a valve for controlling flow of a fluid exerting a fluid pressure . the valve has a body including a fluid passage for the fluid , and a valve seat positioned adjacent to the fluid passage at an orifice coaxial with the fluid passage . the valve seat includes a sealing gland defining a cavity therein , and the sealing gland has a support surface adjacent to the cavity and a resilient valve seat member within the cavity . the valve seat member includes a first pressure responsive surface adjacent to the orifice and a second pressure responsive surface substantially opposed to the first pressure responsive surface . the support surface includes a notch for positioning a portion of the support surface a distance apart from the second pressure responsive surface .