(57) A pump unit (28) for a paint system (10) comprises a pump head (124); a pump body
(126); and a pump plate (128), which are moulded components clamped together. A piston
(100), including a diaphragm (134) retained between the pump body and plate, extends
through a piston aperture (137) in the pump plate. An inlet valve and an outlet valve
each comprise a valve seat (174,182) formed in the pump head and body respectively,
and a flap (172,184) adapted to seal against the seat.
A pressure chamber (196) communicates with the outlet valve, and comprises a control
actuator (104), including a diaphragm !194) retained between the pump body and plate,
which actuator extends though a control aperture (202) in the pump plate selectively
to enable and disable the pump in dependence on pressure in the pressure chamber,
a pump outlet (102) communicating with the pressure chamber.
A dump/yield valve (122) releases excessive pressure in the pressure chamber. A switch
button (30) operates the pump, the switch button serving to adjust spring bias (284)
on the valve between a first high value in which the valve serves as a yield valve,
and a second low value, where the valve serves as a dump valve.
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