152 COMMERCIAL ROSE CULTURE 



In starting a fire under a boiler where everything is cold a small 

 fire should be carried for awhile so that everything may be 

 warmed slowly or there is danger of unequal expansion and 

 injury to the boiler. Also, in a brick set boiler, if for any 

 cause it is shut down and the water is to be blown off, do not 

 attempt this until several hours after the fire is out and the brick- 

 work has had time to cool off somewhat. 



THE SAFETY VALVE AND WATER GLASS 



The most important fixture on a steam boiler is the safety 

 valve; if this is of sufficient size and in good working order 

 there is no possibility of getting an over pressure of steam. The 

 safety valve should have one square inch area for every two 

 square feet of grate surface. It should be tried at frequent 

 intervals by gently raising with the hand on heating boilers and, 

 on pressure boilers, the steam should be run up to the blowing 

 off point when, if it does not start, it will have to be gently 

 started by hand. There is generally about three pounds dif- 

 ference between the opening and closing of a safety valve from 

 the fact that there is a greater surface exposed to the steam 

 when it is open. A pop or spring safety valve, which is locked 

 so that no one can tamper with it, is the safest to use. 



In case a safety valve gets stuck, and the steam is found too 

 high, or in any case where we suddenly want to do away with 

 the heat under a boiler, close the dampers and cover the fire 

 with ashes or fine coal ; this will cool it off more quickly than 

 the old way of drawing the fire. Afterward, if necessary, the 

 fire can be drawn. In case the safety valve is stuck do not at- 

 tempt to release it until the pressure is down to normal, then 

 gently raise it with the hand. If raised when the pressure is too 

 high steam would be rapidly disengaged from the water and the 

 strain on the boiler will be greater than if it was left alone. 



The water glass and gauge cocks are for the purpose of 

 showing the height of water in the boiler and should be blown 



