Valve

An assembly for a pressure relief valve, comprising:

• a valve seat member including:
• a fluid inlet;
• a seat sealing surface;
• and
• an axial bore, the axial bore including a first cavity and a second cavity, wherein the seat sealing surface is disposed axially between the first cavity and the second cavity and the fluid inlet is disposed axially between the seat sealing surface and the second cavity;
• a fluid outlet;
• and
• a piston movable within the axial bore, the piston including:
• a piston sealing surface;
• a first cylindrical portion;
• and
• a second cylindrical portion, the first cylindrical portion configured to be retained by and slidably engage with the first cavity and the second cylindrical portion configured to be retained by and slidably engage with the second cavity, wherein the piston sealing surface is disposed axially between the first cylindrical portion and the second cylindrical portion;
• wherein the piston has a first position in which the piston sealing surface is engaged with the seat sealing surface such that a fluid path between the fluid inlet and the fluid outlet is closed, and a second position in which the fluid path between the fluid inlet and the fluid outlet is open;
• and
• wherein the first cylindrical portion has a first radius, the second cylindrical portion has a second radius and the second radius is less than the first radius;
• wherein a closed end of the axial bore includes a dampening cavity having a damping volume,
• wherein the second cylindrical portion is disposed between the fluid inlet and the dampening cavity, and
• wherein a second radial clearance between the second cavity and the second cylindrical portion is configured to restrict flow of fluid into and out of the damping volume.