Control for reciprocating pumps or the like

Claim 1

A control valve for alternately applying fluid pressure to a first and second work chamber to cause a reciprocating stroke of a work device, comprising: a valve housing having a cylinder therein closed at opposite ends, an inlet in said housing for admitting pressurized fluid into said cylinder, means forming a first delivery passage communicating said cylinder with said first chamber, means forming a second delivery passage communicating said cylinder with said second chamber, means forming first and second outlet passage in said housing and opening into said cylinder, a piston slidable in said cylinder between first and second positions, said piston having annular recesses therein effective when said piston is in said first position to communicate said inlet with said first delivery passage and to communicate the second outlet passage with said second delivery passage, said recesses being effective when said piston is in said second position to communicate said inlet with said second delivery passage and to communicate the first outlet passage with said first delivery passage, an additional passage extending through said piston between opposite ends thereof, said piston having cavities at said opposite ends and said additional passage opening into said cavities, means for admitting pressurized fluid into said additional passage, first vent means controlled by said work device when at one end of said stroke to vent one end of said cylinder whereby to enable pressurized fluid at the opposite end of said cylinder to move said piston to said one end of said cylinder, and second vent means controlled by said work device when at the opposite end of said stroke to vent the opposite end of said cylinder whereby to enable pressurized fluid at said one end of said cylinder to move said piston to said opposite end of said cylinder, said piston having a large diameter portion intermediate certain of said recesses therein, which large diameter portion is in sliding engagement with said cylinder and is undercut toward the root of an adjacent one of said recesses, and said large diameter portion having a circumferential groove therein, the root of said groove extending adjacent the root of said undercut portion whereby to form a ring section having a flexible root section, said ring section flexing about said root section upon application of fluid pressure in said adjacent recess.