Abstract: A hydraulically controllable, leakproof holding valve is disclosed, and which is adapted to be attached in the lifting hydraulic line leading to a working cylinder or the like. The holding valve includes a slidably mounted control piston, which functions as a controlled non-return valve during periods when the working cylinder is stationary or being lifted, and the piston also functions as a throttling valve during periods when the working cylinder is being lowered.

Abstract: A pilot operated relief valve is disclosed which includes a first control space operatively connected to the inlet fluid channel, and a second control space operatively connected to the outlet fluid channel. In one embodiment, each control space is connected to a relief outlet by means of an adjustable valve, whereby the valve is adapted to operate as a pressure relief valve in either flow direction. In another embodiment, one of the control spaces is connected to the opposite channel by means of a one-way check valve, so as to function as a makeup fluid supply valve upon the pressure in the opposite channel reaching a predetermined low level.

Abstract: A hydraulic control system for an elevator or other similar reciprocating user is disclosed, which comprises an adjustable throttle valve and a control or bypass valve disposed in the fluid supply line between the pump and elevator. A pressure difference balance is provided for controlling the operation of the control valve, and the pressure difference balance has one end operatively connected to the pressure provided by the pump, and the other end operatively connected to the pressure in the user or load line. The control valve is thus adapted to maintain a desired pressure difference across the throttle valve which is independent of the load on the user. In addition, the zero setting of the pressure difference balance is adjustable, so as to permit the system to be equally operable in both the upward and downward movements of the elevator.

Abstract: A pilot operated relief valve is disclosed which includes a first control space operatively connected to the inlet fluid channel, and a second control space operatively connected to the outlet fluid channel. In one embodiment, each control space is connected to a relief outlet by means of an ajustable valve, whereby the valve is adapted to operate as a pressure relief valve in either flow direction. In another embodiment, one of the control spaces is connected to the opposite channel by means of a one-way check valve, so as to function as a makeup fluid supply valve upon the pressure in the opposite channel reaching a predetermined low level.

Abstract: A hydraulic control system for use in machine tools, construction machines, hoists and the like, with a driven unit the hydraulic circuit of which is controlled by one or more electromagnetically positioned slide valves, and with an arrangement for automatically regulating the velocity of the hydraulic drive unit regardless of fluctuations in the pressure of the oil supply and similar disturbances. The regulating arrangement includes a potentiometer mechanically controlled by a flow meter interposed in the hydraulic circuit; and an electric comparator the inputs of which are connected to the potentiometer and to a desired-flow-value selector, respectively, and the output of which controls the valve electromagnet(s). In this manner the difference signal developed by the comparator is used to change the setting of the valve in a correcting sense. Several implementations for this regulating circuit and for the design of the flow meter and the valves are disclosed.