TM 1-1520-238-10 2-52 Change 8 (6) Pressure Switch. Senses primary system pressure and informs the pilot and CPG of a low oil pres- sure condition by illuminating the PRI HYD PSI segment on the pilot caution/warning panel and PRI HYD segment on the CPG panel. This switch illuminates the segments until the system pressure is above 2050 psi and will again illuminate the segments when pressure falls below 1250 psi. (7) Pressure Transducer. Measures hydraulic pressure on the pressure side of the manifold and trans- mits this value to the left side of the pilot dual hydraulic gauge. 2.38.2 Utility Hydraulic System. The utility hydraulic system (fig 2-30) provides hydraulic power to the utility side of the lateral cyclic, longitudinal cyclic, collective, and directional servo actuators. This system also provides hy- draulic power to the rotor brake, area weapon, external stores, tail-wheel lock, ammo carrier drive, and APU start- er. The utility hydraulic pump (on the accessory drive case of the main transmission right side) is identical to that in the primary system. The hydraulic heat exchanger may still be installed on some helicopters. The heat exchanger is obsolete and is being removed through attrition. The only significant difference in the two systems is the man- ifold, with an associated accumulator and gas reservoir. Additional components in the system are the accumulator, rotor brake, and the utility hydraulic return accumulator that dampens hydraulic pressure surges caused by sud- den actuation of the gun turret. a. Utility Manifold. The utility manifold (fig 2-31) is installed on the aft main fuselage deck on the right side. It stores, filters, supplies, and regulates the flow of utility hy- draulic fluid. Demands on the utility system are much greater than those on the primary system, and the utility manifold installation is therefore larger, with a reservoir capacity of 1.3 gallons. Total system capacity is about 2.6 gallons. An air-pressure relief valve, low-pressure relief valve, high-pressure relief valve, reservoir low-level indi- cating switch, fluid-level indicator, return filter, pressure fil- ter, pressure switch, and pressure transducer, are identi- cal in function to the primary system components. The pilot caution/warning panel provisions are also similar; but the lights are labeled OIL LOW UTIL HYD, OIL BYP UTIL HYD, and UTIL HYD PSI. Low utility hydraulic pressure also illuminates the CPG UTIL HYD light. The utility man- ifold also incorporates several other features not dupli- cated on the primary manifold. These are the utility accu- mulator hydraulic pressure transducer and rotor brake solenoids. (1) Low-Level and Auxiliary Isolation Valves. Permit hydraulic fluid to flow to the external stores, ammo carrier drive, tail wheel lock actuator, and area weapon turret. If the reservoir fluid level decreases significantly, the reservoir piston, driven by PAS air, will contact and close the low-level valve. The auxiliary isola- tion valve, which normally requires two sources of pres- sure to permit fluid flow, will then close and deny hydraulic power to the area weapon turret, the external stores ac- tuators, and the ammo carrier drive. (2) Shutoff Valve. Located in the pressure line to the directional servo and TAIL WHL lock actuator is ac- tuated by the low-level switch in the utility system reser- voir. The utility side of the directional servo actuator and the TAIL WHL lock actuator will be inoperative if a low util- ity system fluid level is sensed. (3) Accumulator Isolation Valve. Normally iso- lates accumulator pressure from the rest of the utility sys- tem but allows system flow from the pump to pass through a portion of the valve and on to the utility side of the tan- dem servo actuators. (4) Override Solenoid Valve. Normally de-en- ergized closed, permits crew management of the accumu- lator reserve pressure. When the pilot or CPG places his EMER HYD switch ON, the override solenoid valve will energize open and accumulator fluid will pass to the accu- mulator isolation valve via emergency routing. In this case, another portion of the accumulator isolation valve will permit accumulator fluid to flow to the utility side of the servo actuators. The EMER HYD switch is powered through the EMERG HYD circuit breaker on the pilot over- head circuit breaker panel. (5) Accumulator Hydraulic Pressure Transduc- er. Located in the manifold will provide the pilot with a continual indication of accumulator pressure on the accu- mulator hydraulic pressure indicator. During normal op- eration, the indicated pressure will be the same as that of the utility hydraulic system.