_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.