LIFT OF PUMP-VALVES.
When a pump-valve has much lift, it is very liable to pound itself or the cage so heavily that breakage occurs. The proper lift required for pump-valves depends to some extent upon the diameter of the valves themselves, those of liberal thickness requiring less lift than a valve of narrow compass. The engine pulling our train has pump-valves two and one-half inches in diameter: the pump-plunger, being worked from the cross-head, has a diameter of two inches. The bottom valve has three-thirty-seconds of an inch of lift, the middle valve has one-eighth of an inch of lift, and the check-valve rises one-fourth of an inch. These dimensions produce very satisfactory results for all speeds. The pump performs its work with remarkable smoothness, is free from pounding or fluctuating, and gives no trouble about repairs. Engines employed on fast passenger service have their valve-lifts one-thirty-second of an inch less than this one, and slow freight engines are regulated to rise one-sixteenth of an inch more than the dimensions given.
KEEP PIPES TIGHT, AND PACKING IN ORDER.
In order to insure the regular and satisfactory working of a pump, care should be taken to prevent leaks about the feed-pipes or heater-pipes: the packing should be kept in good order, and the chamber-joints should be perfectly air-tight. During the outward stroke of the plunger, a vacuum should be produced inside the pump, into which the water rushes. If this vacuum gets partly filled with air or vapor, the working of the pump will be unsatisfactory. Nothing is so liable to produce this undesirable condition as badly packed glands or leaky joints. A poor pump can often be made to produce fair work, by attention and care bestowed upon its attachment; and lack of care will soon render the best-constructed pump unreliable.
SAND IN THE PUMP-CHAMBERS.
The pump has one arch-enemy, which comes off victor in every conflict. That is sand. The railway idiom which uses the word “sand” to express courage, originated in the knowledge of how certainly and quickly a handful of sand would vanquish the best pump that mechanical skill might produce. The grit works its way among the packing, and tears and cuts the plunger out of shape: it insinuates itself up between the cages and valves, and holds the latter so fast that hard hammering is often needed to dissolve the compact. Proper washing out of the tank, cleansing of feed-pipes, and the use of water free from sand, is the only sure remedy for this evil. Where an engineer is situated so that he must take water containing sand in suspension, partial relief will be obtained by giving the valves free side-room in the cages; but an injector will be found much superior to a pump as a means of putting sand-contaminated water into a boiler.
DELIVERY ORIFICE CHOKED WITH LIME SEDIMENT.
When a pump begins to show distress from over-pressure,—which will be indicated by the breaking out of joints, the rejection of stuffing and box-packing, and the bursting of branch-pipe,—the orifice between the check and the boiler should be examined; for that aperture often becomes almost closed by the accumulation of lime-salts.
MINOR PUMP TROUBLES.
Where the feed-pipes and other connections are perfectly air-tight, some pumps will pound badly when the water is shut off. This can be prevented by making a minute hole in the feed-pipe; or a more convenient place is the upper part of the heater-pipe, away above the water-level.