WO2000070254A1

WO2000070254A1 - Safety valve for chemical tanks

Info

Publication number: WO2000070254A1
Application number: PCT/US2000/013430
Authority: WO
Inventors: David B. Tibott
Original assignee: Ashland, Inc.
Priority date: 1999-05-17
Filing date: 2000-05-17
Publication date: 2000-11-23
Also published as: CA2373354A1; AU5020100A

Abstract

A safety valve comprising a valve body (4) defining a valve chamber (6). An inner tube (8) runs through the valve body (4) from an inlet (9) into an outlet (10). A seal is arranged in an inner tube (8) near the inlet (9). The liquid product enters the valve chamber (6) through the first set of holes (16). A third set of holes (20) are provided near the outlet end to allow the liquid product to exit the valve chamber (6). The third set of holes (20) have a smaller flow area than the first set of holes (16). The valve chamber (6) thus fills with liquid product and a float (22) arranged around the inner tube begins to rise, uncovering a second set of holes (18) in the inner tube. The second set of holes (18) have a flow area substantially the same as the first set of holes (16). The float moves between a full flow position in which both the second (18) and third (20) set of holes are uncovered and a reduced flow position in which only the third set of holes are uncovered.

Description

SAFETY VALVE FOR CHEMICAL TANKS

David B. Tibbott

The present application claims the benefit of priority from commonly-owned provisional application Ser. No. 60/134,537, filed May 17, 1999, entitled "Safety Valve for Chemical Tanks", listing inventor David B. Tibbott, the disclosure of which is hereby incorporated by reference.

FIELD OF THE INVENTION The present invention relates generally to the field of float valves, and more particularly to a safety valve which is used to prevent air from entering a tank which is being filled with a liquid.

BACKGROUND OF THE INVENTION Tank wagons are used to transport liquid products such as chemicals between various sites, for example a plant where the product is manufactured and a location where the product is used.

The tank wagons are typically quite large and contain a great quantity of liquid product. The liquid product is off loaded via a hose from the tank wagon into a storage tank at the delivery site. Typically, compressed air is used as the motive force to discharge the liquid product from the tank wagon into the storage tank. Recently, use of chemical storage tanks made from plastic has become more common. Although plastic storage tanks have advantages, if the compressed air enters the storage tank at a high rate, the storage tank may expand and rupture, resulting in a dangerous situation.

The compressed air used in the off loading process may enter the storage tank in several different ways. As the liquid product is off loaded from the tank wagon into the storage tank, the level of liquid in the tank wagon drops. If the tank wagon is parked on a slope or an uneven surface, the low level of liquid product in the tank wagon may allow the compressed air to enter the hose and subsequently the storage tank. More likely, compressed air enters the hose when the tank wagon is essentially emptied of liquid product. It may take up to one hour to unload the tank wagon and an operator may not be present at the time the tank wagon is empty. Due to the small amount of liquid in the tank wagon and in the hose and the high pressure of the compressed air, which may be for example, up to 30 psi, the compressed air rapidly rushes through the hose and into the storage tank. A large amount of compressed air can enter the storage tank in a short period of time resulting in damage to the storage tank.

Additionally, after the off loading process has been completed, it is necessary to clean out the hoses used to transfer the liquid product from the tank wagon to the storage tank. In some cases, although trained not to do so, the operator may simply use the compressed air to blow the hose clean. If the hose is still connected to the storage tank, the compressed air can rapidly fill the storage tank and cause it to rupture. If enough compressed air enters the storage tank, the storage tank may burst or explode, resulting in bodily injury to any individuals in the area as well as a release of the chemicals into the environment. Thus, there is a need for a device which prevents compressed air from entering the storage tank as it is filled.

SUMMARY OF THE INVENTION A safety valve which limits the amount of compressed air which enters a storage tank during off loading of a liquid product from a tank wagon to a storage tank is provided. The valve includes a float which prevents the full force of the compressed air from entering the storage tank as the liquid in the tank wagon is depleted. The safety valve also includes a self-cleaning feature which permits all the liquid product to be expelled from the valve and the hose .

In an embodiment, the safety valve comprises a valve body defining a valve chamber. An inner tube is arranged within the valve chamber. Stops are arranged on the inner tube. A first stop is arranged at an upper portion of the inner tube and a second stop is arranged at a lower portion of the inner tube. A float is arranged in the valve chamber around the inner tube to be movable between the stops. A first set of holes is provided in the inner tube between the first stop and an μpper part of the valve body. A second set of holes is provided on the lower part of the inner tube above the second stop and a third set of holes is provided on the inner tube between the second stop and a lower part of the valve body. The holes allow the liquid product to flow between an inner bore of the tube and the valve chamber.

Preferably, the first and second set of holes are substantially the same size while the third set of holes has a substantially smaller area than the other sets of holes in the inner tube. The sizes of the holes are chosen so that the valve does not substantially impede the flow of liquid product when it is in an open position. The float moves between a closed position in which it rests against the second stop and an open position in which it rests against the first stop. In the closed position, the float blocks the second set of holes . The second set of holes are uncovered when the float is in the open position. In another embodiment of the invention, the first set of holes is eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross section of a safety valve according to a first embodiment of the invention in a low flow position; FIG. 2 is a cross section of a safety valve according to the embodiment of the invention in a full flow position; and

FIG. 3 is a cross section of a safety valve according to a second embodiment of the invention in a full flow position.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a safety valve which limits the amount of air which can enter a storage tank. The invention is preferably implemented in the context of air off loading a liquid product from a tank wagon into a storage tank. The safety valve may be installed on an outlet of the tank wagon or provided in a hose used to transfer the liquid product from the tank wagon to the storage tank. As the liquid in the tank wagon is depleted during the off loading process, the safety valve prevents the full force of the compressed air, used as the motive force during the off loading process, from entering the storage tank.

The safety valve includes a float arranged in a valve chamber. Guide elements are provided to control the movement of the float in the valve chamber. The liquid product enters the valve chamber from the storage tank through an inlet end and exits the valve chamber via an outlet end. The outlet has primary and secondary flow paths . The secondary flow path has a reduced flow area compared to the primary flow path. The valve is preferably oriented so the inlet end is at a higher level than the outlet end. As the liquid product enters the valve chamber, the float begins to rise exposing a primary flow path arranged near the outlet end. The liquid product can then flow from the valve chamber through the primary flow path and secondary flow paths subsequently into the storage tank. As the level of liquid in the tank wagon is depleted, the amount of liquid in the valve chamber is reduced. Compressed air enters the valve chamber displacing the liquid product. The float descends with the level of liquid product in the valve chamber and blocks the primary flow path. This leaves only the secondary flow path open and substantially reduces the flow of compressed air into the hose and the storage tank to a safe flow rate when the level of liquid in the tank wagon becomes low or it is empty.

In an embodiment of the present invention, an inner tube runs through the valve chamber. The float is arranged around the inner tube to be movable between open and closed positions. The inner tube acts as one of the guide elements limiting the movement of the float . Holes are arranged near the outlet of the valve to act as part of the flow path.

A set of holes acting as part of a secondary flow path are provided. This secondary flow path set of holes is preferably arranged at the outlet end so as not to be covered by the float as the valve chamber is emptied of liquid product. The secondary flow path set of holes are preferably arranged close to the bottom of the valve chamber. Arranging the secondary flow path set of holes in this manner allows substantially all the liquid product to expelled from the valve. The compressed air forces essentially all of the liquid product out of the valve chamber via the additional holes. Also, since the secondary flow path holes are not covered by the float, any liquid product remaining in the hose is forced into the storage tank. This allows the valve to be easily cleaned after the transfer of liquid product is completed by flushing a solvent such as water through the valve and the hose .

In a preferred embodiment, the secondary flow path set of holes is sized to substantially reduce the flow through the valve.

Turning now to Figs . 1 and 2 , an embodiment of the present invention will be described. A valve body 4 defines a valve chamber 6. Inner tube 8 extends longitudinally through the valve body 4 and the valve chamber 6. The inner tube 8 is preferably hollow and has an inlet end 9 through which the liquid product enters the valve chamber 6 and an outlet end 10 through which the liquid product exits the valve chamber 6. A float 22 is arranged in the valve chamber 6, preferably around the inner tube 8. The float 22 is preferably arranged loosely around the inner tube 8 so that the float may travel along the inner tube 8. O-rings (not shown) or a precision machined clearance may be provided to seal the float 22 and the inner tube 8. The inner tube preferably runs straight through the valve chamber 6 such that the inlet 9 and outlet 10 are preferably on opposite sides of the valve body 4. However, other arrangements are possible as shown in Figure 3 discussed below.

A flow path is provided to allow the liquid product to enter the valve chamber 6. The flow path allows the liquid product to flow from the tank wagon into the valve chamber 6. As shown in Figure 1, the flow path comprises a first set of holes 16 which are preferably arranged in the inner tube 8 between a first stop 11 and an upper surface 3 of the valve body 4. A stopper 14 is provided inside the hollow bore of the inner tube 8 to impede the flow of liquid product through the inner tube 8. Preferably, the stopper 14 seals the inner bore of the tube 8 so that the liquid product cannot pass through, bypassing the valve. This arrangement forces the liquid product through holes 16 and into the valve chamber 6. Various other placements of the holes 16 or eliminating holes in that section of tube to allow the liquid product to enter the valve chamber are also possible.

For example, Figure 3 shows a second embodiment of the invention in which the holes 16 have been eliminated. Here, the inlet end 9 of inner tube 8 has been eliminated and the inner tube 8 does not run completely through the valve body 4. Instead of the liquid product entering the valve chamber 6 through holes 16, an inlet 26 is provided in the valve body 4 to allow the liquid product to enter the valve chamber 6.

As the float will rise towards surface 3 during the off loading process, the first stop 11 is provided to limit the movement of the float 22. The stop 11 should prevent the float from covering holes 16 so that the liquid product may continue to enter the valve chamber 7 unimpeded. The stop 11 may simply be a protrusion provided on an exterior surface of the inner tube 8, in between the holes 16 and the float 22 as shown in Figure 1. Alternatively, the stop 11 may be plate-shaped as shown in Figure 3. The stop 11 is arranged to prevent the float from covering inlet 26 and blocking the flow path. Here, the plate- shaped stop 11 is held in place via fastening means such as a screw or nut to the stopper 14. Preferably, the stop 11 has a width substantially equal to that of the float 22.

Additionally, the flow path should allow the liquid product to exit the valve chamber 6 as it becomes filled with liquid product. Second and third sets of holes are provided for this purpose. The second and third sets of holes 18,20 are preferably formed at a lower portion of the inner tube 8. The second set of holes 18 acting as part of a primary flow path are preferably arranged just above a second stop 12 and are substantially the same size as the first set of holes 16. The third set of holes 20 acting as part of a secondary flow path are shown in the figures formed in the inner tube 8 on the side of the second stop 12 opposite from the second set of holes 18, that is, between the stop 12 and a lower surface 5 of the valve body 4. The third set of holes 20 preferably have a much smaller flow area than the first and second sets of holes 16,18. The third set of holes 20 allow the valve chamber 6 to be emptied and cleaned.

Additionally, the holes 20 are preferably arranged as close as possible to the lower surface 5 of the valve body 4.

For the liquid product to be completely expelled from the valve chamber 6 and for the valve to be self-cleaning, the holes 20 should remain open at all times. Since the holes 20 are provided in the inner tube 8 in this embodiment, the float 22 should be prevented from covering holes 20 as the level of liquid in valve chamber 6 is lowered. Therefore, second stop 12 is provided to limit the movement of the float 22. The stop 12, as shown in Figures 1 and 2 is arranged on the inner tube 8 similar to stop 11, however, other arrangements are possible.

The embodiment shown in Figure 3 illustrates one such alternative. The stop 12 is provided at the lower surface 5 of the valve body adjacent to inner tube 8. Since the stop 12 and the hole 20 are substantially at the same level, the stop 12 should not be formed around the inner tube 8 to block holes 20. Holes 18 should still be arranged above stop 12 so that they may be covered by the float 22 to reduce the flow when the valve is in a low flow position. Also, the valve body is formed with an outlet 27 to allow the liquid product to exit valve chamber 6.

The size of the float 22 and the distance between the first stop 11 and the second stop 12 is preferably selected such that when the float 22 comes in contact with the first stop 11, the second set of holes 18 are completely uncovered and there is minimal resistance to the flow of liquid therethrough. Additionally, the float 22 should be made from a material, such as PVC or stainless steel, which is chemically resistant to the liquid being transferred. The float 22 may be either hollow, contain air or it may be solid. In any event, the float 22 should be lighter than the liquid product being transferred and which will fill the valve chamber 6.

In a preferred embodiment, the inner tube 8 is formed from a standardized pipe, for example, a two- inch pipe, that can be readily connected to the outlet of a tank wagon. The first set of holes 16 and the second set of holes 18 are preferably formed to each have a total flow area which is slightly larger than the inlet end 9 of the inner tube 8. The third set of holes 20 preferably have a flow area which is much smaller than the flow area of the first and second sets of holes 16,18. For example, the third set of holes 20 may include two holes which are each one quarter inch in diameter.

Figure 1 shows a safety valve according to the present invention in a closed or low flow position. In this position, the float 22 rests against the second stop 12 so that the second set of holes 18 are covered. It is noted that the third set of holes

20 are not covered by the float. The valve is in the low flow position either at the beginning of the transfer process before the liquid product has entered the valve chamber or at the end of the transfer process and the liquid product in the tank wagon has been depleted. When the transfer process begins, the compressed air forces the liquid product through the outlet of the tank wagon. As described above, the safety valve may be attached directly to the outlet or arranged in the hose. The liquid product then enters the inlet end 9 of the inner tube 8. Since the stopper 14 seals the inner bore of the inner tube 8, the liquid product is forced to enter the valve chamber 6 through the first set of holes 16. The valve body is preferably oriented so that the inlet end 9 is at a level higher than the outlet end 10. The liquid product thus flows to the bottom surface 5 of the valve body 4 and begins to fill the valve chamber 6.

As described above, the float 22 is lighter than the liquid product and it therefore begins to rise and travel towards surface 3 as the liquid product fills the valve chamber 6. The float 22 moves towards the first stop 11 and the second set of holes 18 are uncovered. Next, the liquid product begins to flow from the valve chamber 6 through the holes 18 into the inner bore of the inner tube 8 and subsequently into the storage tank.

As the liquid product is forced out of the tank wagon by compressed air, eventually the valve chamber 6 will completely fill with the liquid product because the liquid is entering the valve chamber faster than it is flowing out of the valve chamber.

This is the case even when the third set of holes 20 are provided. Holes 20 have a much smaller flow area compared to the first set of holes 16 and do not allow any significant amount of liquid product to exit the valve chamber 6 at this time. Thus, the float 22 begins to rise and if unimpeded, would come to rest against surface 3. In this position the float would block holes 16 and impede the flow of the liquid, resulting in a longer delivery time. Therefore, first stop 11 is used to limit the travel of the float 22 in the valve chamber 6. The float 22 contacts the first stop 11 and prevents it from covering the first set of holes 16 or inlet 26. Alternatively, the float 22 may include extensions 24. The extensions 24 extend beyond the float 22 and contact the first stop 11 to prevent the float 22 from encroaching beyond the minimum distance. Figures 2 and 3 show different embodiments of the valve in an open or full flow position. Here, the valve chamber 6 is filled with liquid. Float 22 rests against stop 11 and holes 18 or inlet 26 are uncovered.

On occasion, liquid product with a high viscosity is transferred from the tank wagon and into the storage tank. In these instances, it is necessary to maintain a minimum distance between the float 22 and side surfaces 25 of the valve body 4 when the valve is in the full flow position. Otherwise, the force of the highly viscous liquid as it enters the valve chamber 6 propelled by the compressed air may push the float 22 downward towards the second stop 12, resulting in the second set of holes 18 becoming covered. The valve would then impede the flow of liquid during operation and create a pressure drop through the valve which would lengthen the delivery time. Therefore, a minimum distance between the float 22 and the side surfaces 25 of the valve body 4 should be maintained. The minimum distance may be, for example, designed to obtain a flow area between the float 22 and the surfaces 25 of the valve body 4 which is approximately four times the flow area of the inner tube 8, but this area may vary depending on the circumstances. The minimum distance may be maintained by designing the diameter of float 22 and valve body 4 to maintain the flow area described above.

As the delivery process continues, the liquid in the tank wagon becomes depleted and the amount of liquid entering the valve chamber 6 is reduced. Thus, the float 22 begins to descend towards the second stop 12 as the amount of liquid in the valve chamber 6 is reduced correspondingly. As this occurs, the float 22 begins to cover the second set of holes 18, reducing the flow of liquid therethrough. Eventually, the valve returns to the low flow position shown in Figure 1. The float 22 comes to rest on the second stop 12 and the second set of holes 18 are preferably completely covered.

In this position, the flow area out of the valve is substantially reduced compared to the full flow position. The only exit path from the valve chamber 6 is through the third set of holes 20. However, there is still liquid within the valve chamber 6 and compressed air continues to enter the valve chamber through the inlet end 9 and the first set of holes 16. By providing the third set of holes 20, the liquid product continues to be discharged from the valve chamber 6, although at a much lower flow rate compared with the flow rate when the second set of holes 18 are uncovered. The liquid product will continue to be discharged through holes 20 by the compressed air until all of the liquid has passed through the valve. After all the liquid is discharged from the valve chamber 6, the compressed air will continue flow through the third set of holes 20. This allows any liquid downstream in the hose to be pushed into the storage tank.

However, this also allows compressed air to enter the storage tank. Since the third set of holes 20 have been selected to have a small flow area, the rate of flow of the compressed air is greatly reduced compared to the case where no safety valve is used. This prevents the compressed air from rapidly entering the storage tank. In the embodiment described above with inner tube 8 having a diameter of approximately 2 inches to 2 1/2 inches and the third set of holes consisting of two approximately quarter- inch holes, the flow rate of the compressed air into the storage tank was observed to be reduced to as little as approximately 20% of the flow rate without a valve in the hose. Flow rates much lower than this may easily be obtained. After the liquid product has been discharged from the valve, the valve can then be flushed with water to clean it . The valve can then be used with additional liquid products.

As an additional feature, a fourth set of holes 28 may be provided on inner tube 8. The fourth set of holes are provided to let air bleed out of the inner tube during the transfer process.

As shown in Figures 1 and 2, the fourth set of holes 28 are arranged on the inner tube on the opposite side of stopper 14 as holes 16. The holes 28 may not be necessary for substantial flow rates, but if the valve chamber 6 fills slowly, they may be necessary to allow the air trapped in inner tube 8 to escape. Thus, the present invention provides a safety valve which limits the amount of compressed air which enters a storage tank during the off loading of a liquid product. A float is used to reduce the flow rate from the valve as the level of liquid in the valve decreases. By providing the third set of holes, which are preferably open the entire time the valve is being used, the valve never completely shuts off, but substantially reduces the flow of compressed air into the storage tank. Also, by providing the third set of holes substantially at the bottom surface of the valve, the valve is self-cleaning in that all of the liquid is discharged from the valve body and the hose by the compressed air.

Accordingly, a safety valve for limiting the flow of compressed air into a storage tank has been provided. While a preferred embodiment of the invention has been described above, since variations in the invention will be apparent to those skilled in the art, the invention should not be construed as limited to the specific embodiment described above.

Claims

CLAIMSWhat is claimed is:

1. A valve comprising: a valve body defining a chamber, the valve body having an inlet and an outlet allowing a fluid to enter and exit the chamber, respectively, the outlet defining a primary flow path and a secondary flow path, the secondary flow path having a smaller flow area with respect to the primary flow path; a float movably arranged in the chamber, travel of the float being limited between a first position and a second position by guide elements in the chamber, wherein in the first position the primary flow path is closed by the float and the secondary flow path is open and in the second position both flow paths are open.

2. A valve comprising: a valve body defining a chamber, the valve body having an inlet and an outlet; a float arranged in the chamber moveable between at least a first and a second position, a range of movement of the float being defined by guide members, wherein the float in the second position does not substantially reduce the flow area through the valve and the float in the first position partially blocks the outlet thereby reducing a flow area through the valve.

3. The valve of claim 2 wherein the guide members comprise: an inner tube extending at least partially into the chamber, the float being arranged around the inner tube to travel between first and second stops, defining the first and second positions, respectively.

4. The valve of claim 3 wherein the inner tube is hollow and extends through the chamber from the inlet to the outlet.

5. The valve of claim 4 wherein the first and second stops are arranged on the inner tube near the inlet and outlet respectively.

6. The valve of claim 5 further comprising first holes provided in the inner tube between the first stop and the inlet .

7. The valve of claim 6 further comprising a seal blocking flow of liquid product through the inner tube.

8. The valve of claim 5 further comprising: third holes in the inner tube provided between the second stop and the outlet; and second holes in the inner tube provided on a side of the second stop opposite the third holes, the second holes located such that they are uncovered when the float is in the second position and covered when the float is in the first position.

9. A valve comprising: a valve body defining a chamber, the valve body having an inlet and an outlet allowing fluid to flow through the chamber; an inner tube extending from the outlet into the chamber; a float slidably arranged around the inner tube between a first stop and a second stop; second holes in the inner tube arranged between the first and second stops, the second holes being located such that they are blocked by the float when it rests against the second stop and are uncovered when the float rests against the first stop; third holes in the inner tube arranged near the outlet to be uncovered by the float at all times whereby fluid can flow from the outlet.

10. The valve of claim 9 wherein said first stop forms an upper end portion of said inner tube adjacent said inlet, said first stop having a width substantially equal to a width of said float .

11. The valve of claim 9 wherein the inner tube extends through the chamber from the inlet to the outlet and further comprising: a sealing element arranged in the inner tube preventing flow of fluid from the inlet through the inner tube to the outlet; and first holes provided in the inner tube between the sealing element and the inlet whereby the fluid enters the chamber .

12. The valve of claim 11 wherein the first stop is arranged to prevent the float from covering the first holes.

13. The valve of claim 9 wherein the second stop is arranged to prevent the float from blocking the third holes.

14. The valve of claim 11 further comprising fourth holes in the inner tube on the opposite side of the sealing element of the first holes .

15. The valve of claim 11 wherein the first and second stops are arranged on the inner tube .

16. A method comprising: providing a valve comprising: a valve body defining a chamber, the valve body having an inlet and an outlet allowing a fluid to enter and exit the chamber, respectively, the outlet defining a primary flow path and a secondary flow path, the secondary flow path having a smaller flow area with respect to the primary flow path; offloading a liquid product from a storage device using said valve; and flushing a solvent through said secondary flow path to clean said valve.