A control for oil flow in a hydraulic system wherein a standard open closed type solenoid valve is modified so that the rate of flow through the valve relates to the electrical power supplied to the valve solenoid coil. GATE VALVESIn hydraulic control systems, it may be required to vary the flow of oil controlling the speed of a mechanical element, for example the speed of a hydraulic elevator.Butterfly Valves This can be done by employing known solenoid type proportional valves which respond to the signals given by a computer, this having received measurements of the actual speed of the elevator, Needle & Gauge Valves comparing this speed with the value of a pre-determined target speed and calculating the required adjustment of electrical power to the proportional valve solenoid effecting oil flow to achieve the required correction of elevator speed. It is an object of the invention to employ the major parts of low cost standard open closed type solenoid valves with inexpensive modifications such that the rate of oil flow through the solenoid valve is relative to the electrical power supply to the solenoid coil, as with a proportional valve. A further object of the invention is to reduce manufacturing and stocking costs of two essential types of flow metering valves by providing the options of having the flow path of the solenoid either "open" or "closed" in their position of rest when no electrical power is applied, employing identical parts in the solenoid assembly, with one minor exception. A further object of the invention is to achieve interchangeability between a standard open-close two position type solenoid and a variable flow solenoid without the requirement of additional installation space or any other modification to the main hydraulic valve manifold.

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