GB1601084A

GB1601084A - Safety valves

Info

Publication number: GB1601084A
Application number: GB15060/78A
Authority: GB
Original assignee: Bopp and Reuther GmbH
Current assignee: Bopp and Reuther GmbH
Priority date: 1977-04-22
Filing date: 1978-04-17
Publication date: 1981-10-21
Also published as: IT1097054B; FR2388187A1; IT7822133A0; DE2717860A1; FR2388187B1; DE2717860C3; DE2717860B2

Description

(54) IMPROVEMENTS IN OR RELATING TO SAFETY VALVES (71) We, BOPP & REUTHER GMBH, a German Body Corporate, of 1 Carl-Reuther Strasse, Mannheim-Waldhof, Federal Republic of Germany, 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: The present invention relates to safety valves in particular for low operating pressures, of the kind which have controlled loading from a pneumatic piston and cylinder device in addition to spring loading in the valve.

In known safety valves of the kind described, the piston of the pneumatic piston and cylinder device is solidly connected to the end of a spindle carrying the obturator of the valve, and in this way any movement of the piston in the opening and closing directions of the valve is transmitted via the valve spindle to the obturator and vice-versa.

If there is a fault in the compressed-air system and the supply of pressurised air fails, the safety valve is moved to the closed position and held in this position only by the valve spring and the pressurised medium in the pressurised system which is being safeguarded, which acts on the obturator of the valve, must open the safety valve on its own when the response pressure is reached, in opposition to the pressure from the valve spring.A disadvantages of this is that, should the supply of compressed air used for control fail during the process of opening the valve the pressurised medium has to overcome not only the opposing force of the valve spring but also the frictional forces from the sealing ring of the piston in the pneumatic cylinder before the valve will open, thus giving rise to the danger that the valve will open too late, particularly in the case of safety valves for low operating pressures. What is more, the process of closing the valve is also delayed by the friction of the sealing ring of the piston against the walls of the cylinder.

It is an object of the invention to provide an additionally loaded safety valve of the kind described which will still open and close at the correct time if the supply of raising and loading air fails.

Accordingly, the invention consists in a safety valve having a pneumatic piston and cylinder device for providing a controlled loading on the valve, wherein the pneumatic piston and cylinder device has two floating pistons of which one is operable as a loadingair piston and the other is operable as a raising-air piston in response to pressurised air, the loading-air piston engaging the end of the spindle of the safety valve under the pressure of the pressurised air to bias the latter towards its closed position, the valve spindle passing through the raising-air piston with clearance and having an abutment for engaging the raising-air piston so that movement of the raising-air piston in response to raising-air moves the valve spindle in the opening direction, and wherein a spring is provided between the pistons which biases the two pistons apart.

By an arrangement of this kind of two floating pistons in the pneumatic cylinder for the additional loading, in the event of the raising and loading air failing, the valve spindle carrying the valve obturator is able to move freely in relation to the two pistons by virtue of the fact that they are freely mounted. In the event of a failure in the supply of compressed air, the loading-air piston and the raising-air piston move to their initial positions under the biassing of the spring therebetween, and the valve spindle carrying the valve obturator then moves to the open or closed position of the valve independently of the two pistons so that it no longer has to overcome the friction from the sealing rings of the pistons.

When there is no interference with the additional loading, the loading-air piston is biassed by the pressurised air to transmit additional closing force to spindle of the valve. If the operating pressure in the pressurised system which is being safeguarded is exceeded, the pressure switch responds and allows the compressed air above the loadingair piston to escape, the raising-air piston, to which the compressed air is applied at the same time, then forcing the valve spindle upwards to the open position via the abutment thereon.

It is also proposed that, when the valve is in the closed position, a gap may be left between the inner face of the engagement piece on the valve spindle and the outer face of the raising-air piston which acts on it, thus ensuring that the valve obturator can always sit firmly on the valve seating.

It is useful for the raising-air piston to be cup-shaped in cross-section and to have a cylindrical body into which a tubular guide skirt on the loading-air piston projects. This means that both pistons have simple sliding guidance and at the same time it produces a chamber to accommodate the return spring.

It is also proposed that an annular sliding projection be provided at the free end of the tubular guide skirt on the loading-air piston, thus producing a single, well defined point of contact for the sliding guidance of the pistons.

The return spring can be satisfactorily mounted by providing respective central recesses to receive the ends of the return spring in the bottom of the cup-shaped raising-air piston and in the loading-air piston at the transition to the guide skirt.

Apart from this, it is advisable for the annular chamber for raising air, which is defined by the rim of the cup-shaped raisingair piston and which is sealed off towards the outside by an O-ring, also to be sealed off towards the inside by an O-ring, which is inserted in an external recess in the bottom of the raising-air piston, thus ensuring that the annular chamber for raising air is properly sealed.

In order that the invention may be more clearly understood, reference will now be made to the accompanying drawing which shows one embodiment in axial section by way of example.

Referring now to the drawing, to provide controlled additional loading, there is securely mounted on a safety valve 1 a pneumatic cylinder 2 which comprises a barrel 3 for the pistons to slide in, a cap 4 for the cylinder and a bottom plate 5 for the cylinder. Mounted to slide in the pneumatic cylinder 2 are two floating pistons 6 and 7 of which the upper, 6, forms the loading-air piston, i.e. a piston for loading air, and the lower, 7, the raisingair piston, i.e. a piston for raising air. Between the cap 4 of the cylinder and the piston 6 is situated a chamber 8 for loading air to which the compressed air used for control is fed via a loading-air line 9 which opens into the cap 4 of the cylinder. The line 9 is connected to a source of compressed air (not shown).

To form an annular chamber 10 for raising air, the lower part of the cylindrical sleeve 3 has a cylindrical shoulder 11 into which the cylindrical body 12 of the raising-air piston 7, which is cup-shaped in cross-section, projects. The annular chamber 10 for raising air is bounded at the bottom by the end face 14 of the shoulder 11 and at the top by the underside of the rim 14 of the cupshaped raising-air piston 7 and the raising air is fed in from a line 15, which is connected to the source of compressed air referred to above and opens into the shoulder 11 in the cylindrical sleeve 3 and which communicates freely with the annular chamber 10 for raising air via a bore 16.The loading air and raising air are applied simultaneously, so that the loadng-air piston 6 holds the valve obturator in the closed position under the additional loading force by virtue of the difference in piston area. If the response pressure of the safety valve is reached in the pressurised system being safeguarded, the compressed air above the loading-air piston is relased when the pressure switch responds, so that the compressed air which enters the annular chamber 10 for raising air moves the valve spindle and thus the valve obturator to the open position.

The loading-air piston 6 has a tubular guiding skirt 17 which projects into the cylindrical body 12 of the raising-air piston 7 and whch, at its lower end, has an annular sliding projection 18 to guide the piston 6 in the piston 7. The bottom 19 of the cupshaped piston 7 contains a central recess 20 and at the transition to the guiding skirt 17 the piston 6 contains a central recess 21. These two recesses 20 and 21 are used to receive the ends of a return spring 22. To seal off the piston 6, a resilient O-ring 23 is inserted in a groove in the circumfernetial surface of the piston.To seal its rim 14 which forms the outer boundary of the annular chamber 10 for raising air, the piston 7 carries an O-ring 24 and to seal off the annular chamber for raising air in the inwards direction it carries an O-ring 25 which is inserted in an external recess in the bottom 19 of the raising-air piston.

Under the pressure of the compressed air which flows into the chamber 8 for loading air, the floating piston 6 is applied by force from above to the end 26 of the valve spindle 27, to whose lower end the valve obturator (not shown in detail) is secured and which, together with the valve obturator, is pressed towards the closed position by the valve closing spring. The piston 6 which is applied by force from above against the end 26 of the valve spindle 27 assists in the operation of closing the valve and while the valve obturator is in its closed position presses it against the valve seating with additional force. The position of the piston 7 when the valve is in the closed position with the additional loading applied is shown in the left-hand half of the drawing.

The valve spindle 27 passes through a bore 28 in the bottom 19 of the cup-shaped piston 7 with clearance. An adjustable engagement bush 29 is screwed onto the end of the threaded spindle 27 remote from the valve seating and is locked in place by a lock nut 30. The abutment face 31 of this engagement bush 29 is situated above the bore 28 in the bottom 19 of the piston 7, thus leaving a gap 33 between this abutment face 31 and the upper face 32 of the bottom 19 of the piston. If the response pressure of the safety valve is reached, the pressure in the chamber 8 for loading air is released and the compressed air which builds up in the annular chamber 10 for raising air forces the piston 7 upwards.As it does so the upper face 32 of the bottom 19 of the piston 7 presses against the abutment face 31 of the engagement bush 29 and moves the valve spindle 27, together with the valve obturator, to the open position.

In the right-hand half of the drawing is shown the position which the two floating pistons 6 and 7 assume if the compressed air used for control fails. In this case there is no pressure in the chamber 8 for loading air and the annular chamber 10 for raising air and the return spring 22 therefore forces the piston 6 upwards towards the cap 4 of the cylinder and the piston 7 downwards towards the bottom plate 5 of the pneumatic cylinder 2. In this way the valve spindle 27 is completely released from the two pistons 6 and 7 and can move up and down independently of them.

WHAT WE CLAIM IS:- 1. A safety valve having a pneumatic piston and cylinder device for providing a controlled loading on the valve, wherein the pneumatic piston and cylinder device has two floating pistons of which one is operable as a loadingair piston and the other is operable as a raising-air piston in response to pressurised air, the loading-air piston engaging the end of the spindle of the safety valve under the pressure of the pressurised air to bias the latter towards its closed position, the valve spindle passing through the raising-air piston with clearance and having an abutment for engaging the raising-air piston so that movement of the raising-air piston in response to raising air moves the valve spindle in the opening direction, and wherein a spring is provided between the pistons which biases the two pistons apart.

2. A safety valve as claimed in claim 1, wherein, when the valve is in the closed position, there is a gap between the inner face of the abutment on the valve spindle and the outer face of the raising-air piston which acts thereon.

3. A safety valve as claimed in claim 1 or 2, wherein the raising-air piston is cupshaped in cross-section and has a cylindrical body into which a tubular guiding skirt on the loading-air piston projects.

4. A safety valve as claimed in claim 3, wherein an annular sliding projection is provided at the free end of the tubular guiding skirt on the loading-air piston.

5. A safety valve as claimed in claim 3 or 4, wherein respective central recesses to receive the ends of the return spring are provided in the bottom of the cup-shaped raisingair piston and in the loading-air piston, at the transition to the tubular guiding skirt 6. A safety valve as claimed in claim 3, 4 or 5, wherein an annular chamber for raising air, which is defined by a rim of the cupshaped raising-air piston and which is sealed towards the outside by a first O-ring, is also sealed off towards the inside by a second O-ring, which is housed in an external recess in an end of the raising-air piston.

7. A safety valve of the kind described, substantially as hereinbefore described with reference to the accompanying drawing.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. additional loading applied is shown in the left-hand half of the drawing. The valve spindle 27 passes through a bore 28 in the bottom 19 of the cup-shaped piston 7 with clearance. An adjustable engagement bush 29 is screwed onto the end of the threaded spindle 27 remote from the valve seating and is locked in place by a lock nut 30. The abutment face 31 of this engagement bush 29 is situated above the bore 28 in the bottom 19 of the piston 7, thus leaving a gap 33 between this abutment face 31 and the upper face 32 of the bottom 19 of the piston. If the response pressure of the safety valve is reached, the pressure in the chamber 8 for loading air is released and the compressed air which builds up in the annular chamber 10 for raising air forces the piston 7 upwards.As it does so the upper face 32 of the bottom 19 of the piston 7 presses against the abutment face 31 of the engagement bush 29 and moves the valve spindle 27, together with the valve obturator, to the open position. In the right-hand half of the drawing is shown the position which the two floating pistons 6 and 7 assume if the compressed air used for control fails. In this case there is no pressure in the chamber 8 for loading air and the annular chamber 10 for raising air and the return spring 22 therefore forces the piston 6 upwards towards the cap 4 of the cylinder and the piston 7 downwards towards the bottom plate 5 of the pneumatic cylinder 2. In this way the valve spindle 27 is completely released from the two pistons 6 and 7 and can move up and down independently of them. WHAT WE CLAIM IS:-

1. A safety valve having a pneumatic piston and cylinder device for providing a controlled loading on the valve, wherein the pneumatic piston and cylinder device has two floating pistons of which one is operable as a loadingair piston and the other is operable as a raising-air piston in response to pressurised air, the loading-air piston engaging the end of the spindle of the safety valve under the pressure of the pressurised air to bias the latter towards its closed position, the valve spindle passing through the raising-air piston with clearance and having an abutment for engaging the raising-air piston so that movement of the raising-air piston in response to raising air moves the valve spindle in the opening direction, and wherein a spring is provided between the pistons which biases the two pistons apart.

5. A safety valve as claimed in claim 3 or 4, wherein respective central recesses to receive the ends of the return spring are provided in the bottom of the cup-shaped raisingair piston and in the loading-air piston, at the transition to the tubular guiding skirt

6. A safety valve as claimed in claim 3, 4 or 5, wherein an annular chamber for raising air, which is defined by a rim of the cupshaped raising-air piston and which is sealed towards the outside by a first O-ring, is also sealed off towards the inside by a second O-ring, which is housed in an external recess in an end of the raising-air piston.