WO2005019713A1

WO2005019713A1 - Valve assembly

Info

Publication number: WO2005019713A1
Application number: PCT/GB2004/003444
Authority: WO
Inventors: Craig Antony Furnival
Original assignee: Oliver Twinsafe Valves Limited
Priority date: 2003-08-21
Filing date: 2004-08-10
Publication date: 2005-03-03
Also published as: GB0319643D0

Abstract

The valve assembly is designed for isolation of the fluid in a storage tank from a diaphragm seal (29) of a level monitoring system. The assembly has a cleaning port (54) defined in the housing for directing cleaning or calibration fluid at the diaphragm seal so that it can be cleaned or calibrated in-situ. A flushing drain port (55) is provided to allow used cleaning fluid and dirt to be directed from the assembly. The invention eliminates the need to remove the seal and a pressure transmitter each time cleaning or calibration is required.

Description

AN ISOLATION VALVE ASSEMBLY

The present invention relates to an isolation valve assembly and more particularly to such a valve assembly for isolating a diaphragm seal in a level monitoring system of an industrial storage tank. Diaphragm seals are used as an interface between fluid media such as oil, petroleum or chemicals stored in an industrial storage tank and a level monitoring transducer. The diaphragm seal is located adjacent to an aperture at the base of the tank and comprises a flexible membrane having one face in contact with the media in the tank and the other face in communication with a capillary tube that is filled with hydraulic fluid. The tube is in turn connected to the sensor of a pressure transmitter where the pressure of the hydraulic fluid is converted into an electrical signal. The pressure of the head of fluid in the tank serves to deflect the diaphragm which in turn acts on the hydraulic fluid in the capillary thereby indicating a change in the signal - output from the pressure transmitter. This electrical signal from the transmitter is converted into a value that is representative of the level of the media in the storage tank and can be used in the supervision or control of an industrial process. In applications where the tank is open to the atmosphere only a single diaphragm and pressure transmitter combination is required but in instances where the tank is closed and a head of gas vapour pressure is allowed to develop over the fluid two such diaphragms and pressure transmitters are required to determine a differential pressure that is representative of the level. It is known to provide an isolation valve between the diaphragm seal and the tank. This, enables a seal to be removed for replacement or servicing without emptying the contents of the tank by simply closing the valve. One drawback with this arrangement is that a diaphragm seal has to be removed at regular intervals for cleaning as the diaphragm membrane can become coated with solidified particulate matter from the chemical in the tank or can become contaminated with foreign bodies. The build up of such matter can restrict the flexibility of the membrane and thus result in false pressure/level readings from the pressure transmitter. The diaphragm seal and transmitter have to be isolated via the ball valve and then removed from the tank for cleaning and re-calibration. This is a time consuming and labour intensive operation and therefore incurs significant cost to the industry. The weight, size and fixing arrangements of the diaphragm seal and pressure transmitter unit are such that it is a difficult operation to remove and replace the unit and it can often result in the diaphragm membrane being damaged. It is an object of the present invention to obviate or mitigate the aforesaid disadvantages. According to the present invention there is provided an isolation valve assembly for connection to a diaphragm seal, the valve assembly comprising a housing having an outer surface and an inner surface that defines a flow passage therethrough with an inlet end and an outlet end, connection means for connecting the outlet end of the valve to the diaphragm seal, a valve chamber in the flow passage and a valve member disposed in said passage and movable between open and closed positions, a first port extending through the housing from said outer surface of the housing to said outlet end and a second port extending through the housing from said outlet end to said outer surface. The first port is adapted to direct pressurised cleaning fluid on to the diaphragm seal (when present) so as to clean it. Alternatively the port can be used for calibration of an attached level monitoring system by simulation of the process conditions. The second port is adapted to drain away media prior to calibration or cleaning fluid and dirt removed from the diaphragm seal. The first port preferably has at least a portion that extends in a direction that is inclined at an acute angle to the longitudinal axis of the flow passage so that an inclined jet of cleaning fluid may be, in use, incident upon the diaphragm seal. The first port preferably has a first portion that extends from outer surface at a position spaced from the outlet end and a second portion that extends from the first portion and is directed towards the outlet end. The housing preferably comprises an end member that is releasably received in a bore in the main body and defines said outlet end. The end member ideally has at least part of said first and second ports defined therein. The first portion of the first port preferably extends through the main body of the housing and the second portion may extend through the end member. An annular channel may be defined in an outer surface of the end member, the channel providing communication between first and second portions of the first port. The first portion of the first port may extend substantially radially. The end member is preferably connected to the main body of the housing by a screw thread, although other connections are contemplated. Ideally there is provided aplurality of second portions of the first port that may be equi-angularly spaced around housing. The channel preferably provides communication between all the second portions and the first portion. The second port preferably comprises a first portion defined in said main body of the housing and a second portion that extends substantially axially in end member. A channel defined in the outer surface of the end member preferably provides communication between the two portions. The channel is preferably annular. The first and second ports are preferably closable by valves which may be disposed on the outer surface of the housing. The valves are preferably ball valves having ends that are received in the ports. The valve member in the valve chamber is preferably a ball valve. Two such valve chambers and valve members maybe provided. A specific embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a schematic representation of the isolation valve of the present invention connected in-situ to a storage tank with a diaphragm seal and a pressure transmitter. Figure 2 is a sectioned side view of the isolation valve of the present invention; Figure 3 is a side view of the valve of figure 2; Figure 4 is a plan view of the valve of figure 2; Figure 5 is an end view of the valve of figure 2; and Figure 6 is diagrammatic representation illustrating the function of the isolation valve of the present invention. Referring now to figure 1 of the drawings, the isolation valve assembly 10 of the present invention is shown in-situ in a level monitoring system for a large scale storage tank 11 of chemicals, petrochemicals or other fluid media. The valve 10 has an inlet end in fluid communication with an aperture 12 at the bottom of the storage tank 11. An opposite outlet end of the isolation valve assembly 10 is connected to a diaphragm seal 13 which is, in turn, connected to a pressure transmitter 14 via a capillary tube 15 carrying hydraulic fluid. In operation, with the isolation valve 10 open, fluid in the tank 11 passes into the isolation valve 10 and is incident on the diaphragm seal 13. The pressure applied by the head of fluid in the tank deflects the diaphragm seal 13 and thus pressurises the hydraulic fluid in the capillary tube 15. This change in pressure is sensed at the pressure transmitter 14 and the pressure reading can be used to determine the level of fluid in the tank. The tank 11 shown in figure 1 is open to atmospheric pressure and the pressure reading can therefore be taken directly from the pressure transmitter 14. In an alternative system (not shown) where the tank 11 is closed, the level monitoring system will have an additional valve assembly and diaphragm seal located at the top of the tank for determining the pressure of any vapour or gas present above the fluid. A differential pressure transmitter connected to both diaphragm seals is used to calculate the level of the fluid in the tank. Referring now to figures 2 to 6, the isolation valve assembly is a double-block- and-bleed ball valve that comprises a housing having a main body 20 defining a flow passage 21 along its length. The flow passage 21 has an inlet 22 for connection to the tank 11, an outlet 23 for connection to the diaphragm seal 13 and two valve chambers 24, 25 each of which receives a rotary ball valve 26, 27. In figure 2 the valve assembly is depicted with its outlet 23 adjacent to the diaphragm seal 13. The seal comprises a collar 28 that supports a diaphragm membrane 29 ^"over the outlet 23. The capillary tube is omitted from figure 2 for clarity. Each ball valve 26, 27 as is conventional, has a port therethroug for selective registration with the flow passage 21 and is mounted for rotation between two valve seats (not shown for reasons of clarity). Rotation of the ball valve 26, 27 in each case is effected by a handle 30, 31 that extends on the outside of the housing and connects to the ball valve 26, 27 by a stem 32,33 that passes into the housing in a radial direction. In between the ball valves 26, 27 there is a cavity 34 that can be vented through a vent port in the housing. A needle valve 35 (shown in figures 3 to 6) on the outside of the housing is connected to the vent port and allows selective venting of the cavity 34 as is well known in this field. At the outlet end 23 of the valve assembly, where it is connected to the diaphragm seal, the housing has an end fitting 40. The fitting serves to retain an outer valve seat (not shown) for a first of the ball valves 26 and is designed to provide an interface with an arrangement for cleaning the diaphragm seal 13 and/or calibrating the level monitoring system as will be described below. The fitting 40 is generally cylindrical with a stepped outer surface defining a flange 41 at one end, a first end face 42 that is recessed for receipt of the valve seat and a second end face 43 for abutment with the diaphragm seal 13. A stepped bore extends though the fitting coaxially with the flow passage of the main body 20 of the housing to define the outlet 23. The step 44 marks a decrease in diameter in the direction from the outlet 23 to the first ball valve 26. The interior surface of the main body 20 of the housing at the outlet end 23 has a complementary profile designed to receive the end fitting 40 in a sealing relationship. The flange has a screw thread 45 on its exterior surface for engagement with a complementary thread defined on the interior wall of the main body 20. The remainder of the fitting 40 has a plurality of seals 46 located in annular grooves on its outer surface for sealing engagement with the internal surface of the main body 20. The outer surface of the end fitting 40 has an annular channel 47 that is open to a pair of radial bores 48, 49 arranged at diametrically opposed locations in the main body. A first radial bore 48, intended for use as an inlet for the ingress of cleaning or fluid used in calibration is, in use, disposed vertically above the second radial bore 49 that is intended as a flushing port. The inlet and flushing bores 48, 49 are both opened and closed by a respective ball valve 50, 51 that is mounted on the exterior of the main body 20. Each ball valve 50, 51 is manually operable by a rotary handle 52, 53 as is customary. The end fitting 40 has four equi-angularly spaced passageways 54 that extend from the annular channel 47 to the step 44 in the bore and subtend an acute angle to the longitudinal axis of the housing. A fifth passageway 55 disposed, is use, at the bottom of the fitting, also extends between the channel 47 and the step 44 in the bore. It has a first portion 55a that is substantially aligned with flushing port 49 and a second portion 55b that extends at right angles in a direction substantially parallel to the longitudinal axis of the bore. An end flange 60 of the housing has a plurality of tapped fixing bores 61 that are equi-angularly spaced and designed to receive threaded studs 62 as shown in dotted line in figure 3. In normal operation of the level monitoring system the two main isolation ball valves 26, 27 are open to allow fluid from the tank 11 to pass along the flow passage 21 to the diaphragm seal 13. The needle valve 35 and the ball valves 50, 51 for the inlet and flushing ports are closed. When it is necessary to clean the diaphragm seal membrane 29 the main isolation ball valves 26, 27 are closed so as to isolate the diaphragm seal 13 from the tank fluid. The needle valve 35 is then opened to vent the cavity 34. This ensures that there is no pressure differential between the two ball valves 26, 27 so that both balls are effectively sealed against their respective valve seats. The flushing port valve 51 is then opened so as to drain any fluid trapped between the first ball valve 26 and the diaphragm seal 13. Once the fluid has drained the diaphragm seal 13 can be cleaned or calibrated. In the former base this is achieved by opening valve 50 and applying a pressurised cleaning solution fluid to the inlet port 48. The cleaning fluid passes through the port 48 into the four passageways 54 from whence it emerges as four jets directed to hit the diaphragm seal membrane 29 approximately half-way between its centre and periphery so as to provide the largest possible coverage. The cleaning fluid and any detritus removed from the membrane 29 settles to the bottom of the outlet bore where it drains through passageway 55 and the open flushing port 49. When the diaphragm seal membrane 29 has been cleaned and the cavity 34 has been vented the system can be recalibrated. This is achieved by closing flushing port 49, applying a fluid at known pressure through the open cleaning port 48 and comparing the pressure reading generated at the pressure transmitter 14. When the system is ready for reuse the inlet port 49 is closed and the main isolation valves 26, 27 are opened again. -> It will be appreciated that the present invention allows cleaning of the diaphragm seal 13 and recalibration of the level monitoring system can be performed in-situ without the need to remove the seal or the pressure transmitter. This significantly reduces the labour and time required to perform the operation and eliminates the risk of damage to the diaphragm seal. Moreover, the design provides for an isolation valve and level monitoring system that can be relatively easily installed on the tank by one person. The valve is attached to a flange on the tank by known fixing members. The diaphragm seal and pressure transmitter can then be easily mounted by aligning apertures on the seal collar to the threaded studs 62, pushing the seal collar home and fastening the connection by threading nuts on to the studs 62. It will be appreciated that numerous modifications to the above described design may be made without departing from the scope of the invention as defined in the appended claims. For example, the isolation valve may have only a single ball valve. Moreover, another sort of valve member other than a ported ball valve may be used.

Claims

1. An isolation valve assembly for connection to a diaphragm seal, the valve assembly comprising a housing having an outer surface and an inner surface that defines a flow passage therethrough with an inlet end and an outlet end, connection means for connecting the outlet end of the valve to the diaphragm seal, a valve chamber in the flow passage and a valve member disposed in said passage and movable between open and closed positions, a first port extending through the housing from said outer surface to said outlet end and a second port extending through the housing from said outlet end to said outer surface.

2. An isolation valve assembly according to claim 1, wherein the first port is adapted to direct a jet of pressurised cleaning fluid towards the outlet end.

3. An isolation valve assembly according to claim 1, wherein the second port is adapted to drain away cleaning fluid and/or dirt removed from the diaphragm seal.

4. An isolation valve assembly according to claim 1, 2 or 3, wherein the first port has at least a portion that extends in a direction that is inclined at an acute angle to the longitudinal axis of the flow passage.

5. An isolation valve assembly according to any preceding claim, wherein the housing comprises an end member that is releasably received in a bore in the main body and defines said outlet end.

6. An isolation valve assembly according to any claim 5, wherein the first port has a first portion that extends from outer surface of the housing at a position distal from the outlet end and a second portion that extends from the first portion and extends towards the outlet end.

7. An isolation valve assembly according to claim 6, wherein the end member has at least part of said first and second ports defined therein.

8. An isolation valve assembly according to claim 6 or 7, wherein the first portion of the first port extends through the main body of the housing and the second portion extends through the end member.

9. An isolation valve assembly according to claim 8, further comprising a channel defined in an outer surface of the end member, the channel providing communication between first and second portions of the first port.

10. An isolation valve assembly according to claim 9, wherein the channel is annular.

11. An isolation valve assembly according to any one of claims 6 to 10, wherein the first portion of the first port extends substantially radially.

12. An isolation valve assembly according to any one of claims 6 to 10, wherein the end member is connected to the main body of the housing by a screw thread.

13. An isolation valve assembly according to any one of claims 6 to 12, wherein there are a plurality of second portions of said first ports.

14. An isolation valve assembly according to claim .13, wherein the second portions of first ports are equi-angularly spaced around housing.

15. An isolation valve assembly according to claim 13 or 14 when dependent from claim 9, wherein the channel provides communication between said all the second portions of the and the first portion ports.

16. An isolation valve assembly according to any one of claims 6 to 15, wherein the second port comprises a first portion defined in said main body of the housing and a second portion that extends substantially axially in said end member.

17. An isolation valve according to claim 16 when dependent from claim 9, wherein the outer surface of the channel that provides communication between the first and second portions of the second port.

18. An isolation valve assembly according to any one of claims 5 to 17, wherein the end member retains a valve seat against said valve member.

19. An isolation value assembly according to claim 18, wherein the end member has a recess for receiving said valve seat.

20. An isolation valve assembly according to any preceding claim, wherein the first and second ports are closable by valves.

21. An isolation valve assembly according to claim 20, wherein the valves are disposed on the outer surface of the housing.

22. An isolation valve assembly according to claim 20 or 21, wherein each valve has an end is received in a respective port.

23. An isolation valve assembly according to any preceding claim, wherein the valve member in the valve chamber is a ball valve.

24. An isolation valve assembly according to any preceding claim, wherein two valve chambers and valve members are provided.

25. An isolation valve assembly substantially as hereinbefore described with reference to the accompanying drawings.

26. A level monitoring system for a storage reservoir comprising a diaphragm seal, a pressure transducer and an isolation valve assembly according to any preceding claim.