Abstract: A solenoid valve includes a monitoring circuit adapted to sense the current drop that occurs through the solenoid coil when the solenoid armature moves correctly, sensing of the drop being used to cause a neon to glow continuously so as to indicate correct operation of the solenoid. If the drop is not sensed, the neon is caused to blink so as to indicate incorrect operation of the solenoid. The circuit may in addition or alternatively be arranged to generate a voltage signal, upon correct operation of the solenoid, for transmission to a remotely located programmable logic controller used to control operation of the valve and like valves that form part of a pneumatically controlled machine.

Abstract: A pneumatic actuator comprises a cell through which a normally laminar flow of air passes between an inlet and an outlet to provide, in the outlet, an output pressure. The cell includes an electro-acoustic transducer, for example a piezo-electric element arranged, in response to an oscillating electrical signal, to produce an acoustic signal that disturbs the laminar flow whereby at least some of the air exhausts from the cell via one or more exhaust ports and the output pressure falls. The difference in the output pressures may be used to control a pneumatic device optionally via a pneumatic amplifier. The electrical signal is produced by an opto-electrical transducer to which optical control signals are transmitted, for example along a fibre optic cable.

Abstract: A valve bush for a dynamic multi-port valve comprises a plurality of separately formed hollow cylindrical plastics segments interengaged in end-to-end relationship to form the bush, the or each intermediate set of small diameter apertures being in the form of a plurality of apertures, for example rectangular slots, defined by facing end surfaces of two adjacent segments and by a plurality of spaced fingers extending axially from said end surfaces. A bush of the invention for a five port valve will comprise three such segments, and a bush for a three port valve will comprise two such segments.

Abstract: N.sub.2 and CO.sub.2 are admitted, through separate valves actuated by single high hysteresis actuator, into a mixing device when the mixture is fed to a beer keg. The actuator is dependant upon the relative Co.sub.2 N.sub.2 mixture pressures so as to maintain the mixture pressure within predetermined limits and in one embodiment the use of a venturi mixing device ensures that the mixture composition remains substantially constant when the N.sub.2 and CO.sub.2 gases are at substantially different pressure.

Abstract: A universal circuit-defining device with which logical or other component elements or modules of component elements are to be connected. The device includes a base plate having channels therein closed by a deformable seal held against the channels in the base plate by a cover plate, the channels constituting pre-established circuit elements and having sockets formed therein to receive interchangeable plugs constituting means for the interruption of the circuit and which are removable to bring the corresponding parts of the circuit into operation.

Abstract: A sensing device for sensing the position of a movable element in a fluid-operable actuator including a relatively movable piston and cylinder. The sensing device includes a pair of co-operating pressure tappings in the cylinder wall, a pair of peripheral and axially spaced seals on the piston for sealing between the piston and the cylinder wall and a detector responsive to the pressure at the pressure tappings by producing an output indicating piston position. The spacing of the pressure tappings is greater than the axial width of each of the seals and less than the axial distance between the seals.

Abstract: A slide valve in which the valve member has an apertured interior partition extending in the direction of sliding movement of the valve member in a position intermediate a ported wall with which the valve member is engageable and a further wall of the housing containing a cavity, the surface areas of the partition on each side thereof being substantially equal, whereby fluid pressure inside the valve member is transmitted to the cavity through the apertured internal partition and acts on each side of the latter, thereby to hold the valve member in substantial fluid balance in a direction perpendicular to the ported wall and hence to reduce the force required to slide the valve member into and out of its operative positions.

Abstract: A piston-in-cylinder type pneumatic actuator is provided with an automatic cushioning facility to prevent the piston from returning to its fully retracted position at velocities exceeding a predetermined maximum velocity. Integrally-housed in the actuator is a velocity transducer arranged to sense the pressure in a cylinder working volume, which pressure is related to the piston velocity and is used to control the operation of an exhaust valve operable to vary the rate of flow of gas from the cylinder thereby to vary the rate of return of the piston.