The reservoir’s purpose is to store, receive and supply hydraulic fluid. Some years ago reservoirs simply consisted of a tank with several connections, a filler and sight glass assembly and possibly for some form of filter or strainer for initial filtration of fluid as it being filled up. Indeed, there are still many of this type of reservoir in common use on small or older aircraft,these type of reservoirs would usually incorporate a stack(stand) pipe to ensure a reserve of fluid for use in an emergency.
- The necessity to maintain a head of pressure, under all conditions.so that the tank has to be placed at higher point than the EDP (Engine Driven Pump)
- The possibility of the oil becoming aerated during manoeuvrings.
- Cavitation in the supply pipeline to the pump during banking.
- A lowering of hydraulic fluid boiling point at high altitude.
