referring to fig1 , the numeral 10 generally designates a deck gun elevator of the present invention . deck gun elevator 10 is adapted to mount to the deck of a fire fighting apparatus and , further , adapted to mount a deck gun ( not shown ) to the deck . as will be more fully described below , elevator 10 raises and lowers the deck gun to adjust the range of the gun . elevator 10 includes an extensible tube or pipe 12 that is extended or retracted into an outer tube or pipe 14 by a control system 16 , which increases the range and coverage of the deck gun , as will be understood by those skilled in the art . extensible tube 12 includes an adapter 18 , which is adapted to mount the deck gun to the extensible tube 12 . referring to fig4 and 6 , adapter 18 comprises a cylindrical member 18 a with a projecting annular flange 18 b that inserts into the open end of extensible tube 12 and , further , is mounted to tube 12 , for example , with a threaded connection 18 e . optionally and preferably , an annular seal 18 c , such as an o - ring seal , is positioned between the shoulder 18 d of cylindrical member 18 a and the inner surface of extensible member 12 . as best seen in fig4 , the proximate end of outer tube 14 includes an inlet adapter 20 , which adapts elevator 10 to be mounted to the deck of the fire fighting apparatus . as best seen in fig5 , inlet adapter 20 comprises a cylindrical member with an annular flange 20 a for extending into the open end of outer tube 14 . annular flange 20 a is secured to outer tube 14 , for example , by a threaded connection and , further , includes one or more transverse passages 20 b for communicating with the chamber formed between extensible tube 12 and outer tube 14 , as will be more fully described below . positioned interiorly of outer tube 14 is an inner tube 22 , which is similarly mounted to inlet adapter 20 . for example , similar to outer tube 14 , inner tube 22 may be mounted to adapter 20 by a threaded connection 22 a . however , it can be appreciated , that tubes 14 and 22 may be fixedly mounted to adapter 20 , for example by welding . extensible tube 12 is mounted over inner tube 22 in outer tube 14 . as best seen in fig5 , extensible tube 12 includes mounted thereon a piston 24 that seals against the inner surface 14 b of outer tube 14 and , further , against the outer surface 22 b of inner tube 22 . for example , piston 24 may include one or more seals , such o - rings or u - rings , for sealingly engaging the respective inner and outer surfaces of outer tube 14 and inner tube 22 . in the illustrated embodiment , piston 24 comprises an annular member 24 a that is mounted on the proximate end of tube with an enlarged flange 24 b that projects radially inward over distal end 12 a of tube 12 . flange 24 b includes inner and outer annular grooves 24 c and 24 d , with seals 24 e and 24 f positioned in grooves 24 c and 24 d , respectively , for sealingly engaging inner surface 14 b of outer tube 14 and outer surface 22 b of inner tube 22 . as best seen in fig6 , an annular support collar 26 is mounted to distal end of outer tube 14 . support collar 26 supports a ring bearing 28 through which extensible tube 12 extends for extension and contraction from outer tube 14 . support 26 further includes an annular groove 26 a with annular seal 30 , such as a u - cup seal , positioned in groove 26 a for sealing against the outer surface of extensible tube 12 . in addition , support 26 includes a projecting flange 26 b that extends into open end of outer tube 14 and is mounted therein by a threaded connection . flange 26 b forms an annular shoulder 32 that extends radially inward from outer tube 14 toward outer surface of extensible tube 12 . in this manner , the space between outer tube 14 , extensible tube 12 , piston 24 , and shoulder 32 forms a first chamber 34 . similarly , the space between the shoulder 36 of inlet adapter 20 , outer tube 14 , and piston 24 ( and hence extensible member 12 ) defines a second chamber 38 between outer tube 14 , extensible tube 12 , and inner tube 22 . it can be appreciated , therefore , that the position of extensible tube 12 can be controlled by the pressure in chambers 38 and 34 . to limit the extension of extensible tube 12 through outer tube 14 , extensible tube 12 optionally includes a stop 39 , such as a retaining ring , which abuts shoulder 32 of support 26 to define the fully extended position of extensible tube 12 . a stop may alternately be formed on piston 24 . referring to fig7 , elevator 10 includes a control system 16 that controls the pressures in chambers 34 and 38 to control the extension and retraction of extensible tube 12 . control system 16 includes an actuator 40 that mounts exteriorly of outer tube 14 and that controls the pressure in chambers 34 and 38 to thereby control the extension and retraction of extensible tube 12 . as best understood from fig1 , actuator 40 includes a generally closed body 42 with a cavity 44 and a piston 45 that divides cavity 44 into first and second chambers 46 and 48 , which are respectively in fluid communication with the first and second chambers 34 and 38 defined between the extensible tube 12 and outer tube 14 . in the illustrated embodiment , chamber 46 is in fluid communication with chamber 34 through a valve 52 , preferably a pilot check valve , which permits the flow of fluid from chamber 46 into chamber 34 , but which normally restricts the flow of fluid from chamber 34 into chamber 46 , as will be more fully described below . chamber 48 is in selective fluid communication with second chamber 38 through one or more directional valves 54 and 56 . in the illustrated embodiment , chamber 48 is in fluid communication through valve 56 to an air system , such as a vehicle air system . valve 56 is normally open so that the air system maintains the pressure in chamber 48 to maintain the pressure in chambers 46 and 34 . the fluid communication between chamber 38 and chamber 48 is controlled by direction valve 54 , which is normally in a closed configuration until actuated . for example , valves 54 and 56 preferably comprise solenoid valves , which are actuated by a control circuit 58 . control circuit 58 includes a switch 60 , which is normally in an open position so that valves 54 and 56 are normally in a non - energized state until switch 60 is closed . as a result , extensible tube 12 is normally in a retracted position . when switch 60 is closed , solenoid valve 54 opens to permit fluid communication between chamber 48 and chamber 38 , which applies pressure to piston 24 and in turn which applies pressure to the fluid in chamber 34 . in addition , valve 54 is in fluid communication with valve 52 . when valve 54 is opened and pressure is applied to valve 52 , the flow of fluid through valve 52 is reversed from chamber 34 to chamber 46 . thus , when valve 54 is actuated , fluid can flow from chamber 46 to chamber 34 , which permits extensible tube 12 to be moved to an extended position . in preferred form , the fluid in chamber 34 and chamber 46 comprises an incompressible fluid , such as a hydraulic fluid , while the fluid in chambers 38 and 48 preferably comprise a compressible fluid , such as air . in this manner , control system 16 may provide an “ oil over air ” control for extensible tube 12 . the oil over air control of the position extendible tube 12 is particularly suitable in high water pressure applications where the flow of water through the respective passageways of outer tube 14 and extensible tube 12 would normally exert sufficient pressure to extend extensible tube 12 through outer tube 14 . since the fluid in chamber 34 is incompressible , despite the increase pressure due to the water flowing through passageway , extensible member 12 will not extend through outer tube 14 until the fluid in chamber 34 is discharged into actuator 40 , which only occurs when valve 54 is open . to return extensible member 12 to its retracted position , valve 54 is closed . when valve 54 closes , valve 52 will only permit the flow of fluid from chamber 46 to chamber 34 and the system pressure through valve 56 will increase the pressure in chamber 48 to thereby move piston 45 to urge the fluid in chamber 46 into chamber 34 to return extensible tube 12 to its retracted position , with the pressure in chamber 38 discharging through a vent 62 provided in valve 54 . referring again to fig1 - 13 , actuator 40 includes a cylindrical member 70 with end plates or caps 72 and 74 secured thereto to form closed body 42 . both end plates carry annular seals for sealing cavity 44 . as previously noted , positioned in cavity 44 is a piston 45 that divides cavity 44 into chambers 46 and 48 , with chamber 46 for communicating with chamber 34 and chamber 48 for communicating with chamber 38 . valve 52 is mounted to end plate 74 and is in communication with chamber 46 by a passage 78 formed in end plate 74 . valve 52 in turn communicates with chamber 34 through a passage or opening formed in outer tube 14 . valves 52 and 56 are similarly mount to end plate 74 , with valve 56 in communication with chamber 48 through a tube 80 that extends through end plate 74 and cavity 44 and through piston 45 . tube 80 includes a passage 84 and one or more openings 82 to provide fluid communication between chamber 48 and valve 56 . preferably piston 45 includes a seal such as an o - ring seal , for sealingly engaging the inner surface 70 a of cylinder 70 and a seal , such as an o - ring seal , for sealing against tube 80 . in this manner , actuator provides a compact modular assembly that can be quickly mounted to outer tube 14 of elevator 10 . it should be understood that a control system incorporating separate components may also be used . while one form of the invention has been shown and described , other forms will now be apparent to those skilled in the art . therefore , it will be understood that the embodiment shown in the drawings and described above are merely for illustrative purposes , and are not intended to limit the scope of the invention , which is defined by the claims , which follow as interpreted under the principles of patent law including the doctrine of equivalents .
a deck gun elevator includes a tubular base , with an inlet , a longitudinal axis , and a transverse passage extending along the longitudinal axis , and a tubular member in the transverse passage , which forms an annular space between the tubular base and the tubular member . the tubular member includes an outlet , a longitudinal axis , and a transverse passage , which is in communication with the transverse passage of the tubular base for directing the flow of water through the deck gun elevator . a piston is mounted on the tubular member and positioned in the annular space and defines a first chamber , which is formed between the tubular member and the tubular base , and a second chamber , which is formed between the tubular member and the tubular base . a control controls the flow of fluid into and out of the first and second chambers to control the position of the tubular member along the longitudinal axis of the tubular base .