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.
Should the valves of a pump be leaky on their seats, the pump will not work satisfactorily. Where the lower valve is not properly ground on the seat, the plunger sucks air from the feed-pipe, or through the joints or packing, and, at the return stroke, compresses part of the air in the pump, and forces the remainder back into the feed-pipe through the leaky valve. This process goes on after the feed is put on; the accumulated air stands like a cushion between the plunger and the water; and the pump will not go to work until the pet-cock is opened, when the air rushes out, permitting the water to flow in. Engineers having pumps that will not work till the pet-cock is opened, should have the suction-valve ground in; and they will find a decided improvement from the operation.
For slow train service, pumps perform the service of boiler-feeding fairly well; but, for fast passenger trains, a pump should not be tolerated. A pump can not be constructed for high-speed engines that will throw water regularly at high velocity of stroke.
CHAPTER XI.
INJECTORS.
Injectors have made remarkably rapid strides into public favor during the last ten years. It is a safe prediction to say, that, before the end of another decade, there will be no new pumps put upon locomotives. So long as injectors were imperfectly understood, and were used with no regularity, they retained the name of being unreliable; but, so soon as they began to be made the sole feeding-medium for locomotive boilers, they had to be worked regularly, and kept in order, which quickly made their merits recognized.