GB1582584A - Vapour recovery in a liquid dispensing unit - Google Patents

Description

(54) VAPOR RECOVERY IN A LIQUID DISPENSING UNIT (71) I, JAMES WILLIAM HEALY, a Citizen of the United States of America, of 54 Plymouth Road, Wakefield, Massachusetts, United States of America, do hereby declare the invention for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to vapor recovery systems for preventing the escape of vapors to the atmosphere during the refilling of a volatile liquid container from a dispensing apparatus. In particular, this invention deals with a vapor recovery system for preventing the escape of hydrocarbon vapors from a vehicle's fuel tank during refueling from a service station's fuel dispensing unit.

A number of systems have been proposed for dealing with teh vapors displaced from a volatile liquid container while it is being refilled, such as the hydrocarbon vapors displaced from a vehicle's fuel tank during a refueling operation.

Previous vapor recovery systems for recovering hydrocarbon vapors from a vehicle's fuel tank have included passages in the dispensing nozzle for collecting vapors from the fuel tank, as well as a vapor return line for delivery of the collected vapors to the reservoir. Each of these prior systems, however, has suffered from one or more of various drawbacks.

Some of these systems have relied solely upon vapor pressure within the fuel tank to push the vapor through the vapor return line. Such systems required a large and cumbersome vapor return line to minimize resistance to vapor flow.

Additionally, when that return line became blocked by liquid (e.g., from fuel splash back or condensation), the vapor pressure developed in the vehicle fuel tank was usually insufficient to overcome the blockage. The result was vapor leakage to the atmosphere at the nozzle-fuel tank interface.

Other systems used for fuel dispensing have employed a vacuum-assist for drawing vapor through a vapor return line. To avoid the expense of a separate vacuum pump at each dispensing station, such systems have typically resorted to a powerful, continuouslyoperating blwo-type vacuum pump and a complicated arrangement of electrically actuated valves for connecting the various vapor return lines to the vacuum pump when the various pumps were actuated for dispensing. Acceptance of these systems has been minimal because of the expense and difficulty of both installation and maintenance. Additionally such systems typically draw such a large volume of ambient air, relative to the volume of fuel vapor,- that there is a danger of an explosive mixture being formed.

It has also been suggested that each dispensing unit include a vacuum pump driven by the dispensing unit's conventional meter and connected to a vapor return line.

However, the well-known fragility of such meters renders suspect the practicality of this suggestion.

Finally, some systems utilize a venturi injector as a vacuum source. Such injectors make inefficient use of the liquid power source.

According to the invention there is provided a system for dispensing volatile liquids, such as liquid fuels, from a reservoir the system comprising a hose having a vapor recovery dispensing nozzle at its outlet end, means for pumping the liquid under pressure through the hose for discharge through the nozzle into the inlet of a container such as a fuel tank, a liquid jet gas pump having its liquid inlet in communication with the pump for receipt of a portion of the liquid dispensed by the said pump in use of the system; and a vapor conduit having one end in said nozzle and adapted to be placed in communication with the interior of the container when said nozzle is inserted into said container inlet and the other end in communication with the vapor inlet of the jet pump, the outlet of said jet pump discliarging into said reservoir whereby vapor displaced from the container as it is filled in use of the system will be drawn off through said conduit by suction created by the passage of the liquid through the jet pump. Preferably the liquid jet gas pump comprises a housing having a liquid inlet in communication with the pump source of pressurized liquid so as to receive a portion thereof, and a vapor inlet which comnlullicates with the other end of the vapor conduit, a mixing tube fixed at one end to the housing and communicating with the interior thereof, and communicating at its other end with the reservoir, a surge chamber within the housing adjacent the mixing tube and communicating with the vapor conduit through said vapor inlet, a valve seat having a jet orifice and spaced within the housing adjacent the surge chamber, said jet orifice being positioned over the mixing tube and communicating therewith through the surge chamber, a passage within the housing communicating at one end with the fuel inlet and at the other end with the jet orifice, a pilot valve disposed within said passage, said pilot being biased to a closed posi tion against the valve seat in absence of a pre determined pressure within said passage, and a needle valve disposed within said passage over said jet orifice, said needle valve being biased to a first position in which delivery of liquid from said passage through said jet orifice is substantially unblocked and being arranged to move toward a second position which increasingly blocks the flow of fuel from said passage through the jet orifice as the vacuum level within the surge chamber increase to a predetermined maximum.

In preferred embodiments the vapor conduit comprises a second hose having a predetermined outer diameter less than the inner diameter of the first hose and disposed within the first hose; the second hose has an inner diameter of about 5/16 inch and an outer diameter of about inch; the vapor conduit has a predetermined degree diameter and the jet pump generates a predetermined degree of suction cooperating to produce a vapor velocity in the vapor conduit sufficient to entrain any liquid in the vapor conduit; the vapor conduit has an inner diameter of 5/16 inch and the jet pump generates a suction in the range of 16 to 20 inches of water.

Preferably also the nozzle comprises a body having a liquid conduit leading from the hose to a spout insertable into a volatile liquid container; a manually operable dispensing valve in the liquid conduit; a vapor shut-off valve in the vapor conduit, said vapor shut-off valve comprising a first diaphragm having a first surface facing the vapor conduit and a second surface facing a chamber within the nozzle, said first diaphragm causing the vapor conduit to be blocked when the diaphragm is in a first position and not to be blocked when the diaphragm is in a second position, and biasing means urging the first diaphragm to said first position; and valve opening means for urging the first diaphragm toward the second position only when liquid is flowing past the dispensing valve. This nozzle forms the specific subject matter of our copending Divisional Patent Application No. 31205/78. (Serial No. 1582585).

The nozzle preferably further includes a vapor regulator valve in said vapor conduit operable in response to a predetermined vapor pressure condition in said container; said vapor pressure regulator valve comprising a second diaphragm mounted in said nozzle with a first surface facing said first said diaphragm and a second surface facing said vapor conduit, said second diaphragm blocking said vapor conduit in a first position and not blocking said vapor conduit in a second position, and biasing means urging said second diaphragm to said second position, said nozzle further including a vent linking the region between said diaphragms with the ambient exterior of said nozzle.

In the later described exemplary embodiment a shroud member surrounds a portion of the nozzle spout and defines a portion of the vapor recovery conduit.

One feature of such a shroud is the provision of a magnetic disc as a portion of the shroud end plate, thereby assuring intimate contact of the end plate with the magnetically susceptible material which forms the mouth of the liquid container. The shroud may further include a substantially inextensible, forcetransmitting element extending between the end plate and the body of the nozzle, whereby the magnetic attraction between the end plate and the container mouth may help support the weight of the nozzle to prevent accidential displacement of the nozzle from the container.

Another desirable feature of such a shroud is the provision of one or more pressure relief valves integrally formed with the material of the shroud in order to relieve pressure differentials between the interior and exterior of the shroud.

Other advantages and features of the invention will be apparent from the following description and accompanying drawings of a preferred embodiment thereof.

In the drawings: FIGURE 1 is a schematic illustration of a fuel dispensing system, such as may be used at a filling station, incorporating features of the present invention; FIGURE 2 is a sectional view of a liquid jet gas pump as used in the fuel dispensing system; FIGURE 3 is a partially sectioned side elevation of a vapor recovery dispensing nozzle as used in the dispensing system; and FIGURE 4 is a sectional view taken along line 4-4 of Figure 3.

Turning now to the drawings, there is shown in Figure 1 a generally conventional gasoline dispensing system having an underground reservoir 10 containing a supply of gasoline 12 and a dispensing station comprising a pump housing 14 and a flexible fuel hose 16 extending between housing 14 and a vapor recovery dispensing nozzle 18. A conduit 20 supplies gasoline 12 from reservoir 10 to a fuel pump 22 disposed within housing 14. The fuel pump output is delivered, via conduit 24, to a conventional meter or computer 26 for measuring the amount of gasoline dispensed. Another conduit 28 delivers gasoline from meter 26 to a fitting 30 connected to flexible fuel hose 16.

A portion of the liquid fuel delivered by fuel pump 22 is fed by a conduit 32 to liquid get gas pump 34, the output of which is returned, by pipe 37, to reservoir 10. The suction side of liquid jet gas pump 34 communicates via conduit 38 and fitting 40 to a suction line in the form of a flexible vapor hose 42 disposed within the fuel hose 16. The hose 42 is connected to a vapor recovery dispensing nozzle 18 to receive vapors collected from a vehicle fuel tank being refueled through the nozzle.

For use in a conventional one inch (2.54 cm.) diameter fuel hose 16, hose 42 has a 5/16 inch (0.79 cm.) inner diameter and 1/2 inch (1.27 cm.) outer diameter. Hose 42 is formed from a material which will not be degraded by continuous immersion in gasoline over a wide range of temperature. Additionally, it must be sufficiently strong to withstand 20 to 30 psig (1406 to 2109 grams per sq. cm.) external pressure, which is typically developed within conventional hose 16, while conveying vapors internally at vacuum levels of approximately 16 to 20 inches of water.

One suitable material which achieves all the above requirements for the hose 42 is polyurethane tubing having dimensions as stated above.

Vapor hose 42, with the characteristics described above, will transmit one and one-half standard cubic feet of vapor per minute a distance of six teen feet at a velocity of approximately 2800 feet (853 meters) per minute with a pressure differential of approximately 16 to 20 inches (40.64 to 50.80 cm.) of water. This volume of vapor is substan tially equivalent to the volume of gasoline delivered to the vehicle fuel tank at a rate of about 11 U.S. gallons (41.6 liters) per minute. Thus, a suction line as described, along with a liquid jet gas pump 34 capable of developing a vacuum of 16 to 20 inches of water, can handle the vapor displaced in the vehicle fuel tank by the liquid gasoline entering at rates up to 11 gallons per minute. Further, the vapor velocities developed within vapor hose 42 (e.g., in the range of 1500 to 2800 feet per minute) are sufficient to break up and remove any liquid blocking the vapor hose, thus elim inating that problem.

Conventional gasoline pumps 22 have a pressure setting of approximately 20 psig and an internal liquid bypass system to accommodate variations in fueling rates from the extremes of no flow up to about 11 U.S. gallons per minute when the conventional fuel control valve within dispensing nozzle 18 is at a full open position. The conduit sizes and fluid resistance in the liquid channel defined by conduits 32 and 37 and jet pump 34 are chosen such that approximately 1 1/2 to 2 U.S. gallons (5.7 to 7.6 liters per minute of gasoline are consumed from the pump discharge. The jet pump is designed to generate the desired pressure differential of 16 to 20 inches of water using a liquid flow rate in the range of approximately 2 gallons per minute of liquid when pumping 11/2 cubic feet (0.042 cubic meters) per minute of a saturated air and hydrocarbon vapor mixture.

Referring to Figure 2, the vertically mounted liquid jet gas pump, indicated generally at 34, includes a housing 50 which comprises cover 51, upper body portion 52, and lower body portion 53--all secured by bolts 54. O-ring 56 provides a seal between the upper and lower body portions.

The housing has an interior passage 60 which communicates at its upper end with conduit 32 through liquid inlet 61, and at its lower end with surge chamber 64 through jet orifice 66 in pilot valve seat 62. Pilot valve seat 62 is sealingly positioned in passage 60 by o-rings 65.

Jet orifice 66 is coaxial with mixing tube 36 along central axis c and communicates therewith through surge chamber 64 adacent the lower end of housing 50.

Surge chamber 64 communicates at its upper end with vapor conduit 38 through vapor inlet 72.

A vapor pressure regulator diaphragm 74 is clamped around its periphery between cover 51 and upper body portion 52 to define on its opposite sides, together with cover 51 and upper body portion 52, upper and lower chambers 76 and 78 respectively.

Lower chamber 78 communicates with surge chamber 64 through bore 80. Upper chamber 76 is vented to the atmosphere through vent 81.

Needle rod 82 is connected at its upper end to disc 84 which is biased upwardly against diaphragm 74 by spring 86. The lower end of needle rod 82 passes through a central bore 83 in pilot valve 88, u-cup 98 providing a seal therebetween. The lower end of needle rod 82 is positioned above jet orifice 66--the needle rod 82, jet orifice 66, and mixing tube 36 being coaxially aligned along central axis c.

Pilot valve, 88 is positioned within passage 60 and is biased downwardly against valve seat 62 by spring 90, o-ring 92 providing a seal therebetween. U-cup 94 positioned adjacent the upper end of valve 88 provides a seal between the valve, lower chamber 78, and passage 60.

Referring to Figure 3, the dispensing nozzle includes a body 110, a spout assembly 112, and a spout shroud 114.

Body 110 comprises casting 116 having a liquid conduit 118 extending from fuel hose 16 to the spout. A conventional biased-closed fuel valve 122 is operated by a conventional manual fuel valve operator 124.

The spout assembly 112 includes spout 136, and a fitting 140 which secures the spout to the body casting 116. The shroud 114 includes a flexible bellows 142 surrounding the upper portion of the spout, an attachment portion 144 secured to the fitting 140, and an end plate 146 which includes an opening 148 communicating with the space between the bellows and the spout. End plate 146, which seals against the mouth of fuel tank fill pipe 150 when the spout is inserted into the fill pipe, also includes a disc magnet 152 (preferably, a ceramic-rare earth magnet having eight poles per face). The nozzle can be held in place in the fill pipe by a ring 154 which catches under the lip of the fill pipe mouth.

(Alternatively, a conventional spring wrapped around the lower spout segment could be used.) A series of relatiyely inextensible filaments 155 can be provided extending between the end plate and the attachment portion. When under tension, the filaments would serve to support part of the nozzle's weight by the magnetic attraction to the fill pipe. Naturally, a variety of other structures could perform the same function.

The shroud 114 also includes a resilient receptacle 156 which is integral with a shroud portion 158 adjacent the attachment portion 144 and which has an opening 160 for receiving a tube 162 in a leak-proof friction fit. In the preferred embodiment illustrated, the shroud 114 is molded as an integral unit from a resilient flexible material that is substantially unaffected by hydrocarbon liquid or vapors. One suitable material is urethane rubber. The shroud portions 144 and 158, as well as the receptacle 156 and the end plate 146, preferably have a greater wall thickness than the bellows portion 142. The thicker portions, of course, have functions which require somewhat greater rigidity, and somewhat less flexibility, that the bellows.

It is also preferred that the magnet 152 be completely encased in the material of which the shroud is formed in order to protect the magnet from damage and to eliminate the possibility of sparks which could develop if the magnet were to directly strike the fuel tank fill pipe 150. A shroud formed in this fashion is easily installed on existing conventional fuel dispensing nozzles.

The space between the shroud 114 and the spout 136 forms a channel for receiving vapors displaced from the fuel tank. Such vapors enter that space through the opening 148 and exit through a tube 162 which extends from the receptacle 156 through an opening in a cap assembly 164 of the nozzle to convey the vapors to a chamber 166 in the cap assembly.

The chamber 166, in turn, communicates with a passageway 168, also provided in the cap assembly. The passageway 168 leads to vapor hose 42. Preferably, tube 162, passageway 168, and vapor hose 42 have the same inner diameter (e.g., 5/16 inch) in order to provide a relatively uniform vapor flow conduit.

The cap assembly 164 comprises a stacked arrangement of parts which can be secured to the conventional nozzle body 116 by a series of screws (not shown) passing through all parts of the stack. The main structural elements of the cap assembly 164 are a body 172, spacer 174, and cap 176. The body 172 includes an opening 178 which receives the tube 162 and which communicates with the chamber 166 provided in the body 172. The passageway 168 in the body 172 terminates in an upwardly facing annular surface 180 which, as described below, forms a valve seat.

A vapor pressure regulator diaphragm 182 and a vapor shut-off diaphragm 184 are clamped around their peripheries between, respectively, the body 172 and spacer 174 and the spacer 174 and cap 176. In the rest configuration illustrated, the diaphragms 182, 184 are substantially parallel and are separated by a spacer disc 186, preferably formed from a closed cell foam rubber and having a thickness substantially equal to the thickness of spacer 174. A small opening 188 in the spacer 174 maintains the volume between the diaphragms 182 and 184 at atmospheric pressure. The cap 176 defines a chamber 190 above the shut-off diaphragm 184. A shut-off diaphragm biasing spring 192 is disposed in that chamber and biases the diaphragm 184 toward the diaphragm 182 and the valve seat 180. The regulator diaphragm 182 is biased upwardly by a spring 194 disposed around the valve seat 180 in the chamber 166. The biasing forces of springs 192 and 194 are chosen such that the force of spring 192 can overcome the force of spring 194. Aligned openings 196 and 198 in the spacer 174 and the cap 176 connect the chamber 190 with the conduit 138.

Referring to Figure 4, the srhoud portion 158 is provided with a pair of integral pressure relief valves 200,202. Each valve comprises a pair of adjacent flexible flaps 204, each integral with a biasing panel 206 that is, in turn, integral with the wall 158 at an opening 208 therein. As will be evident to those skilled in the art, valve 200 will permit air to enter the shroud to relieve an excessive vacuum and valve 202 will permit vapor to escape from the shroud to relieve excessive pressure. With tight seal of end plate 146 to the fill pipe 150, the valves serve as an additional protection against pressure extremes which could damage the vehicle fuel tank.

In operation, vapor recovery dispensing nozzle 18 is placed in the fuel tank of the vehicle to be refueled and fuel pump 22 is activated. A portion of the gasoline output of fuel pump 22 is delivered by conduit 32 to interior passage 60 of liquid jet gas pump 34.

Pilot valve 88 is initially biased downwardly by spring 90 against seat 62, o-ring 92 and u-cup 94 providing seals which prevent further flow of the gasoline and, therefore, cause the pressure of the gasoline within passage 60 to rise. Due to the differential sealing areas of ucup 94 and o-ring 92 (u-cup 94 providing a larger sealing area), the gasoline pressure produces a net upward force on valve 88 acting against spring 90. Spring 90 is sized to prevent upward movement of the pilot valve until the pressure within passage 60 exceeds 12 psig (844 grams per sq. cm.). At this threshold level, the pilot valve moves slightly upwardly, lifting o-ring 92 from seat 62 to break that seal, causing the pilot valve to pop upwardly to an open position due to the upward force provided by the gasoline pressure acting against the remaining net sealing area provided by u-cup 94 (the sealing area provided by u-cup 94 minus the sealing area provided by-u-cup 98). Once the pilot valve pops open, it will remain open until the pressure within passage 60 falls below approximately 5 psig (352 grams per sq. cm.), at which point the pressure acting against the net sealing area provided by u-cup 94 will be overcome by the downward force of spring 90 and the pilot valve will close. This operation of the pilot valve mades my jet pump system compatible with fuel dispensing systems which have detection equipment which monitor the system for leaks during an initial pressure buildup.

When pilot valve 88 opens, the gasoline within passage 60 flows through jet orifice 66, drawing vapor from conduit 38, through surge chamber 64, out mixing tube 36, and through pipe 37 into reservoir 10.

The vacuum produced by the liquid jet gas pump is regulated to a predetermined maximum. Upper chamber 76 is maintained at atmospheric pressure by vent 81. Lower chamber 78 communicates with surge chamber 64 through bore 80. As the vacuum level in surge chamber 64 and, therefore, lower chamber 78, increases, vapor pressure regulator diaphragm 74 will produce a downward force acting against spring 86. Spring 86 is sized to support a vacuum level of 16 to 20 inches of water.

Any increase of the vacuum above this threshold level will draw the diaphragm 7 downwardly against disc 84, moving needle rod 82 toward jet orifice 66, increasingly blocking the flow of gasoline through the jet orifice and hence decreasing the rate of withdrawal of vapor from and, therefore, the vacuum within surge chamber 64 and vapor conduit 38 until the predetermined maximum vacuum level is obtained.

For normal refueling rates (5 to 10 U.S.

gallons--18.9 to 37.8 liters--per minute), the vapor velocity in vapor hose 42 is sufficient (e.g., greater than 1500 feet per minute) to entrain any liquid therein and carry it out of the conduit. At lower refueling rates, the vapor will still percolate through any liquid in the vapor hose.

When the vapor flow from vapor control nozzle 18 and the fuel supply from fuel pump 22 are suddenly shut off, liquid remaining in mixing tube 36 will be drawn up into surge chamber 64 by the residual vacuum therein.

The volume of surge chamber 64 is large enough to hold the liquid remaining in the mixing tube--allowing it to drain out once the pressure has stabilized. This prevents liquid from surging into vapor conduit 38 during shutdown.

The dual function valving arrangement provided in the cap assembly 164 can best be described by considering the operation of the regulator diaphragm 182 absent the shut-off diaphragm 184, and then considering the constraints imposed by the presence of the shutoff diaphragm 184. The vapor pressure regulator diaphragm is biased away from the valve seat 180 (i.e., in a "valve open" configuration) by the spring 194. In this "normal" orientation the diaphragm 182, vapor is free to pass through the chamber 166, passageway 168, and vapor hose 42 to the jet pump 34.

Excessive vacuum levels beneath the diaphragm 182, however, can overcome the biasing force of spring 194 and cause the regulator valve to close (i.e., the diaphragm 182 to engage the valve seat 180).

It is very desirable, however, that the vapor conduit be sealed at all times when fuel is not being dispensed by the nozzle.

This is accomplished by the vapor shut-off diaphragm 184. As is illustrated in Figure 3, absent the flow of fuel through the nozzle, the spring 192 overcomes the force of spring 194 and its force is transmitted through diaphragm 184 and spacer disc 186 to force the diaphragm 182 against the valve seat 180. Thus, even if a suction is applied by jet pump 34 to vapor hose 42, air is prevented from being sucked into the vapor return system. When fuel is being dispensed, however, a slight vacuum is created in the chamber 190 above the shut-off diaphragm 184 by the venturi effect as fuel flows past the mouth of conduit 138. The suction is transmitted through conduits 138,196, and 198 to the chamber 190. Spring 192 is chosen to have the force such that the vacuum level produced in chamber 190 (e.g., about 2 to 3 inches [5.1 to 7.6 cm] of water), when acting upon the exposed surface of diaphragm 184, is sufficient to overcome the force of spring 192, thereby causing a compression of spring 192 and a movement of the diaphragm 184 away from the diaphragm 182.

When this occurs, of course, the regulator diaphragm 182 is free to act independently of the shut-off diaphragm 184 and to perform its regulatory function. An interruption in the flow of fuel causes the return of diaphragm 184 and spring 192 to the configuration shown in Figure 3, so that the operation of diaphragm 182 is overridden by the shut-off diaphragm 184.

As will be evident to those skilled in the art, the vapor shut-off valving arrangement shown in Figure 3 can be provided in a system where no vapor pressure regulator valve is required. In the socalled 'vapor balance' systems for example, there is no suction applied to the vapor hose 42 and no possibility of damage to the vehicle's fuel tank by excessive vacuum levels. The regulator valve is thus superfluous. It would still be desirable, however, to positively seal the vapor return conduit system when the nozzle is not in use in order to prevent air from entering that system. The vapor shut-off valve arrangement shown in Figure 3 would provide a simple and effective way of achieving this, with the diaphragm 184 engaging the valve seat 180 directly.

The cap assembly 164 which provides the vapor conduit valving arrangements can be provided as a replacement assembly for the conventional caps which enclose the full tank shut-off mechanism in existing fuel dispensing nozzles. Naturally, there may be modification of the cap assembly parts as illustrated in Figure 3 in order to accommodate slightly different structural features of existing nozzles and/or different vapor handling systems (e.g., with a 'vapor balance' system the diaphragm 182, spring 194, spacer 174, and spacer disc 186 could be eliminated). Similarly, the shroud 114 can be provided as an 'add-on' feature for existing nozzles.

Claims (28)

WHAT I CLAIM IS:

1. A system for dispensing volatile liquids, such as liquid fuels, from a reservoir, the system comprising a hose having a vapor recovery dispensing nozzle at its outlet end, means for pumping the liquid under pressure through the hose for discharge through the nozzle into the inlet of a container such as a fuel tank, a liquid jet gas pump having its liquid inlet in communication with the pump for receipt of a portion of the liquid dispensed by said pump in use of the system; and a vapor conduit having one end in said nozzle and adapted to be placed in communication with the interior of the container when said nozzle is inserted into said container inlet and the other end in communication with the vapor inlet of the jet pump, the outlet of said jet pump discharging into said reservoir whereby vapor displaced from the container as it is filled in use of the system will be drawn off through said conduit by suction created by the passage of the liquid through the jet pump.

2. A system according to claim 1, wherein the vapor conduit comprises a second hose having a predetermined outer diameter less than the inner diameter of the first hose and disposed within the first hose.

3. A system according to claim 2, wherein the second hose has an inner diameter of substantially 5/16 inch (0.79 cm.) and an outer diameter of sub stantially inch (1.27 cm.).

4. A system according to claim 1, 2 or 3, wherein the vapor conduit has a predetermined inner diameter and the liquid jet gas pump is arranged to generate a predetermined degree of suction such that the predetermined inner diameter and the predetermined degree of suction co-operate to produce a vapor velocity in the vapor conduit sufficient to entrain any liquid in the vapor conduit in use of the system.

5. A system accordnig to claim 4, wherein the vapor conduit has an inner diameter of substantially 5/16 inch (0.79 cm.) and the jet pump is arranged in use to generate a suction in the range of 16 to 20 inches (40 to 50 cm.) of water.

6. A system according to any preceding claim, wherein the liquid jet gas pump includes a pilot valve between the liquid inlet and the outlet of the gas pump.

7. A system according to claim 6, wherein said pilot valve is biased to a closed configuratoin in absence of a predetermined threshold pressure in the liquid inlet.

8. A system according to any preceding claim, wherein said liquid jet gas pump includes an interior liquid passage for conducting the liquid through the pump, and a needle valve provided in said passage, said needle valve being biased toward a first position in which delivery of liquid through said liquid passage is substantially unblocked, said needle valve being arranged to move in a direction toward a second position increasingly blocking the flow of fuel through said liquid passage as the vacuum produced by the suction in the vapor conduit increases toward a predetermined maximum.

9. A system as claimed in any one of claims 1 to 5, wherein the liquid jet gas pump comprises a housing having a liquid inlet in communication with the pump source of pressurized liquid so as to receive a portion thereof, and a vapor inlet which communicates with the other end of the vapor conduit, a mixing tube fixed at one end to the housing and communicating with the interior thereof, and communicating at its other end with the reservoir, a surge chamber within the housing adjacent the mixing tube and communicating with the vapor conduit through said vapor inlet, a valve seat having a jet orifice and spaced within the housing adjacent the surge chamber, said jet orifice being positioned over the mixing tube and communicating therewith through the surge chamber, a passage within the housing communicating at one end with the fuel inlet and at the other end with the jet orifice, a pilot valve disposed within said passage, said pilot valve being biased to a closed position against the valve seat in absence of a predetermined pressure within said passage, and a needle valve disposed within said passage over said jet orifice, said needle valve being biased to a first position in which delivery of liquid from said passage through said jet orifice is substantially unlocked and being arranged to move toward a second position which increas ingly blocks the flow of fuel from said passage through the jet orifice as the vacuum level within the surge chamber increases to a predetermined maximum.

10. A system as claimed in any preceding claim, wherein the nozzle comprises a body having a liquid conduit leading from the hose to a spout insertable into a volatile liquid container; a manually operable dispensing valve in the liquid conduit; a vapor shut-off valve in the vapor conduit, said vapor shut-off valve comprising a first diaphragm having a first surface facing the vapor conduit and a second surface facing a chamber within the nozzle, said first diaphragm causing the vapor conduit to be blocked when the diaphragm is in a first position and not to be blocked when the diaphragm is in a second position, and biasing means urging the first diaphragm to said first position; and valve opening means for urging the first diaphragm toward the second position only when liquid is flowing past the dispensing valve.

11. A system according to claim 10, wherein said biasing means comprise a spring disposed in said chamber.

12. A system according to claim 10 or 11, wherein said valve opening means comprise a conduit so extending between said chamber and a portion of the liquid conduit that liquid flow in the liquid conduit will produce a reduced pressure in said chamber.

13. A system according to claim 12, wherein the conduit comprising said valve opening means communicates with said liquid conduit substantially at the location of the dispensing valve.

14. A system according to any one of claims 10 to 13, further including a vapor regulator valve in said vapor conduit operable in response to a predetermined vapor pressure condition in said container, said vapor pressure regulator valve comprising a second diaphragm mounted in said nozzle with a first surface facing said ifstr said diaphragm and a second surface facing said vapor conduit, said second diaphragm blocking said vapor conduit in a first position and not blocking said vapor conduit in a second position, and biasing means urging said second diaphragm to said second position, said nozzle further including a vent linking the region between said diaphragms with the ambient exterior of said nozzle.

15. A system according to claim 14, wherein said biasing means for each said diaphragm each comprise a spring, the spring biasing said second diaphragm having a lower biasing force than the spring that biases said first diaphragm, thereby enabling said shut-off valve to cause blockage of said vapor conduit in the absence of liquid flow in said liquid conduit but enabling independent operation of said vapor pressure regulator valve in response to pressure conditions in said container when liquid is flowing in said liquid conduit.

16. A system according to claim 15, wherein the spring that biases said first diaphragm has a biasing force which can be overcome by a vacuum level in the range of from two to three inches of water in the chamber.

17. A system according to claim 14, 15 or 16, wherein said first and second diaphragms are mounted to be substantially parallel when said first diaphragm is in said first position.

18. A system according to claim 17, wherein said first and second diaphragms are spaced apart with the nozzle including a spacer disc intermediate the first and second diaphragms.

19. A system according to claim 18, wherein said spacer disc is formed from a closed-cell foam rubber.

20. A system according to any preceding claim, wherein a flexible enclosure is provided spaced apart from and encircling said spout at the end thereof adjacent the nozzle body.

21. A system according to claim 20, wherein the flexible enclosure terminates in an end plate disposed to engage the container mouth when said spout is inserted into the container, said flexible enclosure comprising an attachment portion for securing it to said nozzle, said end plate comprising a magnetic material, thereby enabling positive contact of said end plate with said tank mouth to prevent the escape to the ambient of vapors from said tank, the shroud comprising a member secured to said attachment portion and to said end plate and having a length along said spout such that said member is taut when said end plate engages said fuel tank mouth.

22. A system according to claim 20 or 21, wherein a pressure relief valve is provided in the flexible enclosure for altering the pressure in the vapor conduit when it deviates by more than a predetermined amount from the ambient pressure exterior of the flexible enclosure, said pressure relief valve comprising an opening in a wall of the flexible enclosure, a pair of flexible flaps in face-to-face contact with each other when the pressure within said vapor conduit deviates from said ambient pressure by no more than said predetermined amount, and flap biasing panels urging said flaps together and being sealed around the edges of said opening.

23. A system according to claim 22, wherein said wall of said flexible enclosure, said flexible flaps, and said flaps biasing panels are formed integrally from a flexible material.

24. A system according to claim 22 or 23, wherein said flaps are provided interiorly of said vapor conduit, whereby said pressure relief valve is a negative pressure relief valve enabling the relief of excessive vacuum conditions within said vapor conduit.

25. A system according to claim 22, 23 or 24, wherein said flaps are provided exteriorly of said vapor conduit, whereby said pressure relief valve is a positive pressure relief valve enabling relief of excessive over-pressure conditions within said vapor conduit.

26. A system according to any one of claims 22 to 25, wherein said flap biasing panels abut along lines of contact with their respective flexible flaps, the panels together forming an acute angle.

27. A system according to claim 26, wherein said acute angle is approximately 300.

28. A system for dispensing volatile liquids constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.