GB2157657A - Dry-line liquid delivery system - Google Patents

Abstract

A liquid delivery system of the dry-line type, suitable for delivery of liquid from a liquid vessel such as a mobile tanker, has a first pump to supply liquid into a liquid delivery line, a second pump (P) to provide an independent supply of air under pressure, and valve means to introduce the pressurised air into the liquid delivery line, downstream of the liquid pump, when liquid delivery is completed. In a preferred system the second pump is switched on automatically when the first pump is operated and the valve means is operated automatically when the first pump ceases to operate. Pump (P) passes air via valve (5) and line (11) to pressure tank (T) monitored by manometer (12) and supplied with a relief valve. On delivery completion, lever (9) is moved to the position shown, air from (4), via valves (6) opens valve (V3), allowing air from (T) to pass via (15) and clear the hove. <IMAGE>

Description

SPECIFICATION Liquid delivery system The present invention is concerned with the delivery of liquids, in particular liquid hydrocarbon fuels, from a road tanker to the user by means of a delivery hose.

When such liquids are unloaded from the delivery tanker, one of two systems is used, that is a so-called "wet line" system or a "dry line" system.

Using the wet line system, the delivery hose is kept full of liquid at all times, a delivery valve, for example of the hand-controlled trigger type, being fitted at the free end of the hose to prevent loss of liquid in transit. However wet line systems suffer from several disadvantages.

First of all, when the tanker has several compartments, each of which may contain a different liquid, it is necessary for the driver to be aware at all times of which particular liquid is in the delivery hose; otherwise contamination between liquids may result and a customer may have a whole storage tankful of liquid contaminated. The driver therefore needs to plan his sequence of deliveries before they are made and to keep to that plan, at least in general terms, irrespective of diversions such as a customer unable to take delivery as arranged. The close control of the operation may become more difficult if a change of drivers becomes necessary.

A further disadvantage of the wet line system is that the driver has to manipulate a full hose (and therefore a relatively heavy one) each time he makes a delivery.

There is therefore a real incentive for the tanker owner to convert to a dry line system, in which the delivery hose is emptied of liquid after each delivery and in which there is no need for a delivery valve at the free end of the hose. However there are only a very few dry line systems available and they suffer from various disadvantages which discourage their widespread adoption.

We are aware of one dry line system which relies upon the main liquid delivery pump to clear the hose of liquid after delivery is completed. Not only does that entail running the pump longer than is required for liquid unloading, there is the further disadvantage that the driver must wait for the pressure in the line-clearing air system to build up after the normal liquid delivery is completed, before he can blow the delivery hose clear of liquid.

Such delays are clearly undesirable.

Another dry line system is based upon an electrical switching arrangement to initiate line clearing after delivery. In the context particularly of the delivery of liquid fuels, such electrical switching is a potential source of hazard.

With the disadvantages of prior liquid delivery systems in mind, an aim of the present invention is to devise an improved dry line liquid delivery system.

The liquid delivery system according to the present invention is characterised by a second pump, separate from the main liquid delivery pump, which second pump provides an independent supply of air under pressure, and valve means to introduce the pressurised air into the liquid delivery line, downstream of the liquid delivery pump, when the desired quantity of liquid has been delivered.

The second pump, which provides the air supply, may if desired be switched on manually at the beginning of the delivery operation or during delivery. However, we much prefer that it be switched on automatically when the liquid delivery pump is brought into operation, for example when the power take-off from the tanker is switched into play.

The air pump may conveniently supply air to an air receiver tank, to allow the pressure to build up,during the delivery operation, to the level desired for subsequently clearing the delivery hose. A suitable relief valve may be fitted to control the air pressure at the desired level.

When the desired quantity of liquid has been delivered, the valve means is operated to introduce the pressurised air into the liquid delivery line. The valve means may be operated manually but it is preferred that it be operated automatically. Since the liquid delivery is usualiy stopped automatically by the liquid meter when the pre-set quantity of liquid has been delivered, it is convenient for the same trip arrangement which switches off the liquid pump to operate the valve means and introduce the pressurized air to the delivery hose.

One specific form of the liquid delivery system according to the present invention will now be described with reference to the accompanying drawing, which is a diagramatic illustration of a suitable air flow circuit.

In the specific embodiment, a road tanker having three discrete storage compartments, each of which is loaded with a different hydrocarbon fuel, supplies fuel to a customer through a delivery system incorporating a main fuel pump, a flow meter and a delivery hose. The flow meter measures the quantity of fuel delivered and controls the operation of a fuel flow valve in the form of a hydraulically balanced, two-storage slow-closing valve.

When fuel is to be delivered to a customer, the meter is pre-set to the quantity of fuel required to be delivered and, with the pump operating, fuel flows into the delivery hose at the higher of two flow rates. When a quantity of fuel slightly less than the pre-set quantity has been delivered (say 10 litres less), the meter automatically switches the flow valve to a slower rate (the so-called "dwell flow rate") and fuel flows into the hose at that slower rate until the exact pre-set quantity has been delivered, whereupon the flow valve is automatically closed by the flow meter.

Referring now to the drawing, when the main fuel pump is switched on, an auxiliary pump, P in the drawing, is automatically switched on and begins to supply air through the supply line 4 to two mechanically interconnected air valves V1 and V2.

Each of these valves is spring-loaded towards the closed position and the valve rods 5 and 6 are controlled by a rocker arm 7 such that only one is in the open, "flow-through" position at a given time.

The rocker arm 7 is pivoted about a pivot point 8 and its position is controlled by a control lever 9.

When the pump P is first switched on, the control lever 9 is in its left-hand position and the valve rod 5 is depressed against the action of a spring 10, so that air from line 4 can flow through the valve V1 into line 11 and thence to an air receiver tank T. Air pressure builds up in tank T to a pressure of approximately 80 p.s.i. and the level at any time is displayed on the scale of a marometer 12.

The pressure is controlled at the desired level by a relief valve (not shown).

When the pre-set quantity of fuel has passed through the flow meter and the main flow valve is automatically closed by the associated trip mechanism, the same trip mechanism moves the rocker arm 7 to its right-hand position as illustrated. This action allows the spring 10 to close the valve V1 and shut-off further flow of air into the tank T. The same action opens the valve V2 against the action of the spring 13 and diverts air into an air-controlled, spring-closed valve V3. Opening the valve V3 releases air at 80 p.s.i. from the tank T, via the lines 14 and 15, into the delivery line at the upstream end of the hose and immediately blows out residual fuel from the hose.

The control level 9 may now be set for the beginning of the next delivery operation.

In a second embodiment of the liquid delivery system according to the present invention, the two mechanically interconnected valves V1 and V2 are replaced by one double-acting valve, which is spring-loaded in both directions and has five ports, namely a single inlet port, two outlet ports and two exhaust ports.

Claims (12)

1. A liquid delivery system comprising a liquid delivery line, a first pump arranged to supply liquid to said delivery line, a second pump to provide an independent supply of air under pressure, and valve means to introduce said pressurised air into said liquid delivery line, downstream the said first pump, when the desired quantity of liquid has been delivered.

2. A liquid delivery system as claimed in claim 1, wherein said second pump is arranged to be switchable on manually.

3. A liquid delivery system as claimed in claim 1, wherein said second pump is arranged to be switched on automatically when the first pump is brought into operation.

4. A liquid delivery system as claimed in any of the preceding claims, wherein said second pump is arranged to supply air to an air receiver tank.

5. A liquid delivery system as claimed in claim 4, wherein said air receiver tank is fitted with a relief valve.

6. A liquid delivery system as claimed in any of the preceding claims, wherein said valve means is operable manually.

7. A liquid delivery system as claimed in any of claims 1 to 5, wherein said valve means is arranged to be operated automatically when the desired quantity of liquid has been delivered.

8. A liquid delivery system as claimed in claim 7, having trip means which both switches off the first pump and also operates the valve means when the desired quantity of liquid has been delivered.

9. A liquid delivery system as claimed in claim 8, having two valves alternatively supplied with air by said second pump, the first of which valves admits air to a first air line supplying an air receiver tank and the second of which valves admits air to a second air line feeding air to operate a third valve which allows air from said air receiver tank to flow into said liquid delivery line.

10. A liquid delivery system as claimed in claim 9, wherein said two valves are combined in a single double- acting valve.

11. A liquid delivery system substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawing.

12. A liquid-delivery mobile tanker fitted with a liquid delivery system as claimed in any of the preceding claims.