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.