Abstract: An electromagnetic reciprocating compressor has a body (1, 2), a piston (10) reciprocating in a cylinder (12) in the body and a piston guide (14) in the form of an insert which is radially located relative to the axis of the cylinder (12) by fitting against a registration surface (25a), the registration surface is on a body part (1) which also provides the internal cylinder surface (12a) of the cylinder. To improve the alignment of the insert (14), the registration surface (25a) and the internal cylinder surface (12a) are formed to their respective final diameters in the same machining operation by reference to a common axis. The piston guide (14) is axially located related to the cylinder (12) by being resiliently clamped between the stator (23) and an end portion (27a) of the body (1, 2) opposed to the stator (23) with a resilient member (27) interposed between the body end portion (27a) and the piston guide (14).

Abstract: An electromagnetic linear compressor has a linearly reciprocating piston (10) biased in one direction by a helical coil spring system. A rotational bearing (40) supports one end of the spring system (20a, 20b). To avoid uneven wear due to forces applied by the spring system, the spring system comprises two helical coil springs (20a, 20b) acting in series to bias the piston (10), and the rotation bearing (40) transmits thrust between the two springs while permitting relative rotation of the two springs about their common axis. The compressor also has a turbine (30) for exerting a unidirectional rotational force to rotate the piston (10) about its axis gradually during operation of the compressor.

Abstract: A cushion for the seat of a chair is provided, having at least two groups of cyclically inflatable tubes (4, 6, 8, 10), each group comprising at least one tube. Control means (18) inflates and deflates each group sequentially. The cushion also has a buffer chamber (12, 14) maintained by the control means (18) in communication with the inflated group or groups of cyclically inflatable tubes. The buffer chamber comprises at least one inflatable buffer tube which provides a part of the sitting surface of the chair.

Abstract: A cushion for the seat of a chair, has at least two groups of inflatable tubes arranged in a side-by-side relationship and oriented in a direction corresponding to the front to back direction of the chair seat. The tubes of each group are inflatable together. The first group is a single tube or two or more adjacent tubes, and the other group is at least two spaced apart tubes arranged on opposite sides of the first group of tubes. The groups of tubes are inflatable sequentially. Symmetrical but periodically varying support for the user is thus provided.

Abstract: A fluid distributor for sequentially distributing pressurized fluid from at least one inlet port to a plurality of distribution ports and exhausting fluid from said distribution ports to at least one exhaust port, said distributor having a valve actuated by pressure of fluid supplied at said inlet port and arranged to close said exhaust port when said fluid pressure drops below a predetermined minimum. The distributor is suitable for use in conjunction with an inflatable human body support.