Shutoff valve for high-pressure spray guns

Claim 1

A valve assembly for a high-pressure medium, especially for a high-pressure spraygun comprising: a valve housing formed with an outlet for said medium, an inlet for said medium spaced from said outlet, and a cylinder bore between said inlet and said outlet, said cylinder bore having a rear wall remote from said outlet; a valve seat formed in said cylinder bore at said outlet; a differential piston slidably received in said cylinder bore and having a front end engageable with said seat to block flow of said medium from said inlet to said outlet, said differential piston having a rear end defining a pressure chamber in said cylinder bore, rearwardly of said seat, said piston further defining with the wall of said cylinder bore a throttle path between said inlet and said chamber; a bypass passage formed in said housing and communicating between said outlet ahead of said seat and said chamber; a control piston shiftable in said housing between a blocking position interupting communication between said chamber and said passage and an open position communicating said passage with said chamber; and an operating mechanism on said housing for displacing said control piston between said blocking position thereby enabling said medium to shift said differential piston away from said seat, and for releasing said control piston to permit pressure in said chamber to displace said control piston into said blocking position whereby fluid pressure is increased in said chamber through said passage and said medium thereby displaces said differential piston into contact with said seat, said operating mechanism comprising: a valve body sealingly received in said cylinder bore behind the rear end of said differential piston and ahead of said rear wall and formed with at least one channel communicating between said chamber and said passage, said control piston being wholly received in and shiftable in said body to selectively block and unblock said channel; a pin sealingly received in said body and shiftable therein to displace said control piston, and a lever on said housing engageable with said pin for shifting same.