| Size Gallons Per Minute Capacity. | 500 | 750 | 1,000 | 1,500 |
| Ratio of Steam Piston Area to Water Piston Area. | 4 Times | 3 Times | 3 Times | 23⁄4 Times |
| Water Pressure lbs. Per Sq. in. | 100 | 100 | 100 | 100 |
| Steam Pressure Theoretically Necessary, Disregarding Friction. | 25 | 33 | 33 | 36·5 |
| Excess of Steam Pressure Needed to Overcome Friction, Back Pressure, Etc. | 15 | 12 | 12 | 13·5 |
| Actual Steam Pressure Found Necessary at the Pump. | 40 | 45 | 45 | 50 |
b. The steam pressure needed will vary slightly with the freedom of the exhaust pipe and with the tightness of the packings, etc., but a steam pressure of 45 pounds at the steam chest should suffice for 100 pounds water pressure on pump in proper adjustment.
50. Test of Strength and Tightness.
a. First, shut the main valve between the pump and the fire system lest a sprinkler head be burst, then shut all water outlets nearly, but not quite tight, so pump will move very slowly. Screw safety valve down hard. Slowly and carefully admit steam pressure sufficient to give 240 pounds per square inch water pressure.
b. With this extreme pressure all joints should remain substantially tight, and the slow motion of the pump should be tolerably smooth and uniform. (The leakage of a few drops here and there and a little unsteadiness of motion are to be expected.)
c. If boiler pressure is above 85 pounds, the safety valve on pump should be attached and screwed down only enough to hold the required pressure. For with 100 pounds or more of steam the water pressure might be carried too high.
After completing the above test slack off on safety valve, setting it so that it will begin to open at about 100 pounds pressure.
51. Test of Capacity of Safety Valve.
a. The relief valve may next be tested by first adjusting it to “pop” at 100 pounds, then shut the main outlet to pump, and then shut the hose gates one by one, and thus force all the discharge through the relief valve, meanwhile opening steam throttle, so as to run pump first at two-thirds speed or about 50 revolutions per minute, and finally at full speed (70 revolutions). The safety valve (relief valve) should carry all this and not let the pressure rise above 125 pounds.