After cushion valves are adjusted there should be no noteworthy water hammer or valve-slam. Sometimes valve-slam is not the fault of the pump, but arises from an obstructed suction pipe. It is objectionable to doctor water hammer in a pump by “snifting” air into the suction, as this cuts down the efficiency and is a poor expedient. The quietness of that part of the hose near the pump, or its freedom from rubbing back and forth crosswise an inch or more with each pulsation of the pump, is a good index of the pump maker’s skill in securing uniform delivery. Bad pulsation quickly wears holes in the hose, and to reveal this is the object of testing _with hose connected directly to the pump_. 49. TEST OF THE INTERNAL FRICTION. _a._ This is shown by the reading of steam gauge compared with water pressure gauge at air chamber. Tests have generally run about as follows, for pumps running at full rated speed: ===============+=========+=========+=========+============= Size Gallons | 500 | 750 | 1,000 | 1,500 Per Minute | | | | Capacity. | | | | ---------------+---------+---------+---------+------------- Ratio of Steam |=4= Times|=3= Times|=3= Times|=2-3/4= Times Piston Area to | | | | Water Piston | | | | Area. | | | | ---------------+---------+---------+---------+------------- Water | 100 | 100 | 100 | 100 Pressure | | | | lbs. Per | | | | Sq. in. | | | | ---------------+---------+---------+---------+------------- Steam Pressure | 25 | 33 | 33 | 36·5 Theoretically | | | | Necessary, | | | | Disregarding | | | | Friction. | | | | ---------------+---------+---------+---------+------------- Excess of Steam| 15 | 12 | 12 | 13·5 Pressure Needed| | | | to Overcome | | | | Friction, Back | | | | Pressure, Etc. | | | | ---------------+---------+---------+---------+------------- Actual Steam | 40 | 45 | 45 | 50 Pressure Found | | | | Necessary at | | | | the Pump. | | | | ---------------+---------+---------+---------+------------- _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.