Abstract: An arrangement for supplying pilot oil to a servo-valve arranged to activate a main valve of a hydraulic system. The hydraulic system also includes a hydraulic oil pump, a valve located between the pump and the main valve, a pressure reducing valve located between the pump and the servo-valve, and at least one auxiliary assembly is arranged to deliver an electric signal to electromagnetic means arranged to activate the servo-valve. In accordance with the invention, the valve located between the pump and the main valve is arranged to be substantially or fully closed when standing at a given, pre-determined pressure corresponding to the servo pressure required by the servo-valve in order to carry out its intended function, and is arranged to be open when the pressure slightly exceeds the aforementioned pre-determined pressure. An electromagnetically operable shunt valve is located between the pump and pressure reducing valve and, when open, to pass oil direct from the pump to a tank.

Abstract: A control assembly comprises a housing; a control lever extending from the housing and pivotally mounted therein; spring means arranged in the housing and effective to return the control lever automatically to a neutral position; and a potentiometer for converting movement of the control lever relative to the housing from the aforesaid neutral position to an electrical signal. According to the invention, the spring means (4) comprises two mutually connected tubular parts (8,9), between which the end of the control lever (3) located in the housing (2) is mounted for pivotal, but not rotational, movement, wherein in the neutral position of the control lever (3) the longitudinal axis of respective tubular parts (8,9) extends substantially at right angles to the longitudinal axis of the lever.

Abstract: A safety device at remote control of hydraulic or pneumatic machine tools where electric signals are used for controlling hydraulic or pneumatic valves, for example machines comprising a selector valve for different hydraulic functions, which is controlled by electrohydraulic or electropneumatic converters (N), and where a control unit is capable by means of electric impulses to transfer orders via a cable to a receiver unit (H), which is capable to control said converters (N) via signal converters (L) and amplifiers (M) for amplifying received signals.

Abstract: A device for remote control of hydraulic or pneumatic machine tools, comprising a selector valve for different hydraulic functions provided with a number of spring-centered slides and two electrohydraulic or -pneumatic converters connected to each slide, and comprising a control unit capable by electric impulses to transfer orders via a cable to a receiver unit capable to control the converters.According to the invention, the control unit comprises a ring counter (B), which is controlled by an oscillator (A) and capable to emit in turn a scanning signal to each of a number of transducers (C1-C6), which are manually actuated by levers (1-6), each transducer being capable during the duration of the scanning signal to convert the direction and deflection from a centered zero position of the associated lever (1-6) into two signals, one (y) of which corresponds to said direction and one (z) to said deflection. An encoder (E) is provided to allot an address to the output signals.

Abstract: A converter for electromagnetic operation of a valve is provided with a tubular, hydraulically balanced piston which has an upper end whose outer diameter is only slightly larger than its inner diameter so that it forms a valve seat with the pressure pin of the magnet to produce a slight difference in coupling back pressure in magnetic operation of the valve. Preferably, the electromagnet only operates in on-off states.

Abstract: A control system for remote proportional positioning of hydraulic directional control valves includes pulse duration modulation control of electrohydraulic converters controlling hydraulic valve spool positioners. Pulse groups supplied to the converters have a repetition rate of the order of 50 Hz to cause mechanical vibrations in the hydraulic liquid and the valve positioners, thereby reducing frictional hysteresis.