GB2317382A - Overfill prevention device - Google Patents

Abstract

An overfill prevention device (OPD) is disclosed for preventing overfilling of a fuel tank 1, comprising two chambers divided by a diaphragm or piston, 26 said diaphragm or piston carrying a valve stem 20 controlling axial movement of a fill valve 21 located within a fill tube 2 (either offset or direct filling) leading to the tank, one of the said chambers A being exposed to tank vent line pressure or atmospheric pressure and the other of the said chambers B being exposed to the pressure in the fuel filling line 5 and being connected to a sensor tube 50 having an orifice B within the tank ullage, said orifice being normally open but being closed by movement of a float 12 when the liquid in the tank reaches a predetermined level, whereby closure causes pressure in said other chamber to rise and displace said diaphragm or piston 26 to cause closure of the fill valve 21.

Description

Overfill Prevention Device for Fuel Tanks This invention relates to fuel storage tanks and in particular provides devices for protecting liquid storage tanks (particularly fuel tanks) from over filling.

The invention is particularly concerned with storage tanks for bulk storage of fuel.

Conventional methods of preventing overfilling of fuel storage tanks normally make use of a float valve having a float which senses the level of liquid in the tank and by means of a lever action shuts off an internal valve to prevent overfilling of the tank. The installation of such float operated valves is difficult since it involves interference with internal tank pipe work or introduces additional obstructions.

In our co-pending application 9404105 there is described an overfll prevention valve for use in a filling station fuel storage tank. The overfill prevention valve is in the form of a fill-valve located within the fill drop tube tee fitting leading to the tank. In one embodiment descibed in our above application, the valve is in the form of a sleeve valve which includes an internal and an external sleeve which are moveable relatively to each other. Ports are formed in the sleeves and, in the open position of the valve, the sleeves are aligned and allow fuel to pass into the tank. Operation of the valve is controlled by a diaphragm which senses an increase in pressure in the ullage of the tank. In the event of an untoward increase in pressure in the ullage the sleeve valve closes and prevents further fuel entering the tank.

One object of the present invention is to improve the fuel control valve described in our above co-pending application. Another is to provide an overfill prevention device which will automatically shut off the fill valve when the level of fuel in the tank reaches a predetermined level.

According to one aspect of the present invention there is provided an overfill prevention device (OPD) for preventing over filling of a fuel tank which comprises two chambers divided by a diaphragm or piston, said diaphragm or piston carrying a valve stem, axial movement of which causes opening and closing of a fill valve located within a fill tube leading to the tank, one of said chambers being exposed to tank vent line pressure or atmospheric pressure and the other being exposed to pressure in the fuel filling line and being connected also to a sensor tube having an orifice within the tank ullage, said orifice being normally open but being closed by movement of a float when liquid in the tank reaches a predetermined fill level, whereby closure of said orifice causes pressure in said other chamber to rise and thus to displace said diaphragm or piston and cause closure of the fill valve.

The position of the float with respect to the orifice in the sensor tube is preferably set so that the orifice closes just before the tank is fully filled. Typically this will be when the tank is about 95% filled. Thus in normal operation of the over fill prevention device, the fill valve will close when the volume in the tank reaches about 95% of capacity. As a further precaution and in case of any malfimction of the fill valve the float may be associated with a secondary valve (or a separate valve may be provided for this purpose) which is designed to shut off the tank ullage from the vent line when the tank is filled to a slightly greater degree, e.g to about 97% of capacity.

In a preferred embodiment the sensor tube itself carries a secondary valve seat which closes onto an opening leading to the vent line on reaching about 97% ofthe tank capacity. Thus if the OPD malfimctions the vent line will be automatically closed after a small additional amount of fuel has entered the tank. Closure of the vent line will seal the tank and prevent further fuel entering the tank because the liquid head from the road tanker will equal the pressure in the tank. The vent line may also however include an emergency pressure relief valve to prevent rupturing of the tank, should the pressure in the tank reach an unacceptable high level in such circumstances.

The fill valve may be a sleeve valve, eg. of the kind described in our above co-pending application. Alternatively, a butterfly valve design may be used. Both kinds of valves are of a pressure-balanced type in that the control force required to operate the valves is similar irrespective of the fluid velocity or pressure in the fuel fill line.

The two embodiments of the present invention will now be described with reference to the accompanying drawings in which: Figure 1 is a general 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 dispensing pump.

Figure 2 is a sectional view on larger scale showing the overfill prevention device (OPD) and extractor float valve fitted into the top of a fuel storage tank.

Figure 3 is the same view as Figure 2 which shows the direction of flow of fuel and vapour during filling of the storage tank.

Figure 4 is a sectional view of a float operating sensor valve for use with the OPD of the present invention and Figure 5 is a sectional view of an OPD with a butterfly type valve with a piston actuator instead of a diaphragm.

Figure 1 shows an underground storage tank 1 having a drop tube 2 which is connected to a fill line 5 via an over pressure fill device 3 housed within a crane T-piece 4. T-piece 4 is connected at one end to the drop tube 2 and at its over end, via an offset fill line 5, to a standpipe 6 fitted with a filling port 7. Port 7 is designed for connection to a road tanker filling hose in conventional manner The device 3 is linked by a hose line A to the vent line 10 leading from the tank. Device 3 is also linked by a hose line B to a sensor tube housed within a tube 11 connecting the vent line to the tank 1. Mounted on the end of the sensor tube is a float 12.

Referring to Figure 2 this shows the OPD and its connections to the sensor tube and float valve. The OPD is constructed in a similar manner to the over pressure valve described in our co-pending application 9404105.0. The device 3 comprises a fill valve portions having a valve stem 20 which carries a moveable internal sleeve 21 formed with a circumferentially elongated port 22. Port 22 is similar to port 30 as shown in Figure 2 ofthe above co-pending application. Sleeve 21 is slidably moveable within an external sleeve 23, the external sleeve having similar shaped ports 24. When ports 22, 24 align fuel may flow from the fuel line 5 into the drop tube 2 as indicated by the arrow in Figure 3. External sleeve 23 is held in place in the top of drop tube 2 by a spring which presses a flange of tube 23 against seal 25. Vertical movement of valve 20 to open and close the fill valve is controlled by diaphragm 26 and spring A. Diaphragm 26 divides housing 27 into chambers A and B. A spring A within chamber A holds the fillvalveinitsnormal position as shown in the left hand side of the drawing. Chamber B is connected via a non-retum valve 28 and a test valve 29 to a sensor tube 30 which leads to an orifice B opening into the tank ullage. As shown more clearly in Figure 4 float 12 is connected to a tube 31 which is slidable upwardly vertically on a stem portion 32 which supports the lower end of the sensor tube 30. Tube 31 has a hole 33 which aligns with an opening 34 in the end of the sensor tube 30. Thus when the tube moves upwardly as shown in the upper arrow in Figure 4, tube 31 covers the orifice B and closes off the sensor tube 30 and thus the hose line B. A damper chamber 35 is provided to ensure that an upward sliding movement ofthe float 12 is controned. The positioning ofthe float 12 is arranged so that orifice B will close at just less than full tank volume e.g about 95% Referring to Figure 5, this shows a modified fill valve and actuating arrangement. In Figure 5 parts which are similar to the embodiment of Figures 2 and 3 are indicated by like reference numerals. The differences in the Figure 5 emobdiment is that the diaphragm is replaced with a piston 51, which is carried on the valve stem 20, and also that the piston controls the operation of a butterfly valve 52 instead of a sleeve valve.

Butterfly valve 52 is pivotally mounted on a horizontal axis 53 and is linked to the valve stem 20 by an actuator linkage 54 so that movement ofthe piston causes the butterfly valve to open and close.

The system works in the following manner. During normal operating condition, the fill valve is open and ports 24 and 22 of the sleeve valve are aligned or butterfly valve 52 is open. Accordingly, fuel enters the tank as shown by the arrows in Figure 3 allowing unrestricted fuel line flow.

Pressure in the tank fill line leads into chamber B via orifice A as the tank is filled.

Chamber B is drained to the tank ullage via a hose line B and the sensor tube 30. Orifice B is significantly larger in area than orifice A so that excessi pressure is not generated in chamber A and spring A holds the fill line sleeve valve or butterfly valve in the fully open posltlon, When the tank is filled to approximately 95% of the capacity, float 12 closes orifice B as described above. Consequently, the flow through orifice A is no longer drained to the ullage and head pressure from the fill line acts on the diaphragm 26 or piston 51. The only resistance to the pressure in chamber B is the spring A. Chamber B is set to operate at a nominal fill line head pressure of about 0.5 psig (ca. 105 kPa) or above.

Accordingly, when chamber B is filled and the sleeve valve or butterfly valve is in the closed position, the main fill line flow in line 5 is arrested. The tank cannot now be filled further until the level of the tank falls below the predetermined level of say 95% capacity.

When the tank falls below such filled level float 12 drops back in the direction shown in lower arrow in Figure 4 and this reopens the orifice B. When the fill line 5 is disconnected from the road tanker or when the fill line head pressure is reduced below about 0.5 psig spring A moves the diaphragm and sleeve valve back or piston and butterfly valve to the filly open position as shown in the left hand side ofthe fill valve in Figure 2.

The non return valve 28 prevents tank vapour flowing back into the fill line via orifice k As shown in Figure 2, chamber A may be connected by hose line A to the vent line 10.

As shown in Figure 2 and 3, the float valve may include a secondary valve seat 40 which may be mounted on the sensor tube. As can be seen in Figure 2, the valve seat 40 is moveable upwardly on the sensor tube as the valve rises with increasing flow of fuel into the tank. A port 41 linking the tank ullage to the vent line is closed when the valve seat 40 sits onto the port 41. The distance between the valve seat 40 and the port 41 are selected so that the valve will seat against the port 41 at say 97% of fill capacity. Thus if there is a malfunction of the OPD and the tank level continues to rise above about 95% capacity the valve seat on the float valve closes entry to the vent line, this effectively seals the tank. If filling continues there will be a rapid rise in tank vapour pressure in the ullage which will stop the fill line flowing. Closing the vent line also prevents cross over of product into other tanks inside where the vapour line is connected with other vapour lines from other tanks aT a rnnnifold.

Damper chamber 35 prevents shock damage to the float valve due to high gas velocities as the level of liquid within the tank fall rises above the 95% filled level and the vent opening starts the close.

Special features of the design of the present invention includes the following: 1. The design allows the retro fitting ofthe device to existing installations with minimal modification of existing tank connections. Only the fill and vent line connections are used by the device and no third sensor connection is required. The sleeve valve or alternative butterfly valve fitted into the "4" T-piece offers minimal reduction in cross section of area of the fill line. Compared with existing fill valves the present invention permits reduced filling times.

2. In the installation of the device of the present invention it is unnecessary to interfere with the integrity of the drop tube by means of making additional joints or perforations. The float sensor and the OPD working parts can be removed for inspection or repair without disturbing pipe work. The satisfactory operation of the device can be tested by operating the valve 29 in the hose line B. The external sleeve assembly and spring B provides additionally a means for retaining the drop tube.

3. The stirrup cage 54 (Figure 5) achieves the same functions.

4. The diaphragm or piston actuator combined with orifice A produces a soft, dampened closing action preventing shock pressures damaging the fill line, drop tube or tank.

5. The float level sensor has a vertical movement which avoids interference with surrounding pipe work within the tank.

Claims (2)

Claims

1. An overfill prevention device (OPD) for preventing overfilling of a fuel tank, comprising two chambers divided by a diaphragm or piston, said diaphragm or piston carrying a valve stem controlling axial movement of a fill valve located within a fill tube (either offset or direct filling) leading to the tank, one of the said chambers being exposed to tank vent line pressure or atmospheric pressure and the other of the said chambers being exposed to the pressure in the fuel filling line and being connected to a sensor tube having an orifice within the tank ullage, said orifice being normally open but being closed by movement of a float when the liquid in the tank reaches a predetermined level, whereby closure causes pressure in said other chamber to rise and displace said diaphragm or piston to cause closure of the fill valve.

2. A device as claimed in claim 1, wherein a float is adapted to seal the tank ullage from the vent line in the event that due to malfunction the fill valve does not close when said orifice is closed.