13-10-615 Page 31
Figure 4-5 – SHUTTLE VALVE
Purge Air Valve
- The purge valve is a normally closed two-way air actuated valve that admits purge air
from the final discharge manifold to the compressor to counteract the oil knock that occurs in oil-flooded
rotary screw compressors when they are completely unloaded with pressure in the oil reservoir. This
valve is controlled by the same control pressure which controls the inlet valve.
Turn Valve
- The turn valve is a helical valve which, when rotated, opens and closes a series of ports
cast into the compressor cylinder. When these ports are open, they direct some of the air which would
otherwise be compressed back to the inlet, reducing both capacity and power consumption.
Turn Valve Actuator
(Figure 4-6, page 31) - The turn valve actuator is a rotary rack and pinion device
which positions the turn valve according to system demand. Filtered oil from the reservoir is directed to
the outboard ends of the two actuating cylinders to move the rack and rotate the valve. Located on the
end of the cylinders are adjusting screws which limit the travel of the actuator. When looking at the rear
of the compressor, the adjusting screw on the right on the compressor adjusts the fully closed (full load)
position of the valve. The full load position of the actuator may be checked by removing the adjusting
screw at the unloaded end of the actuator (left side of the compressor) and using a rod to push the
pistons to the full load position. The rod must be clean and free of burrs and scale. Take care not to
scrape the cylinder walls when moving the pistons.
Figure 4-6 – TURN VALVE ACTUATOR (SECTIONED)
209EAU797
(Ref. Drawing)
