Fluid handling – Liquid level responsive or maintaining systems – By float controlled valve
Reexamination Certificate
1999-11-10
2001-06-19
Lee, Kevin (Department: 3753)
Fluid handling
Liquid level responsive or maintaining systems
By float controlled valve
C137S588000
Reexamination Certificate
active
06247492
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to fuel storage tanks and in particular provides an arrangement for automatically shutting off the incoming flow of fuel when the fuel tank is essentially full, thereby preventing overfilling and loss of fuel.
BACKGROUND OF THE INVENTION
In our co-pending UK Application No. 9619580.5, (Publication No. 2317382), an overfill protection device (OPD) for fuel tanks is disclosed. One embodiment described in our co-pending application includes a butterfly or sleeve-type fill valve which is positioned in the fuel fill line and is controlled by a diaphragm or piston. Air in the fill line is allowed to bleed into the ullage through a valve controlled by a float during a normal filling stage. However, when the tank is almost full, e.g. about 95% full, the bleed line is shut off. This causes pressure to rise in a chamber on one side of the piston or diaphragm, resulting in movement of the piston or diaphragm which movement is transmitted to and closes the fill valve. While the constructions described in our above application function satisfactorily, the arrangement is complicated and requires a significant number of seals.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an overfill prevention system which is less complex and can be operated with no dynamic seals for extended operational life.
According to one aspect of the present invention there is provided a fuel storage tank having an overfill protection device (OPD) for shutting off flow of fuel into the tank when the amount of fuel in the tank reaches an intended maximum fill level, said OPD including a fill valve located in or connected to a fuel fill tube and linked to a piston or diaphragm, which is displaceable in a chamber, said chamber communicating with an aperture which is arranged to vent the chamber into the tank when said aperture is open to cause displacement of the piston or diaphragm and the consequential closure of the fill valve, said aperture being controlled by a vent valve which normally maintains said valve closed, but is linked to fuel level sensing means for sensing when the level of fuel in the tank reaches said intended maximum fill level and causing said vent valve to open.
According to one form of the invention there is provided a fuel storage tank having an overfill protection system for shutting off flow of fuel into the tank when the amount of fuel in the tank reaches an intended maximum fill level said overfill protection system including a fill valve located in a fuel fill tube and linked to a diaphragm or piston, which is displaceable in a chamber, said chamber communicating with an aperture within the ullage above said maximum fill level, and a float valve for controlling said aperture and maintaining said aperture closed until fuel in the tank reaches a predetermined fill level whereupon the aperture is opened and the piston or diaphragm is displaced to cause closure of the fill valve.
Fuel storage tanks are commonly replenished by connection to a road tanker and filled by gravity from the road tanker. As a consequence, during the filling procedure, the pressure in the fill line leading from the tanker to the fill or drop tube is greater than the pressure in the tank ullage by an amount approximately equal to the hydrostatic pressure of the tank fuel level above the drop tube exit. When the fill valve is closed, pressure is equal to the hydrostatic pressure of the road tanker above the fill valve. The piston is preferably spring-biased with a light spring so that the piston is in its retracted position and the fill valve is normally in the open position. Alternatively, the fill valve may be separately spring-biased into its closed position but only to the extent that it is opened by flow of fuel into the drop tube.
When the float valve opens, the difference in pressure between the fill line and the ullage is sufficient to move the piston and cause closure of the fill valve. The fill valve is preferably a butterfly valve or a sleeve valve or other valve which will move easily between its open and closed position. A butterfly valve meets these requirements because there is equal pressure on each side of the valve. However, a poppet valve may also be employed, especially if it is lightly spring-biased towards the closed position.
In contrast with the overfill prevention device (OPD) described in our above co-pending application, a piston seal is unnecessary in the OPD of the present invention. The annular gap between the piston and cylinder wall acts as a balance orifice with significantly less area than the open float valve orifice and test valve orifice. When the test valve or float valve is opened during filling, a pressure imbalance across the piston is generated causing the piston to rise against a light spring biasing the butterfly valve into its closed position. When the piston reaches its full travel it is sealed against the cylinder cap preventing further flow through the float valve. Also, it is unnecessary to provide an elastomer seal between the butterfly valve and its seat because a small leak at this point will not matter.
In practice, the fuel will be flowing during normal peak filling at about 1000 liters per minute and closure of the fill valve will reduce the flow to about 1% or less.
Closure of the fill valve will be immediately apparent to the road tanker driver, since the sudden closure will give a kick to the delivery hose and he will then know that the tank is fill and will shut off the supply valve at the tanker.
An important feature of the system of the invention is that the operation of the fill valve can be readily tested by providing a test valve in the line communicating the cylinder with the float valve. If the test valve at this point is open with a positive hydrostatic pressure within the fill line, the fill valve will immediately operate. Also, failure of the interconnecting hose or other conduit between the fill valve and float valve will cause the fill valve to close to provide a fail safe condition.
In a modified form of the invention, it is possible to dispense with the float valve and instead control the vent valve by means of electrical control means. This arrangement has the advantage that the OPD can be located entirely within the drop tube or crane T-piece and no other connections need be made to the tank. In this form of the invention, the aperture for venting pressure from the chamber may be closed by an electrically operated vent valve which may be actuated to vent pressure into the tanks e.g. through a tubular valve stem into the drop tube below the fill valve.
During the filling of a fuel tank, it is highly desirable to be able to reduce tank fluid turbulence. The main benefit from reduction of turbulence is that there will be less disturbance of the heavy fuel vapour layer on top of the liquid fuel, and this will consequently reduce vapour line fuel losses.
Normally, the fill tube into a fuel tank terminates just short of the base of the tank and is cut off at approximately a 45 degree angle, and may terminate, for example, about 6 inches above the tank base. Turbulence is particularly a problem during the initial stage of the fill cycle when the air in the connecting pipes from the tanker is driven down the fill tube by the incoming fuel. This initial “slug of air” rebounds off the tank bottom and produces a large concentration of air bubbles causing a break up of the normal vapour layer.
Another aspect of the invention seeks to reduce such turbulence by fitting a diffuser to the delivery end of the fill or drop tube.
According to a further aspect of the invention, therefore, there is provided a fill or drop tube for a fuel storage tank in which the delivery end of the drop tube is closed by a diffuser having apertures which cause fuel emitted from the drop tube to exit therefrom under substantially laminar flow conditions.
The exit aperture or apertures from the diffuser are preferably defined by two or more substantially parallel plates arranged substantially at right angles to the lo
Andrus Sceales, Starke & Sawall
Lee Kevin
W & J Risbridger Limited
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