Three-way poppet valve, method and apparatus

Claim 1

In a fluid applicator system including a source of fluid and an applicator, a three-way poppet valve having a housing provided with a longitudinally extending internal chamber; a fluid supply port in the housing connected to said source to allow fluid to enter the chamber at a first region thereof; a fluid return port in the housing connected to said source to return fluid thereto, said fluid return port being disposed to communicate with the chamber at a second region thereof; a first valve seat between the first and second regions and having a circular cross-section flow bore; a fluid exit port connected to said applicator and disposed to allow fluid to exit from the chamber at a third region thereof and provided with a second valve seat between the first and third regions having a circular cross-section flow bore of diameter substantially smaller than the diameter of the flow bore of the first valve seat, said valve seats being aligned longitudinally of said chamber; valving gate means disposed to reciprocate in said chamber between the valve seats, said valving gate means comprising a piston having a shaft extending longitudinally in said chamber through the bore of said first valve seat with a piston head at one end of the shaft between said valve seats, said piston head having opposite tapered surfaces disposed to engage said valve seats alternately, the piston head surface engaging said second valve seat being a conical surface with a tip portion that enters the bore of said second valve seat, said conical surface contacting said second valve seat along a line-contact circle the diameter of which has a magnitude that is a minor portion of the magnitude of the diameter of the base of said conical surface, the piston head surface engaging said first valve seat contacting that valve seat along a line-contact circle the diameter of which is substantially larger than the diameter of the first-mentioned line-contact circle; and means connected to the opposite end of said shaft for switching the gate means alternately between said valve seats alternately to close off fluid flow to the return port and to direct fluid from the fluid supply port through the chamber to and through the exit port, and to close off the fluid flow through the exit port and to direct fluid from the fluid supply port through the chamber to and through the return port, the configuration of the piston shaft, piston head, and valve seats being predetermined to maintain substantially constant flow area from said supply port out of said chamber, thereby to maintain substantially constant pressure in said chamber regardless of the position of said piston head relative to said valve seats.