MAN'S USE OF COMPRESSED AIR 



13 



As the pressure on the inside of a caisson is increased, 



the water level inside . All water may be removed if 



sufficient is applied. To keep the water from enter- 

 ing the caisson a pressure (greater, less) than the 



pressure tending to force water in must be maintained. 



OTHER INVESTIGATIONS WHICH YOU CAN MAKE 



Take apart a compressed-air door stop and study its 

 construction. 



Visit a service station or garage and study the con- 

 struction of an air compressor. 



Measure the air pressure in the tires of an automobile. 



Study the operation of the air brakes on a street car or 

 bus. 



AIR 



EXHAUST 



PLATFORM DOWN 



x^ ^ 



LATFOR13J, ^^O 



DISPLACED 



,.., ff FROM TANK 

 c <" ' x INTO CYLINDER 



ORtt UP 



READINGS WHICH WILL HELP ANSWER THE 

 PROBLEM QUESTIONS 



What are some of the modern devices that use 

 compressed air? Many of our largest buildings, our 

 great bridges, and our dams were built much more 

 easily and quickly because man has learned how to 

 compress air and then to use its great "spring," as it 

 was once called by Robert Boyle, an Irish scientist. 

 Compressed air is used on many of our modern 

 transportation devices such as buses, street cars, and 

 trains, for operating the brakes, thus making our 

 travel much safer. 



Have you ever noticed the large lifts that are used 

 at oil stations to raise automobiles from the ground 

 that greasing the under parts may be made easier? 

 Many of these are operated by compressed air which 

 pushes on oil and raises the piston and platform. 

 When the air is released by opening the exhaust valve 

 E (Fig. 27), the weight of the car and piston pushes 

 the oil back into the tank T. 



If there is such a lift near your home, you will find 

 it interesting to study. No doubt you will find, inside 

 the filling station, the compressor which supplies the 

 air both for the lift and for tires. If you study it care- 

 fully you will see that it has a piston which is driven 

 in a cylinder by an electric motor. Air is taken into the 

 cylinder through a valve and is then compressed when 

 the piston pushes it into the storage tank. The com- 

 pressor is automatic. When the pressure reduces to 

 a certain point as air is used, an electric switch which 

 starts the motor is closed, and the pressure is again 

 built up inside the storage tank. 



Compressed air is used in hammers, riveters, and 

 drills. Study the cross section diagram in Figure 27 



COMPRESSED AIR HAMMER 



1. Cylindrical valve. 2. Cylinder threaded into handle. 

 4. Locking ring preventing handle from loosening. S. 

 Exhaust deflector. 6. Trigger control. 7. Throttle valve. 8. 

 Spring clip set retainer. 



and see if you can explain how the compressed air 

 drives the piston back and forth. Air comes in first on 

 one side of the piston and then on the other, causing 

 the piston to move rapidly back and forth. When the 

 piston is made to strike against a tool such as a drill 

 or a hammer, many powerful blows can be struck in 

 a short time. The compressed air is controlled by a 



