EP0353009A1

EP0353009A1 - Fluid transport container loading and unloading control system

Info

Publication number: EP0353009A1
Application number: EP89307514A
Authority: EP
Inventors: Simon H.A. James
Original assignee: Emco Wheaton UK Ltd
Current assignee: Emco Wheaton UK Ltd
Priority date: 1988-07-22
Filing date: 1989-07-24
Publication date: 1990-01-31
Anticipated expiration: 2009-07-24
Also published as: GB8817487D0; ES2057131T3; DE68915633T2; DE68915633D1; EP0353009B1

Abstract

A fluid transport container (1) comprises a foot valve (2) arranged in a lower part of the container (1) through which the container (1) may be loaded and unloaded, and control means (5,6,7,8) for rapidly closing said foot valve (2) the arrangement being such that the foot valve (2) is closed more rapidly in a discharge mode than in a load mode.

Description

This invention relates to fluid transport containers, such as containers forming part of or carried by road and rail tankers, and to control means therefor.
Fluid containers of e.g. road tankers are often provided with a so-called foot valve located in a lower region of the container through which fluid may be discharged from the container during unloading and by means of which a container may be filled with fluid by bottom loading under pressure. During either loading or unloading of the container the foot valve is connected by a flexible conduit to, say, either a supply of fluid or a storage tank respectively.
In an emergency, for example when there is a leak of fluid, it is desirable to be able to close the foot valve rapidly. During discharge of fluid from the container rapid closing of the foot valve presents no difficulty. However if the foot valve is closed very rapidly while the container is being loaded under pressure, a substantial shock is generated in the conduit and in any valves connected to the conduit. This problem is exacerbated by the fact that fluid is normally loaded at a greater rate than it is discharged. The conduit and associated valves are typically only designed to operate at a normal pressure of up to about 70 psi. However when the foot valve is closed against the flow of fluid in the conduit, a transient pressure of the order of 300 psi may be generated. Clearly exposure of the conduit to such shocks is deleterious and to be avoided; failure and fluid leakage can even occur, in the extreme.
It has been proposed to meet this difficulty by using a slow-action foot valve arrangement which cannot close rapidly enough to generate a shock. While this proposal does prevent the generation of shocks in the conduit during loading, it has the disadvantage that very rapid closing of the foot valve during discharge, when there is no problem with the generation of shocks, is prevented. In the event of a leak in the conduit, say, a delay in closing the foot valve would result in an additional and even dangerous loss of fluid.
Viewed from a first aspect the invention provides a fluid transport container comprising a foot valve arranged in a lower part of the container through which the container may be loaded and unloaded, and control means for rapidly closing said foot valve, the arrangement being such that the foot valve is closed more rapidly in a discharge mode than in a load mode.
In this way very rapid closing of the foot valve in a discharge mode is permitted, while during loading the speed of the closing of the valve is reduced to prevent the generation of shocks in the conduit.
Preferably the control means is responsive to a control signal indicative of whether the container is in a discharge or load mode and is operable automatically to adjust the speed of closing of the foot valve accordingly.
In a preferred such embodiment the foot valve is opened in response to an actuating signal received from said control means, and means are provided for changing the speed of removal of said signal to close the valve at different rates in drop and load modes. Preferably the changing means has two states corresponding to discharge and load modes and is switched automatically between these states.
It is particularly preferred that the foot valve be actuated by a pneumatic signal, although electrical or hydraulic signals may also be employed. When a pneumatic actuation signal is used the speed changing means may comprise a pilot valve adapted to exhaust the pressure at the foot valve at different rates. Preferably the pressure may be exhausted through a relatively wide orifice or directly to atmosphere in the discharge mode, and through a more restricted orifice in the load mode. The restricted orifice may be variable to enable adjustment of the closure speed in the discharge mode.
It is also possible that the control means may be employed to ensure that an overspill protection system is operational during loading of the container through the foot valve.
Accordingly viewed from another aspect the present invention provides a fluid transport container comprising a foot valve arranged in a lower part of the container through which the container may be loaded and unloaded, control means for actuating said foot valve in load and discharge modes, and an overspill protection system adapted to interrupt loading should the level in the container exceed a predetermined maximum, wherein an electrical interface is provided whereby said overspill protection system is automatically enabled whenever the foot valve is open in the load mode.
Previously the overspill protection system was enabled manually independent of the foot valve open/close position, and was thus subject to human error.
Preferably the interface comprises a pressure switch responsive to signals received from the control means and the foot valve.
An embodiment of the invention will now be described by way of example and with reference to the accompanying drawing which is a schematic view of a lower part of a container with associated control means.
The drawing shows the bottom of a container 1 with a foot valve 2. In a road tanker, the container would in fact be divided into a plurality of longitudinally spaced compartments each with its own foot valve. The foot valve is shown connected to a flexible conduit 3 at the other end of which is an adaptor 4. The conduit may be fitted to a bottom loading arm for loading of fluid into the container, or alternatively to a delivery hose for discharge of fluid, e.g. petrol, from the container. The opening of the foot valve is controlled by control means which will now be described in detail.
The foot valve is pneumatically operable and is opened in response to a pneumatic signal generated by a control unit 5 and applied via a control line 6. A shuttle valve 7 is provided in the control line and is connected to the foot valve by a pilot line . The shuttle valve 7 enables a rapid exhaust of the pressure at the foot valve and thus rapid closing of the foot valve. As soon as the signal pressure in the control line begins to fall, when the foot valve opening signal is removed, by means of the pilot line 8 the shuttle valve 7 is switched to vent the pressure at the foot valve 2 via a pilot operated valve 9.
The pilot valve 9 has two positions. In a first position, shown in the drawing, the foot valve is connected directly to atmosphere. In the second position the foot valve is connected to atmosphere through a variable restricted orifice 10. Thus when the pilot valve is in the second position the pressure at the foot valve is released more slowly and the foot valve closes relatively slowly compared to when the pilot valve 9 is in its first position.
The pilot valve is switched from its first to second position in response to a signal, indicative of the load mode, applied by the control unit 5 via line 11. When the container is being loaded a signal is generated by the control unit 5 and applied to the pilot valve 9 to switch the valve to its second position.
In a typical arrangement, in a discharge mode fluid is unloaded at a rate of about 1000 litres/min. and the foot valve is closed in under 2 secs. In a load mode however the load rate is about 2400 litres/min. and the foot valve is closed in about 10 secs.
A further line 12 leads away from the foot valve 2 for transmitting a signal indicative of the foot valve condition. In particular when the foot valve is open a signal is returned to the control unit 5. A branch of line 12 also leads to a pneumatic "and gate" 13. The other input of the and gate 13 is a branch of line 11. The output of the and gate is connected to a pressure switch 14 for activating an overspill protection system. Thus when the and gate receives signals from both the foot valve 2 and control unit 5, indicating that the foot valve is open for loading of liquid, the overspill protection system is activated.
By using a variable restricted orifice the rate of air exhaustion from the foot valve may be controlled. However because of the design of the foot valve and since a compressible fluid is being controlled, the actual speed of closure for any restrictor setting will be dependant upon the rate of product flow and thus the system becomes self-compensating.

Claims

1. A fluid transport container comprising a foot valve arranged in a lower part of the container through which the container may be loaded and unloaded, and control means for rapidly closing said foot valve, the arrangement being such that the foot valve is closed more rapidly in a discharge mode than in a load mode.

2. A fluid transport container according to claim 1, wherein the control means is responsive to a control signal indicative of whether the container is in a discharge or load mode and is operable automatically to adjust the speed of closing of the foot valve accordingly.

3. A fluid transport container according to claim 1 or claim 2, wherein the foot valve is opened in response to an actuating signal received from said control means, and means are provided for changing the speed of removal of said signal to close the valve at different rates in discharge and load modes.

4. A fluid transport container according to claim 3, wherein the speed changing means has two states corresponding to discharge and load modes and is switched automatically between these states.

5. A fluid transport container according to any one of the preceeding claims, wherein the foot valve is actuated by a pneumatic signal.

6. A fluid transport container according to claim 5, wherein the speed changing means comprises a pilot valve adapted to exhaust the pressure at the foot valve at different rates.

7. A fluid transport container according to claim 6, wherein the pressure is exhausted through a relatively wide orifice or directly to the atmosphere in the discharge mode, and through a more restricted orifice in the load mode.

8. A fluid transport container according to any one of the preceeding claims wherein the control means is employed to ensure that an overspill protection system is operational during loading of the container.

9. A control system for a foot valve of a fluid transport container as claimed in any preceeding claim, comprising means responsive in use to whether the container is being loaded or filled for closing the foot valve more rapidly in a discharge mode than in a load mode.

10. A fluid transport container comprising a foot valve arranged in a lower part of the container through which the container may be loaded and unloaded, control means for actuating said foot valve in load and discharge modes, and an overspill protection system adapted to interrupt loading should the level in the container exceed a predetermined maximum, wherein an electrical interface is provided whereby said overspill protection system is automatically enabled whenever the foot valve is open in the load mode.

11. A fluid transport container according to claim 10, wherein the interface comprises a pressure switch responsive to signals received from the control means and the foot valve.