Abstract: A suction-actuated control system (10) for a whirlpool bath/spa installation includes a suction-side transducer (52) connected in the suction inlet path and a controller (54). The suction-side transducer (52) transmits an air pulse to the controller (54) when pressure in the suction path drops below a pre-determined value caused, for example, by a full or partial blockage of a suction cover (26) by a wash cloth or an article of clothing. The controller (54) includes an electric switch (62) in circuit with the recirculation pump (34) and a bi-state controller (66) that actuates the electric switch (62) between its ON state and its OFF state. An abnormally low pressure in the suction path to the recirculation pump (34) caused by a full or partial blockage of the suction cover (26) will cause the controller (54) to shut-off the recirculation pump (34). After the obstruction is removed and a short time delay, the user can actuate a user ON/OFF control (56) to restart the pump (34).

Abstract: An optical fibre sensor includes an elongate optical fibre and a casing for the fibre, the casing including a first elongate, flexible and substantially inextendable strip portion and a second elongate, flexible strip portion arranged so that the fibre therebetween is sandwiched between the strip portions, at least the first strip portion being provided with a series of transverse ridges for engaging the fibre, with grooves being formed between the ridges, and the other strip portion being adapted to bend the fibre into the grooves upon pressing together of the strip portions.

Abstract: A pressure operated switch has a bistable or multi-stable latching mechanism disposed between a bellows unit and an electrical switch. The latching mechanism has two relatively axially moveable elements which extend and contract with subsequent operations of the bellows unit to provide the bistable action.

Abstract: A remotely operable switching arrangement comprises a master and slave providing variable volume chambers in air communication with each other. A switch is operably connected to the slave so that variation in the volume of the master chamber causes switching of the switch between two states. The arrangement is such that the switch is stable in only one of the states. Preferably the master, or alternatively the slave, includes a means to provide a snap-action upon switching from one of the states to the other.