GB1039221A - Improvements in or relating to bellows - Google Patents

Abstract

1,039,221. Fluid actuation of switches; thermal switches. J. ARCHER, and J. L. OWNER. Aug. 31, 1962 [June 7, 1961], No. 20646/61. Heading H2B. A bellows 1 has a displaceable port to which is fixed a rigid member 13 carrying an armature 12 displaceable with respect to a permanent magnet 9, and the magnetic force between the armature and magnet is opposed to the bellows stiffness force over a range of displacement (see Figs. 2, 4, 5, 7, not shown) of the said port, and means are provided for preventing the armature from touching the magnet, i.e. a non-magnetic shim 17. Armature 12 and magnet 9 may be exchanged. For heater control purposes the bellows 1 is made temperature responsive and moves to actuate switch contacts 29, 31 (Fig. 3, not shown), to make or break a circuit to a heater. The switch sensitivity is increased by the magnetic biasing. The magnet 9 may be adjustably positioned by clamps 10, 11, and there may be a second adjustable magnet 40 (Fig. 6, not shown), to provide a magnetic force for each direction of movement of the bellows. Alternatively, shaped polepieces 47, 48 (Fig. 8, not shown), provide the "over-centre" action and the two stable states. A resilient strip 16, to which portion 14 of member 13 is joined, also affects the bellows movement.