Note B — SPECIFICATIONS OF THE National Board of Fire Underwriters FOR THE MANUFACTURE OF STEAM FIRE PUMPS AS RECOMMENDED BY THE National Fire Protection Association.
Reading edition
This boiler power is required for continuous running at full speed and pressure. It is, however, often best to put in a larger pump than the existing boilers could drive at full capacity, as a small boiler will drive a 750-gallon pump at the 500-gallon speed with very nearly as good economy as it can drive a 500-gallon pump at full speed. The pump then does not have to be changed when the plant is enlarged and the boiler power increased.
A steam piston relatively larger than necessary is a source of weakness. It takes more volume of steam, and gives more power with which to burst the pipes if the throttle is opened wide suddenly during excitement.
It has been common to make all fire-pumps with water plunger of only one-fourth the area of steam piston, with the idea that pump could thereby be more readily run at night, when steam was low. The capacity in gallons is thus reduced 25 per cent. as compared with a 3 to 1 plunger on the same steam cylinders.