GB2275677A

GB2275677A - Overpressure prevention device for storage tanks

Info

Publication number: GB2275677A
Application number: GB9404105A
Authority: GB
Inventors: Barry C Risbridger
Original assignee: W&J Risbridger Ltd
Current assignee: W&J Risbridger Ltd
Priority date: 1993-03-05
Filing date: 1994-03-03
Publication date: 1994-09-07
Anticipated expiration: 2014-03-03
Also published as: GB9304548D0; GB9404105D0; GB2275677B

Abstract

An underground or overground liquid storage tank (1, Figure 1) which is connected by filling pipe 5 to an external filling port (7, Figure 1) for supplying liquid, eg. fuel, to the tank, includes an overpressure valve 3 which senses the pressure in the tank ullage and is adapted to shut off the filling port when pressure in the ullage exceeds a predetermined value. The valve may comprise a diaphragm 23 one side of which is connected via a pipe 26 (8, Figure 1) to the tank ullage, the diaphragm, which may be a bellows or rolling diaphragm, moving an inner sleeve 27 within an outer fixed sleeve 28 when over pressure is applied to the diaphragm. Ports 30, 30a, 29 in the sleeves are aligned for liquid flour only when overpressure does not exist and diaphragm 23 is biassed by spring towards pipe 26. A gap between the sleeves may be provided to allow excess liquid to leak from the filling pipe 5 into the tank when the valve is closed and the ports not aligned. The tank includes a vent pipe with a liquid level sensing valve which closes off the vent pipe when the liquid reaches a predetermined level. A vapour recovery line may be connected to the overpressure valve so that the valve senses the pressure in the vapour recovery line from the tank (Figure 3), and the vapour recovery line may be contained co-axially within the filling line (43, Figure 3). The over pressure valve may move horizontally (Figure 4) or vertically. <IMAGE>

Description

OVERPRESSURE PREVENTION DEVICE FOR STORAGE TANKS This invention relates to storage tanks and, in particular, provides a device for protecting liquid storage tanks from overfilling or overpressure. The invention has particular reference to fuel storage tanks whether overground or underground.

Fuel storage tanks, particularly in filling stations, are normally filled via an offset or remote pipeline to which the road tanker hose is connected.

Various designs of float operated valves are available to prevent the accidental overfilling of storage tanks. These valves sense the level of fluid in the tank and shut off internal valves to prevent overfilling. Such valves however do not protect the storage tank from over pressurisation in the event of a blocked vent line.

Pressure in this circumstance can build up before the level at which the floats operate is reached. Eventually, the tank pressure equals the liquid head pressure and no more fluid flows into the tank. This condition known as a "lock-up" prevents the disconnection or final emptying of the tanker hose and off set fill line until such time as the tank can be vented. This condition is dangerous as the fuel may be spilt in an effort to disconnect the tanker hose. Furthermore, the excessive pressure (which equals the tanker liquid head pressure), may cause damage to the tank itself, even at quite low pressures. The pressure may also cause liquid to be forced up the suction line and through the petrol pump meter and out through the air separator valve into the nozzle storage boot. This is a significant hazard.

According to one aspect of the present invention there is provided a liquid storage tank which is connected to an external filling port for supplying liquid to the tank, said storage tank including a valve which senses the pressure in the tank ullage and shuts off the filling pipe as soon as the pressure in the tank exceeds a predetermined level . As a result, any pressure build up in the tank is sensed before any damage can be done and the flow of fuel or other liquid from the tanker is automatically shut off.

The system can also act as a normal overspill prevention device, since it is normally used in conjunction with a liquid level sensing valve of conventional type which closes off a vent pipe to the tank, when the desired liquid level has been reached. As soon as the vent pipe is closed a small increase in pressure is developed in the tank, which is transmitted to the pressure sensing valve and this shuts off the flow of liquid to the tank. The tanker driver can then close the bottom discharge valve at the tanker end and drain the hose back into the tank through a leak path, which can be provided in the pressure-sensing valve for this purpose.

It will be appreciated that it is not essential to have an extended filling pipe to the tanker, but the tanker hose could be connected directly to a port on the main lid of the storage tank.

The pressure-sensing valve need not provide a sharp cut-off of flow to the storage tank but may, by suitable arrangement of levers or toggles, provide a staged closure of the valve depending on the level of pressure generated in the tank.

The pressure-sensing valve assembly can be detachable from the main body so that a dip stick can be introduced into a vertical filling pipe to check the liquid level in the tank.

The pressure-sensing valve may also be fitted in series or mounted above a conventional overspill prevention device to act as an additional safety device sensing excessive gas pressure.

The invention is illustrated by the following specific embodiment shown in the accompanying drawings, in which:- Figure 1 is a diagrammatic representation of a typical underground fuel storage tank, showing the method of filling the tank from an external stand-pipe and for supplying fuel to a fuel pump, Figure 2 is a sectional view on a large scale of a pressure-sensing valve arrangement for protecting a storage tank against excessive pressure.

Figure 3 is a sectional schematic view of the overpressure valve fitted to a tank and connected to a coaxial tanker filling hose, and Figure 4 shows an.alternative arrangement in which the overpressure valve is oriented for direct filling of the tank.

Referring to the drawings, an underground storage tank 1 has a filler tube 2 connected via a pressuresensing valve (3) which is housed within a 4" 'Crane' tee piece 4. The tee piece 4 is connected at its other end via an offset filling line 5, to a stand-pipe 6 having a filling port 7. Pressure-sensing valve 3 is linked by a tube 8 to the tank ullage so that one side of the valve is exposed to the pressure prevailing within the tank 1. A float valve 9 of conventional type is arranged to close off the vent pipe 10 once the fuel within the tank 1 reaches a predetermined height. A suction line 11 is provided to supply fuel to a petrol pump 12.

Referring to Figure 2, this shows the pressuresensing valve in more detail. The pressure-sensing valve 3 is fitted into the vertical arm of the tee piece 4, e.g.

by a suitably threaded spigot portion 20 and an O-ring seal 21. The valve includes a body portion 22 which is formed from two cooperating hollow portions between which is accommodated a diaphragm 23. Diaphragm 23 carries a valve stem 24 which is spring-biased by a spring 25 to the position shown in the drawing. The upper part of the hollow body member 22 is connected by a pipe to the tank ullage through a swivelling pipe connector boss 26. Thus, the diaphragm will be.deflected downwardly against the pressure exerted by the spring 25, as soon as there is any increase in pressure in the tank ullage. The spring 25 may be selected so that the valve is operated once a predetermined overpressure is detected.

Downward movement of the valve stem 24 causes the inner sleeve 27 to be moved downwardly within a coaxial fixed outer sleeve 28. Sleeves 27 and 28 are formed with valve ports 29, 30 and 30a. The outer fixed sleeve 28 is provided with an upper port 30a (indicated in dotted lines) and in the normal condition of the diaphragm is aligned with a matched port 30 in the movable inner sleeve. Outer sleeve 28 also has a second port 29 of similar dimensions located in its lower end. Typically, the ports each have a width of about 10 inches and a depth of about 1 inch. When there is no excess pressure in the storage tank, fuel flows in the direction indicated by arrow 31 through ports 29 and 30a/30 into the interior of the sleeve valve 27, and hence into the internal tube 32, leading to the main tank.Where an overpressure arises in the storage tank, the inner sleeve moves downwardly and closes off the flow of fluid into the tank through ports 30a and 29. It should be noted that very low forces are required to operate the valve as the pressures applied to the valve through the matched ports are balanced and the top wall of the inner sleeve is apertured at 33 to balance the pressures applied to the valve by the fuel pressure in pipe 5. A leak path is provided between the inner and outer sleeves of the valve to permit fuel to drain from the tanker filling hose into the tank after the pressuresensing valve has closed.

Although Figure 2 shows a diaphragm comprising a planar membrane, it is possible to use instead a bellows or rolling diaphragm, since the latter produce more linear movement of the movable component of the valve. One suitable diaphragm of this kind is manufactured by George Angus of Gateshead, Tyne & Wear.

Figures 3 and 4 (together with the scrap additional views Figure 3A and Figures 4A, 4B and 4C), show how the overpressure valve can be utilised with a tanker filling hose having a vapour return pipe contained within the fuel filling hose, preferably coaxially.

The overpressure valve 1 is mounted on the tank top 40 and a flexible pressure sensing tube 3 connects the top of the valve to the tank ullage at 2. The construction of the overpressure valve is as shown in Figure 2, except that the swivelling pipe connector boss 26 is a straight through bore instead of a blind bore and is connected at the side remote from the tank to a flexible tube 11 by a connector 4. Flexible tube 43 is supported by a centralising jig (shown in Figure 4C), coaxially within a tanker delivery hose 44. Inlet fitting 10 is designed for attachment to the fuel filler outlet of the road tanker.

In the arrangement shown in Figure 3, fuel is delivered from the tanker through the delivery hose via the annular space 41, through the valve 1 and into the tank via the valve outlet part 42. At the same time, vapour which is displaced passes through the tubes 3 and 4 into the internal tube 43, to the tanker where it is recovered by the tankers vapour recovery system. This system avoids the need for a separate vapour recovery hose from the tank to the delivery tanker.

The valve may include a connector at its inlet port 45 comprising a connector 11 which is screwed into a manifold fitting 5. The portion of the delivery hose 44 may include a flexible end 7 which can be drawn back in order to link up the vapour tube connector 11. One method of connecting the outer portion of the delivery hose is shown in Figure 4B.

In Figure 4, the overpressure valve 1 is mounted on the top of the tank 50, across a vertical delivery pipe 51. The overpressure valve operates in a similar way to that shown in Figure 3, except that the movable sleeve slides horizontally in response to pressure applied to the valve along pressure sensing line 9. Vapour recovery is achieved in a similar way to Figure 3, by feeding vapour through the valve boss 26, into flexible tube 4 and into fitting 53 which can be connected to a delivery hose 54.

Claims

CLAIMS:

1. A liquid storage tank which is connected to an external filling port for supplying liquid to the tank, said storage tank including an overpressure valve which senses the pressure in the tank ullage and is adapted to shut off the filling port when pressure in the ullage exceeds a predetermined value.

2. A tank as claimed in claim 1 wherein the overpressure valve includes a diaphragm which is exposed on one side to the pressure in the tank ullage, said diaphragm being linked to a movable valve component so as to cause the valve to open or close, depending on the pressure applied to the diaphragm.

3. A tank as claimed in claim 2 wherein the movable valve component comprises a first sleeve which is slidable relative to a second sleeve.

4. A tank as claimed in claim 3 wherein the first and second sleeves include valve ports which are aligned in the open position to allow passage of liquid from the external port to the tank.

5. A tank as claimed in claim 4 wherein a gap between the first and second sleeves provides a leakage path for liquid in the closed position of the valve.

6. A tank as claimed in any one of the preceding claims which includes a liquid level sensing valve which is adapted to close off a vent pipe to the tank when liquid in the tank reaches a desired level.

7. A tank as claimed in any one of the preceding claims in which a vapour recovery line is connected to the tank and to the filling port so that the vapour line is contained within the port, the vapour recovery line being connected to the overpressure valve so that the valve senses the pressure in the vapour recovery line.

8. An overpressure valve for controlling supply of liquid to a tank, said valve comprising a diaphragm one side of which is adapted to be connected to the ullage of the tank, said diaphragm being linked to a first sleeve which is movable in relation to a second sleeve under the influence of pressure applied to the diaphragm, the first and second sleeves each having at least one port which allows liquid to pass through the valve when the ports are aligned.

9. An overpressure valve as claimed in claim 8 wherein the diaphragm is a rolling diaphragm.

10. An overpressure valve as claimed in claim 8 or 9 wherein the first and second sleeves are movable one inside the other and a gap exists between the sleeves of sufficient size to allow excess liquid to leak back from the tank to an inlet port for the valve.