referring to fig1 - 4 , the water driven fan means shown therein is indicated generally at 10 and comprises a water powered turbine 12 constructed and arranged to drive a fan 14 by way of a common shaft 16 . turbine 12 is of a conventional construction and comprises a runner 20 mounted on and keyed to one end of shaft 16 to rotate within the interior of the turbine body 22 , which is provided with an inlet 24 and an outlet 26 for directing the water into and out of body 22 . shaft 16 is rotatably supported at a medial portion by a pair of bearings 30 contained in housing 32 . fan 14 comprises a hub or rotor 34 mounted on and keyed to the other end of shaft 16 by an arrangement shown in fig3 . the arrangement using the common shaft 16 eliminates the cost and other problems of providing a coupling between the turbine 12 and the fan 14 . hub 34 has five variable pitch fan blades 36 mounted thereon at their base 37 so as to extend radially outwardly from the axis of shaft 16 on an angle of about 35 ° as shown in the drawings . the fan blades 36 are contained within a shroud 38 and are enclosed by a pair of fan guards 40 formed from an open wire - like configuration as is shown in the drawings . as shown in fig3 shroud 38 has a special shape whereby the air flow entering the fan 14 is smoothly accelerated and the air flow leaving the fan 14 is subjected to further acceleration to improve the control of the direction of the air flow . to this end , in the direction of air flow through fan 14 , the entry portion 71 of shroud 38 is formed to converge gradually , the medial portion 72 of shroud 38 is generally cylindrical , and the exit portion 73 of shroud 38 , starting from the location where the air leaves the edges of the fan blades 36 on their outer diameter , converges in a nozzle shape . the diameter of exit portion 73 at its downstream end 74 is equal to or less than the outer diameter of the blades 36 as is shown in fig3 . by this arrangement , the air is smoothly accelerated as it comes into the fan 14 and it is subject to further acceleration by the nozzle shape for improving the directional control of the air flow . this acceleration of the air flow reduces some of the vortexes in the air flow through fan 14 and provides a smooth flow of the air delivered from the fan 14 so that the fan 14 becomes more directional . accordingly , the firefighter can direct the air flow more accurately toward a window , a door , or whatever , as is appropriate for the positive pressure ventilation procedure being utilized . a typical fan means 10 in accordance with the invention comprises a 20 horsepower water turbine 12 operating at 1750 - 2000 rpm with a fan 14 having a 30 inch diameter . fan means 10 is made of a lightweight construction . to this end , turbine 12 is made of lightweight cast aluminum , shroud 38 is made of a lightweight spun aluminum , and fan blades 36 are made of a strong lightweight material including &# 34 ; kevlar &# 34 ; which is an aramid fiber made by dupont company . in the operation of the water driven fan means 10 , water under pressure is supplied through a supply line 42 to the inlet 24 of turbine 12 which directs the water to cause rotation of runner 20 and the shaft 16 keyed thereto , with the water being discharged from turbine 12 through outlet 26 . the operation of water driven turbine 12 to drive shaft 16 is entirely conventional . fan 14 is driven by the rotating common drive shaft 16 to blow air under positive pressure by the action of rotating blades 36 which direct the air along the axis of shaft 16 . referring to fig5 - 8 , there is shown the water driven fan system in accordance with the invention as it is hooked up for using positive pressure ventilation for the fighting of fires . the system includes a flow control valve 50 movable between a first flow control position shown in fig5 ( the off position ), a second flow control position shown in fig6 ( the fan position ), a third flow control position shown in fig7 ( the fan and mist position ), and a fourth flow control position shown in fig8 ( the nozzle position ). a water supply line 52 is connected from a pressurized supply source to an inlet port 54 of valve 50 . supply line 52 has a source shut - off valve 53 connected therein to control flow therethrough . typically , the pressurized supply source is a fire pump located on a fire truck and having its suction connected to a tank of water on the fire truck . valve 50 is provided with three outlet ports 56 , 57 and 58 and a rotatable valve member 51 containing a flow passage as is shown in the drawings . outlet port 56 is connected to a fire hose nozzle 60 by way of a flow line 61 . outlet port 57 is connected to the inlet 24 of turbine 12 by line 42 as described above . outlet port 58 is connected to a plurality of small mist nozzles 64 by way of a flow line 63 . mist nozzles 64 are constructed to discharge small water spray at a location adjacent the upstream side of the fan blades 36 . the outlet 26 of turbine 12 is connected back to the water supply source ( ie ., the water tank on the fire truck ) by way of flow line 44 . alternatively , flow line 42 may be connected to dump the water into a sewer if this is more convenient . as is apparent from a consideration of fig5 - 8 , the fan system of the invention can be converted between an off position and three different operating positions . in the off position shown in fig5 valve member 51 is positioned to block flow from the inlet port 54 to any of the outlet ports 56 , 57 or 58 , whereby there will be no flow of water through any of the flow lines 61 , 42 or 63 connected to valve 50 . in the fan position shown in fig6 valve member 51 is positioned to provide flow communication between inlet port 54 and outlet port 57 . in this operating position , the source shut - off valve 53 , when it is moved to an open position , allows water under pressure to be delivered through line 52 , flow control valve 50 and line 42 to the inlet of turbine 12 which causes the runner 20 to rotate and causes operation of fan 14 through the common shaft 16 whereby fan blades 36 direct an air stream in the direction of the arrowed lines shown in fig6 . by the proper positioning of fan 14 , the firefighters can fight a fire by positive pressure ventilation by directing an air stream into a building and providing an outlet on the other side of the fire so that smoke is discharged from the building resulting in the cooling of the fire area . in the fan and mist position shown in fig7 valve member 51 of valve 50 is positioned to provide flow communication between inlet 54 and both the outlet ports 57 and 58 . in this position , water under pressure is directed through line 42 to operate the turbine 12 and fan 14 as described above with respect to fig6 and also through line 63 to the mist nozzles 64 which direct a small spray of water to the back of fan blades 36 . in this position , as shown in fig6 both a small mist of water and a strong clear air stream can be directed onto the fire to both cool the fire and blow smoke away from the fire area by the use of the positive pressure ventilation technique . in the nozzle position shown in fig8 valve member 51 of valve 50 is positioned to provide flow communication between inlet 54 and outlet port 56 . in this position , water under pressure is delivered through line 61 to the nozzle 60 which can be used by the firefighter to direct a straight fire stream onto the fire at a desired time in the firefighting procedure as described . while there has been show and described what is considered a preferred form of the invention , it will be understood that obvious changes in form can be made without departing from the spirit of the invention and it is therefore intended that the invention be not limited to precise forms herein shown and described and that the invention is to be construed broadly and restricted by the following appended claims . for example , the mist nozzles may be provided with a separate water supply line as shown in the drawings or may be arranged on the turbine body to receive flow directly from the interior of the turbine and the flow control valve means may include a separate valve for controlling the flow of water supplying the mist nozzles . furthermore , the fire nozzle 60 may be a separate nozzle as shown in the drawings or it may be arranged to direct its fire stream from the middle of the fan means 10 .