GB2119480A - Double seat valve - Google Patents

Abstract

A double seat valve, comprises a lower seat 17 mounted on a seat member 12 which is movable under the influence of springs 13. This enables the lower head seal 18 on the lower valve disc 16 to be maintained closed until the leakage space is closed by engagement of the valve disc 16 on the valve disc 25. Also, it enables the valve discs 16 and 25 to engage their respective seats with metal-to-metal contact, thus providing better control of the compression of the head seals 18 and 26. <IMAGE>

Description

SPECIFICATION Double seat valve This invention relates to double seat valves It is frequently necessary that when a valve is used to isolate one part of a fluid flow circuit from another, any leakage past the valve seat should not be allowed to enter the other part of the flow circuit For example, if a section of pipeline is being cleaned while a food liquid is being stored in the other part of the flow circuit, it is clearly important that leakage of the cleaning iiquids past a valve seat should not go undetected and should not contaminate the food liquid.

There is now a well defined kind of double seat valve comprising two valve members each cooperable with a respective one of two spaced valve seats and defining between them a leakage chamber, one of the valve members being solidly connected to an actuating shaft and the other valve seat being mounted on a hollow shaft surrounding the said actuating shaft and spring urged towards the said one valve member to close the leakage chamber whereby on closure of the valve the said other valve member engages its seat and the said one valve member then separates from the other said valve member prior to completing closure of the valve, with the reverse sequence of steps taking place on opening of the valve.

Valves of this kind will hereinafter be referred to as valves of the kind described.

In general, while opening, such valves have a short period within which the valve is partly open and the leakage path is not closed. This can lead to loss of feed liquid and to the necessity for more regular cleaning of the leakage path to remove the residues of such feed liquid.

In accordance with the present invention, there is provided a valve of the kind described (as hereinbefore defined) in which the seat cooperating with the said one valve member is movably mounted and is caused to follow the movement of the said one valve member and remain in engagement therewith until the leakage path is closed by engagement of the two valve members.

The movable seat is preferably spring urged into engagement with the said one valve member.

Additionally or alternatively, it may be pneumatically urged into engagement with the said one valve member when the latter is actuated in an opening direction.

The invention will be further described with reference to the accompanying drawing, of which the single figure is an axial section showing the movable valve elements in both open and closed positions of the valve.

The left hand half of the drawing shows the valve components in closed position, while the right hand shows them in the open position of the valve.

The valve consists of an upper valve chamber 1 and a lower valve chamber 2 having port connections 1 a and 2a respectively. An actuating shaft 3 runs through the valve chambers 1 and 2, and is sealed by means of double lip shaft seals 4 and 5. The lower part of the shaft 3 is shown as having a hollow interior 6 providing a leakage path from the valve, and the upper part of the shaft passes through a yoke 7 and into an operating pneumatic cylinder 8. The various parts of the valve body are shown as being joined together by clamping rings 9.

The upper valve chamber carries at its lower end a fixed valve seat 11 , while the lower valve chamber 2 has sealingly and slidably mounted therein a movable seat member 12 spring urged in an upward direction by springs 13 towards a position in which it engages with and seals, by means of a sealing ring 14, against an under surface 1 5 associated with the seat 11. The lower part of the actuating shaft 3 has associated therewith a valve member or disc 1 6 cooperable with a seat 1 7 on the seat member 12 and adapted to seal thereagainst by means of a lower head seal 18, as illustrated in the left hand side of the figure.

Coaxially located on the actuating shaft 3 and extending through the lip seal 4 is a hollow shaft 21 carrying at its upper end a spring abutment collar 22. The actuating shaft carries a further spring abutment collar 23 and a spring 24 mounted between the collars 22 and 23 urges the hollow shaft 21 in a downward direction as illustrated in Figure 1 along the shaft 3. The lower end of the hollow shaft 21 carries a further valve member or disc 25 which is cooperable with the seat 11 and seals thereagainst by means of an upper head seal 26, when in the position illustrated on the left hand of the figure. An O-ring seal 27 seals the annular cavity between the shaft 3 and the hollow shaft 21.

The valve disc 25 carries a face seal 28 which enables the valve disc 25 to seal against the valve disc 16 as illustrated in the right hand half of the figure.

The hollow interior 6 of the lower portion of the shaft 2 communicates via radial bores 29 with a leakage space 30 between the valve discs 1 6 and 25 and which is sealed by the face seal 28 when the valve is in the open position.

In the closed position of the valve, as illustrated in the left hand half of the figure, the seat member 1 2 is pressed downwardly against the action of the spring 13 by the valve member 1 6 and the seal is maintained by the lower head seal 1 8. The u'pper valve disc 25 is in engagement with the seat 11 and the seal is maintained by the upper head seal 26. In this position the discs 1 6 and 25 are spaced to leave the leakage space 30 open, so that if either the lower head seal 1 8 or the upper head seal 26 should fail, any leakage will pass into the leakage space 30 and the cross bores 29 and can be carried away through the hollow part 6 of the shaft 3.Suitable means may be provided for the detection of any such leakage so that the appropriate remedial action may be taken before the second seal fails, which might lead to potentially damaging mixing of the two fluids.

When the valve is opened, the actuating cylinder 8 is operated appropriately and the shaft 3 moves upwardly. During the initial part of this operation, the spring 13 moves the seat member 12 upwardly to maintain the seat 1 7 against the lower head seal 18 so that the leakage space 31 remains isolated from the lower valve chamber.

When the lower valve disc 1 6 engages the upper valve disc 25, the face seal 28 closes the leakage.

space 31 and, simultaneously, the seal 14 on the seat member 12 engages the surface 1 5 associated with the seat 11. Continued movement upward of the shaft entrains the valve member 25 and its hollow shaft 21 in the upward movement and the valve opens, eventually reaching the position illustrated in the right hand side of the figure. In closing the valve, the reverse sequence of operations takes place so that the upper head seal 26 engages the seat 11 at substantially the same time as the lower head seal engages the seat 17 on the movable seat member 12.

Continued movement of the shaft opens the leakage space 31.

It will thus be seen that by using the movable lower seat, there is negligible leakage from the valve during valve operation. In addition, because of the greater manufacturing tolerance allowed by having the lower seat 1 7 mounted on a movable seat member 12, the engagement between the valve discs 16 and 25 and their respective seats can be metal-to-metal, thereby giving controlled compression of the rubber seals 18 and 26 forming the head seals.

It sometimes happens, particularly during cleaning operation, that there is a pressure shock wave in the system which tends to lift the valve for a brief instant. The provision of a movable lower seat should enable the seal even to the leakage space to be maintained during such lifting, but if the total lift is sufficient to engage and lift the upper valve disc, which could give rise to dangerous contamination if a food liquid is being protected from a cleaning liquid, then the-total movement of the shaft 3 is going to be fairly substantial and can easily be detected by the use of an appropriate feed-back micro-switch located within the yoke 7 or elsewhere.

Since the leakage space 30 is closed when the valve is open, and the lower head seal 1 8 is closed until the upper head seal is opened, special provision has to be made for cleaning the leakage space 30, and for this purpose connection bosses 31 are provided, so that when the valve is closed, cleaning fluid can be circulated to flush out the leakage space 30 and the hollow interior 6 of the lower part of the shaft. Similarly, it is felt advisable that the chamber holding the springs 13 should be cleaned out and for this purpose cleaning fluid connection bosses 32 are provided.

Various modifications may be made within the scope of the invention. Thus, provision may be made for supply of compressed air to the chamber housing the springs 13 in order to urge the seat members 12 in an upward direction at least when the valve is opening and opened.

Claims (4)

1. A valve of the kind described (as hereinbefore defined) in which the seat cooperating with the said one valve member is movably mounted and is caused to follow the movement of the said one valve member and remain in engagement therewith until the leakage path is closed by engagement of the two valve members.

2. A valve as claimed in claim 1, in which the said movable seat is spring loaded into engagement with the said one valve member.

3. A valve as claimed in claim 1 or 2, in which the said movable seat is pneumatically urged into engagement with the said one valve member when the latter is actuated in an opening direction.

4. A valve of the kind described substantially as hereinbefore described with reference to the accompanying drawing.