MXPA01008407A - Testing vapour recovery systems - Google Patents

Abstract

A method of testing a volatile liquid tank farm together with a vapour recovery system, to collect vapour from the tanks at the time of re-filling them with volatile liquid. The tank farm has individual fill-pipes (13) for each tank (10) with each fill-pipe outlet below the normal minimum liquid level in the tank and each tank having a vent-pipe (11) connected to a common manifold (25). To perform the test, the common manifold is closed to atmosphere and one side of a shut-off valve (17) is connected to the manifold (25), a flow meter (20) being connected to the other side of the shut-off valve. Flow meters (22, 23) are coupled to all but one of the fill-pipes (13), the shut-off valve (17) is opened to allow liquid to be supplied to the remaining fill-pipe so as to increase the volume of liquid in the associated tank, and the out-flow of gas or wet vapour from the common manifold (25) is monitored for substantial correlation to the volume of liquid admitted to the tank associated with the remaining fill-pipe. The method can be modified also to allow the testing of individual tanks of a tank farm, where the vent-pipes of the tanks individually vent to atmosphere,the test then being performed one at a time, on each tank.

Description

TEST VAPOR RECOVERY SYSTEMS DESCRIPTION OF THE INVENTION The invention relates to a method for testing a recovery system to a tank for a volatile liquid, such as a tank for containing fuel or gasoline (hereinafter referred to simply as sometimes as gasoline or fuel). As installed in a fuel filler station for motor vehicle. The invention relates to a method for testing a system for recovering a group of tanks from a tank comprising a plurality of such fuel tanks and a method for testing a tank installation. Historically a fuel tank in a fuel filling station has a simple installation pipe leading to the atmosphere, this steam that is allowed to move from the tank during a filling operation must be vented to the atmosphere. Among the supplies, the ventilation pipe allows natural ventilation of the tank to take place, as well as the entry of air over the fuel that is removed from the tank, which is provided through a fuel supply pump. To eliminate the problem of environmental pollution arising from the natural ventilation process, the fuel tank groups have been modified in various ways to operate on a current standard known as stage IB, where the steam moves from a tank during a supply process and it is returned to a road tank that supplies the fuel. A typical modification is to connect all the tank vent pipes of the individual fuels to a common header that has a single vent tube fitted with a vacuum valve (hereinafter referred to as a valve p / v), or sometimes a plurality of ventilation tubes each provided with a valve p / v. A valve p / v is normally closed but opens if the pressure in the head to which it is connected drops below a pre-established sub-atmospheric value caused by supplying the fuel, or if the pressure rises above another pre-established value that is above of the atmospheric. When the fuel is to be loaded into one or more of the tanks the head is connected to a steam head on the supply road tank and the fuel vapor is removed to the tanker to be processed to liquid fuel.

In this way much of the previously released steam to the atmosphere can be contained at the time of filling the tanks at a supply station. In the UK, it is now a legal requirement that all steam recovery systems at retail gasoline filling stations registered with the appropriate authority should soon be a requirement that such a system be tested to ensure that the system works correctly and efficiently with any leakage falling within the limits established within the European lines. The present invention seeks to provide a test method of one or more tanks intended to maintain fuel first to ensure that the installation is suitable to fit as a vapor recovery system and secondly once a recovery system has been installed. of steam, that the system is functioning properly efficiently and safely without significant leaks that prevent the recovery system from functioning properly efficiently and safely. According to a first aspect of the present invention, a test method of a volatile liquid tank installation having a filling tube projecting down into the tank with the outlet of the filling tube below the liquid level is provided. normal minimum normal and the tank also having a vent tube method in which one side of a shut-off or cut-off valve is connected to the valve tube, a flow meter is connected to the other side of the shut-off valve, the valve is opened, the liquid supply to the tank to increase the volume of liquid there, and the outflow of gas or wet steam from the ventilation pipe is controlled for the essential ratio to the volume of liquid admitted to the tank. It will be appreciated that this method allows the testing of gasoline and / or diesel tanks installed for example in a fuel supply station where these tanks are naturally intended as described above, before the installation of a vapor recovery system. such as the one known in the United Kingdom, such as the IB stage system. By controlling the steam volume output flow from the installation pipe for an essential correlation with the volume of flow into the tank and preferably also the steam flow rate and the flow exit time, to be compared with the time and the inflow of the liquid fuel, there can be reasonable assurance that there is no significant leakage that allows escaping into the vapor atmosphere from some other point in the facility. If the correlation falls outside the expected limits, a blockage, flight or restriction could be suspected and a suitable investigation initiated. Advantageously, a pressure gauge is arranged to sense the pressure in the vent pipe, liquid is supplied to the fill pipe to increase the volume of liquid in the tank and the shut-off valve is operated to control the pressure build-up in the tank. vent pipe to some maximum value, consistent with the displacement of steam or wet steam from the tank. When the supply of liquid to the tank is completed, the blocking valve is closed and the subsequent pressure drop in the ventilation pipe is controlled. By controlling this flow it is possible to determine if there are leaks and taking into account several important parameters (such as tank volume, storage space, initial pressure, etc.), then the severity of a suspected leak can be determined.

Preferably, the test is performed in the order mentioned - this is the outward flow of the vapor in the liquid that is supplied to a tank before testing for the pressure drop allowed to form in the vent pipe, when the valve is closed. Even before performing the test described above, a preliminary step can be performed in which the shut-off valve is closed, and the pressure inside the vent pipe is controlled as liquid is removed from the tank, such liquid extraction it can be in the course of filling the tanks of the vehicles and must create a negative pressure in the ventilation pipe; This part of the test can also be used to make sure there are no or only minimal leaks. Once the individual tanks have been tested and - it is found that they meet the pre-established limits, the Stage IB vapor recovery system can be installed. Then, the system can be tested for compliance and it is recommended that the installation be tested periodically for continuous compliance typically once every twelve months. According to a second aspect of this invention, therefore, there is provided a method of testing a steam recovery system installed in a group of liquid tanks comprising a plurality of tanks with volatile liquid, each having an individual packing tube that is projected inside the tank with the outlet of the filling tube below the normal minimum liquid level in the tank and each tank having a ventilation pipe coupled to a common head, method in which the common head is closed to the atmosphere and one side of the block valve is connected to the head, a flow meter is connected on the other side of the block valve, flow meters are coupled to all but one of the filling tubes, the block valve is open , the liquid is supplied to the remaining filling tube in order to increase the volume of liquid in the associated tank, and the outflow of gas or wet steam from the common head n is controlled for a substantial correlation to the volume of liquid admitted to the tank associated with the remaining fill tube. Preferably, a pressure gauge is arranged to sense the pressure in the head, the liquid is supplied to the remaining filling tube in order to increase the volume of liquid in the associated tank, the blocking valve is operated to control the formation of pressure in the head as a result of displacement of gas or wet steam from the tank, the block valve is closed when the supply of liquid to the tank is completed and the subsequent pressure drop in the head is controlled. In an alternative form, the blocking valve does not need to be closed, until all the tanks have received the liquid supply and the fall for the complete system is measured, precisely at the end of the test procedure. In a vapor recovery system Stage IB, the common head is provided with one or more valves p / v, for such case, the vacuum operation of the valve p / v, must be tested before carrying out the test method having the valve closed and verifying negative pressure in the head. The pressure side of the valve p / v, can be checked again later with the shut-off valve closed and allowing the pressure to be formed until the valve opens, which normally should be at 35mbar, for the systems currently In use. With a Stage IB system, the steam displaced from a gas tank when receiving fuel in the tank is recovered when it is returned to the supply tank vehicle from the head, and this happens in the tank vehicle generating a sub-atmospheric pressure for Pull the steam. For this purpose, a hose is arranged to connect the other side of the blocking valve to a vapor recovery system (such as in a tank vehicle), and a pressure apparatus is arranged to sense the pressure in the hose, to test a sub-atmospheric pressure generated by the vapor recovery system as it is in the tank vehicle. For a group of tanks, the test method must be repeated for tank with the liquid supplied to the different tanks during each performance of the test method. The repeated performance of the test method can be effected by the transfer of a flow meter from one filling tube to another and then supplying the liquid to the tube from which the flow meter is withdrawn and controlling the outflow of the gas or of wet steam from the other filling tubes.

In order that the invention is better understood, two specific examples of the test method of this invention will now be described in detail, with reference to the accompanying drawings, in which: Figure 1, diagrammatically represents a group of tanks having naturally ventilated tanks in the course of testing; Figure 2 is similar to Fig. 1, but shows a group of tanks provided with a vapor recovery system Stage IB; Figure 3 is a diagramatic cross section through an underground tank of a group of tanks; Figure 4 is a vertical diagrammatic cut through a filling set for a tank showing possible leaks; and Figure 5 is a sectional view taken on an enlarged scale of a tank piece T together with a stuffing tube. Referring initially to Fig. 1, there is shown a group of tanks having a plurality of fuel or gasoline 10A, 10B, 10C and 10D, each having its own individual vent tube HA, 11B, 11C and 11D. Each vent tube leads from an upper portion of the respective tank and has a simple weather hood 12, fitted to the upper end of the tube. Each tank 10A ... 10D, has a filling tube of a respectively relatively long diameter 13A ... 13D, filling pipe leading to a lower portion of the respective tank. All the upper ends of the filler tubes are usually arranged in a closed group (as shown), for easy access by the tank vehicle, as illustrated in 14, which is supplying fuel to the tank group. The tank vehicle 14, is provided with a steam recovery mechanism, where the steam driven from the empty space of a tank can be returned to the tank vehicle to be processed by returning liquid fuel and reused. For a ventilation system such as is illustrated in Fig. 1, the steam recovery mechanism of the supply tank vehicle is not normally used, the supply tank vehicle "breathes" by its own valves p / v, arranged at the top of each supply compartment . The storage tank when receiving the incoming fuel, ventilates the atmosphere, steam driven from the tank through the ventilation pipe. The fuel supply is made by connecting a flexible hose 15, from a tank vehicle key to the filling pipe and then opening the associated supply valves in the tank vehicle. In the arrangement shown in Fig. 1, tank 10D is intended to contain diesel fuel. A flexible hose 16, is connected to the ventilation tube of the fuel tank HA, after removing the weather hood 12, that flexible hose 16, connected to a side of the blocking valve 17, mounted on a support. The side of ventilation tube of that valve is provided with an apparatus vacuum pressure 18, to sense the pressure that prevails in the associated ventilation tube. The other side of the blocking valve 17, is connected to another hose 19, to the vapor recovery mechanism of the tank vehicle 14, through a flow volume meter 20, and another pressure / vacuum apparatus 21, during the discharging fuel from the 10D tank, the vacuum (negative pressure created by the supply of the tank vehicle can be controlled in the apparatus 21, then at the beginning of the fuel drop inside the tank 10A, the filling tube for the 10D diesel tube , it is sealed and the fuel pipes 13B and 13C, of the other two fuel tanks are equipped with respective flow meters 22 and 23. The installation of the flexible hose 16, and of the blocking valve 17, can be carried out before the arrival of the tank vehicle 14. The blocking valve 17 must be in the closed position before the connection to the tank vehicle by the hose 19, during which time the pressure / vacuum apparatus 18, can be used to control the pressure drop in the ventilation tube HA, when the fuel is pulled from the tank 10A, when the supply station is using motor vehicles. The pressure / vacuum apparatus 18 will show that the pressure in the vent pipe is falling and remains low as more and more fuel is removed from the tank. When the tank vehicle reaches the place, it is connected to the filling tube 13A, by a flexible hose 15, and to the blocking valve 17, by the hose 19, as described above.

The valve 17 is opened and the vapor recovery system of the tank vehicle is put into operation; the pressure / vacuum apparatus 21, will show if the vapor recovery system of the tank vehicle is producing a sub-atmospheric pressure suitable for vapor recovery. At the beginning of the fuel drop in the tank 10A, a corresponding outward flow of steam can be verified by the flow meter 20. In addition, the flow meters 22 and 23, can also be checked to ensure that there is no flow to inside nor a flow outward as tank 10A is being filled. Apart from possible errors of work on the tube, this will also verify the correct operation of the ventilation tubes. Finally, valve 17 closes partially and. it is then operated as appropriate to prevent excessive pressure buildup in the vent pipe when the fuel inlet in the tank 10A continues to use the apparatus 18 to check the pressure. When the supply is complete, the valve 17 is closed and then the pressure drop in the ventilation tube is controlled by means of the measuring device 18. If the pressure does not fall in the expected manner (this is a small initial pressure drop after from which the pressure is stabilized), the presence of leaks must be suspected. The above procedure is repeated for the three tanks, and assuming that the results obtained are within acceptable limits (but very low), then a Stage IB vapor recovery system can be installed. This is shown in Fig. 2, during the course of the test and equal parts to those in Fig. 1, are presented with equal reference numbers, and will no longer be described in detail. As can be seen in Fig. 2, the three ventilation tubes HA, HB and 11C, are connected to a common head or tube 25, which has a single atmospheric ventilation tube 26, equipped with a valve for / 27, valve that is arranged to open and thus ventilate the head to the atmosphere, should the pressure inside the head or manifold drop below or exceed a pre-set limit. While the pressure in the ventilation tube remains within these limits, the p / v valve will remain closed. The head 25 also has a common connection 18 for the recovery system of the tank vehicle 14. Below are the precise steps to be followed in a specific example of a stage IB vapor recovery system. Here the system is described in broader and more general terms. To realize a method of this invention, the blocking valve 17, in its support is coupled to the connection 28, by a flexible hose 16, and also to the tank vehicle by a hose 19, as described above. The blocking valve 17 is opened and the vapor recovery system of the tank vehicle operates as fuel enters the tank 10A; the steam flow through the tube 19 can be controlled in the meter 20, and must fall within a range generally comparable to the supply of fuel vlumen to the tank 10A. In addition, the proper operation of the vapor recovery system in the tank vehicle can be controlled by a pressure meter or apparatus 21. The valve 17 can be temporarily closed at the start of a fuel supply to verify that there is a pressure drop in the tank. the apparatus 21, confirming thus, that the vapor recovery system of the tank vehicle is working. Then, valve 17 is closed, as fuel continues to enter tank 10A. Relatively short periods of fuel flow will be sent from different compartments (tanks), from the tank vehicle one at a time, within each tank in sequence to allow the reaction time of the steam flow rates, and that the current flow rates are recorded in the device 20. By supplying fuel in sequence and only for a short period to each tank, corruption of the data is avoided and what could otherwise happen if each tank received its full charge at one stroke, because the group of tanks would then be progressively loaded with excessive steam pressures making the readings more and more inaccurate. When the remaining fuel in the reservoir of the tank vehicle is sent to the first tank 10A, the displacement or empty space of the tank will be gradually distributed through the empty spaces of the other tanks and thus a much lower increase in Pressure. In addition, a rapid rise in pressure can be anticipated when fuel is loaded on the other lines. tanks, again depending on the volumes that already exist in the tanks. The valve 17, conveniently operates to prevent excessive pressure buildup in the head when the fuel continues to the tank 10A, using the apparatus 18, to check the pressure. At the end of the complete supply to all the fuel tanks, the valve 17 closes and then the pressure drop in the head 25 is controlled by means of the apparatus 18. If there is an excessive pressure drop (say more than amber in a period of 6 minutes), the presence of leaks can also be suspected if there is an outward flow of steam from any of the filling tubes 13B and 13C, as determined by the flow meter 22 and 23, it can be suspected that there is a leakage in the connection between the filling tube and the same tank. Fig. 3 illustrates a portion of an underground fuel tank, a manhole and a cover through which the filling tube passes, as can be seen, the tube has a neck 30, provided with a cover 31, the lid is arranged in a manhole 32, below the floor surface 33. The filling tube has a connection flange 34, at its free end on the floor, the tube then passes through a side wall of the hole of man and connects to a piece in T 35, put on the tank lid. Below the lid, the filling tube extends down towards the bottom of the tank, also shown in Fig. 3, a test valve 37, and a ventilation tube 38. Figs. 4 and 5, show in greater detail the construction of the tank cover 31, a nipple 39 of the tank cover is screwed in a threaded opening in the tank cover 31, and a T-piece 35, is screwed in that nipple . A drop tube with flange 40 passes through the nipple 39, a sealing being made between the flange 41, of the drop tube 40, and the nipple 39, by means of an O-ring 42. The flow tube is keeps down on the ring -O, by means of a cage 43, retention of the drop tube 43, which has a low pressure member 44, supported on the flange 41, of the drop tube and a threaded ring 45, coupled with the threads on the top of the piece -T. By rotating the ring 45, the pressure on the seal of the drop tube can be increased to the required level.

The upper part of the piece -T, is closed with a plug 46. The lower end of the drop tube 40, is connected to a valve that prevents overfilling 47, the lower end of which is connected to the lower portion of the tube of filling 48, which descends to the bottom of the tank. As shown in Fig. 4, leakage of liquid vapor may occur at several of the joints described above and as illustrated by arrow A (the valve connection to prevent overfilling 48/47 / lower portion of the tube filling), B (the valve that prevents overflow / connection of drop tube 47/40) C (drop tube / nipple connection 40/39). In addition, leakage may occur in the nipple connection 31/39 / tank lid or in the connection piece T 46/35 / plug. It will be appreciated that the test procedures described above allow adequate and complete testing of a group of tanks initially by functioning as a simple naturally ventilated system and subsequently when a Stage IB vapor recovery system has been installed. The complete procedure to be followed to perform a complete test method of the Stage IB vapor recovery system will now be described in detail, referring to Figs. 1 and 2. 1. Put on the test equipment as shown in figure 2. Band 17 is closed. The hose 16 is connected to the connection to establish steam recovery 28. 2. The supply tank arrives at the place. The hose 19 connects one end to the tank and the other end to the valve 17. 3. The vacuum side of the valve p / v 27 is checked for correct operation with the valve 17 closed, any negative pressure in the tank group will be recorded in the apparatus or meter 18. A negative pressure will be caused by gasoline sales in the pumps and will indicate that the vacuum side p / v 27 is working properly. 4. The supply hose 15 is connected to the diesel tank 10D at the filling point at the top of the filling tube 13D. The valve 17 is closed, and as diesel is pumped into the tank 10D a negative pressure must be created inside the tank hose 19 and recorded in the apparatus 21, this should be recording approximately -20 mbar. If the auto tank recovery equipment is working properly. 5. The pumping or emptying of the entire compartment of the tank car (pot) of diesel to be emptied is measured in time. This is the total pot delivery time (TPDT) in minutes and seconds. 6. Valve 17 opens during the diesel supply to verify again the correct operation of the vacuum side of the valve for p / v 27. 7. The TPDT measured for this shipment of diesel is a convenient mark that measures the TPDT of all other deposits. Diesel will normally be discharged at a slower rate than gasoline. 8. After the diesel has been completed, the hose 15 is connected to the tank 10A at the point of lining at the top of the filling tube 13A and with the valve 17 open, the gasoline is sent from the tank to the auto 10A, this will cause the steam to flow through the ventilation HA and the reaction time (RT) is measured from when the fuel is sent from the auto tank until the steam flow reaches the measuring device 20. This measured amount of time (usually in seconds) will be known as the initial reaction time IRT. The maximum value flow rate (MFR) in the apparatus 20 and also the time to reach the maximum flow rate (TRMFR) is measured. The fuel delivery to tank 10A stops after one minute. This is the completed first stage for the tank 10A 9. The hose 15 is transferred to the filling point of the tank 10B at the top of the filling tube 13B and to the correct fuel nozzle in the tank. The process is then repeated with the fuel emptied from another tank of the tank, to tank 10B. The IRT, MFR and TRMFR are now measured for this mouth or tank and the fuel supply is stopped after one minute. The one minute period is usually more than enough time to get all the important readings, but it must be continued as long as it is necessary to get all the readings and make a note of the time used. 10. The hose 15 is then transferred to the filling point of the tank 10C at the top of the filling tube 13C and the process is repeated again by emptying fuel from another mouth or tank of the supply tank. 11. With regard to the configuration of place as in figure 1, sufficient readings are obtained. - TPDT for the 10D diesel tank in minutes and seconds. IRT for gas tanks 10A, 10B, 10C in seconds. MFR for the same three tanks in liters of steam per minute. - TRMFR for the same three tanks in seconds. - The time of the fall of the first stage for each tank of gasoline (usually 1 minute). 12. Analyzing the previous times and the flow rates for the different tanks and comparing them to each other, the characteristics that may cause faults within the vapor recovery system of the place or station will be presented, for example if all the tanks they are placed too close to each other in the deposit, we can expect that all the readings are similar. However, if one tank has a very slow IRT and TRMFR and a very low MFR in comparison to the others, this probably indicates some form of blockage or restriction in the ventilation tube 11 of that tank. 13. The hose 15 is reconnected to the filling point in the tank 10A and to the correct mouth in the tank for the second stage of the emptying. The emptying of the remaining fuel in that tank is measured in time and added to the time of the first stage (normally one minute) to give the TPDT for each tank. To calculate the supply rate for each tank or tank tank, the volume of fuel discharged in each tank is divided by TPDT. This value (in liters / minutes) should be closely related to the maximum vapor flow rate recorded in the device 20. 14. During the emptying of the fuel from each tank, the valve 17 closes briefly to verify that a negative pressure is registered or a drop pressure in the apparatus 21. This will indicate that the valve p / v located in the upper part of that tank in the supply tank is working correctly. 15. During the second stage of the fuel discharge in each of the tanks 10A, 10B, 10C, it is necessary to use two or more hoses simultaneously connected to the reservoir of the respective tank and to the tank to measure the combined vapor flow rate through the head 25. This will be recorded in the apparatus 20. This reading (1 hour / minutes) allows the analysis of the characteristics of any blocking restriction in the head. 16. Once this "dual flow rate" has been measured, the valve 17 is partially closed, while the fuel is still discharging into the tanks. This allows the formation and maintenance of continuous pressure within the IB stage of place which is the vapor recovery system. 17. While this pressure is being formed and being controlled from the apparatus 18, the flow rate apparatuses 22 and 23 are placed on the filling point connection at the top of the filling tubes 13B and 13C (not shown). in figure 2). These devices close before filling. 18. When the pressure in the vapor recovery system has been reached and is maintained just below the release pressure of the p / v valve 27 (typically 35 mbar) the flow rate tubes 22 and 23 are opened, and The indicator needle is allowed to normalize. Any leakage of the filling tubes 13B and 13C will be recorded as a continuous and permanent rate in these devices or meters. This process is repeated at all filling points of all gasoline or fuel tanks as the hose 15 is moved around from tank to tank. 19. As long as the second lid fall of the last tank of the tank being discharged is carried out, the valve 17 is fully established to form the pressure in the system in order to verify the pressure of passage or release of the valve. / v 27. The pressure formed is controlled in the apparatus 18 and will be around 35 mbar, the p / v valve must be activated and opened, temporarily letting the pressure and vapor pass to the atmosphere. If the p / v valve is working correctly the needle in the apparatus 18 will oscillate up and down when the p / v valve opens and closes in pulses (the opening can easily be heard and closed quickly and it must be easy to see the steam escaping from it). If it is not operating correctly, the needle in the apparatus 18 will continue to rise higher than 35 mbar, indicating that the valve has been locked. The entire valve will need to be replaced if the steam or vacuum sides do not work properly. The valve will also be considered faulty if it opens prematurely below 35 mbar. 20. Once this has been verified, valve 17 is partially opened to maintain a stable pressure in the system just below the valve's release pressure w / v 27. In order to maintain a constant pressure, continuous attention to the device is required. 18 and a minimum adjustment of valve 17 until the last fuel tank has been completed. The valve 17 is immediately tightened by blocking in this pressure within the vapor recovery system Step IB 21. 21. This, reading of pressure of just below 35 mbar in the apparatus 18, will fall slightly for a short period of time, as that fuel is set in the tank. The pressure should then remain stable at approximately 30 mbar. Any significant pressure drop (greater than a drop of 10 m bar) in the next ten minutes will indicate the presence of leaks inside the steraa. 22. With the valve 17 tightened, the auto tank impeller has completed the discharge and the supply hose 15 and the vapor recovery hose 19 are disconnected and the place or station supplied can be aband. 23. The hose 16 is disconnected from the vapor recovery connection valve 28 which must then automatically become tight. Another flow measuring device (similar to 22 and 23) is fitted to a hood connected to the valve 28. Before putting on the device is closed. After a short period the flow rate apparatus opens and the indicator pointer is allowed to settle. Any continuous flow recorded in this apparatus will indicate that the steam recovery connection valve 28 has failed and needs to be replaced. 24. A.ora, the stage IB vapor recovery test has been completed, all that remains is to analyze the results of the test and prepare the report.

Claims (17)

1. CLAIMS 1. A method to test a volatile liquid tank installation that has a fill pipe that projects down into the tank with the outlet of the fill pipe below the minimum normal liquid level in the tank and having the tank as well A vent pipe, method in which one side of a shut-off or cut-off valve is connected to the vent pipe, a flow meter is connected to the other side of the shut-off valve, the valve opens, liquid is supplied to the tank to increase the volume of liquid inside and control the outflow of gas or wet steam from the vent pipe for a substantial correlation to the volume of liquid that is admitted to the tank. A test method, according to claim 1, wherein the reaction time of the humid gas or steam output to register on an apparatus or calibrator associated with the shut-off valve is also controlled. 3. A test method, according to claim 2, wherein the reaction time is controlled from the start of the supply of liquid to the tank. 4. A test method, according to claim 1, in which a pressure measuring device is arranged to measure the pressure in the ventilation tube, liquid is supplied to the filling tube in order to increase the volume of liquid in the tube. tank, the shut-off valve is operated to control the formation of pressure in the ventilation pipe, consequently with the displacement of steam or wet steam from the tank. A method according to claim 4, in which the shut-off valve closes upon completion of the supply of liquid to the tank and the subsequent drop of the pressure in the vent pipe is controlled. A test method according to any of the preceding claims, in which the shut-off valve is closed and the pressure inside the vent pipe is controlled as the liquid is removed from the tank, as a first step of the method test. 7. A test method according to claim 6, in which the ventilation tube is equipped with one or more pressure / vacuum valves, ie valves p / v, arranged to limit the maximum and minimum pressures in the air duct. 8. A test method of a group of volatile liquid tanks comprising a plurality of tanks, each having a single fill tube projecting down into the interior of the tank with the outlet of the fill tube below the level of the tank. minimum normal liquid in the tank and each tank possessing a ventilation tube coupled to a common manifold or head, method in which the common head is closed to the atmosphere and one side of a shut-off valve is connected to the head, a meter flow is connected to the other side of the shut-off valve, flow meters are coupled to all but one of the filling tubes, the shut-off valve is opened, fluid is communicated to the remaining filling tube in order to increase the volume of liquid in the associated tank, and the outflow of gas or wet steam from the common header is controlled for a substantial correlation to the volume of liquid that is admitted to the tank associated with the fill pipe. or remaining. 9. A method according to claim 8, wherein liquid is simultaneously supplied to two tanks for a part of the general test method, the combined outflow of gas or wet steam being controlled during this time. A method according to claim 8, wherein the shut-off valve is closed during the start of liquid supply to a tank and the pressure in the common head is controlled to test whether there is leakage in the filling tubes of the tanks. other tanks. A method according to claim 5, in which a pressure calibrating apparatus is arranged to record the pressure in the head, liquid is supplied to the remaining filling tube in order to increase the volume of liquid in the associated tank, the closing valve is operated to control the formation of pressure in the head, consequent with the displacement of gas or water vapor from the tank. 12. A method according to claim 11, wherein the shut-off valve closes upon completion of the supply of liquid to all tanks and the subsequent release of pressure in the head is controlled. A method according to one of claims 8 to 12, wherein the flow meters coupled to the other filling tubes are controlled for the outflow of the moist gas or vapor as it supplies liquid to the tank and the Pressure buildup is controlled by the operation of the shut-off valve. A test method according to any of claims 8 to 13, wherein the pressure within the common head is controlled when the liquid is taken from the tank as a first stage of the test method and before the liquid is removed. supply the tanks. A method according to any of claims 8 to 14, in which the common head is equipped with a pressure / vacuum valve arranged to vent the head to the atmosphere, provided that the pressure differential between that in the common head and the atmosphere exceeds a predetermined value, method in which the normal operation of the pressure / vacuum valve is verified by the operation of the shut-off or cut-off valve during the performance of the test method. 16. A method according to any of claims 8 to 15, wherein the test method is repeatedly performed by transferring a flow meter from one filling tube to another and then supplying liquid to the aforementioned filling tube and controlling the flow of outgassing or wet steam from the other filling tubes. A method according to any of the preceding claims, in which a hose is arranged to be connected to the other side of the shut-off valve, to a vapor recovery system of a tank and a pressure gauge is It has to record the pressure in that hose, verifying the correct operation of the steam recovery system. SUMMARY A method to test a group of tanks for volatile liquids together with a vapor recovery system, to collect the vapor from the tanks at the moment they are filled with volatile liquids. The tank group has individual filling pipes (13) for each tank (10) with each outlet of the filling pipe below the minimum normal liquid level in the tank and each tank having a vent pipe (11) connected to the tank. a common distributor (25). To perform the test, the common manifold is closed to the atmosphere and one side of a throttle valve (17) is connected to the distributor (25), a flow meter (29) is connected to the other side of the throttle valve,. The flow meters (22,23) are coupled to all but one of the filling pipes (13), the throttle valve (17) is opened to allow the liquid to be supplied to the rest of the filling pipes to increase the volume of liquid in the associated tank, and the expulsion of gas or wet steam from the common distributor (25) to be monitored with respect to the correlation to the volume of liquid admitted into the tank associated with the remaining filling pipes. The method can also be modified to allow testing of the individual tanks of the tank group, where the tank ventilation pipes are individually emptied into the atmosphere, testing each tank one by one.