the aircraft is controlled by the
ism remains in the last position it was
load select valve.
set to by the operator unless power to
the hydraulic module is turned off.
operation of the load select valve
When POWER switch S1 is set to OFF, out-
involves three steps as follows:
put connector pin H is connected to 28
(a) OUTPUT switch S4 is set to
vdc and pin G becomes the return line.
ON which applies 28 vdc to the pilot
This causes the pump pressure mechanism
to move to the position of minimum pres-
sure (500 psig).
(b) Activation of the solenoid
pushes the pilot valve against the
(3) Prior to servicing an aircraft
is set to the maximum allowable pressure
be applied to the load valve.
for that particular aircraft.
operator increases the pump pressure be-
(c) Fluid pressure pushes the
load valve against its spring allowing
yond the allowable maximum, the PRESSURE
hydraulic system output to be applied to
RELIEF valve will open to prevent excess
(7) When the OUTPUT switch is set
(4) A high and low pressure filter
is provided to remove any solid contami-
valves all return to their original po-
nation in the hydraulic fluid. A switch
sitions and the fluid pressure trapped
is connected across each filter. If the
between the valves is released back to
filter gets dirty and the difference be-
The output and return
tween input and output fluid pressure
hoses are each 30 feet in length. The
exceeds 50 psi the switch closes. As
output hose is 1/2 inch in diameter and
the return hose is 3/4 inch. Quick dis-
pressure switch DS1 or DS2 causes the
REPLACE FILTER light to illuminate.
connects containing check valves on each
end hold the fluid in the hose so it
will not drain out between uses.
tective caps are attached to keep quick
disconnect fittings clean when hoses are
pressure fluctuations at aircraft input
not in use.
The OUTPUT PRESSURE gauge pro-