When priming and draining a pump the air cock in the air chamber should also be opened. The drain and cylinder cocks at the steam end should be opened before closing the throttle; the steam should be shut off at the boiler when stopping at night so as to drain the entire pipe.
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Pumps that are exposed to low temperatures in winter should be provided with removable drain plugs or drain cocks for emptying the cylinders and valve chambers of water and also allowing the water to flow out of the suction pipe.
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The friction in pipes, whether of cast iron, steel or copper, depends upon the internal smoothness of the pipe and the velocity of the water, as well as the number and kind of ells, tees and valves in the pipe. Wrought iron lap welded pipe, for steam, is preferable to either cast iron or copper. It is smoother internally than cast iron, and is lighter and costs less than copper, and is much stronger and safer than either.
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It may be said when an engine is run without a condenser the steam with which the cylinder is filled at the end of the stroke has to be forced out against the pressure of the atmosphere, about 15 pounds to the square inch. It is possible from the nature of steam to remove the atmospheric pressure with a decided gain in almost all cases.
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One pound of steam at atmospheric pressure occupies 1,642 times as much room as it does in the state of water. If, therefore, when the stroke has been completed, and we are ready for the piston to come back, we inject a little cold water into the spent steam, it will condense to about one 1600th of its volume, and leave a vacuum into which the piston can return without having to force back the atmosphere. This is the way the earlier vertical engines were run, the condensation taking place in the cylinder itself, and, moreover, the vacuum was all that made the engine operative, for the steam carried was but little above atmospheric pressure.