Safety Valves and Inward Relief Valves

Safety Valves and Inward Relief Valves

Valves should be cleaned and installed in a similar manner to discharge valves. Where facilities allow, bellows-type safety valves should be subjected to a leak test before installation in the manner described in the Aircraft or Component Manufacturer’s Maintenance Manuals.

In some installations, safety valves are provided with electrical and manual override controls, in such cases functioning checks on the controls must be made after installation (e.g. limit switches of electrical actuators which may need to be adjusted to cut off the power supply when the valve is at the fully open and fully closed positions). Manual controls should be correctly rigged and checked to ensure that the controls and valve move in phase and operate freely over their full range of travel.

NOTES:

(1)    Limit Switch adjustment is normally carried out when the component is workshop tested.

(2)    After carrying out override control system checks, the appropriate controls should be reset to their normal positions.

Some valves incorporate an electrically-operated position transmitter which signals the valve position to an indicator in the crew compartment; checks should therefore also be made to ensure that the indicated positions correspond.

 Filters and Air Driers

Before installing a cartridge type of filter unit the cartridge and casing should be inspected for signs of damage and also to ensure freedom from dirt and other foreign matter.

In some unit designs the case is made of rubber and for this reason it may have been stored in French Chalk. Before fitting the cartridge into this type of case, all traces of chalk must be removed by lightly brushing the rubber with a suitable cleaning agent as recommended in the relevant Aircraft Maintenance Manual.

In some installations, air driers are of the type which utilises Silica Gel Crystals as drying media. Before installation, the units should be detached and charged with a fresh quantity of Silica Gel Crystals. After installation, a check should be made to ensure that the inspection windows, where provided, are readily visible.

When installing baffle-type air driers, it must be ensured that the sealant necessary for fixing is of the correct type and is correctly applied to the appropriate area of the fuselage skin and air drier casing.

After installation, the connections between the filters, air driers and all appropriate pressure sensing lines must be securely made and leak-tested in the manner described in the relevant Aircraft Maintenance Manual.