Abstract:
A liquid delivery apparatus includes a vessel having an inlet and an outlet, and a valve between the vessel and the outlet. The valve has an opening, a closure member for closing the opening, and a biasing means to hold the valve in a normally-closed position. A valve control mechanism controls operation of the valve in response to pressure of liquid and air in the vessel. A transmitting means transmits the pressure to the valve control mechanism. The valve control mechanism includes a moveable element that can be acted on by the pressure in the vessel and transmit a resultant force to the closure member to thereby open the valve. The respective effective surface areas of the moveable element and the closure member and the force of the biasing means are chosen such that the closure member is openable when the pressure in the vessel reaches a predetermined level.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a U.S. National Stage filing of Patent Cooperation Treaty (“PCT”) Patent Application No. PCT/GB01/02830, filed Jun. 26, 2001, which in turn claims priority to Great Britain patent application serial number GB0015992.1, filed in The United Kingdom on Jun. 29, 2000. 
   FIELD OF THE INVENTION 
   The present invention relates to a liquid delivery apparatus, such as a liquid delivery apparatus that is to be used for distributing liquid waste over agricultural land. 
   BACKGROUND 
   In European Patent No. 0548159 (and the corresponding U.S. Pat. No. 5,316,215), there is claimed a liquid delivery apparatus comprising 
   (i) a liquid reservoir into which a liquid may be introduced via an inlet to pressurise said liquid in the reservoir; 
   (ii) an outlet via which said liquid may be discharged from the reservoir under the pressure of the liquid in the reservoir; 
   (iii) a valve between the reservoir and the outlet to control passage of liquid from the reservoir to the outlet, said valve having (a) an opening, (b) a closure member adapted to close the opening, and (c) a biasing means, the arrangement of the components of the valve being such that the valve is normally held closed under the force of the biasing means and the pressure of the liquid in the reservoir; 
   (iv) a valve control mechanism for controlling the operation of the valve in response to the pressure of the liquid in the reservoir; and 
   (v) a means for transmitting the pressure in the reservoir to the valve control mechanism; 
   wherein the valve control mechanism comprises a moveable element which is capable of being acted on by the pressure of the liquid in the reservoir and transmitting a resultant force to the closure member of the valve in a direction to open the valve, and wherein the respective effective surface areas of the moveable element and the closure member and the force of the biasing means are chosen such that the closure member is openable when the pressure of the liquid in the reservoir reaches a predetermined level. 
   The liquid delivery apparatus disclosed in the aforesaid patents includes a housing and an inner moveable wall which sub-divides the housing into first and second chambers which are of variable volume depending upon the position of the inner moveable wall in the housing, the first chamber containing air as a compressible fluid and the second chamber defining the liquid reservoir, and the inner moveable wall being a flexible membrane such as a flexible bag. 
   SUMMARY 
   It has now been found according to one aspect of the present invention that the presence of an inner moveable wall (such as a flexible membrane) in the housing is not necessary. 
   According to one aspect of the present invention, there is provided a liquid delivery apparatus comprising 
   (i) a vessel into which a liquid may be introduced via an inlet to partially fill the vessel and to pressurise the liquid that partially fills the vessel and the air that fills the remainder of the vessel; 
   (ii) an outlet via which said liquid may be discharged from the vessel under the pressure of the liquid and air in the vessel; 
   (iii) a valve between the vessel and the outlet to control passage of liquid from the vessel to the outlet, said valve having (a) an opening, (b) a closure member adapted to close the opening, and (c) a biasing means, the arrangement of the components of the valve being such that the valve is normally held closed under the force of the biasing means and the pressure of the liquid and air in the vessel; 
   (iv) a valve control mechanism for controlling the operation of the valve in response to the pressure of the liquid and air in the vessel; and 
   (v) a means for transmitting the pressure of the air in the vessel to the valve control mechanism; 
   wherein the valve control mechanism comprises a moveable element which is capable of being acted on by the pressure of the air in the vessel and transmitting a resultant force to the closure member of the valve in a direction to open the valve, and wherein the respective effective surface areas of the moveable element and the closure member and the force of the biasing means are chosen such that the closure member is openable when the pressure of the liquid in the vessel reaches a predetermined level. 
   Thus, the apparatus according to the first aspect of the invention does not have, or need to have, an inner moveable wall in the housing. 
   However, it has been found, according to another aspect of the present invention, that the apparatus can be provided with a second vessel that includes an inner moveable wall (such as flexible member). 
   According to another aspect of the present invention, there is provided a liquid delivery apparatus comprising 
   (i) a first vessel into which a liquid may be introduced via an inlet to partially fill the first vessel and to pressurise the liquid that partially fills the first vessel and the air that fills the remainder of the first vessel; 
   (ii) an outlet via which said liquid may be discharged from the first vessel under the pressure of the liquid and air in the first vessel; 
   (iii) a valve between the first vessel and the outlet to control passage of liquid from the first vessel to the outlet, said valve having (a) an opening, (b) a closure member adapted to close the opening and (c) a biasing means, the arrangement of the components of the valve being such that the valve is normally held closed by the biasing means; 
   (iv) a valve control mechanism for controlling the operation of the valve in response to the pressure of the liquid and air in the first vessel; 
   (v) a means for transmitting the pressure of the liquid and air in the first vessel to a first chamber of a second vessel that includes an inner moveable wall which sub-divides the second vessel into said first chamber and a second chamber which are of variable volume depending upon the position of the said inner moveable wall in the vessel; and 
   (vi) a means for transmitting the pressure of the air in the second chamber of the second vessel to the valve control mechanism; 
   wherein the valve control mechanism comprises a moveable element which is capable of being acted on by the pressure of the air in the second chamber and transmitting a resultant force to the closure member of the valve in a direction to open the valve, and wherein the respective effective surface areas of the moveable element and the closure member and the force of the biasing means are chosen such that the closure member is opened when the pressure of the liquid and air in the first vessel reaches a predetermined level. 
   The vessel into which the liquid is introduced, or the first and/or second vessels, as the case may be, is normally a rigid vessel, but could be a non-rigid vessel (e.g. a flexible or resilient vessel) if it is such that the liquid introduced therein, and the air present therein, can be pressurised therein. 
   Preferably, the inlet includes an upright tube extending upwardly into the vessel or the first vessel. In this case, the height of the tube in the vessel determines the level of liquid remaining in the vessel after discharge. 
   Alternatively, a baffle plate is preferably disposed in the vessel or the first vessel, between the valve opening and the inlet, so as partially to subdivide the interior of the vessel or the first vessel into first and second compartments such that flow of liquid from one compartment to the other is possible. 
   The inlet to the vessel or the first vessel may include a non-return valve. 
   The moveable element of the valve control mechanism may comprise either a diaphragm in a pressure chamber or a bellows. In the latter case, the apparatus preferably includes means for varying the length of the bellows. 
   Preferably, the biassing means comprises a compression spring, and the apparatus includes means for varying the degree of compression of the compression spring. 
   Preferably, the means for transmitting the pressure to the valve control mechanism comprises either (a) a pressure line directly connecting the vessel to the pressure chamber containing the diaphragm or to the bellows, or (b) a first pressure line directly connecting the first vessel to the first chamber of the second vessel and a second pressure line directly connecting the second chamber of the second vessel to the pressure chamber containing the diaphragm or to the bellows. Preferably, a regulating tank is disposed in the pressure line, or in either of both of the first and second pressure lines. 
   The closure member of the valve is preferably one that is able to open in two or more stages in which the closure member has different effective surface areas such that the force required to open the valve is less in the second (or subsequent) stage than it is in the first (or previous) stage. 
   In another preferred embodiment, the diaphragm or the bellows is acted on directly by the pressure of the liquid introduced via the inlet. 
   The outlet via which the liquid may be discharged preferably comprises an upright rotatable discharge tube having one or more offset discharge nozzles connected thereto. A moveable flap may be mounted at the end of the discharge nozzle, or a moveable ball mounted in the discharge nozzle. 
   Preferably, the rotatable discharge tube has a rope or strap wound around it via which reciprocating movement of the rope or strap can cause or allow rotation of the discharge tube in a stepwise manner. 
   The rotatable discharge tube is preferably rotated by a drive mechanism that in turn is driven by a bellows that in turn is driven by pressure change. 
   The apparatus may further comprise a pump for pumping air into the vessel or the first vessel. 
   The invention will now be described, by way of example, with reference to the drawings in which: 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a view of a liquid delivery apparatus as already in use, in accordance with European Patent No. 0548159; 
       FIGS. 2  (and  2 A) and  3  show various improvements, in accordance with the present invention, in the apparatus shown in  FIG. 1 ; 
       FIGS. 4  (and  4 A,  4 B and  4 C) and  5  show other liquid delivery apparatus in accordance with the present invention; 
       FIGS. 6 and 7  show alternative valves for use in the apparatus shown in  FIGS. 2 to 5 ; 
       FIGS. 8 ,  9  and  10  show regulator valves for use in the apparatus shown in  FIGS. 2 to 5 ; 
       FIG. 11  shows a pump for use in the apparatus of  FIGS. 2 to 5 ; 
       FIG. 12  shows an apparatus for rotating the nozzle arm of the apparatus of  FIGS. 2 to 5 ; 
       FIG. 13  shows a flap that may be fitted at the end of the nozzle; and 
       FIG. 14  shows a modification of the nozzle itself. 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , there is shown an existing liquid delivery apparatus, as more fully disclosed in European Patent No. 0548159 (and U.S. Pat. No. 5,316,215). Liquid under pressure is fed via an inlet  1  to a chamber  2  and from there via a filter  3  to the interior of a rubber bag  4  disposed within a cylindrical pressure vessel  5 . The pressure within the bag  4  compresses the air in the annular space, around the bag, within the vessel  5 . The annular space is connected via an air line  6  and a diaphragm relief valve  7  to a chamber  8  containing an actuating member, i.e. a diaphragm, of a poppet valve  9 . Thus, the introduction of liquid under pressure into the bag  4  causes an increase in pressure in the chamber  8  until, at a given pressure, as more fully disclosed in the above patents, the poppet valve  9  opens for a brief period of time to allow liquid under pressure to enter a chamber  10  and from there to be discharged from a nozzle  11 . 
   The release of the pressure in the vessel  5  and in the chamber  8 , as a result of the opening of the poppet valve  9 , allows the poppet valve to close again, by the action of a compression spring  13 , and this cycle is then repeated upon the introduction of more liquid under pressure through the inlet  1 . 
   When the poppet valve  9  closes, the air in the chamber  8  returns via a non-return valve  12  to the air line  6 . 
     FIGS. 2 and 3  show a modification of the apparatus of  FIG. 1 . In this modification, in accordance with the present invention, the pressure vessel  5  does not contain the rubber bag  4 . Instead, a small slave accumulator  14 , containing a diaphragm or bag  15 , is disposed in the air line  6 . 
   In the case of the use of a diaphragm  15  (rather than the use of a bag  15 ), the diaphragm does not tend to scuff along the wall of the accumulator  14  (unlike the bag  4  in the vessel  5  of  FIG. 1 ). 
   Also, in place of the inlet filter  3 , there is provided a tube  16  ( FIGS. 2 and 2A ) mounted on a mounting plate or bar  17  extending across the inlet to the pressure vessel  5 , between the chamber  2  and the vessel  5 , leaving two semicircular gaps between the bar  17  and the wall of the inlet. 
   The tube  16  and the mounting plate or bar  17  are so dimensioned that a vortex is created to allow excess air to be bled from the vessel  5  into the chamber  2 . Thus, the rate of flow of liquid around the tube  16  has to be less than the rate of flow of liquid in the tube, so that a vortex is created around the top of the tube  16  so that, as the level of liquid falls in the vessel  5 , excess air is bled into the chamber  5  (i.e. the amount of air left in the vessel  5  upon discharge of the liquid). 
   The height of the tube  16  controls the level of liquid in the vessel  5 . 
   In accordance with another modification, as shown in  FIG. 4 , a fixed baffle plate  18 , containing a hole  19  or V-shaped slot  20  ( FIGS. 4A and 4B ), can be used to control the water level in the pressure vessel  5 . The plate  18  (also shown in  FIG. 5 ) has a sloping semicircular portion extending from the walls of the vessel  5 , and an upright rectangular portion extending downwardly from the sloping portion to leave a gap below it through which liquid can flow. 
   Furthermore, the inlet  1  can be in the form of a non-return valve. 
   Also, in accordance with another modification, also shown in  FIG. 4  (and also  FIG. 5 ), the air line  6  can be connected directly to the chamber  8  containing the poppet valve actuating diaphragm (or a bellows, that can be used in place of the diaphragm). Alternatively, the air line  6  can be connected to the chamber  8  via a small tank  21  ( FIG. 4C ). A restriction can be placed in the line leading to the chamber  8 , or in the line leading to the vessel  5 , to control the time for which the poppet valve  9  is open. Also, the restriction in the line leading to the chamber  8 , and the size of the tank  21 , can be varied to vary the speed of the opening and closing of the poppet valve  9  and the time for which it is open. 
     FIG. 5  shows on an enlarged scale the poppet valve  9  and the mechanism, in the form of a bellows  22 , for actuating the poppet valve  9 . As shown in  FIG. 5 , the bellows  22  and the compression spring  13  are held between plates  23  and  24  (the spring  13  itself being held on plate  53 ) which in turn are mounted on threaded bars  25  (three or four, usually) and held by nuts. By changing the distance between plates  23  and  24 , it is possible to change the opening and closing pressures of valve  9 , i.e. the higher the pressure on the spring  13  the higher are the opening and closing pressures of valve  9 . 
   The apparatus shown in  FIG. 1  has proven to be satisfactory in use, but needs to have its performance improved, and needs to be made easier to service and cheaper to build. Also, the rubber bag  5  used as the bladder has a tendency to fail. 
   The apparatus shown in  FIG. 2  is an improvement since the removal of the bag  4  from the vessel  5  increases reliability and the absence of the filter  3  increases flow and allows coarser materials to be handled. It is still necessary to use the diaphragm relief valve  7 , the non-return valve  12  and filters as on the apparatus of  FIG. 1 . 
   The valve opening pressure is controlled by the diaphragm relief valve  7 . If, for instance, the main valve  9  opens at 5 bar without the diaphragm relief valve  7 , then, to make the valve  9  run reliably, the diaphragm relief valve  7  needs to be set at 5.5 bar, i.e. at a point which is above the point at which the poppet valve  9  could shimmer. 
   The improvement shown in  FIG. 2  is one which could be retrofitted to the apparatus of  FIG. 1 . 
   The apparatus of  FIGS. 4 and 5  is preferred in that it has no air control gear and no bag  4  or  15 , since the opening pressure as well as the closing pressure of the poppet valve  9  are adjusted (or pre-set) on the valve itself. There are two methods of doing this, namely:
         (1) By adjusting the length of the spring  13  by moving the plate  23 , the opening and closing pressures change, i.e. the more pressure there is on the spring  13  the higher will be the opening and closing pressure of the poppet valve  9 .   (2) By adjusting the length of the bellows  22  by moving the plate  24 , the effective area of the bellows is changed, i.e. if the bellows is lengthened the effective area goes down and the valve opening and closing pressure goes up.       

   By a combination of the above and by changing the spring itself, most opening and closing pressures can be achieved. 
   It should be noted that changing the diameter of the bellows (or the diaphragm) and the poppet valve ratio also changes the valve opening and closing pressures. 
   The valves of the apparatus shown in  FIGS. 1 to 3  have the problem that the valves tend to shimmer on their seats and not to open clearly (if they were to be used without the regulator valve). 
   Referring to  FIG. 6 , there is shown an alternative poppet valve layout that can be used in place of the poppet valve shown in  FIGS. 1 to 3 . This valve has a closure member  26  mounted on a shaft  27  that is moveable by the action of the compression spring  13  ( FIG. 5 ) and the bellows  22  ( FIG. 5 ), or of the compression spring  13  and the poppet valve actuating diaphragm. 
   The closure member  26  has a first seal  30  and a second seal  31 . As the valve begins to open (i.e. as the closure member  26  moves to the left), the first seal  30  looses contact with its respective seat, whereas the second seal  31  remains in contact with its respective seat. Upon further opening, the second seal  31  looses contact with its respective seat. Thus, the geometry of the valve changes during its opening, in that the effective diameter of the valve (and hence the resistance to be overcome in opening the valve) changes from diameter D to diameter d. The valve therefore has a reduced tendency to shimmer. 
   Referring to  FIG. 7 , there is shown an alternative poppet valve layout that can be used in place of the poppet valve shown in  FIGS. 1 to 3 . This valve has a closure member  26  mounted on a shaft  27  that is moveable by the activation of a diaphragm  28  against the action of a compression spring  29 . The closure member  26 , like that of  FIG. 6 , has a two stage opening area, i.e. a first seal  30  and a second seal  31 , the first seal  30  being of larger diameter than the second seal  31  and the first seal  30  opening before the second seal  31  (as already described with reference to  FIG. 6 ). This again overcomes the problem of the valve shown in  FIGS. 1 to 3 , namely the problem that the valve tends to shimmer on its seat and not to open cleanly. 
   The valve seals  30  and  31  are preferably made of flexible rubber. 
   The valve of  FIG. 7  is driven by the pressure of the liquid under pressure that enters the inlet of the valve. This (increasing) pressure acts on the diaphragm  28  until the pressure is sufficient to overcome the force exerted on the diaphragm by the spring  29  and on the closure member  26  by the liquid. The valve then opens in two stages for a short period of time (by movement of the closure member  26  to the right), until the pressure falls to allow the diaphragm  28 , and the closure member  26 , to return to their original positions. 
   The valve can alternatively be driven by a separate supply of air under pressure. 
   One or more shims  32  can be located as shown to vary the pressure exerted by the spring  29  on the diaphragm  28 . 
   In an alternative embodiment, the diaphragm  28  can be replaced by a bellows. Furthermore, the shaft  27  and the diaphragm  28  (or bellows) can be replaced by a plunger, with the spring  29  being located within the plunger. The stoke of the bellows can be adjustable so as to vary the pressure at which the valve is activated, i.e. opens. 
   The reciprocal movement of the shaft  27  ( FIGS. 6 and 7 ) can be used to do work, for example to rotate the nozzle. The shaft  27  can also be used to mechanically hold the valve open or closed. 
   The purpose of the valves of  FIGS. 6 and 7  is to provide poppet valves that do not shimmer on their seats but rather open cleanly. Since there is no bag  4  in the tank  5 , any regulator valve in the air line  6  has to be able to deal with dirt. These regulator valves are described below with reference to  FIGS. 8 ,  9  and  10 . 
   The two-seal poppet valves of  FIGS. 6 and 7  open cleanly. However, if they were to be used with only seal  31  in position, the valves would sometimes open far enough to allow water to leak through but would not fully open. 
   In the case of the use of two seals, seal  30  opens but seal  31  remains closed (since it runs parallel to the valve shaft), and the pressure applied to surface  33  after seal  30  has opened makes sure that seal  31  opens. In other words, the effective areas of the two seals  30  and  31  are different, and seal  31  is well past its balance point by the time it is asked to open. 
   The two-seal valves shown in  FIGS. 6 and 7  overcome the problem of valve shimmering. However, this can be overcome by other means such as single rubber assembly. In its simplest form this can be a flexible part  70  able to flex so as to allow point  71  to open before point  72 . 
   It is possible to make a slight modification to seal  31  by cutting a groove (6 mm×2 mm) from point  73  to point  74  to release water trapped between the two seals  30  and  31  to allow them to close properly. 
   As already noted, a single seal valve gives rise to the problem that the single seal tends to shimmer. As an alternative way to solve this problem, a flap  75  can be fitted on the end of the nozzle  11  ( FIG. 1 ), as shown in  FIG. 13 , which also shows a pivot point  76 , a rubber seal  77  and a weight  78 . 
   Thus, any flap or steel ball mounted in the discharge tube could replace the two seal valve shown in  FIGS. 6 and 7 . 
   As mentioned above,  FIGS. 8 ,  9  and  10  show regulator valves for use in regulating the apparatus of  FIGS. 1 and 2 . In  FIGS. 8 and 9 , there are shown valves each having a diaphragm  34  on which impinges a jet of air from a nozzle  35 , the valves being adjustable by rotation of a threaded shaft  36  that varies the pressure applied on the diaphragm  34  by a coil spring  37 . 
   The valves shown in  FIGS. 8 ,  9  and  10  replace the pressure valve  50  (consisting of diaphragm  52  and spring  54 ) of  FIG. 3  of European Patent No. 0548159 (i.e. to replace valve  7  of  FIG. 1  herein). 
     FIG. 8  shows more detail of a first air regulation system. Part  51  is mounted so that face  52  comes into contact with plate  53  ( FIG. 5 ). When the main valve  9  closes, a gap forms at point  56  allowing spring  37  to close the regulator valve. Nozzle  35  is joined to air line  6  ( FIG. 5 ), and tube  54  is joined to the main tank  5  ( FIG. 4 ). 
   The mode of operation of the regulator valve is as follows. When the pressure in the tank  5  rises to a predetermined level, spring  37  allows plunger  55  to release diaphragm  34  allowing air to pass from the tank to the bellows on the valve head. As plate  53  ( FIG. 5 ) moves away from part  51  no spring pressure is exerted on plunger  55  giving free passage of air at point  56 . When the main valve  9  closes, gap  54  is reset ready for the next cycle. 
     FIG. 9  shows more detail of another air regulation system, which is not mechanically connected to main valve  9 . Tube  35  is joined to the main tank  5  ( FIG. 4 ). Tube  57  is joined to air line  6  ( FIG. 5 ), and tube  58  is joined to air line  6  (to equalise the pressure in chamber  59 ). 
   The mode of operation of this regulator valve is as follows. 
   When the pressure in tank  5  rises to a predetermined level, spring  37  allows plunger  60  to release diaphragm  34  allowing air to pass from the tank  5  to the bellows on the valve head. Also, after the diaphragm has opened, a greater surface area is exposed on the diaphragm face. Fluid in chamber  61  is forced into chamber  59  via an orifice  62 . As the pressure in the main tank  5  falls the closure of the regulator valve is delayed by the size of the orifice  62  and the viscosity of the fluid, as it returns to chamber  61 . 
     FIG. 10  shows more detail of a third air regulation system. The lever at point  63  is joined (usually by a spring) to plate  53 . Tube  64  is joined to air line  6  ( FIG. 5 ), and tube  65  is joined to the main tank  5  ( FIG. 4 ). 
   The mode of operation of this regulator valve is as follows. 
   When the pressure in tank  5  rises to a predetermined level, spring  66  allows plunger  67  to release diaphragm  34  allowing air to pass from the tank  5  to the bellows on the valve head. As the valve opens (because lever  68  is joined to the valve at plate  53 ), all the spring pressure is released between plunger  67  and jet  64  allowing free passage of air so as not to restrict debris. The regulator is held open by a damper  69  until the main valve has closed. 
   The arrangement of  FIG. 10  provides a more reliable mechanical coupling of the regulator to the main valve with a dampening system. 
   It would be possible to use a hand operated valve or tap to run on its own or in series with the above, so that a pulse of water could be controlled by hand, for fire fighting, etc. 
     FIG. 11  shows a diaphragm pump for pumping air into the pressure vessel  5 , and consisting of a diaphragm  38 , a spring  39 , and inlet valve  40 , an outlet valve  41 , and a non-return valve  42 . The diaphragm  38  separates the pump into chambers  43  and  44 , the latter chamber being in communication with chamber  10  of the apparatus, so that the operation of the poppet valve  9  causes the diaphragm pump to operate to pump air into the pressure vessel  5 . 
     FIG. 12  shows a mechanism for rotating the arm holding the nozzle  11 . An assembly  45  is arranged to rotate around column  46 , and a rope  47  is attached at points  48  to the rotating assembly  45 , is wound around the assembly  45 , and held tight by a spring  49 . 
   When the rotating assembly  45  is turned in the direction of arrow  50 , the rope  47  (or a strap) slides around the column  46 . When the assembly  45  is reversed, the rope  47  locks onto column  46  and rotates it. 
   Thus, reciprocating movement of the spring  49  causes the rope or strap  47  to grip, or not to grip, the column  46 , thereby causing or allowing stepwise rotation of the column  46 . 
   A diaphragm or bellows unit in communication with chamber  10  of the apparatus provides a reciprocating movement to the assembly  45 . The drive could also be taken from the tank side of the poppet valve  9 , as could the drive for the pump of  FIG. 11 . 
     FIG. 14  shows another modification, in that the (main) nozzle  11 , is provided with a second nozzle  80  at the end of a tube  81  connecting to the tube leading to the nozzle  11 . The object of the two nozzles is to wet the ground evenly from the furthest range right back to the machine. Although the liquid from the nozzle does fall back as the pressure falls there can be an area in the middle which does not get wet enough. The second nozzle  80  is sized to overcome this problem. There are two main adjustments, namely (1) the sizes of tube  81  and of nozzle  80  (coarse adjustment), and (2), the presence of a restrictor in the tube  81 , usually at point  82  (fine adjustment).