Brake fluid is a subtype of hydraulic fluid with high boiling point and low freezing point. Aircraft hydraulic fluid applications require special care as they are critical to flight safety. Keeping these fluids free from contamination is the main concern.

Hydraulic transmissions need a different grade of light hydraulic fluid, and manually shifted transmissions use a heavier gear oil similar to that for rear axles to resist heavy loads on the gear. Multi-grade hydraulic fluid is designed to be free of heavy metals.

Shell has launched a multi-grade hydraulic fluid that will perform in extreme conditions called Shell Tellus Oil STX. This blend is a zinc-free, ashless hydraulic fluid with high shear stability, formulated with group II base oils with additive technology.

The best hydraulic fluids offer a wide temperature range and high shear stability and versatility.

Bypassing contaminated filter elements is accomplished by using a bypass line. Contaminated hydraulic fluid is delivered, but it will bypass and avoid malfunctioning the axial piston. The quantity of hydraulic fluid which flows through the filter element and/or the bypass line can be influenced via the pressure switching valve and the indicating means. FLOOR TRANSMISSION JACK It is thus possible for the pressure switching valve to be controlled by the pressure of the hydraulic fluid. This occurs upstream of the filter element or by the difference in pressure of the hydraulic fluid at the filter element. The hydraulic fluid which bypasses the filter element by means of the bypass line does not get fed into the closed circuit.

An electrical evaluating and indicating unit can be to reduce the operating rate of the delivery pump. Temperature-sensing devices can be used to indicate when the temperature drops below a certain minimum value. This activates the device for reducing the quantity of hydraulic fluid which flows to the filter element and/or through the bypass line within the hydraulic circuit. These measures help avoid excessively low temperatures of the hydraulic fluid.

The hydraulic fluid path works in a serial fashion, fluid flows via a screen, through an intake line, and into the filling pump. The filter element thus receives unfiltered hydraulic fluid which then leaves the via the discharge channel and passes to the low-pressure side of the filling circuit. The weight of the hydraulic fluid alone may apply sufficient pressure to keep the valve open, even with the loss of normal surface pressure.

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