STEAM BOILERS 169 



Inspection of Vertical Boilers. Vertical boilers as a general 

 rule, except in the largest sizes, have no manhole to admit a 

 person to the inside, and such internal inspection as is possible 

 must be made through the handholes. Defects to be looked 

 for are pitting and uniform corrosion of the shell and tubes 

 near the usual water-line, and cracks in the heads between the 

 tubes, the lower head being especially liable to show this injury. 



HYDROSTATIC TEST 



Value of Test. While a hydrostatic test is usually demanded 

 by boiler laws and official rules and regulations, it does not at 

 all follow that a boiler that has successfully stood this test will 

 be safe. The chief value of the test lies in showing leaks. 

 Under no consideration should the test pressure be such as to 

 strain the parts of the boiler beyond the elastic limit of the 

 material. 



Care in Making Test. When applying the hydrostatic test, 

 the escape of air from the boiler while filling it with water 

 should be provided for, as by raising the safety valve. After 

 the boiler is full, all outlets must be tightly closed and the 

 safety valve so blocked that it cannot open; the pressure must 

 then be pumped up very slowly and carefully, the gauge being 

 watched for any drop of pressure, which denotes a sudden 

 yielding of some part of the boiler. When the desired test 

 pressure has been reached, the boiler is inspected for leaks, and 

 if any are found they are marked. Before calking to stop a 

 leak, the pressure must be left off by opening some convenient 

 valve or cock. In cold weather, when subjecting the boiler 

 to the hydrostatic test, it is customary to heat the water to a 

 lukewarm temperature. 



Use of Blank Flange. If the boiler to be tested is one of a 

 battery, and the others are to be in use while this one is being 

 inspected and tested, it is unwise to rely on a closed main stop- 

 valve to break communication with the other boilers. It is 

 good practice to put a blank flange between the boiler to be 

 tested and its main stop-valve. 



INSPECTION OF FITTINGS 



Inspection of Safety Valve. The safety valve requires very 

 careful inspection. If this valve is known to leak, it should be 



