STEAM BOILERS 359 



there is about 20 pounds of steam, blow off through the 

 lower valve until the proper water level has been reached. 

 When the boiler is in operation the circulation keeps the 

 dirt mixed and it does not avail much to blow off then. 



A good way to wash a boiler is to allow it to cool down 

 until one can bear his hand in it; then open the blow-off 

 valve and let the water run out. Remove the manhole 

 and handhole plates and scrape all tubes and the shell 

 with a scraper made for the purpose, then wash well with 

 a hose and force pump. 



498. Cleaning the flues. Fire tubes should be cleaned 

 at least once a day, and sometimes oftener. This is done 

 by means of a scraper or a steam jet. Scraping should 

 always be done in the morning before firing up. Never 

 do it just after the fire is started, for then the tubes are 

 wet and pasty. If they have to be cleaned while running, 

 do it as quickly as possible and let as little cold air as 

 possible get into them. 



499. Boiler compounds. Often there are cases where 

 the impurities in boiler waters are such that they form 

 a hard scale. In these cases it is nearly always advisable 

 to use a boiler compound. If the proper compounds are 

 used, they will dissolve the scale and throw it down in the 

 form of a mud. Then it can be blown out. Wherever 

 the scale does not become hard it is very seldom advisable 

 to use a compound. 



Wherever a compound is necessary it is best to have a 

 chemist analyze the water and make a compound to suit 

 the case, giving directions as to use and quantity to be 

 used. For traction and small creamery service this is 

 not practical. Soda ash gives very good results for 

 creamery service. It has no offensive odors and is com- 

 paratively cheap. Sal soda has also been used with good 

 results. For boilers where steam is used only for en- 



