STEAM BOILERS 147 



still allowed to rise slowly until the desired pressure has been 

 reached. 



Trying the Fittings. After the pressure at which the boiler 

 is to run has been reached, and before cutting it into service, 

 all the valves and cocks should be tried. The safety valve 

 should be raised and its action noted; the water column should 

 be blown out and the gauge-cocks tested; the feeding apparatus 

 should be tried; and it should be noted particularly whether 

 the check-valves seat properly and the valve in the feedpipe 

 is open. All the accessible parts should be examined for leaks. 



CONNECTING BOILERS 



Cutting Boiler Into Service. Cutting a boiler into service 

 is accomplished by opening the stop-valve, thus permitting 

 the steam to flow to the engine or other destination. The stop- 

 valve should be opened very slowly to prevent a too sudden 

 change in the temperature and consequent expansion of the 

 piping through which the steam flows, and also to prevent 

 water hammer. The steam-pipe drain should be kept open 

 until the pipe is thoroughly warmed up. In large plants with 

 many boilers and long steam mains it takes several hours to 

 warm these pipes thoroughly by a slow circulation of the 

 steam, but not until then should the main stop-valve be fully 

 opened. 



Connecting Boilers to Main. Before connecting the differ- 

 ent boilers of a battery to the same steam main, the precaution 

 of equalizing the pressures in the different boilers must be 

 observed in order to prevent a sudden rush of steam from one 

 boiler to another. All the pressures should be equal within a 

 variation of about 2 Ib. before an attempt is made to connect 

 the boilers. 



Changing Over. In plants where there are duplicate sets of 

 boilers, one set being in operation while the other is under- 

 going repairs, overhauling, and cleaning, the method of chang- 

 ing over, or connecting, is as follows: Start the fires and raise 

 steam in the boilers that are to be cut into service. Allow 

 the pressure to rise in all to within 5 Ib. of that which is in the 

 boilers in operation. All arrangements before changing over 

 should be made with a view to getting all the heat that can be 



