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Utility Hydraulic Problem


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Hi C-130H expert, we got problem on utility hydraulic system. we found that the hydraulic quantity in the reservoir reducing and found hydraulic come out from auxiliary drain after start up . Is there any possible valve defect on this situation? Thank you in advance.

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Here is some information from years past.

HERCULES Service Information Letter


Dated 1 AUG 1978, Issue Number 27


Due to certain malfunctions or incorrect procedures, hydraulic fluid may interchange between systems causing one system to be low and the other to possibly overflow.

Ground Test Interconnect Valve

Occasionally the ground test interconnect valve is suspected bad and changed when it is not malfunctioning. All ground crews must remember that: ALL UTILITY ANO AUXII.IARY HYDRAULIC SYSTEMS PRESSURES, INCLUDING NORMAL AND EMERGENCY BRAKES, MUST BE ZERO PRIOR TO SHIFTING THE GROUND TEST INTERCONNECT VALVE HANDLE.

It is imperative that the following precautionary steps be strictly adhered to prior to shifting the ground test interconnect valve handle in either direction:

1.       System hydraulic pressure must read zero on all utility and auxiliary system gages, and all accumulator air pressure gages must read pre-charge pressure only. (Utility system pressure can be depleted by cycling the controls.  Auxiliary system pressure can be depleted by cycling the aft cargo door.)

2.       Actuate the normal and emergency brakes until pressure on both cockpit gages is zero.

If the utility system is pressurized while the ground test valve is in the normal position, approximately 50 cubic inches of fluid will be pumped from the utility reservoir to the normal brake accumulator.  If the utility pumps are then shut off, the fluid will remain trapped in the brake accumulator.  Assuming then that the ground test interconnect valve is switched, if the brakes are actuated several times, the 50 cubic inches of fluid which came from the utility reservoir will return to the auxiliary reservoir.  If the ground test interconnect valve is then positioned to normal, the transfer of the fluid from the utility system to the auxiliary system will be complete.


The utility system and normal brake accumulators can cause a fluid interchange if leaking air across the piston.  With the interconnect valve in NORMAL position, air leaking from these accumulators will seep into the utility return line and displace fluid which wi11 return to and eventually overfill the utility reservoir.

The actual transfer of fluid occurs when the utility system is pressurized with the auxiliary pump.  Fluid pumped from the auxiliary reservoir goes to fill the partially empty utility system lines; if the interconnect valve is then repositioned to NORMAL, the fluid is lost from the auxiliary system and added to the utility system.  The transfer may occur in the opposite direction (from utility system to auxiliary system) depending on the positioning of the interconnect valve and operation of the system.

Other Causes

If fluid is still being interchanged between the utility and auxiliary systems, the following components should be checked for internal leakage:

o   Nose landing gear shuttle valve.

o   Four main brake shuttle valves.

o   Two brake metering valves.

o   Nose landing gear uplock cylinder.

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