About Air Controls for catheads
The friction clutch of automatic catheads must be capable of an infinitely variable line pull through its entire range and of 100% slippage at the desired pull. Disengagement must be instant.
To control this clutch by a lever or pedal the operator regulates his effort on the lever or pedal to produce the desired amount on engagement.
When the clutch is to be actuated by pneumatic means, it is essential that the control equipment be capable of duplicating the type of control effort exerted by the operator on a regular basis.
Thus a set of air controls must be able to produce and maintain a line pull of any certain amount in the range of the cathead without further increase until the operator desires to vary the pull.
The variation of pull is accomplished by pneumatic means. This is done by the use of fully graduated control valve, which is able to change the cathead actuator, any pressure from 0psi to 100psi. It is very desirable to have the ability to to control the pressure with accuracy in the lower pressure range.
We distribute a special control valve that is equipped with a graduating cam that delivers 0 to 40 psi in the first 60° of lever travel and 40 to 100 lbs in the remaining 30° of travel. The lever returns to its original position when it is released and all pressure is relieved. The excess pressure is bled off bled off from the control system, if the operator desires to reduce his line pull without entirely releasing the clutch.
A quick release valve is provided to release the air from the actuator. This valve acts when the air pressure in the line from the control valve is reduced below the pressure in the actuator. It is obvious the smaller the volume of air in the line from the control valve to the quick release valve the shorter the time required to exhaust it. We recommend a ¼” OD copper tube or a 3/16” ID high-pressure hose for this section of the piping. Any larger diameter is detrimental to the performance of the cathead. Any stretching in the hose may also delay the operation of the quick release valve.