ATA 29

Does your emergency hydraulic pump cycle too often? The problem could be a faulty thermal relief value. If there is no evidence of external leakage the thermal relief valve should be suspect for bypassing. This valve performs two functions, it provides pressure relief at 1250 +/- 100 psi.and has a built-in check valve to prevent pressure from backing up thru the pump. This happens to be the only check valve in the emergency hydraulic system. Emergency pressure should hold for at least 60 seconds and pump running time should not exceed 45 seconds.

The hydraulic restrictors in the thrust reverser system can cause erratic operations of the thrust reverser if they are installed in the wrong port of the T/R actuator. The restrictor and the regular union are similar in appearance and can be interchanged if not properly identified before installation. The restrictor should be installed in the “stow “line port and the regular union should be installed in the “extend” line port.