This invention relates to a process and device for purifying the active liquid within hydraulic control circuits.
In the manufacture of hydraulic control circuits which are operated by remote control, such as those used in aircraft, maximum reliability and safety in operation must naturally be sought. This is the reason why such circuits are often employed in duplicate, i.e., so that one can be substituted for another in case of a breakdown.
The presence of corrosive ions or ionic groups in the active liquid, in particular, chlorine or fluorine ions, or hydrochloric acid, presents a particular problem, however. These ions generally result from the chlorous or fluorous solvents, such as trichlorethylene and particularly trichlorethane, which are used for the cleaning of hydraulic circuits by personnel handling aircraft or in maintenance workshops during inspection, despite the fact that use of these solvents is expressly forbidden by the manufacturers.
The traces of solvent which are thus formed in the liquid are more or less dissipated, particularly by the heat which is produced during operation, for example in the annular covers of servo-control valves where the shearing effect can be very great and causes a very high thermal increase locally, or in the pump which pressurizes the liquid. The corrosive ions which are released, however, in time attack the metal of the main parts of the circuit, such as the control valves, thus jeopardizing the operation and safety of the entire circuit.
Even an aircraft which has not had its hydraulic circuit contaminated by the use of the above-noted solvents, can have its hydraulic circuits polluted by being serviced in a maintenance workshop where an aircraft with contaminated control circuits has previously been serviced.
The carelessness of certain users can therefore jeopardize the safety even of aircraft which have been handled in a careful manner.
The applicants have considered this sensitive problem and have found a solution which is very simple to put into practice.