Air tool with speed responsive shutoff

Rotary kinetic fluid motors or pumps – With control means responsive to non-cyclic condition... – Centrifugally initiated valve controlling fluid flow in...

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173 12, F01D 2500

Patent

active

040048594

ABSTRACT:
A speed responsive shutoff for a pneumatic tool such as a nut runner is disclosed. The shutoff, effective to terminate air supply to the air motor under load, employs a centrifugally operated air valve having a flat valve head which is biased against a valve seat through which pressurized air travels en route to the motor. A small orifice in the valve head leads to an expansible chamber behind the head. In operation of the tool, when the throttle valve is open, initial air is supplied to the motor by a slight opening of the air valve due to a higher pressure in front of the valve head than behind it. The motor quickly reaches a predetermined speed level at which time the air valve is fully opened by centrifugal weights. Under loading approaching stall, the motor slows to a speed low enough to allow the air valve to move toward closure under the influence of a spring. Pressure builds up in front of the valve head but has sufficient time to pass through the orifice and pressurize the chamber behind the valve head, equalizing the two pressures and allowing the spring to fully close the air valve. Because the shutoff occurs before the stall condition is attained, stall jerking is substantially eliminated.

REFERENCES:
patent: 3373824 (1967-11-01), Whitehouse
patent: 3608647 (1971-09-01), Bories
patent: 3740174 (1973-06-01), Amtsberg
patent: 3785442 (1974-01-01), Amtsberg
patent: 3791458 (1974-02-01), Wallace
patent: 3904305 (1975-09-01), Boyd
patent: 3930764 (1976-01-01), Curtiss

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