Figure 3-26 Relief valve

a. Check valve b. Membrane d. Pressure regulating valve e. Air bleed stem f. Air bleed port

Working principle:

Refer to Figure 3-26. The compressed air from the air compressor gets into chamber (B) through the inlet (A), then to the outlet (C) through the check valve (a). It will be stored in the air tank.

When the pressure in the air tank reaches 0.748MPa, the air will get into the chamber (D) to push the membrane (b). The regulating valve (d) is opened so that the air gets into chamber (E) to push the valve stem (e) downward. It will make the air bleed valve (f) opened so that the air in chamber (B) and the water and dirt accumulated on the bottom of chamber (B) will be bled via the air bleed port (F). At this moment, the air compressor is running idly. If the pressure in the air tank decreases, the pressure regulating valve (d) and the air bleed valve (f) will be closed, and the relief valve supplies air to the air tank.

The relief valve should be mounted correctly at servicing. The inlet and outlet must not be mounted adversely. The set screw was well preset before shipment. User must not adjust it.

C. Air brake valve (refer to Figure 3-27)

Working principle:

When the operator depresses the brake pedal (2), a force will be applied to the spring (4) through the push rod so that the piston (6) moves downward and the air can not be bled out through the outlet. The air opens the inlet valve and the compressed air is supplied to the brake actuators via outlet. The air pressure at the outlet is released through the air bleed port.

The dustproof cover is made of rubber and mounted at the upper end of air brake valve. It must be kept in good condition. Clean the inside of brake valve periodically. Oil the surface of piston for lubrication. The rubber membrane and valve must not be damaged. They are made of oil-resistant rubber and must not be replaced with other material.

The brake fluid must be clean. Filtration is needed at filling. The oil complementing hole of booster pump must not be blocked. Fill the synthetic brake fluid 719 through the oil cup of main pump so as to assure the reliability and eliminate the “vapor block” in the oil lines.

Do not mix different kinds of brake fluid. If different fluid has to be filled, drain the old fluid thoroughly from the system and clean the system with new fluid. Then drain the used fluid and fill new fluid. Mineral oil must not be used in the system for it may damage rubber parts.

Figure 3-27

1. Adjusting screw 2. Pedal 3. Push rod 4. Balance spring

5. Return spring 6. Piston 7. Air inlet valve

D. Booster pump

Working principle:

Refer to Figure 3-28. The booster pump is air actuated and oil boosted. It includes air cylinder and hydraulic master cylinder. At operation, the air gets into the inlet to move the push rod and piston forward. The push rod moves the push rod seat. The oil inlet valve blocks the oil complementing hole in the hydraulic piston so that high pressure is generated in the hydraulic cylinder. The pressure of outputted oil is 10x90% times of the inputted air pressure. When the air pressure is relieved, the oil complementing hole is opened by the force of spring to let the hydraulic oil return.