TM 1-1520-238-T-5 7–30 Change 6 7–7. SYSTEM DESCRIPTION (cont) 7–7 (c) During GSE operation, an AGPU sends high pressure fluid to the GSE pressure port. A flow limiting orifice restricts flow to a maximum of eight gallons per minute at 3000 psi. The back pressure from the GSE return isolation valve piston forces the GSE check valve open. The GSE return isolation valve opens the reserve return system to the GSE return port so that fluid flows out evenly. A pressure bleed orifice between the GSE pressure and return ports prevents hydraulic lock on the GSE return isolation valve. Hydraulic lock prevents the GSE check valve from reseating. GSE pressure flows through the GSE check valve and through the normal and return utility hydraulic manifold system. Normal operating leakage across the GSE check valve leaks back into the return system through the GSE return isolation valve, this prevents pressure build up and actuation of the isolation piston. The utility GSE panel assembly provides connections for direct external hydraulic power and nitrogen servicing. A hand pump services the primary and utility reservoirs from a bulk container of hydraulic fluid and charges the accumulator to 3000 psi (accumulator must be properly serviced prior to using the hand pump). The nitrogen is charged by the use of a nitrogen fill–bleed valve. A nitrogen pressure gauge provides an indication of nitrogen pressure. PRESSURE RETURN CHECK VALVE AIR INLET VALVE CHECK VALVE CHECK VALVE LOW LEVEL PASSAGE PUMP AIR BLEED LOW PRESSURE RELIEF VALVE SCT RTN BYP LOW LEVEL SWITCH RTN INDICATOR DIRTY FILTER APU ACCUMULATOR TO AND FROM DRAIN PORT HIGH PRESSURE RELIEF VALVE SYSTEM RETURN GSE PANEL VALVE ISOLATION GSE RETURN TO GSE RTN CHECK VALVE ISOLATION INLET DIRTY FILTER INDICATOR ACCUMULATOR TRANSDUCER PRESSURE SYSTEM GSE PRESSURE PRESSURE PUMP SWITCH HIGH PRESSURE FILTER PRESSURE S1 SOLENOID S2 SOLENOID BRAKE VALVE SW PRESS RTR BK BRAKE TO ROTOR RELIEF VALVE TRANSDUCER EMERGENCY PRESSURE PRESSURE TO UTILITY SYSTEM ACCUMULATOR ISOLATION VALVE CHECK VALVE AUXILIARY ISOLATION SYSTEMS PRESSURE TO AUXILIARY PUMP FILL FROM HAND PUMP M68–111A OVERRIDE SOLENOID AIR PRESS BLEED VALVE AIR PRESS RELIEF VALVE BRAKE METERING VALVE GSE CHECK VALVE LEGEND RESERVOIR PISTON Figure 7–13. Utility Hydraulic Manifold Functional Diagram