Abstract: An inlet port provides a fluid entrance to a body. A chamber has an inner surface. An outlet port is in fluid communication with the chamber and provides a fluid exit from the body. The piston is moveable within the chamber between a first set position, in which the inlet port is not in fluid communication with the outlet port, and a second open position, in which the inlet port is in fluid communication with the outlet port through the chamber. A seal guard is slidably disposed within the chamber. The seal guard is moveable between a first seal-guard position and a second seal-guard position in which the seal guard shields the seal. The seal guard is in the first seal-guard position when the piston is in its first set position and in the second seal-guard position when the piston is in its second open position.

Abstract: A second piece nests within a first piece and has a circumferential groove. A vent penetrates the first piece and matches the circumferential groove when the second piece is nested within the first piece. An o-ring is modified to allow equal pressure on either side of the o-ring.

Abstract: An inlet port provides a fluid entrance to a body. A chamber has an inner surface. An outlet port is in fluid communication with the chamber and provides a fluid exit from the body. The piston is moveable within the chamber between a first set position, in which the inlet port is not in fluid communication with the outlet port, and a second open position, in which the inlet port is in fluid communication with the outlet port through the chamber. A seal guard is slidably disposed within the chamber. The seal guard is moveable between a first seal-guard position and a second seal-guard position in which the seal guard shields the seal. The seal guard is in the first seal-guard position when the piston is in its first set position and in the second seal-guard position when the piston is in its second open position.