Patent ID: 7044157

Claim:
A by-pass valve unit for a high pressure liquid delivery unit, the delivery unit comprising: a motor-driven high pressure pump ( 11 ) having a delivery side ( 13 ) and a suction side ( 14 ), and a delivery gun ( 15 ) connected to the pump delivery side ( 13 ) by a delivery conduit ( 16 ) and having a flow on-off valve, a source of liquid being connected to the pump suction side ( 14 ), the valve unit comprising a by-pass valve ( 25 , 33 ) arranged to close or alternatively, when in the open state, to enable direct flow passage between the delivery side ( 13 ) and the suction side ( 14 ), and having a control means ( 31 , 32 ) sensitive to the liquid pressure in the delivery conduit ( 16 ), characterized in that said control means comprises two valving elements ( 31 , 32 ) which are normally joined together to form one piece in contact with the liquid of the delivery conduit ( 16 ), but which separate when the pressure in the delivery conduit ( 16 ) exceeds the normal delivery value (P 1 ) following flow interruption by the delivery gun ( 15 ), to hence provide direct passage for the liquid from the delivery conduit ( 16 ) to the suction side ( 14 ), and further comprising: an upper chamber ( 21 ) connected to the delivery conduit ( 16 ), a lower chamber ( 22 ) connected to the pump delivery side ( 13 ) and having a lower liquid passage orifice ( 25 ) connected to the suction side ( 14 ) to enable said direct flow passage between the delivery side ( 13 ) and the suction side ( 14 ), and a third orifice ( 33 ) arranged to close or open the lower passage orifice ( 25 ), the first ( 31 ) of said two valving elements ( 31 , 32 ) of the control means being positioned to separate the two chambers ( 21 and 22 ) and presenting an upper orifice ( 26 ) for direct liquid passage from the delivery conduit ( 16 ) to the suction side ( 14 ), the second ( 32 ) of said two valving elements ( 31 , 32 ) being normally positioned to close the upper passage orifice ( 26 ), and opening this latter when the pressure in the delivery conduit ( 16 ) exceeds the normal delivery pressure (P 1 ) following flow interruption by the delivery gun ( 15 ).