Towmotor Corporation

Ralph D Porter

Edward V Leskovec

A control system for a fluid pressure-actuated cylinder or the like includes a pump supplying fluid from a reservoir to a control valve which may be selectively operated to cause cylinder extension or retraction and to immobilize the cylinder at a selected position. A unidirectional flow device connects an accumulator to the flow passage between the control valve and cylinder to smooth pressure fluctuations which can otherwise occur when the control valve is closed and which can otherwise produce erratic cylinder motions. Means are provided to relieve excessive pressure in the accumulator, at times when the control valve is shifted to release fluid from the cylinder, without in the process causing unwanted cylinder drift from feedback of the fluid from the accumulator to the cylinder. The excess accumulator pressure is vented to the reservoir through a pilot-operated check valve which is responsive to the pressure differential across the unidirectional flow device in order to allow communication between the accumulator and the reservoir but only when the pressure in the passage between the control valve and cylinder is less than that in the accumulator by a predetermined amount.

Fluid cylinder control with precision stop action

Cushioning apparatus for cushioning a hydraulic jack is disclosed which includes a plunger reciprocably mounted within a blind bore. The plunger sequentially closes off a plurality of axially spaced orifices provided through the wall of the bore as the plunger moves from a first position adjacent the open end of the bore to a second position adjacent its closed end, thereby progressively restricting the escape of fluid from the bore so as to slow the movement of one of the telescopic members of the jack toward another.

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Euclid, OH, United States of America

Ralph D Porter