Abstract: A differential pressure gauge 10 utilizes a piston member 18 provided with a series of grooves 19 right around it, so that the piston member 18 itself forms the rack of a rack-and-pinion device (pinion 22) for converting linear displacement of the piston member into rotary displacement of the pinion. For sensitivity and accuracy, the seal between the piston member 18 and the passage 13 is a hard-surface-to-hard-surface engagement between substantial (total) hard surface areas at any one time of the passage 13 and the piston member 18, including regions of the surface area of the piston member 18 intermediate mutually adjacent end ones of the grooves 19. In this way, the gauge is insensitive to the base pressure, there being no soft seals to deform under pressure. A magnetic coupling is used through the wall of the housing, which can thus be made completely pressure-tight.

Abstract: This invention concerns a fluid operated valve with a slidable valve member having formations enabling differential operating forces to be applied thereto and preferably having means to relieve pressure from the leading formation during travel of the member to promote `snap` action and preferably being associated with a pneumatic piston and cylinder motor driving an hydraulic pump in an integrated unit constituting a pneumatic/hydraulic convertor.

Abstract: A bistable, electromagnetically-actuated valve has a closed chamber containing a moving armature with a valve orifice in each end of the closed chamber, one of which is formed by the end of a tube, a space around the tube forming the third fluid connection to the closed chamber. The armature has valve seats for closing the valve orifices.