Abstract:
A valve for dispensing water and air in installations for spraying water under pressure, includes: firstly, a body ( 2 ) equipped with two independent circuits (C 1 , C 2 ), each for circulating a fluid, one air, the other water, each of the circuits including (i) a chamber ( 5, 15 ) accommodating a shutter member ( 6, 16 ) in the form of a spool, (ii) a duct ( 7, 17 ) for admitting the fluid, (iii) a discharge duct ( 8, 18 ) for discharging the fluid, and (iv) a drain duct ( 9, 19 ) for draining the fluid contained in the discharge duct; and, secondly, control elements for controlling the shutter members so as to make each one move between an open position which allows the fluid to pass and in which the drain duct is shut off, and a closed position in which the fluid is prevented from passing and the drain duct is open.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a valve adapted to dispense water and air, and suitable for equipping installations for spraying water under pressure, in particular for making artificial snow. 
     2. Description of the Related Art 
     Current snow-making installations for making artificial snow incorporate much technological progress that has made it possible to improve their effectiveness and their efficiency by making better use of weather conditions. 
     This applies, in particular, to the spray devices equipping such snow-making installations, for making artificial snow, and that can operate at very different water and air flow-rates so as to take better advantage of weather conditions. 
     Such flow-rate regulation is usually implemented by means of valves adapted to dispense water and air, and that equip the feed circuits connected to such spray devices. 
     A valve of that type that is currently used in snow-making installations is described, for example, in Document FR-2 573 854. 
     That valve consists of a device in the form of a slide valve connected to the water and air feed pipes of the installation. A single cylindrical slide is driven to slide inside a chamber provided in the valve body, in order to control the water, air, and emptying flow-rates. 
     Although it is particularly advantageous and effective, that valve suffers from the drawback of having only a single emptying point provided in its water circuit downstream from the closure point. In very cold weather, any water present in the air circuit can then cause the spray device situated downstream to freeze. Another drawback is that water might leak into the air in the event of failure of the seals because the bore is common to both circuits. 
     Valves are also known that are of a universal type, adapted to dispense water, or possibly air, in installations for spraying water under pressure. 
     Such valves, e.g. as described in Document FR-2 795 494, are, in practice, effective and flexible in use, but they are relatively voluminous when they are combined, and they make it necessary for the water and air circuits to be managed independently, which is relatively complex. 
     In addition, that increases the number of control members and associated components, in particular hydraulic and electrical connectors, with ensuing economic consequences. 
     In addition, with the increase in the size of snow-making networks, new problems are arising:
         the air network can, in certain places, trap large quantities of water; that water can constitute a major risk of the snow-makers freezing; and   the water network can also contain air that might disturb the regulation of the valves.       

     Neither of the above-mentioned systems makes it possible in satisfactory manner to solve the problems relating both to bleeding the circuits, i.e. to purging the upstream circuits on opening the valve, and also to emptying, i.e. to removing the fluid contained in the downstream circuit on closing the valve. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is thus to propose a valve for dispensing water and air, which valve is of compact and inexpensive structure while also enabling the downstream fluid flow-rates to be controlled effectively. Another object of this valve is to allow the two circuits to be emptied and also preferably to allow them (in particular the air circuit) to be bled. 
     To this end, the valve of the invention is characterized in that it comprises: 
     firstly, a body provided with two independent circuits, each of which enables a respective fluid to flow through it, one air and the other water, each of which circuits includes: (i) a chamber in which a closure member in the form of a slide is received; (ii) a fluid inlet channel that enables the fluid to enter said body via an upstream orifice, and that is connected to said chamber via a downstream orifice; (iii) a fluid outlet channel that enables the fluid to exit, that is connected to said chamber via an upstream orifice, and that opens out from said body via a downstream orifice; and (iv) a channel in communication with said outlet channel or suitable for coming into communication therewith, provided with an upstream orifice and opening out (advantageously at the bottom end of the associated chamber) via a downstream orifice, in particular in order to enable the fluid contained in said outlet channel to be emptied; 
     and secondly, means for controlling said closure members as disposed and guided in their respective chambers, so as to cause each of them to go between:
         an open position, in which said inlet channel is in communication with said outlet channel via a through zone of said chamber, and in which said emptying channel is closed off; and   a closed position, in which said through zone (and advantageously the downstream orifice of the inlet channel and/or the upstream orifice of the outlet channel) is closed off by said associated closure member, and in which the emptying channel is open;       

     and in that said control means comprise—a single motor-drive unit for driving said closure members; and—a structure for mechanically coupling together the two closure members so as to ensure that said two closure members are driven simultaneously within their respective chambers. 
     In a particular embodiment, the motor-drive unit co-operates with one of the closure members, and the coupling structure mechanically interconnects the top ends of the two closure members so as to ensure that they are driven simultaneously. 
     According to another characteristic, the valve is structured so that the closure members are suitable for being driven into a configuration in which the closure member of the air circuit is situated in its open position while the closure member of the water circuit is in its closed position. 
     It is also structured so that driving the closure members into the open position makes it possible to regulate the flow rate and to control the pressure of at least one of the fluids. 
     According to another feature, the valve of the invention comprises a channel in its air circuit and/or a channel in its water circuit, which channel is suitable for co-operating with the closure member of the corresponding circuit to bleed water from the air or to bleed air from the water, as applicable, from the upstream pipes, before opening said air and/or water circuits. 
     Also according to another characteristic, the emptying channel for the air circuit is provided in the valve body, outside the volume of the associated chamber so that its upstream orifice opens out into the outlet channel of said air circuit, and so that its downstream orifice opens out at the bottom end of said chamber; and the closure member of said air circuit is drivable by the control means into an intermediate position, situated between the closed position and the open position, in which intermediate position firstly said inlet channel is in communication with the outlet channel via the through zone of the associated chamber and secondly the emptying channel is open, so as to make it possible, in particular, for the air circuit to be subjected to an active bleed operation on opening said air circuit. 
     According to another characteristic, the outlet channel of the air circuit comprises a baffle-forming portion, including a chamber in two portions, namely an upstream portion and a downstream portion, separated by a transverse partition provided with a through orifice offset upwards relative to the inlet orifice of said upstream portion, which downstream portion of the chamber is extended at the top via the downstream orifice of the air circuit and, at the bottom, is provided with the upstream orifice of the bleed/emptying channel. 
     This baffle-forming outlet channel of the air circuit offers the advantage of making it possible to separate out the condensates contained in the air. 
     In addition, the emptying channel of the water circuit is advantageously provided in the closure member of said water circuit, at its bottom end, which emptying channel comprises a downstream orifice opening out facing the bottom end of the associated chamber, and an upstream orifice opening out into the fluid through zone of said chamber, which emptying channel is opened or closed, depending on the position of said closure member, by means of a plug provided at the bottom end of said chamber. 
     Preferably, for the water circuit, the downstream orifice of the inlet channel is situated below the upstream orifice of the outlet channel; and for the air circuit, the downstream orifice of the inlet channel is situated above the upstream orifice of the outlet channel. 
     The present invention also provides a method of operating at least one valve for dispensing water and air, in installations for spraying water under pressure, e.g. with a view to making artificial snow, which valve or each of which valves comprises: 
     firstly, a body provided with said independent circuits, each of which enables a respective fluid to flow through it, one air and the other water, each of which circuits includes (i) a chamber in which a closure member in the form of a slide is received, (ii) a fluid inlet channel that enables the fluid to enter said body via an upstream orifice, and that is connected to said chamber via a downstream orifice, (iii) a fluid outlet channel that enables the fluid to exit, that is connected to said chamber via an upstream orifice, and that opens out from said body via a downstream orifice, and (iv) an emptying channel in communication with said outlet channel or suitable for coming into communication therewith, provided with an upstream orifice and opening out via a downstream orifice, in order to enable the fluid contained in said outlet channel to be emptied; 
     and secondly, means for controlling said closure members as disposed and guided in their respective chambers, so as to cause each of them to go between:
         an open position, in which said inlet channel is in communication with said outlet channel via a through zone of said chamber, and in which said emptying channel is closed off; and   a closed position, in which said through zone is closed off by said associated closure member, and in which the emptying channel is open;       

     said closure members of the air circuit and/or of the water circuit also being drivable into an intermediate position, situated between the closed position and the open position, in which intermediate position firstly said inlet channel is in communication with the outlet channel via said through zone of the associated chamber and secondly the emptying channel is open; 
     which method consists in implementing the following steps in succession, starting from a closed position for the two fluid circuits: 
     a) moving at least one of said closure members into the intermediate position so as to bleed the corresponding circuit; 
     b) moving the closure member of the air circuit only into the open position so as feed said circuit with air; and then 
     c) moving the closure member of the water circuit into the open position so as feed said circuit with water; 
     which steps are implemented in reverse order for returning said two closure members to the closed position when water and air cease to be supplied. 
     In a particular implementation, the closure members of the air circuit and of the water circuit are drivable into an intermediate position so as to bleed the two circuits; and said intermediate position of the closure member of the water circuit is then advantageously reached before the intermediate position of the closure member of the air circuit. 
     When the valve is structured so that the position of the closure members makes it possible to regulate the fluid flow rate and to control the fluid pressure, the position of the closure members in the open configuration, and the time for which said position is maintained, are advantageously dependent on the measured value of the fluid pressure and/or of the fluid flow rate, or on information delivered by a water presence sensor in the outlet channel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       The invention is further illustrated, without being limited in any way, by the following description of a particular embodiment given with reference to the accompanying drawings, in which: 
         FIG. 1  is an elevation view of a valve of the invention; 
         FIG. 2  is a view seen from above of the valve shown in  FIG. 1 ; 
         FIG. 3  is a section view of the valve of  FIGS. 1 and 2 , on a vertical section plane III-III of  FIG. 1  containing the axis of the closure member of the water circuit (shown in the open position); 
         FIG. 4  is a section view of the valve of  FIGS. 1 and 2 , on a vertical section plane IV-IV of  FIG. 1  containing the axis of the closure member of the air circuit (the closure member being shown in the open position); 
         FIG. 5  is a section view of the valve of  FIGS. 1 and 2 , on a vertical section plane V-V of  FIG. 2  containing the axes of the closure members of the water and air circuits (the closure members being shown in the closed position); 
         FIG. 6  is a fragmentary view on a slightly larger scale of  FIG. 5 , showing in detail the component elements of the water circuit; 
         FIG. 7  is a fragmentary view in detail of  FIG. 5 , showing the component elements of the air circuit; and 
         FIGS. 8 to 11  show how the corresponding moving parts are driven to cause the closure members of the air and water circuits to go from their closed position to their open position. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The valve  1  of the invention, as shown in general in  FIGS. 1 to 5 , is particularly suitable for equipping installations for spraying water under pressure, in particular snow-making installations (snow makers) with a view to making artificial snow. 
     In such snow-making installations, valves  1  are advantageously installed in shelters that are distributed along a ski run to be covered with snow, and each valve is suitable for connecting firstly to upstream supplies of air and water under pressure in the form of pipes disposed along the ski run and coming from a machine room containing pump and compressor units, and secondly to downstream pipes associated with the spray devices (e.g. in the form of snow guns). 
     This valve  1  comprises a body  2 , in the general shape of a compact parallelepiped block with control means  3  on top. 
     For example, the valve body  2  is made of aluminum; it is advantageously obtained by assembling together a plurality of molded portions. 
     This valve body  2  is provided with two independent circuits C 1 , C 2 , each of which is suitable for enabling a respective fluid to flow through it:
         a first circuit C 1 , shown in detail and in isolated manner in  FIG. 6 , enables pressurized water to flow through it; and   a second circuit C 2 , shown in detail and in isolated manner in  FIG. 7 , is designed to channel pressurized air.       

     In order to facilitate the description below, the terms “upstream” and “downstream” are used in relation to the normal flow direction of the fluids through the corresponding circuits C 1  and C 2 . 
     The water circuit C 1 , as shown in particular in  FIG. 6 , includes a chamber  5  that is specific to it, and in which a moving closure member  6  described in detail below is received and guided. 
     The chamber  5  consists of a through orifice that is cylindrical in general shape, that is provided over the height of the valve body  2 , and that is centered on an axis  5 ′. It has two axial ends  5   a  and  5   b  opening out respectively upwards and downwards when the valve  1  is operated. 
     This circuit C 1  also includes three channels  7 ,  8 , and  9  for channeling the water inside the chamber  5 :
         one channel  7  for water inlet or feed, defined by an upstream orifice  7   a  forming an inlet into the valve body  2  and by a downstream orifice  7   b  (in the form of a volute in this example) opening out into the chamber  5  ( FIGS. 3 and 6 );   one channel  8  for water outlet, defined by an upstream orifice  8   a  (in the form of a volute in this example) opening out into the chamber  5  ( FIGS. 3  and  6 ), and a downstream orifice  8   b  forming an outlet from said valve body  2 ; and   a channel  9  for emptying, defined by an upstream orifice  9   a  and by a downstream orifice  9   b , described in more detail below.       

     The upstream end  7   a  of the feed channel  7  is designed to be connected, in leaktight manner, to the general supply of the installation to be equipped (not shown); the downstream orifice  8   b  of the outlet channel  8  is connectable to the snow-maker, in leaktight manner, advantageously via a flexible hose. 
     The inlet channel  7  and the outlet channel  8  open out into the chamber  5  in such a manner that the downstream orifice  7   b  of the inlet channel  7  is situated below the upstream orifice  8   a  of the outlet channel  8 . This characteristic is advantageous, in particular, during emptying operations, as described below. 
     When it is not closed off by the closure member  6 , the intermediate portion  5   c  of the chamber  5  that extends between the two orifices  7   b  and  8   a  constitutes the water flow zone through which water flows inside the chamber  5  (in an upward direction in this example). 
     In order to optimize emptying of the downstream circuit by gravity, the axis  8 ′ of the outlet channel  8  is inclined upwards, going towards its outlet, e.g. at a slope of 45°. 
     The above-mentioned closure member  6  consists of an integrally formed elongate part forming a slide, and suitable for sliding longitudinally inside the chamber  5 . 
     In particular, this closure member  6  is made up of two cylindrical portions, one of which is a top portion  6   a  and the other is a bottom portion  6   b , the two portions being interconnected by an integrally formed central rod  6   c.    
     The two cylindrical portions  6   a  and  6   b  have the same diameter, corresponding, ignoring clearance, to the diameter of the guide chamber  5 . They are provided with O-ring seals for sealing the water circuit C 1 . 
     The rod  6   c  has a diameter of about one half of the diameter of the above-mentioned cylindrical portions  6   a  and  6   b.    
     Each of the top and bottom cylindrical portions  6   a ,  6   b  is guided in a portion of the chamber  5 , respectively in the vicinity of its top end  5   a  and in the vicinity of its bottom end  5   b.    
     In this example, the bottom cylindrical portion  6   b  of the closure member  6  is guided facing the downstream orifice  7   b  of the feed channel  7 , so as to form a kind of valve member and so as to regulate the flow rate of water exiting from the circuit C 1  at the outlet channel  8 . 
     This bottom cylindrical portion  6   b  of the closure member  6  is more precisely guided in a bushing or sleeve  10  mounted at the bottom end  5   b  of the chamber  5  (thus constituting its bottom end). 
     This sleeve  10  has a cylindrical tubular portion  10   a  that fits into the valve body  2 , over a portion of the height of the chamber  5 . 
     A bottom flange  10   b  makes it possible to fasten this sleeve  10  to the bottom portion of the valve body  2 ; the end-wall  10   c  of this sleeve  10  is also provided with orifices (not visible in the figures due to the section plane) that enable water to drain away during emptying as described in detail below. 
     The cylindrical bottom portion  6   b  of the closure member  6  has a frustoconical top end  6   b   1  converging going upwards. 
     This profile of varying section is designed to enable the flow-rate to be adjusted in co-operation with the profile  5   c  of the chamber  5 , and to enable the pressure to be controlled between the inlet channel  7  and the outlet channel  8 . 
     The emptying channel  9  is provided directly in the closure member  6 . 
     In this example, the emptying channel  9  is in the form of a bore provided in the bottom cylindrical portion  6   b  of the closure member  6 , and centered on the axis  6 ′ of said closure member. 
     Its upstream orifice  9   a  is situated in the vicinity of the top end  6   b   1  of the bottom cylindrical portion  6   b . It is in the form of a slanting duct that is connected to the chamber  5 . 
     Its downstream orifice  9   b  faces towards the emptying sleeve  10 , i.e. in the vicinity of the bottom end  5   b  of the chamber  5 . 
     The end-wall  10   c  of the sleeve  10  is provided with a plug  11 , in the form of a rod or of a finger, and that extends coaxially relative to the chamber  5 , to the closure member  6 , and to the emptying channel  9 . 
     This plug  11 , provided with an O-ring seal at its end (not shown in the figures), is designed to close off the emptying channel  9  when the closure member  6  is driven into the open position, as described below. Conversely, when the valve  1  is in the normal closure position, the plug  11  is separated from the channel  9 , thereby enabling the water circuit C 1  to be emptied automatically. 
     The air circuit C 2 , shown in isolation in  FIG. 7 , is similar to the water circuit C 1  as described above with reference to  FIGS. 5 and 6  (apart from its original bleed/emptying system). 
     In particular, a chamber  15  is to be found again, in which a closure member  16  is received and guided. 
     In this circuit too, the chamber  15  consists of a through orifice that is cylindrical in general shape, that is provided over the height of the valve body  2 , and that is centered on an axis  15 ′. 
     This chamber  15  has two open axial ends  15   a  and  15   b  designed to face respectively upwards and downwards when the valve  1  is operated. 
     The axes  5 ′ and  15 ′ of the two chambers  5  and  15  of the valve body  2  extend parallel to each other. 
     This circuit C 2  also includes three channels for channeling the air through its chamber  15 :
         one channel  17  for air inlet or feed, defined by an upstream orifice  17   a  forming an inlet into the valve body  2  and by a downstream orifice  17   b  (in the form of a volute in this example) opening out into the chamber  15 ;   one channel  18  for air outlet, defined by an upstream orifice  18   a  (in the form of a volute in this example) opening out into the chamber  15  ( FIG. 7 ), and a downstream orifice  18   b  forming an outlet from the valve body  2  ( FIGS. 2 and 7 ); and   a bleed/emptying channel  19 , also defined by an upstream orifice  19   a  and by a downstream orifice  19   b.          

     The upstream end  17   a  of the feed channel  17  is designed to be connected, in leaktight manner, to the general supply of the installation to be equipped (not shown); the downstream orifice  18   b  of the outlet channel  18  is connectable to the snow-maker, in leaktight manner, advantageously via a flexible hose. 
     The inlet channel  17  and the outlet channel  18  of the air circuit C 2  open out into the chamber  15  in such a manner that the downstream orifice  17   b  of the inlet channel  17  is situated above the upstream orifice  18   a  of the outlet channel  18 . 
     If it is not closed off by the closure member  16 , the intermediate portion  15   c  of the chamber  15  that extends between the two orifices  17   b  and  18   a  constitutes the air flow zone through which air flows inside the chamber  15  (in a downward direction in this example). 
     The outlet channel  18  extends approximately in a plane that extends perpendicularly to the plane defined by the axis of the chamber  15  and by the axis  17 ′ of the inlet channel  17 . 
     In addition, the inlet and outlet orifices  17   a  and  18   b  of the air circuit C 2  are situated on the same side of the valve body  2 , and they are centered on axes that extend in parallel vertical planes. 
     The outlet channel  18  of the air circuit C 2  is also specific in that it has a baffle-forming portion that is designed to separate out and to extract the condensates contained in the air. 
     For this purpose, the outlet channel  18  has a chamber  20  made up of two portions, namely an upstream portion  20   a  and a downstream portion  20   b  (defined relative to the normal direction of flow of air through the channel  18 ), separated by a transverse partition  20   c.    
     Each of these upstream and downstream portions  20   a  and  20   b  of the chamber  20  is of cylindrical general shape, and each of them is centered on a respective one of axes  20   a ′ and  20   b ′ that are parallel to each other and relative to the chamber axis  15 ′. 
     This chamber  20  is also provided with a set of orifices arranged suitably for modifying the direction of flow of the air; in particular, the transverse partition  20   c  is, in this example, provided with a transverse orifice  20   c   1  that is offset upwards relative to the inlet orifice  20   a   1  of the upstream portion  20   a . This inlet orifice  20   a   1  corresponds to the end of a small feed channel  18   c  that comes from the upstream orifice  18   a , the axis of this channel  18   c  extending perpendicularly to the axis  15 ′ of the chamber  15 . 
     In advantageous manner, these orifices  20   a   1  and  20   c   1  of the chamber  20  are centered on axes that are parallel to each other, and that are offset in height. In addition, these orifices  20   a   1  and  20   c   1  extend perpendicularly relative to the facing walls, which are respectively an upstream wall of the partition  20   c  and a downstream wall of the downstream chamber  20   b , this configuration making it possible to stop any micro-drops of water entrained by the air. 
     In addition, the downstream portion  20   b  of the chamber  20  comprises—a top orifice centered on the axis  20   b ′ of said downstream portion and that leads to the downstream orifice  18   b  of the outlet channel  18 , and—a bottom orifice, also centered on said axis  20   b ′ and that corresponds to the upstream orifice  19   a  of the bleed/emptying channel  19 . 
     Unlike the water circuit C 1  described above, the bleed/emptying channel  19  for the air circuit C 2  is provided directly in the valve body  2 , outside the volume of the associated cylindrical chamber  15 . 
     In this example, this bleed/emptying channel  19  is provided such that:
         its upstream orifice  19   a  opens out into the outlet channel  18  of the air circuit C 2 , as described above; and   its downstream orifice  19   b  opens out at the level of the bottom end  15   b  of the chamber  15 .       

     The closure member  16  of this air circuit C 2  is similar to the closure member  6  described above for the water circuit C 1 . It is in the form of a moving slide having two cylindrical portions  16   a  and  16   b  interconnected by an integrally formed rod  16   c.    
     The two cylindrical portions  16   a  and  16   b  have the same diameter, corresponding, ignoring clearance, to the diameter of the chamber  15 . They are also provided with O-ring seals for sealing the air circuit C 2 . 
     Each of these top and bottom cylindrical portions  16   a    16   b  is guided in a portion of the chamber  15 , respectively in the vicinity of its top end  15   a  and in the vicinity of its bottom end  15   b.    
     The rod  16   c  has a diameter corresponding to about one half of the diameter of the above-mentioned cylindrical portions  16   a  and  16   b.    
     The cylindrical bottom portion  16   b  of the closure member  16  constitutes a valve member designed to move at:
         the upstream orifice  18   a  of the outlet channel  18  so as to enable the flow rate to be adjusted and the pressure to be controlled, at the outlet of the circuit C 2 ; and   the downstream orifice  19   b  of the bleed/emptying channel  19 , so as to obtain the open position and the closed position thereof.       

     The profile of the top end of the bottom portion  16   b  of the closure member  16  may be of varying section so as to optimize the above-mentioned flow-rate adjustment and the above-mentioned pressure control. 
     In addition, the control means  3  of the valve  1  are structured so as to enable the two closure members  6  and  16  to be driven simultaneously or synchronously in their respective chambers  5  and  15 . 
     As shown, in particular in  FIG. 5 , it can be seen that, for this purpose, these control means  3  mainly include two elements:
         a single motor-drive unit  25  for driving the closure members  6  and  16 ; and   a structure  26  for mechanically coupling together the two closure members  6  and  16 .       

     The single motor-drive unit  25 , e.g. constituted by an electric motor and gearbox unit, is flange-coupled to the top face of the valve body  2  and it is protected by a cover structure. 
     This motor-drive unit  25  may be a variable-speed unit having position control (e.g. a motor and gearbox unit of the brushless type); it is associated with suitable driver means that are suitably configured (in particular, controlling the speed and the position can make it possible to manage the time taken for each phase of the sequence described below). 
     For operation purposes, the valve  1  is also advantageously equipped with various pressure sensors  27  that may be air or water pressure sensors. In this example, these pressure sensors are in communication with the feed channels  7  and  17 , and with the outlet channels  8  and  18  of the two circuits C 1  and C 2 . 
     The valve body  2  is also provided with orifices that enable the power and/or control wires to pass through. 
     This valve  1  is also provided with end-of-stroke devices associated with various components that enable it to operate and that enable parameters related to such operation to be collected. 
     The driver means may be programmed such that the positions of the closure members  6  and  16  are servo-controlled to the value of a measured physical magnitude, e.g. the water and/or air flow-rate and/or pressure, or the presence of water (as detected by a suitable sensor, e.g. inside the chamber  20 ). The time for which one of the positions (described below) is held can thus be dependent on the value of at least one of said measured physical magnitudes. 
     In the present embodiment, the motor member  25  drives a screw  28  in rotation about its axis, which screw  28  co-operates with a threaded internal bore  29  provided axially inside the cylindrical top portion  6   a  of the closure member  6  which, in this example, equips the water circuit C 1 . 
     The structure of the mechanical coupling  26 , between the two closure members  6  and  16 , consists of a kind of plate, secured by any suitable means (e.g. by screw-fastening) to the top ends of the component cylindrical portions  6   a  and  16   a  of the closure members  6  and  16 . 
     In this way, the stroke in translation applied to the closure member  6  of the water circuit C 1  by the motor-drive unit  25  corresponds, in this example, exactly and continuously to the stroke of the closure member  16  equipping the air circuit C 2 . Thus, given the structures of the valve body  2  and of closure members  6  and  16 , the air circuit is opened before the water circuit is opened. 
     In practice, and in accordance with the invention, the control means  3  cause the two closure members  6  and  16  to slide in their respective cylindrical chambers  5  and  15 , each closure member sliding between:
         an open position ( FIGS. 3 ,  4 , and  11 ), in which the inlet channels  7  and  17  are in communication with the associated channels  8  and  18 , via the intermediate chamber zones  5   c  and  15   c , and in which the emptying channels  9  and  19  are closed off; and   a closed position ( FIG. 5 ), in which the intermediate chamber zones  5   c  and  15   c  are closed off by the associated closure members  6  and  16 , and in which the outlet channels  8  and  18  are in communication with the respective open emptying channels  9  and  19 .       

     More precisely, in the closed position, as shown in  FIG. 5 , the closure members  6  and  16  of the two circuits C 1  and C 2  are in the high positions in their respective chambers  5  and  15 . 
     In this closed position, the water circuit C 1  and the air circuit C 2  are closed:
         the bottom cylindrical portion  6   b  of the closure member  6  of the water circuit C 1  closes off the downstream orifice  7   b  of the inlet channel  7 ; and   the bottom cylindrical portion  16   b  of the closure member  16  of the air circuit C 2  closes off the upstream orifice  18   a  of its outlet channel  18 .       

     Also in this closed position, the water of the installation downstream from the valve can flow merely by gravity through the emptying channel  9 , which is open (the plug  11  being out of the emptying channel  9 ), and can drain away via the orifices provided in the end-wall  10   c  of the sleeve  10 . 
     Similarly, the bottom end of the closure member  16  of the air circuit C 2  is situated above the downstream orifice  19   b  of the channel  19 , allowing any water present in the outlet channel  18  and in the installation downstream from the valve to drain away. 
     Starting from this closed position, in order to feed water and air to the installation downstream from the valve, the control means  3  drive the closure members  6  and  16  towards the bottom ends  5   b  and  15   b  of their respective chambers  5  and  15 . 
     Before the water circuit C 1  is opened, the particular structure of the valve  1  makes it possible to obtain various safety and start-up positions. 
     One of these positions makes it possible, in particular, for the air feed pipe to be actively bled, thereby, in particular, preventing any water present in this pipe from reaching the downstream spray device (the presence of water giving rise to a risk of freezing of certain portions of the spray device, in particular the nucleators). This action is optimized by the baffle shape of the outlet channel  18 . 
     Thus, as shown in  FIGS. 8 and 9 , the structure of the valve  1  allows the closure members  6  and  16  to be driven into a first intermediate configuration in which:
         the closure member  6  is still in a closure position in which the water circuit C 1  is closed; and   the closure member  16  of the air circuit C 2  takes up an “intermediate” position, situated between the closed and the open positions.       

     In this intermediate position, the air circuit C 2  has the following configuration:
         firstly the inlet channel  17  comes into communication with the outlet channel  18  via the intermediate chamber zone  15   c , which is at least partially opened up by the bottom portion  16   b  of the closure member  16  (the upstream orifice  18   a  of the outlet channel  18  is partially open); and   secondly, the downstream orifice  19   b  of the channel  19  remains in an open position (it is not closed off by the closure member  16 ).       

     The pressurized air, coming from the inlet channel  17 , then flows both towards the downstream orifice  18   b  of the outlet channel  18  and through the channel  19 ; and the air pipe downstream from the valve is bled. 
     Any water present in the air is removed actively via the channel  19  (hence this channel is referred to as the “bleed/emptying” channel). It is thus possible to avoid problems of the downstream spray devices being clogged with water in solid form. 
     The closure members  6  and  16  continuing to be driven towards their respective open positions leads to a second intermediate configuration, as shown in  FIG. 10 , and in which:
         the closure member  16  of the air circuit C 2  is still in its open position (with communication between the inlet channel  17  and the outlet channel  18  via the intermediate zone  15   c  of the chamber  15 ), but with a bleed/emptying channel  19  (and in particular its downstream end  19   b ) now closed off by the bottom cylindrical portion  16   b  of the closure member  16 ; and   the closure member  6  maintains the water circuit C 1  in its closed position.       

     Thus, the air circuit of the snow-maker is pressurized before the water arrives, thereby avoiding any water return via any mixing chambers. 
     Then, as shown in  FIG. 11 , the closure member  6  of the water circuit C 1  also reaches its open position in which its bottom cylindrical portion  6   b  opens up the downstream orifice  7   b  of the feed channel  7 . 
     In this position, and at the water circuit C 1 , the inlet channel  7  is in communication with the outlet channel  8  via the intermediate chamber zone  5   c , and the emptying channel  9  is closed off by the plug  11 . 
     When the feed to the spray devices needs to be interrupted, the closure members  6  and  16  are driven in the opposite direction, so as to cause them to return to the closed positions as shown in  FIG. 5 . 
     During this return to the closed position, the water circuit C 1  closes before the air circuit C 2 , thereby enabling cleaning to take place and enabling any water situated in the downstream spray device to be bled off. 
     In the closed final position, after operation, the two circuits C 1  and C 2  are automatically emptied, the water draining away by gravity through the respective channels  9  and  19  in the open position. 
     In a variant embodiment (not shown) the water circuit C 1  is equipped with an outlet channel identical or similar to the outlet channel equipping the air circuit C 2 . 
     An intermediate position of the closure member of the water circuit then makes it possible to bleed the upstream circuit, in particular for removing any air contained in the water, e.g. while the water pipe is being filled. 
     This intermediate position for bleeding the water circuit is advantageously reached before the air circuit bleed position, in particular so as to enable action to be taken on the upstream water circuit without consuming air. 
     These water and air bleed operations are followed by opening the air circuit and then by opening the water circuit (as described above). 
     Thus, the valve makes it possible to remove air contained in the water pipes and that might disturb the pressure regulation. 
     Such a valve makes it possible to limit the use of members dedicated to this air removal function; it is then necessary to provide appropriate control of the motor drive and of the sequences implemented. 
     In general, these bleed means on the water circuit may be provided independently of the presence of bleed means on the air circuit. 
     In addition, the bleed means on the air circuit and the bleed means on the water circuit may be provided independently of the channels for performing emptying (by means of dedicated orifices or channels provided in the valve body, co-operating appropriately with the associated closure member  6  and/or  16 ).