GB2126661A

GB2126661A - Device for calibrating flow rate counters for liquids

Info

Publication number: GB2126661A
Application number: GB08323580A
Authority: GB
Inventors: Beurden Cornelis Joannes A Van
Original assignee: BRABANTGAS HOLDING BV
Current assignee: BRABANTGAS HOLDING BV
Priority date: 1982-09-08
Filing date: 1983-09-02
Publication date: 1984-03-28
Also published as: GB8323580D0; NL8203498A; DE3331934A1; IT1195627B; BE897655A; IT8383459A0; FR2532747A1; FR2532747B1

Abstract

A device for calibrating flow rate counters for liquids having a boiling point below 20 DEG C with the aid of a calibration vessel 1 of known capacity for receiving an amount of liquid having passed through the counter, the device being provided with a closed system comprising a stock container 6 for receiving the amount used in the calibration and a compressor 7 by which vapour can be sucked out of the stock container 6 and passed into the calibration vessel 1 so that the liquid contained in the calibration vessel can be pressed towards the stock container. <IMAGE>

Description

SPECIFICATION Device for calibrating flow rate counters for liquids The invention relates to flow rate counters for liquids operating on the flow principle. Such counters are used, for example, in petrol pumps and also in LPG pumps.

Measuring the amount passing through a flow rate counter in the case of petrol does substantially not give rise to particular problems because the boiling point of petrol is higher than 200C at mean atmospheric pressure. Since the boiling point of petrol is higher than 200C petrol can be tapped and hence be measured without the system being closed. The situation is, however, different in the case of LPG or other liquids having a boiling point below 200C. Owing to the low boiling point LPG, a mixture of propane and butane in different ratios, can occur as a fluid only at pressures exceeding-the atmospheric pressure.

Therefore a delivery system for LPG and hence also a system for calibrating the delivery counters have to be subjected to pressure. For the delivery system devices have been designed in which the coupling between the delivery pump and the vessel to be filled, for example, the tank of a car, is completely closed. In calibrating the counter of a delivery pump it is also necessary for the entire measuring system to be a closed circuit, since otherwise due to the low boiling point of the liquids, for example, the propane-butane mixture, a very great error would be involved, whilst in addition risk of fire would occur. In a known method of calibrating an LPG delivery pump a calibration vessel of known, predetermined capacity is used, said vessel being inserted into a closed connection with the flow rate counter to be measured.In principle, the measuring method does not differ from that for many other fluids, including petrol, that is to say, it is a comparison of the value indicated by the delivery pump with the amount contained in the calibration vessel. For this purpose the calibration vessel is provided with a marking line.

Since in calibrating the whole system has to be closed for the above-mentioned reasons, it is not possible to simply allow the filled calibration vessel to empty after the measurement. Since in general several measurements have to be carried out in order of succession at different delivery rates, it has to be ensured that for a measurement the liquid present in the calibration vessel during the preceding measurement should be completely removed. For this purpose the known devices are provided with a pump emptying the calibration vessel. Due to the low boiling point of the fluid to be measured it is never certain in this method whether all fluid has been removed. Of course, pumping can be continued until there is absolute certainty that no liquid is left. However, this has the disadvantage that finally the pump runs dry.

This adversely affects the pump so that for a further measurement it is even less certain whether all liquid is removed. The main purpose of the present invention is to provide improvement in this respect.

A device embodying the invention for calibrating flow rate counters for liquids having a boiling point below 200C comprises a calibration vessel of known capacity for receiving an amount of liquids having passed through the counter and is characterized in that a closed system is provided which comprises a stock container for receiving the amount of liquid used in the calibration and a compressor by which vapour can be sucked out of the stock container and be passed into the calibration vessel so that the liquid contained in the calibration vessel can be pressed towards the stock container.

Consequently a device embodying the invention is not provided with a pump for emptying the calibration vessel and hence there is no risk for the pump to run dry. Moreover, it is easy to continue the admission of vapour from the compressor into the calibration vessel until it is absolutely certain that the calibration vessel is empty. Since the vapour by which the compressor empties the calibration vessel is emanating from the stock container containing vapour of the same liquid for the calibration and the liquid pressed out of the calibration vessel gets again into the stock container the whole system is closed. Although in compressing the vapour the vapour is heated, which could affect the measuring result, cooling occurs when the liquid enters the stock container so that heating of the vapour by the compressor can be neutralized. This is only possible in the closed system.

The calibration vessel of a device in accordance with the invention preferably has, on the top side, a level gauge for reading the degree of filling of the calibration vessel. It is true, a single marking line would be sufficient, but with a view to the spread of the counter of the delivery pump it is desirable to provide a level gauge from which the calibration of the value indicated by the pump can be easily read. For practical reasons the level gauge cannot be so large that large deviations can be read. A deviation of about 1.5% is found to provide a practical value. If the delivery pump deviates more, it has to be readjusted, for example, by connecting it with a so-called mother counter which may be provided as an additional part on the device embodying the invention.

The use of a stock container has furthermore the advantage that in order of succession a plurality of measurements can be performed on the delivery counter, as is desired for measuring at different delivery rates. It may seem a simple solution to feed the liquid removed from the calibration vessel back to the stock container to which the delivery pump is fastened. However, as stated above, this has the disadvantage that during the measurement constancy of temperature cannot be guaranteed. Moreover, this method is particularly circuitous. In the device embodying the invention several measurements can be carried out during which the stock container is gradually filled. When the degree of filling has reached a given value, usually 80% of the overall capacity, the stock container has to be emptied.For this purpose the stock container has preferably connected with it a liquid pump which transfers the liquid from the stock container to a storing vessel located outside the device, for example, the vessel with which the delivery pump is connected.

Furthermore the use of a stock container has the advantage that, when the whole device embodying the invention is mobile, for example, mounted on a mobile frame, measurements can be carried out on a plurality of different pumps. It is not necessary to pass the calibration liquid after every calibration of a gauge back into a storing tank. In a practical embodiment of a device in accordance with the invention the stock container has a capacity of about 500 litres and the calibration vessel a capacity of about 50 litres.

With such a device the conventional delivery pumps can be readily calibrated.

As a matter of course it is necessary to open and to close respectively valves in the various ducts during the various manipulations required for the calibration. For this purpose a device embodying the invention is preferably provided with a hydraulic-electronic system for controlling said valves: The electronic system is preferably designed so that by means of a limited number of control-knobs the valves are closed or opened respectively in the correct order of succession to ensure correct, safe operation of the device. In this embodiment the device can be actuated by operators needing little skill.

Preferably the pump emptying the stock container, the compressor and the pump producing the pressure in the hydraulic system are driven by a single combustion engine, for example a Diesel engine. In this way the device embodying the invention is fully independent of an external source of energy, for example, an electric mains.

If desired, a level gauge may be provided on the underside of the calibration vessel for checking whether all fluid is removed out of the calibration vessel. This level gauge may, in addition, be employed for assessing the composition of the fluid to be measured when it is formed by a mixture of fluids having a boiling point below 200 C. For this purpose, however, the compressor should be capable of operating in a reversible manner. This means that the suction side and the compression side should be interchangeable. This may be done mechanically by changing over valves or by inverting the direction of rotation of the compressor. During this inverse operation of the compressor the calibration vessel has produced in it a subatmospheric pressure after it has been filled so that the liquid evaporates very rapidly.From the level gauge on the underside of the calibration vessel can then be read a liquid level from which the composition of the liquid mixture can be calculated.

For all measurements the calibrated vessel should be provided with a manometer for measuring the pressure and with means allowing the connection of thermometers.

The invention will now be set out with reference to a drawing which schematically shows a device in accordance with the invention.

Reference numeral 1 designates the calibration vessel with a level gauge 2 on the top side. At the top of the level gauge is provided the inlet duct 3, which is coupled with the counter of the delivery pump to be calibrated. The duct 3 terminates in the tube above the level gauge in a nozzle to spread the liquid. The construction of said nozzle is substantially identical to that of the nozzles used in LPG tank wagons. On the underside the calibration vessel 1 is connected via the level gauge 4 and the duct 5 with the top side, that is the vapour side of the stock container 6.

Reference numeral 7 designates the compressor connected on the suction side through the duct 8 with the top side of the stock container 6. The compression side of the compressor 7 is connected through the duct 9 with the top side of the calibration vessel 1.

The top side of the stock container 6 is connected through a duct 10 with a mother counter 11. On the other side this mother counter is connected through a filter 12 with a connecting duct 13.

On the underside the stock container 6 is connected with a fluid pump 14. This fluid pump is connected on the other side with a hose reel 15, which terminates in a connection 1 6. Between the pump 14 and the hose reel 1 5 is connected a safety duct including an excess pressure safety 1 7. This duct terminates at the top in the stock container 6. Reference numeral 1 8 designates an air pump which is driven by a Diesel engine 1 9.

This Diesel engine 1 9 also drives the compressor 7 and the pump 14.

The various ducts include the necessary valves.

The valves marked by a circle are actuated by means of a hydraulic-electronic system. The valves marked by a T can be manually actuated. In some ducts the valves are double with a view to legal provisions. Between these valves there may ) be provided a relief member indicated by an arrow.

The manipulations required for calibrating a flow rate counter and the use of a device in accordance with the invention will now be briefly described.

Between the counter to be calibrated and the calibration vessel 1 a liquid-tight connection is established through the duct 3 and the level gauge 2, for example by using the commercially available ACME couplings. The calibration vessel is filled up to a given marking line on the level gauge 2. The counter in the pump to be calibrated is read and the reading is compared with the known amount in the calibration vessel 1 by reading the level gauge 2. When the calibration vessel is being filled the cocks in the duct 9 are closed. Of course, the cocks in the duct 3 have to be open. After the comparison of the counter to be calibrated with the amount of liquid in the calibration vessel, whilst the cocks of the duct 3 may be closed, the cocks in the duct 9 are opened as well as the cocks in the duct 5.Moreover, the compressor 7 is switched on so that liquid is pressed out of the calibration vessel via the level gauge 4 and the duct 5 into the stock container 6. Subsequently the valves are moved back into a position required for a next-following calibration and the compressor is stopped or shortcircuited so that pressure does no longer prevail in the duct 9.

If the counter to be calibrated exhibits great deviation from the correct value, usually more than 1.5%, the reading of the level gauge 2 cannot be correct. Then the counter of the pump to be calibrated has first to be corrected so that the deviation lies below this maximum error value. For this purpose the mother counter 11 can be used.

A connection is established between the counter to be calibrated via the duct 13 and the mother counter 11 and a given amount of liquid is allowed to flow through the duct 10 into the stock container. A comparison between the two counters will then provide the correct correction for the counter on the pump to be calibrated. After the performance of this correction, the correct correction value for the pump can be assessed in the conventional manner in accordance with the invention with the aid of the calibration vessel 1.

As the case may be, the pump can be readjusted for this required correction or, which is more usual, the deviation may be indicated in the pump.

When the stock container 6 becomes overfilled, that is to say, filled with liquid for more than 80%, it is no longer allowed to calibrate. The liquid of the stock container 6 can then be removed via the pump 14, the hose reel 1 5 and the connection 16, preferably towards the storing vessel of the device with which the pump to be calibrated is connected.

Although in the foregoing description reference is made to propane and butane or mixtures thereof, for example, LPG, a device embodying the invention permits of calibrating any flow rate counter for liquids having a boiling point below 200 C. For liquids having a boiling point exceeding 200 C, in general, a simpler method will be preferred, It is possible to calibrate counters for liquid carbon dioxide and ammonia by means of a device embodying the invention.

The hydraulic-electronic control-system of the valves in the ducts is not described in detail. Such a combination of electronic and hydraulic components may be constructed in various ways.

As stated above, it is particularly important to ensure a control-series by a limited number of knobs for actuating the valves in the correct and safe order of succession.

The drawing furthermore shows a duct 20 and a manually operated valve 21. This duct 20 and the valve 21 are used for calibrating the mother counter 11 with the aid of the calibration vessel 1.

This calibration may, if desired, be carried out daily.

The hydraulic-electronic system for controlling the valves in the ducts of the device may, as an alternative, be a hydraulic-pneumatic system or a system comprising both electronic and pneumatic or hydraulic components.

Claims

1. A device for calibrating flow rate counters for liquids having a boiling point below 2O0C with the aid of a calibration vessel of known capacity for receiving an amount of liquid having passed through the counter characterized in that the device comprises a closed system comprising a stock container for receiving the amount of liquid used in the calibration and a compressor by which vapour can be sucked out of the stock container and be introduced into the calibration vessel so that the liquid contained in the calibration vessel can be pressed towards the stock container.

2. A device as claimed in Claim 1 characterized in that on the top side the calibration vessel is provided with a level gauge for reading the degree of filling of the calibration vessel.

3. A device as claimed in Claim 1 or Claim 2 characterized in that the stock container is furthermore connected with a duct including a calibrated mother counter.

4. A device as claimed in Claim 1, 2 or 3 characterized in that the stock container is furthermore connected with a liquid pump for transferring the liquid in the stock container towards a storing vessel located outside the device.

5. A device as claimed in Claim 1,2, 3 or 4 characterized in that the device is provided with a hydraulic-electronic system for controlling the valves included in the ducts of the device.

6. A device as claimed in Claim 5 characterized in that the hydraulic-electronic system opens and closes respectively the valves through a limited number of control-knobs in the order of succession required for the correct and safe operation of the device.

7. A device as claimed in Claim 1, 2,3,4, 5 or 6 characterized in that the compressor, the pump for emptying the stock container and the pump for the hydraulic system are driven by a single combustion engine.

8. A device as claimed in Claim 1, 2, 3, 4, 5, 6 or 7 characterized in that all parts of the device are mounted on a mobile frame.

9. A device as claimed in Claim 1, 2, 3, 4, 5, 6, 7 or 8 characterized in that the calibration vessel is provided on the underside with a level gauge.

10. A device as claimed in Claim 9 characterized in that for assessing the composition of a mixture of liquids having a boiling point below 200C the suction side and the compression side of the compressor can be connected with the calibration vessel and the stock container respectively in a sense opposite the sense employed in calibrating the flow rate counter.

11. A device as claimed in any one of Claims 3 to 10 characterized in that it is furthermore provided with means for calibrating the mother counter with the aid of the calibration vessel.