Dover HEIL LIBERTY TP1L-SM-0520, Service Manual

Page: 46 / 136

Issued May 2020
Pumps Copyright 2020, Heil Environmental
Printed in the U.S.A.
Pumps
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TANDEM VANE PUMP O.I.G.A.I. HYDRAULIC SYSTEM TROUBLESHOOTING
The Operate-in-Gear-at-Idle (OIGAI) system is designed to perform the loading operations at standard idle speed. It is
comprised of two major components, the monoblock tandem vane pump and attached unloader valve assembly.
On the OIGAI REL systems the P1 closest to the pump input shaft while the P2 farthest from the input shaft supplies flow
to the complete hydraulic systems.
The unloader valve assemblies consist of a manifold (pressure) block, a normally open (N.O. or NO) cartridge valve and a
12VDC-solenoid coil. In operation mode, the current is supplied to the valve coil causing the valve to close, forcing pump
flow to the hydraulic circuit. In bypass mode, the coil is de-energized causing the valve to open, allowing the oil to re-
circulate either back to tank or to the pump inlet.
A. Troubleshooting
The symptoms of a problem in the pump circuit are either slow operation or no operation at all.
There are three primary causes for the pump circuit to not operate properly:
Low or no voltage to the unloader valve coil.
Malfunction in the unloader valve assembly.
Internal problem with the pump.
Perform the following test after finding that there is insufficient or no flow to the loader and/or body valves.
1. Check the Electrical Supply to the Unloader Valve Coils
a. With the system turned on and the engine operating at idle, test the voltage at the coil. It should read a minimum
of 10 VDC. If proper voltage is present and the problem persists, proceed to step 2. If the voltage is below 10
VDC, check the electrical system for problems that can cause a drop or loss of voltage to the unloader valve
solenoid coil. Some examples are a broken or shorted wire, blown fuse, fault in the side door switch (if equipped),
no alternator input or a failed PLC calibration.
b. Use an ohm meter to check resistance in the coil. If the measurement is less than 5 ohms or more than 20 then
the circuit coil is damaged. If the coil is damaged, replace the coil.
2. Eliminate the Unloader Valve from the Circuit
a. With the engine off, Cap and plug the tube connection for the bypass to the pump inlet. This forces all oil to the
hydraulic circuits as if the pump is on. (NOTE: Pump control switches in the cab are no longer effective.)
b. Restart the truck and test the functions. If the hydraulic system functions return to normal operation (speed and
pressure within specifications), replace or repair the unloader assembly.