Tronair 5731, Operation & Service Instructions

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Model: 5731
Hydraulic Power Unit
08/2016 | Rev. 08 Page | 13
5.5 PRELIMINARY ADJUSTMENTS FOR OPERATION (continued)
5.5.2 Pressure Control Adjustment
a. Open bypass valve.
b. Select "Hydraulic Power Unit" position with reservoir selector valve.
c.
Start HPU.
d. Close bypass valve.
e. Adjust pressure control for desired pressure; observing the system pressure gauge, read in psi (bars). Be sure the control
shaft lock nut is loose during adjustment. Tighten after adjustment to maintain setting.
NOTE: Once the flow and pressure controls have been adjusted, it is not necessary to change these settings after
each operation unless desired.
5.5.3
Reservoir Selector Valve Operation
Operation of the reservoir selector valve allows the operator to select either the aircraft reservoir (closed loop) or the HPU
reservoir (open loop).
CAUTION!
The reservoir selector valve should only be operated when the HPU is not running. The operation of the
reservoir selector valve should be done prior to starting the HPU.
a. Aircraft Reservoir Position (Closed Loop)
In this position, the HPU is dependent on the aircraft reservoir and system for an adequate supply of fluid. Cavitation, due to
an inadequate fluid supply from the aircraft, may be indicated by erratic fluctuation of the system pressure gauge or flowmeter.
At times, the aircraft fluid supply will be restricted due to small return oil lines in the aircraft. If this is a problem, decrease the
flow control setting until the cavitation is eliminated.
b. HPU Reservoir Position (Open Loop)
In this position, the HPU reservoir supplies fluid to the pump and accepts return fluid from the aircraft. It is desirable to operate
the HPU in this mode since it eliminates any possibility of cavitation.
Since the HPU reservoir is vented to atmosphere and the aircraft is at a higher level, it is normal for the aircraft reservoir to
drain into the HPU reservoir. It is, therefore, necessary to be sure that sufficient room is available in the HPU reservoir to
accommodate the additional fluid.
CAUTION!
The aircraft system reservoir must be serviced after completion of operational testing.
In the "HPU Reservoir" position, faster landing gear swings are usually possible since there is no restriction to flow at the
pump inlet.
5.5.4
Bypass Valve Operation
The bypass valve is used for unloading the pump. The valve should be either in the fully open or fully closed position only. Do
not operate the valve in a partially open position.
a. Start Up Operation
The bypass valve must be opened prior to starting the HPU in order to allow the motor to start under a no load condition and
not pressurize the aircraft hydraulic system.
b. Shut Down Operation
Prior to shutdown, the bypass valve must be opened to bleed off any residual system pressure.
CAUTION!
Excessive heat, which could damage machine components, will be generated if the bypass valve is
partially open or is used for regulating flow or pressure.

Use the flow and pressure controls for regulation.

Use the bypass valve for unloading the system only.