GB1595256A - Valves - Google Patents

Description

(54) VALVES (71) We, CRANE PACKING LIMITED, a British Company, of Slough, Buckinghamshire SL1 4QX do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to the seat of a ball or other type of valve design using a material which is capable of meeting the "fire safe" requirements.

The seats of ball valves, currently being supplied, are manufactured in plastics, such as nylon or PTFE. PTFE is extensively used because of its low friction properties and high chemical resistance. However, PTFE and any other plastics materials have a major drawback, in that they completely disintegrate in the event of fire, and so reliance must be placed upon some secondary seal.

The use of graphite foil as a gland packing for the valve stem, satisfies "fire safe" requirements and thus the only area remaining to meet this requirement is the valve seat.

According to the invention we now propose to provide a shut-off valve with a seating having a circumferentially continuous sealing region against which a movable valve member normally engages in the closed position, that normally engaged region being formed of a material other than graphite, and a further sealing region of the seating being made of graphite, this graphite region only being engaged by the valve member on disintegration of the normally engaged region.

Thus the normally engaged region may be made of PTFE, with its known properties of low friction and high chemical resistance, but in the event of fire leakage is largely or wholly prevented by the engagement of the valve member against the graphite region.

The invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a section through a typical ball valve to which the invention may be applied; and Figures 2, 3 and 4 show various forms of graphite-containing seating according to the invention, suitable for use in the valve of Figure 1.

The ball valve illustrated in Figure 1 is of a conventional kind, comprising a housing 1 in which a spherical valve member 2 with an opening 3 m it is rotatable between open and closed positions by means of a stem 4.

The member seats against annular seatings 5 received in machined recesses in the housing 1; these seatings have a roughly triangular cross section, the longer side of the triangle being, however, an arc of a circle centred on the axis of the valve member.

In the past such seatings have been made of traditional packing materials but more recently nylon and PTFE have been used.

These have low friction properties but poor thermal resistance and so when such a valve is subjected to temperatures of the order of 700"C, such as might arise in a fire, the seating will be destroyed. Although it is sometimes possible to arrange that in such an event the surface of the ball comes into contact with the metal of the housing, there is still severe leakage. Seatings of graphite have also been proposed.

In the constructions according to the present invention there is an emergency seating of graphite, but it only comes into action when the normal seating is destroyed.

In the embodiment shown in Figure 2 the seating is of composite construction, comprising a portion 6 of PTFE for normal use, backed by a graphite ring 7 which is received in a counterbore 8 specially machined in the housing 1 to receive it. The arrow A shows the direction of flow of fluid through the valve. The PTFE portion maintains the seal normally, with all the advantages of that material, but in the event of a fire, causing disintegration of the PTFE part, the ball valve member is arranged to move under the influence of the pressure of the fluid in the line controlled by the valve, so that the ball valve member will make line contact with the now-exposed corner of the moulded graphite ring 7.In practice the graphite is sufficiently flexible and yielding to give under the high local pressure so that the contact is over an appreciable width, rather than a narrow line, and an effective seal is maintained.

Figure 3 shows an arrangement with similar behaviour to that of Figure 2, in that normally the sealing function is fulfilled by a main PTFE portion 9 but in the event of its destruction the function is taken over by a backing ring 10 of die-formed graphite, in this case extending the full width of the PTFE portion. This version has the advantage that it can be inserted as a direct substitute for an existing seating without requiring modification of the housing 1.

The same is true of the version of Figure 4 which differs from that of Figure 3 only in that the graphite ring 11 is narrower and is therefore flanked on each edge by PTFE 12.

The graphite rings described above are preferably made from powdered graphite by a die-forming process. Various additives may be included in the graphite to enhance is properties. For example zinc or other corrosion inhibitors may be added in order to minimise graphitic attack and/or reinforcing fibres may be included. Furthermore the graphite seats may be impregnated with, for example, resins in order to improve their resistance to wear.

It will be understood that, although illustrated in connection with ball valves, the invention is applicable equally well to other kinds of valves, for example slide valves and butterfly valves, i.e. anywhere where it is desired that a seating against which a valve member engages in the closed position is to maintain its sealing action at least partially after exposure to very high temperatures such as arise in the event of fire.

WHAT WE CLAIM IS: 1. A shut-off valve with a seating having a circumferentially continuous sealing region against which a movable valve member normally engages in the closed position, that normally engaged region being formed of a material other than graphite, and a further sealing region of the seating being made of graphite, this graphite region only being engaged by the valve member on disintegration of the normally engaged region.

2. A shut-off valve according to claim 1 in which the normally engaged region of the seating is made of PTFE.

3. A shut-off valve according to Claim 1 or Claim 2 in which the valve member is spherical and the seating is of annular shape with the normally engaged region having a part-spherical concave annular surface engaged by the valve member.

4. A shut-off valve according to Claim 1 with a seating substantially as described with reference to any one of Figures 2 to 4 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. the contact is over an appreciable width, rather than a narrow line, and an effective seal is maintained. Figure 3 shows an arrangement with similar behaviour to that of Figure 2, in that normally the sealing function is fulfilled by a main PTFE portion 9 but in the event of its destruction the function is taken over by a backing ring 10 of die-formed graphite, in this case extending the full width of the PTFE portion. This version has the advantage that it can be inserted as a direct substitute for an existing seating without requiring modification of the housing 1. The same is true of the version of Figure 4 which differs from that of Figure 3 only in that the graphite ring 11 is narrower and is therefore flanked on each edge by PTFE 12. The graphite rings described above are preferably made from powdered graphite by a die-forming process. Various additives may be included in the graphite to enhance is properties. For example zinc or other corrosion inhibitors may be added in order to minimise graphitic attack and/or reinforcing fibres may be included. Furthermore the graphite seats may be impregnated with, for example, resins in order to improve their resistance to wear. It will be understood that, although illustrated in connection with ball valves, the invention is applicable equally well to other kinds of valves, for example slide valves and butterfly valves, i.e. anywhere where it is desired that a seating against which a valve member engages in the closed position is to maintain its sealing action at least partially after exposure to very high temperatures such as arise in the event of fire. WHAT WE CLAIM IS:

1. A shut-off valve with a seating having a circumferentially continuous sealing region against which a movable valve member normally engages in the closed position, that normally engaged region being formed of a material other than graphite, and a further sealing region of the seating being made of graphite, this graphite region only being engaged by the valve member on disintegration of the normally engaged region.

2. A shut-off valve according to claim 1 in which the normally engaged region of the seating is made of PTFE.

3. A shut-off valve according to Claim 1 or Claim 2 in which the valve member is spherical and the seating is of annular shape with the normally engaged region having a part-spherical concave annular surface engaged by the valve member.

4. A shut-off valve according to Claim 1 with a seating substantially as described with reference to any one of Figures 2 to 4 of the accompanying drawings.