A pinch mechanism, which can be used as part of a pump, includes a deformable
tube
(10) enclosed within a body (11) which has a first chamber (11a).
The deformable tube (10) defines a flow passage. A second chamber (19)
is coupled via passage (17) to the first chamber (11a). A
piston (20) is located within the second chamber (19) and movable
between first and second positions. Upon moving to the first position a pressure
increase occurs in the first chamber (11a). Upon moving to the second
position a negative pressure is created in the first chamber (11a).
A vent means (25) is located at a point during movement of the piston (20)
between the first and second positions which enables pressure equalisation within
the second chamber (19) to occur.
