Patent ID: 7258131

Claim:
A safety valve for use with a fluid piping system, the piping system having an upstream portion upstream of the safety valve and a downstream portion downstream of the safety valve, the safety valve comprising: (a) a cylindrical housing through which the fluid flows, the housing having a diameter; (b) a piston assembly comprising: (b1) a first disc-shaped piston having a diameter slightly smaller than the housing diameter such that the first piston freely slides within the housing, wherein the first piston has at least one orifice defined therein, and wherein the first piston has an upstream face and a downstream face; (b2) a second disc-shaped piston positioned downstream from the first piston, the second piston having a diameter substantially equal to the first piston diameter, wherein the second piston has at least one orifice defined therein, wherein the second piston has an upstream face and a downstream face, and wherein fluid entering the safety valve housing exerts a fluid force on the first piston and the second piston in the direction of fluid flow; (b3) a shaft connecting the first piston to the second piston; (b4) a valve stem extending from the downstream face of the second piston, wherein the second piston is attached to a first end of the valve stem; and (b5) a stop attached to a second end of the valve stem; (c) a valve seat with an opening substantially shaped and sized to matingly receive the stop; and (d) a spring positioned in the housing against the downstream face of the second piston assembly such that the spring exerts a spring force on the second piston in a direction opposite the general direction of fluid flow, wherein when the fluid forces acting on the piston assembly sufficiently exceed the spring force acting on the downstream face of the second piston, the piston assembly moves in the direction of fluid flow until the stop engages the valve seat and substantially shuts off the fluid flow to the downstream portion of the system piping.