(57) The invention refers to a pump in which a diaphragm (8) is reciprocated to cause
cycles of high and low pressure in a chamber (9), and two conduits (10,11) communicating
between the chamber and the exteriors, contain oppositely directed one way valve elements
(12,13). Because the forward directions of those valve elements may offer even very
low resistance to such effects as gravity (Fig.3), an entire reservoir could empty
inadvertently through the pump. The invention proposes that a single body (27) be
shaped to contain the one-way elements (12,13), to fit in the lower pump body (24),
to assist in clamping the diaphragm (8), and to present to the chamber (9) one or
other of the conduits, preferably that destined as the inlet conduit (10A), with an
orifice (27C) which will act as a valve seat. A portion (6) of the diaphragm is contrived
as a valve flap, and can close that conduit which is presented with the orifice (27C).
Return bias (5) of the pump acts on the diaphragm (8) such as to close the orifice
under quiescent or switched off conditions of the pump.
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