turning first to fig1 there is illustrated the cross sectional view of the basement and foundation of a typical building . there is a concrete wall 10 which forms the foundation of the house and is embedded in a footing 12 at its bottommost portion . the earth 14 is against the outer surface of the concrete wall 10 . on the opposite side of the concrete wall 10 is a basement 16 . a basement floor 18 is generally made from concrete . beneath the building is a residential building sewage pipe 20 which is normally 4 &# 34 ; or 6 &# 34 ; in diameter . this leads into a municipal or outside sewage pipe 22 which is connected to the municipal sewage system . extending vertically from the building sewage pipe 20 is a stand pipe or clean out tee 24 which intersects the building sewage pipe 20 at its bottommost portion and extends up through the floor 18 . the stand pipe is to allow access to the outside sewage pipe 22 should it become clogged with debris , tree roots , or other foreign matter . a router can be snaked through the stand pipe 24 and into the outside sewage pipe 22 to remove this clogging debris thereby permitting free passage of the sewage from the building into the municipal sewage system . the inventive pneumatic valve system 26 is installed in the stand pipe 24 as will be described more fully when describing the other figures . a control box 28 is mounted on the wall and contains the controls and air compressor for the pneumatic valve 26 . the components of the pneumatic valve 26 can be clearly seen in fig2 . at the top of the stand pipe 24 and approximate the top surface of the basement floor 18 is a threaded insert 30 which is integral with the stand pipe 24 . a threaded cap 32 is received by the threaded insert 30 to be firmly held in place thereby . an air cylinder 34 is mounted to the threaded cap 32 by means of a bolt 36 passing centrally through the threaded cap 34 and through the central end portion of the air cylinder 34 . the bolt 36 has a hex head 38 at its top portion and a similar fastening nut 40 which is placed internally in the air cylinder 34 . the bolt 36 has a hollow central passageway along its long axis and is connected to an air hose 42 at the hex head 38 . thus , air passing through the air hose 42 will pass through the bolt 36 and into the air cylinder 34 . within the air cylinder 34 is a piston 44 which is free to move up and down . a spring 45 tends to push the piston 44 towards the top of the air cylinder 34 . a piston rod 46 is connected at one of its ends to the piston 44 and has its opposite end extending through a front end 48 of the air cylinder 34 . a connector tee 50 is fastened to the end of the piston rod 46 which extends through the front end 48 . opposite the connection of the piston rod 46 to the tee 50 is a rubber bladder 52 which is connected to the tee 50 by means of a fluid coupling 54 . also affixed to the connector tee 50 is a second air line 56 which is fluidly coupled to the connector tee 50 such that air passing through the second air line 56 will pass through the connector tee 50 , into the fluid coupling 54 and into the rubber bladder 52 . no fluid connection is made between the connector tee 50 and the piston rod 46 . the second air line 56 passes through a passageway 59 in the threaded cap 32 which is large enough to permit the air line 56 to freely slide without binding or catching on the cap 32 . a fluid probe 58 is connected to the wall of the air cylinder 34 and is positioned along the cylinder wall 34 so that it senses fluid at a predetermined height in the stand pipe 24 . a mounting bracket 60 or a similar device is used to connect the probe 58 to the air cylinder 34 . during normal sewage flow , the sewage from the building flows through building sewage pipe 20 in the direction indicated by arrow a . during normal operations of the sewage system , the water is wholly within the pipes 20 , 22 and the stand pipe 24 is empty of all fluid . thus , the probe 58 does not sense the presence of liquid . during times of heavy rains or conditions giving rise to flooding in the sewage system , the municipal treatment of sewage and rain water is at times insufficient to accommodate the rapid rise of water and sewage levels in the sewage system . thus , a back flow of sewage is experienced as illustrated by the arrows b . this causes fluid and sewage to back up into the stand pipe 24 as illustrated in fig2 . as the back flow fills the stand pipe 24 it reaches the probe 58 . this causes the probe 58 to send a signal to the control system . the operation of the pneumatic valve 26 can be most clearly illustrated by looking at the schematic drawing illustrated in fig4 in conjunction with the graphic representation of fig3 . as seen on fig4 there is a power line 62 and a neutral 64 . normally this would be 110 volts ac to power the system . there is a ground wire 66 also part of the electrical system . a master switch 68 is connected in the power line 62 and is closed when the system is ready for operation . a visual indication such as indicating light 70 goes on to indicate that power is now on in the system . connected to the line 62 is a dropping resister 72 of approximately 5k ohms and connected thereto is a diode 74 and a capacitor 76 . this provides the direct current necessary to operate a dc coil 78 in a control relay 80 . as the probe 58 senses liquid , it goes to ground thereby completing the circuit energizing the coil 78 . this closes a seal in contact 82 within the relay 80 which will then maintain the coil 78 in its energized condition regardless of whether the probe senses liquid or not . a second contact 84 within the relay 80 also closes which is connected into the circuit to control the compressed air system . with the contact 84 closed , a second indicating light 86 and other annunciators such as a buzzer 88 can be energized to indicate that the relay 80 has closed . a pressure switch 90 is placed between the contact 84 and a compressor motor starter 92 . as the pressure switch 90 is normally closed , the motor starter 92 is energized which in turn starts an air compressor 94 . the air compressor 94 has its air output connected to a manifold 96 which feeds the compressed air system . a pressure gauge 98 gives a visual indication as to what the pressure is in the manifold 96 . a pressure switch take off 100 is fluid connected to the pressure switch 90 . in operation , the pressure switch is set to open , that is the pressure switch will turn the air compressor off , when the pressure in the manifold reaches 25 psi . the pressure switch recloses , that is completes the circuit to the motor starter 92 , when the pressure in the manifold drops to 15 to 18 psi . the air hose 42 is connected to the manifold 96 and thus supplies the compressed air to the air cylinder 34 . the compressed air forces the piston 44 down ( as seen in fig3 ) which forces the piston rod 46 down towards the building sewage pipe 20 . thus , the rubber bladder 52 is positioned approximately midway into the sewage pipes 20 , 22 . a control valve 102 is connected between the manifold 96 and the second air line 56 and is preset to open at approximately 23 psi . the control valve 102 permits compressed air to flow from the manifold 96 into the rubber bladder 52 . as the pressure in the manifold 96 is building , the air cyinder 34 immediately receives the compressed air and causes the piston to position the rubber bladder in the sewage pipes . however , the bladder is not inflated until the pressure in the manifold has reached approximately 23 psi . thus assuring accurate positioning of the bladder within the sewage pipe . when the pressure comes up to 23 psi ., the control valve 102 opens and the rubber bladder 52 is inflated . this is clearly illustrated in fig3 wherein the rubber bladder 52 seals off the flow of liquid in either direction a or b through the building sewage pipe and the outside sewage pipe 20 , 22 respectively . thus , as long as the bladder 52 remains inflated it will continue to seal off the flow of fluid past it . after the flood condition or back flow condition has subsided , there is no longer any need to leave the bladder in the pipe and in fact it is necessary to remove it so that normal fluid flow can once again occur . when the user is aware of the return to normal conditions , and that there is no longer any back flow problem , switch 68 is opened which shuts power off to the system . a spring loaded ventilation valve 104 which is connected to the manifold 96 and normally spring biased to a closed position , is manually opened . this causes the air pressure within the manifold and air cylinder to drop to zero . as the pressure in the system is reduced to approximately 2 or 3 psi ., the control valve 102 automatically opens which causes the rubber bladder 52 to be deflated . the spring 45 within the air cylinder 34 forces the piston 44 back up towards the threaded cap 32 and draws the rubber bladder 52 back into the stand pipe 24 as illustrated in fig2 . any water within the stand pipe 24 should have been removed by the building sewage pipe 20 by this time . the master switch 68 is reclosed and if in fact a back flow condition still exists , the system will once again be energized and the air compressor will begin a new cycle . if the back flow condition does not exist , the probe will not go to ground and a new compression cycle will not begin . if the system is desired to be manually tested , a test switch 106 is provided in the electrical circuit which simulates the probe sensing a fluid . thus , the system can be manually tested by closing the test switch 106 to see if the motor starter , air compressor and associated pneumatic components are operative . there is an optional bypass system which is clearly illustrated in fig3 such that the plumbing within the building can still be used even when the rubber bladder is inflated and the normal flow of fluid is prohibited . a first bypass pipe 108 is connected to the building sewage pipe 20 at the upper portion of the sewage pipe 20 just before the stand pipe 24 . the first bypass pipe 108 discharges into a sewage sump 110 . a sewage ejector pump 112 has a float 114 which turns the pump 112 on when the fluid in the sump 110 reaches a predetermined height . the pump 112 then discharges via its discharge pipe 116 past a check valve 118 which only permits flow in one direction , that is out from the sump 110 . the sewage is pumped into an exit pipe 120 which discharges into the outside sewage pipe 22 just past the inflated bladder 52 on the other side of the stand pipe 24 . the check valve 118 prohibits the back flow from entering the sewage sump 110 . a ventilation pipe 122 is located on the top of the sewage pump to permit the controlled escaping of sewage gases . otherwise the sewage bypass system is completely sealed . fig5 illustrates an alternate embodiment for the positioning and inflation of the bladder from its normal position in the stand pipe 24 into the sewage pipes 20 , 22 . there is still present the threaded cap 32 which has an air cylinder 124 firmly affixed at its base end to the cap 32 . again there is an air hose 42 which is connected to the air compressor via a manifold 96 . the air is permitted to pass through the fastener used to fasten the cylinder 124 to the air hose 42 . placed around the air cylinder and towards its top end near the threaded cap 32 is a collar 126 which is securely fastened around the cylinder 124 . there is a seating channel or groove 128 around the circumference of the collar 126 . a modified expandable rubberlike bladder 130 is used for sealing and it is a variation of the previous embodiment . the bladder 130 has a neck 132 with a bead 134 along its inner circumference . the bead 134 is closely received by the seating channel 128 . a locking ring 136 is securely fastened around the neck 132 and tightly fastened such that the neck 132 cannot be pulled away from the collar 126 . the bladder 130 has numerous accordion - type pleats 138 along its body such that it can expand to approximately three times its collapsed size . as the compressed air fills the cylinder 124 it forces the piston 44 down and away from the air inlet . this in turn forces the piston rod 46 out from the air cylinder 124 and down towards the bottom of the sewage pipes 20 , 22 . fastened to the end of the piston rod 46 is a flat disk 140 which pushes against the bottom of the bladder 130 . thus , the bladder 130 is stretched out from the stand pipe 24 and into the sewage pipes 20 , 22 . a port 142 is placed in the air cylinder wall 124 towards the bottom of the cylinder which is near the end of the stroke of the piston 44 . thus , compressed air does not fill the bladder 130 until the piston 44 has passed through most of its stroke and has passed the port 142 . at the time when the piston 44 passes the port 142 compressed air will flow into the bladder 130 thereby inflating it . it should be noted that the bladder 130 is thus not inflated until the piston rod 46 has forced the flat disk 140 to expand and stretch the bladder 130 into the sewage pipes 20 , 22 . it is readily apparent that the alternate embodiment thus alleviates the need for the control valve 102 which was part of the control circuitry . as the compressed air is bled from the system after the flooding or back flow condition has been corrected , the bladder and air cylinder will lose pressure simultaneously and a spring 144 within the air cylinder 124 will cause the piston 44 to be forced back up towards the top of the cylinder 124 . the expandable pleats 138 having a memory will draw the bladder back up into the stand pipe 24 . it should also be noted that this alternative embodiment will alleviate one of the air lines 56 which was previously required to inflate the bladder . a second alternate embodiment is illustrated in fig6 which completely alleviates the need for a piston to position the bladder in the sewage pipes . instead , a very flexible material which is capable of substantial vertical flexing is used to form a bladder 146 having numerous pleats 148 . as the bladder 146 inflates , it expands downward and fills the intersection of the sewage pipes 20 , 22 with the stand pipe 24 . the inflated configuration is shown in phantom in fig6 . retainer rings ( not shown ) could be placed around the top of the bladder 146 to restrict horizontal expansion of the top of the bladder within the stand pipe 24 . furthermore , a modified coupling 150 must be used to pass through the cap 32 . the coupling 150 should have a groove 152 to receive a necked portion 154 of the bladder 146 . a fastening clamp 156 similar to the locking ring 136 is used to hold the bladder 146 in place . the simplicity of this configuration is its greatest attribute as the air cylinder and piston are not required reducing cost and potential repair problems which always rise with the increase of components . thus , it is apparent that there has been provided , in accordance with the invention a pneumatic valve system which will stop sanitary sewer back ups into buildings . the invention fully satisfies the object , aims , and advantages set forth above . while the invention has been described in conjunction with specific embodiments thereof , it is evident that many alternatives , modifications , and variations will be apparent to those skilled in the art in light of the foregoing description . accordingly , it is intended to embrace all such alternatives , modifications , and variations as fall within the spirit and broad scope of the appended claims .