Abstract: An automatic aspirator-transfer valve is disclosed which controls the delivery of washing and rinsing fluid from a supply to a cleaning gun. The device includes a valving piston which moves between a first or rinsing position to open communications to the bypass conduits and a second or washing position to close the bypass conduit. The injector aspirates washing fluid from a reservoir through a non-return valve, a side inlet and conduit of the side inlet, the side inlet conduit being separated from a passage within the housing bore. By this novel aspect, a user may change from the washing mode to the rinsing mode without the aspiration of dangerously high concentrations of washing agent and without unnecessary waste of the washing agent during operation.