单项选择题
A.check and regulate the water level
B.close the air cock once fires are lit
C.blowdown the gage glass
D.crack the steam stop to assure protective steam flow
单项选择题 After a normal, or safety shutdown, automatic combustion control systems for an auxiliary boiler are designed to prevent the immediate re-firing of a burner in order for the （）.
单项选择题 （） will be used to blow away soot and the combustion products from the tube surfaces.
单项选择题 The correct pH value of boiler water is achieved by continuous addition of a suitable （） to the feed.