GB2130687A

GB2130687A - A valve, especially for a blowpipe

Info

Publication number: GB2130687A
Application number: GB08329557A
Authority: GB
Inventors: Marchand Alain Le; Francis Moumaneix
Original assignee: Guilbert & Fils Leon
Current assignee: Guilbert & Fils Leon
Priority date: 1982-11-08
Filing date: 1983-11-04
Publication date: 1984-06-06
Also published as: DE3340166C2; FR2535817B1; GB2130687B; IT8368154A0; DE3340166A1; FR2535817A1; IT1162992B; GB8329557D0

Abstract

In one of three arrangements, a blowpipe valve comprises a control system 15 formed by a hand-wheel 18 and a trigger 23 rigidly fixed to a sleeve 24, the control system 15 being capable of tilting, in order to open the valve closure member 14 under the action of the trigger in opposition to a spring 28, about a localized contact zone C which forms a pivotal bearing point. The valve seat 13 has local depressions 49 which permit a pilot-flame flow when handwheel 18 is displaced upwardly and the trigger 23 is not depressed. When screwed down handwheel 18 prevents operation of trigger 23. In a second arrangement (Fig. 11) trigger 23 and spring 28 are omitted. In a third arrangement (Fig. 12) trigger 23 and all springs are omitted and closure member 14 is rigidly fixed to and rotates with handwheel 18. <IMAGE>

Description

SPECIFICATION A valve, especially for a blowpipe The present invention relates to a valve, especially for a blowpipe, comprising a valve body in which is formed a fluid passageway in which at least part of the said passageway is defined by a bore provided with an annular shoulder forming an annular valve-seat, and a closure member slidably engaged within the said bore in order to be moved towards and away from the said valve-seat under .he action of a control system.

Valves of the type considered are sometimes of the double control type. In such cases the said control system usually comprises on the one hand a hand-wheel which serves to adjust the pilotflame of the blowpipe and on the other an actuating trigger which permits pilot-flame operation in the released position and permits operation at a high flow rate in the depressed position. The advantage of this arrangement lies in the fact that the pilot-flame setting remains unchanged, no matter how often the trigger is operated.

In addition, the regulating hand-wheel makes it possible to close the valve completely and if necessary to lock the trigger in position when the valve is closed.

In valves of this type, the hand-wheel and the trigger are usually mounted separately and, in the majority of instances, the trigger is mounted on the valve body in such a manner as to be capable of pivotal displacement about an axis located at right angles to the axis of the bore which receives the closure member.

One of the objects of the present invention is to provide a double-control valve which is primarily applicable to a blowpipe and is of simplified design, especially by virtue of the choice of a suitable assembly of the hand-wheel and of the trigger. Another distinctive feature of the said valve lies in the fact that it has a body which can be employed in a standard manner both in conjunction with a double control consisting of hand-wheel and trigger and in conjunction with a single control consisting of a hand-wheel alone.

In accordance with the invention, a valve of the aforementioned type is primarily distinguished by the fact that the control system comprises on the one hand a regulating hand-wheel adapted to exert a thrust on the closure member in order to close the valve and, on the other hand, an actuating trigger rigidly fixed to a sleeve in which the hand-wheel is mounted by screwing. The said sleeve has an annular flange which is applied against an annular seating of the valve body at the entrance of the said bore under the action of a resilient means interposed between the said annular flange and an opposite annular seating formed on a bell-housing attached to the valve body. The control system as a whole is positioned on the valve body under the action of a resilient means which tends to maintain the annular flange generally applied and centred on the seating of the valve body.The said control system is capable of tilting as a single unit for opening under the action of the trigger in opposition to the resistance of the resilient means. The annular flange is capable of moving away from the seating of the valve body, except for a localized contact zone which forms a pivotal bearing point.

By virtue of this arrangement, the constructional design is simplified since the assembly consisting of trigger and hand-wheel constitutes a pivotal unit.

In accordance with another feature of the invention, means are provided for preventing rotation of the trigger about the axis of the handwheel in one direction or in the other. To this end, the trigger which has the general shape of an inverted trough is adapted to come into position astride a lug formed on a handle which is rigidly fixed to the valve body.

In accordance with yet another feature of the invention, the sleeve is rigidly fixed to the trigger, on the one hand axially by means of a shoulder on which the sleeve is abuttingly applied against the trigger and-by means of a crimped edge which serves to clamp the said sleeve against the trigger and on the other hand angularly by local deformation of the crimped edge of the sleeve into at least one recess of the trigger.

In accordance with again another feature of the invention, the range of travel corresponding to upward displacement of the annular flange at the time of operation of the trigger in order to open the valve is defined by a stop. This latter preferably consists of an internal annular shoulder of the bellhousing.

It should be noted that, at the point of application of thrust at which a contact is provided between the hand-wheel and the closure member, it is necessary to ensure that the conditions of contact just mentioned are such as to reduce any tendency of the closure member to be driven in rotation by the hand-wheel in order to maintain the said closure member in a fixed angular position. Likewise at the time of operation of the trigger which involves a pivotal displacement, any tendency of the closure member to undergo a lateral displacement should also be reduced and in any case limited to a lateral travel of negligible value.

To this end, in accordance with still another feature of the invention, the top surface of the closure member which defines a zone of contact with the hand-wheel is intended to be located in close proximity to the annular seating of the valve body on which the annular flange is applied. This makes it possible in particular to achieve a compact design as well as economy of material.

Preferably, the hand-wheel is brought into contact with the top surface of the closure member by means of a nose which has a higher degree of hardness than this latter and can consist, for example, for a ball which is permitted to form during operation a small cup-shaped depression in the top surface of the closure member. In this case, in order to minimize the effect of transmission of motion to the closure member at the time of pivotal displacement of the trigger, it is ensured that the centre of the ball is located in a plane which is coplanar with the seating provided on the valve body for the annular flange when the trigger is located at a point midway between the open position and the closed position.

In one form of construction, the resilient means comprises a helical spring which extends between the sleeve and the bell-housing whilst the handwheel is provided on the one hand with a threaded central stem which serves to screw the said handwheel within the sleeve and is adapted to cooperate by exerting thrust on the closure member and, on the other hand, with a peripheral gripping ring adapted to surround a portion of the trigger which is adjacent to the sleeve. The said portion of trigger which is adjacent to the sleeve has two concentric skirts in spaced relation, namely an inner skirt which is attached to the sleeve and an outer skirt which surrounds the bellhousing and is in turn surrounded by the peripheral gripping ring of the hand-wheel.

In a preferred embodiment, the seating of the valve body on which the annular flange of the sleeve is applied is defined by an annular boss of the valve body on which the bell-housing is screwed in order to be attached to the said valve body.

The closure member is preferably adapted to cooperate with the valve-seat by deformation of an O-ring seal of elastomer material which is carried by the closure member and is intended to be applied against the valve-seat which is of rigid material and advantageously has a conical shape.

The said valve-seat is provided with one or a number of local depressions which permit a small pilot-flame flow through the valve-seat when the O-ring seal is brought lightly into contact with the valve-seat but which are sealed-off in order to permit total closure when the seal is compressed against the valve-seat.

The valve in accordance with the invention also has a remarkable property in that it can be employed either with a double control involving the use of a hand-wheel and trigger in the manner indicated in the foregoing or with a single control with a hand-wheel but without any trigger.

For the type of service just mentioned, the hand-wheel is screwed directly into a member which has the general shape of an inverted annular trough and alone serves to replace the bell-housing and the sleeve, the resilient means being no longer provided.

Whether the control is double or single, the hand-wheel is advantageously adapted to cooperate with the closure member in the application of thrust by means of a ball whilst the said closure member is restored to the open position by a spring which is applied against the valve body and is remote from the hand-wheel.

However, in a simplified embodiment which achieves a reduction in capital cost, the closure member is intended to be mounted directly on and rigidly fixed to the hand-wheel, in which case the said closure member is not fitted with a restoring spring.

A further object of the present invention is to provide a single-control valve in which the closure member is rigidly fixed to the hand-wheel and is permitted to rub directly on the valve-seat in rotational motion. In theory, it would appear that such operating conditions are liable to give rise to premature wear. Surprisingly, experience has nevertheless demonstrated the fact that the performance of the valve remains satisfactory over an acceptable period of service.

Preferably, in this simplified version, the handwheel is adapted to carry a radial web which facilitates operation and indicates the exact position of the valve at each instant.

Different embodiments of the invention will be described below, reference being made to the accompanying drawings in which: - Fig. 1 is a diagrammatic longitudinal sectional view of a blowpipe having a doublecontrol valve in accordance with the invention, the valve being shown in the closed position and the trigger being shown in the unlocked position; - Fig. 1A is a corresponding partial view in transverse cross-section taken along line IA--IA of Fig. 1; - Fig. 2 is a view which is similar to Fig. 1 but in which the valve is open in the pilot-flame position; - Fig. 3 is a view which is similar to Fig. 1 or to Fig. 2 but in which the valve is open in the fulldelivery position as a result of operation of the trigger;; - Fig. 4 is a view which is similar to any one of the preceding figures but in which the valve is closed whilst the trigger itself is in the locked position; - Fig. 5 is a view to a larger scale showing the pivotal mounting of the sleeve on the valve body, the trigger being shown in the closed position; - Fig. 6 is a view which is similar to Fig. 5 but in which the trigger is in the half-open position; - Fig. 7 is a view which is similar to Fig. 5 or to Fig. 6 but in which the trigger is in the fully open position; - Fig. 8 is another view to a larger scale showing the closure member and the valve-seat in a low-delivery position; ; - Fig. 9 is a view which is similar to Fig. 8 but in which the closure member is in the completely closed position; - Fig. 10 is a view in perspective showing the valve-seat provided with its localized depressions for permitting pilot-flame deiivery; - Fig. 11 is a view of an alternative embodiment in which provision is made for a single control instead of a double control; - Fig. 12 relates to another alternative embodiment which is similar to that shown in Fig.

11 but in which the construction is simplified.

Reference will first be made to Figs. 1 to 10 which relate to one application of the invention to a double-control valve for a blowpipe.

The valve has a body 10 to which the blowpipe handle P is attached and in which is formed a passageway 11 for the flow of fluid. At least a portion 12 of said passageway 11 is defined by a bore. The bore 12 is provided with a shouldered portion 13 forming an annular valve-seat.

A closure member 14 is slidably engaged within the bore 12 in order to be moved towards and away from the valve-seat 13 under the action of a control system generally designated by the reference numeral 1 5.

The closure member 14 has a generally cylindrical shape and is provided laterally with an O-ring seal 1 6. In the vicinity of its lower end, said member 14 is adapted to carry an O-ring seal 17 of elastomer material (shown in Figs. 8 and 9) which cooperates with the valve-seat 1 3. In the example illustrated, the said valve-seat 1 3 is conical and is of rigid material.

The closure member 14 is adapted to cooperate with the valve-seat 1 3 by deformation of the O-ring seal 1 7 which is applied against the valve-seat 13. Provision is made in the said valveseat for one or a number of local depressions 49 which permit a small pilot-flame flow through the valve-seat (as shown in Fig. 8) when the seal 1 7 is brought lightly into contact with the said valveseat but which are sealed-off in order to permit total closure (as shown in Fig. 9) when the seal 1 7 is compressed against the valve-seat 1 3.

The control system 1 5 (shown in Figs. 1 to 4) comprises a regulating hand-wheel 18. The said hand-wheel has a threaded control rod or stem 1 9 and a peripheral gripping ring 20. By means of the central stem 19, the hand-wheel 18 has the effect of exerting a thrust on the closure member 14 in order to close this latter through the intermediary of a ball 21. The closure member 14 is urged to its open position by a spring 22 which is applied against the valve body 10 and placed at the end remote from the hand-wheel 1 8.

The control system 1 5 is also provided with an actuating trigger 23. Said trigger is rigidly fixed to a sleeve 24 in which the hand-wheel 18 is mounted by screwing of its central stem 19 within the said sleeve.

Means are provided for preventing the trigger 23 from rotating in either direction about the axis of the hand-wheel 1 8. To this end, the trigger 23 having the general shape of an inverted trough (as shown in Figs. 1 and 1A) is permitted to come into position astride a lug 41 formed on the handle P.

As shown in Fig. 1, the sleeve 24 is rigidly fixed to the trigger 23 on the one hand axially by means of a shoulder 42 on which the sleeve 24 is abuttingly applied against the trigger 23 and by means of a crimped edge 43 which serves to clamp the sleeve 24 against the trigger 23, and on the other hand angularly by local deformation 44 of the crimped edge 43 of the sleeve 24 into one or a number of recesses 45 of the trigger 23.

The sleeve 24 has an annular flange 25 which bears on an annular seating 26 of the valve body 10 at the entrance 27 of the bore 12 under the action of a resilient means 28 interposed between the annular flange 25 and an opposite annular bearing face 29 formed on a bell-housing 30 which is attached to the valve body 1 0.

The resilient means 28 comprises a helical spring which extends concentrically between the sleeve 24 and the bell-housing 30.

It will be noted that the peripheral gripping ring 20 of the hand-wheel 18 surrounds a portion 31 of the trigger 23 which is adjacent to the sleeve 24.

Said portion 31 of the trigger 23 which is adjacent to the trigger 24 has a two concentric skirts in spaced relation: an inner skirt 32 which is attached to the sleeve 24 and an outer skirt 33 which surrounds the bell-housing and is in turn surrounded by the peripheral gripping ring 20 of the hand-wheel 1 8.

It will further be noted that the seating 26 of the valve body 10 on which the annular flange 25 of the sleeve 24 is applied is defined by an annular boss 34 of the valve body 10 on which the bellhousing 30 is adapted to be screwed at 35 in order to be attached to the valve body 1 0.

By means of the construction just described, the entire control system 1 5 is positioned on the valve body 10 under the action of the resilient means 28 which tends to maintain the annular flange 25 generally applied and centered on the seating 26 of the valve body 10. The said control system 1 5 is capable of tilting as a single unit for opening under the action of the trigger 23 and in opposition to the resistance of the resilient means 28. The annular flange 25 is permitted to move away from the seating 26 of the valve body 10, with the exception of a localized contact zone C (shown, in Fig. 3) which forms a pivotal bearing point.

The range of travel corresponding to upward displacement of the annular flange 25 (as shown in Figs. 3 and in Figs. 5 to 7) at the time of operation of the trigger 23 in order to open the valve is defined by a stop consisting of an internal annular shoulder 46 of the bell-housing 30.

It is worthy of note that, in the contact zone (shown in Figs. 5 to 7) in which a thrust is exerted by the hand-wheel 1 8 on the closure member 14 (as shown in Figs. 1 to 7), the conditions of contact should be such as to reduce any tendency of the closure member 14 to be driven in rotation by the hand-wheel 1 8 while this latter is being either screwed or unscrewed and therefore to maintain the said member 14 in a fixed angular position. Similarly, when the trigger 23 is actuated and thus produces a pivotal displacement or tilting movement, it should also be ensured that any tendency towards lateral displacement of the closure member 14 is also reduced and in any case limited to a lateral travel of negligible value.

To this end, the top surface 47 of the closure member 1 4 which defines a zone of contact with the handwheel 1 8 is intended to be located in close proximity to the annular seating 26 of the valve body 10 on which the annular flange 25 is applied. This results in a compact design and also achieves economy of material.

Preferably, the hand-wheel 1 8 is brought into contact with the top face 47 of the closure member 14 by means of a nose which has a higher degree of hardness than the said member.

By way of example, provision can accordingly be made for a ball 21 which is adapted to form during operation a small cup-shaped depression 48 in the top surface 47 of the closure member 14. In order to minimize the effect of transmission of motion to the closure member 14 at the time of pivotal displacement of the trigger 23, steps are accordingly taken to locate the center 0 of the ball 21 in a plane L which is coplanar with the seating 26 provided on the valve body 10 for the annular flange 25 when the trigger 23 is located at the mid-point (Fig. 6) between the open position (Fig. 7) and the closed position (Fig. 5).

When the blowpipe is not in use, the handwheel 18 is screwed right home (as shown in Fig.

4). This has the effect on the one hand of applying the closure member 14 in a closed position against the seating 1 3 and on the other hand of causing the sleeve 24 which carries the trigger 23 to move upwards until the annular flange 25 is abuttingly applied against the annular shoulder 46 of the bell-housing 30, which in turn has the effect of locking the said trigger 23 by placing this latter in a condition in which it cannot possibly be operated.

When it is desired to put the blowpipe into service, the hand-wheel 1 8 is unscrewed in order to release the trigger 23 and Figs. 1 to 9 show the valve in a condition in which the closure member 14 is fully closed against the seating 1 4 but in which the trigger 23 is released and can be actuated at will.

Starting from this position of Figs. 1 and 9, it is necessary to place the valve in a position in which the pilot burner is set.

To this end, the hand-wheel 18 is opened to a slight extent and the pilot flame is ignited. By screwing or unscrewing the hand-wheel 18, the said pilot flame can be adjusted, the seal 1 7 being brought to the same level as the valve-seat 13 so as to allow a small flow through the depressions 49 (as shown in Figs. 8 and 10). This adjustment is carried out once and for all. Thereafter, the pilot flame burns continuously within the blowpipe if the trigger 23 is not depressed. On the other hand, if the trigger 23 is depressed, the control system 1 5 is tilted back, thus having the effect of opening the valve to the full extent and producing the maximum rate of flow. When the trigger is released, the valve returns to the low-burner position in which the pilot flame remains adjusted.

The simple and convenient constructional design of the valve in accordance with the invention will be readily appreciated.

Another feature of a valve of this type lies in the fact that it permits the standard use of the same valve body 10 described in the foregoing both for double control with hand-wheel 1 8 and trigger 23 as shown in Figs. 1 to 4 and for single control by hand-wheel 18, namely without a trigger 23.

Reference will be made to Fig. 11 which illustrates a valve of this type with a single handwheel control. In this case the trigger 23 and the sleeve 24 as well as the spring 28 have been dispensed with. The central stem 1 9 of the handwheel 1 8 is screwed directly into a member 40 which has the general shape of an inverted annular trough and alone serves to replace the bell-housing 30 and the sleeve 24, the resilient means 28 being dispensed with.

In the design shown in Fig. 11 , it will be understood that the ball 21 is always interposed between the central stem 1 9 of the hand-wheel 1 8 and the closure member 14 whereas provision is again made for the spring 22 in order to restore the closure member 14 to the open position.

In a simplified design (illustrated in Fig. 12) which permits a reduction in cost and in which the same valve body 10 is again employed, the closure member 14 is so arranged as to be rigidly fixed to the hand-wheel 18, in which case the restoring spring 22 is dispensed with.

As shown in Fig. 12, the upper end portion 36 of the closure member is splined and the handwheel 1 8 is force-fitted directly on the said end portion 36. Preferably, the hand-wheel 1 8 is adapted to carry a radial web 37 which facilitates the operation and indicates at each instant the position in which the valve is located. At the moment of force-fitting at 36, it is advisable to take the precaution of giving the web 37 a predetermined orientation, for example in alignment with the handle P in the closed position.

It will be noted that, in the simplified design of Fig. 12, the closure member 14 which is directly attached to the hand-wheel 1 8 is permitted to rub on the valve-seat 1 3 in rotational motion. It might be expected that such operating conditions could lead to premature wear of the seal 1 7, especially by reason of the existence of the depressions 49.

Experience has shown, however, that the performance of the valve remains satisfactory over an acceptable period of service.

It will be understood that, in the different embodiments described and illustrated, abutment means are provided for preventing excessive unscrewing of the hand-wheel 1 8 in the direction of opening. These means consist for example of a snap-ring J in Figs. 1 to 11 and of an annular shoulder E in Fig. 12, the snap-ring J or the shoulder E being adapted to cooperate with a bearing face A which forms a stop.

Claims

1. A valve, especially for a blowpipe, comprising a valve body, a passageway for the flow of fluid within the said body, at least part of the said passageway being defined by a bore provided with an annular shoulder forming an annular valve-seat, and a closure member slidably engaged within the said bore in order to be moved towards and away from the said valve-seat under the action of a control system which permits a double control, characterized in that the said control system comprises on the one hand a regulating hand-wheel adapted to exert a thrust on the said closure member in order to close the valve and on the other hand an actuating trigger rigidly fixed to a sleeve in which the hand-wheel is mounted by screwing, the said sleeve being provided with an annular flange which is applied against an annular seating of the valve body at the entrance of the said bore under the action of a resilient means interposed between the said annular flange and an opposite annular seating formed on a bell-housing attached to the valve body, the said control system as a whole being positioned on the said valve body under the action of a resilient means which tends to maintain the annular flange generally applied and centered on the seating of the valve body, the said control system being capable of tilting as a single unit for opening under the action of the trigger in opposition to the resistance of the resilient means, the annular flange being capable of moving away from the seating of the valve body, with the exception of a localized contact zone which forms a pivotal bearing point.

2. A valve in accordance with claim 1, characterized in that means are provided for preventing rotation of the trigger about the axis of the hand-wheel in one direction or in the other.

3. A valve in accordance with claim 2, characterized in that the trigger which has the general shape of an inverted trough is adapted to come into position astride a lug formed on a handle which is rigidly fixed to the valve body.

4. A valve in accordance with any one of claims 1 to 3, characterized in that the sleeve is rigidly fixed to the trigger on the one hand axially by means of a shoulder on which the sleeve is abuttingly applied against the trigger and on the other hand angularly by local deformation of the crimped edge of the sleeve into at least one recess of the trigger.

5. A valve in accordance with any one of claims 1 to 4, characterized in that the range of travel corresponding to upward displacement of the annular flange at the time of operation of the trigger in order to open the valve is defined by a stop.

6. A valve in accordance with claim 5, characterized in that the said stop consists of an internal annular shoulder of the bell-housing.

7. A valve in accordance with any one of the preceding claims, characterized in that the closure member has a top surface which defines a zone of thrust contact with the hand-wheel and is located in close proximity to the seating of the valve body on which the annular flange of the sleeve is applied.

8. A valve in accordance with claim 7, characterized in that the hand-wheel produces action in contact with the top surface of the closure member by means of a spherical surface having a higher degree of hardness than the said top surface and capable of forming a cupshaped depression in the said surface during operation, the centre of the said spherical surface being substantially coplanar with the seating provided on the valve body for the annular flange of the sleeve when the trigger is located at a point mid-way between the open position and the closed position.

9. A valve in accordance with any one of the preceding claims, characterized in that the resilient means comprises a helical spring which extends between the sleeve and the bell-housing in concentric relation thereto.

10. A valve in accordance with any one of the preceding claims, characterized in that the handwheel is provided on the one hand with a threaded central stem which serves to screw the said handwheel within the said sleeve and is adapted to cooperate by exerting thrust on the closure member and, on the other hand, a peripheral gripping ring adapted to surround a portion of the trigger which is adjacent to the sleeve.

11. A valve in accordance with claim 10, characterized in that the aforesaid portion of trigger which is adjacent to the sleeve has two concentric skirts in spaced relation, namely an inner skirt which is attached to the sleeve and an outer skirt which surrounds the bell-housing and is in turn surrounded by the peripheral gripping ring of the hand-wheel.

12. A valve in accordance with any one of the preceding claims, characterized in that the handwheel is adapted to cooperate with the closure member in the application of thrust by means of a ball.

13. A valve in accordance with any one of the preceding claims, characterized in that the closure member is restored to the open position by a spring which is applied against the valve body and is remote from the hand-wheel.

14. A valve in accordance with any one of the preceding claims, characterized in that the seating of the valve body on which the annular flange of the sleeve is applied is defined by an annular boss of the valve body on which the bell-housing is screwed in order to be attached to the said valve body.

1 5. A valve in accordance with any one of the preceding claims in which the valve body is intended to be employed in conjunction with a single hand-wheel control without a trigger, characterized in that for this type of service the hand-wheel is screwed directly into a member which has the general shape of an inverted annular trough and alone serves to replace the bell-housing and the sleeve, the resilient means aforesaid being no longer provided.

16. A valve in accordance with claim 15, characterized in that, in a simplified embodiment, the closure member is rigidly fixed to the handwheel and is not fitted with a restoring spring.

1 7. A valve, especially for a blowpipe, comprising a valve body, a passageway for the flow of fluid within the said body, at least part of the said passageway being defined by a bore provided with an annular shoulder forming an annular valve-seat, and a closure member slidably engaged within the said bore in order to be moved towards and away from the said valve-seat under the action of a control system which permits single control, characterized in that the said control system comprises a hand-wheel screwed into a member having the general shape of an inverted annular trough, the closure member being rigidly fixed to the hand-wheel and permitted to rub directly on the said valve-seat in rotational motion.

1 8. A valve in accordance with claim 1 6 or claim 17, characterized in that the hand-wheel is adapted to carry a radial web which facilitates operation and indicates the exact position of the valve at each instant.

19. A valve in accordance with any one of the preceding claims, characterized in that the closure member is adapted to cooperate with the valveseat by deformation of an O-ring seal of elastomer material carried by the said closure member and applied against the valve-seat which is of rigid material.

20. A valve in accordance with claim 19, characterized in that the said valve-seat is provided with one or a number of local depressions which permit a small pilot-flame flow through the valve-seat when the O-ring seal is brought lightly into contact with the valve-seat but which are sealed-off in order to permit total closure when the said seal is compressed against the said valveseat.

21. A valve which is primarily applicable to a blowpipe, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.