Seating arrangements for poppet or non return valves

A poppet valve or non-return valve including:

• (i) a valve chamber,
• (ii) an annular valve seat,
• (iii) a valve member movable in the valve chamber and having an O-ring retainer chamber and having an O-ring retainer member projecting towards the annular valve seat, and
• (iv) an elastomeric O-ring on the retainer member to provide a seal between the valve member and the annular valve seat when the valve is in its closed position,
• and wherein the O-ring retainer member has:
• (v) a head portion remote from the valve member, and,
• (vi) a groove between the head portion and the valve member which comprised by:
• (a) a first conical portion extending inwardly from the head portion and having a cone angle no greater than about 25.degree..
• (b) a second conical portion spaced inwardly from the first conical portion and having a cone angle of at least about (90-2.gamma..sub.E) where .gamma..sub.E is given by the formula:
• ##EQU8## wherein R.sub.o is the cross sectional radius of the O-ring when the valve is open, and,
• X.sub.1 is the reduction in cross-sectional radius of the O ring when the valve is closed.
• (c) a curved zone between the two conical portions which provides a smooth transition therebetween, the incremental value of the angle (90.degree.-2.gamma..sub.E) of the curved zone being given by the formula ##EQU9## wherein R.sub.o has the above meaning and,
• X is the reduction in the cross-sectional radius of the O-ring at the incremental conical portion of the curved zone
• so that the O-ring retainer member does not interfere with or constrain the O-ring during its deformation sequence as the valve closes and opens.