HOW THE CONDITION OF PUMPS CAN BE TESTED.
If an engineer is in the habit of pumping regularly, and of watching his engine closely, he can tell immediately from the steam when the pump stops working. Then he will open the pet-cock; and its action will indicate, to some extent, where the trouble lies. If the pet-cock throws a feeble stream of water, the trouble probably is in the lower valve. If that sticks up, or part of the bottom cage breaks, the plunger will push the water back into the feed-pipe on the return stroke, consequently there will be no pressure to throw a strong stream through the pet-cock. When the upper or pressure-valve is damaged, or is stuck up, the pet-cock will throw a full stream during the inward stroke of the plunger; but, on the outward stroke, the plunger will draw the water out of the branch-pipe, and air will be sucked in at the open pet-cock. When the check-valve is damaged, or stuck up, steam and water will blow back through the branch-pipe when the pet-cock is left open. If the steam thus escaping from the check-valves heats the pump and valves to a high temperature, it will be prevented from working, from several causes. The heat generates a low form of steam, which fills up the space behind the plunger; therefore, no vacuum is formed to draw the water. Not infrequently the pump-valves expand so much from the heat, that they stick fast away from their seats. If the pump has stopped through the presence of impurities on either of the valves or cages, the engineer knows that he may remove the obstruction by steam-pressure; so, after letting the feed-pipe fill with water, he opens the heater-cock, and closes the foot-cock, letting the steam and water blow through the pump. If he considers the obstruction to be in the strainer, and has not time to stop and take it down, he blows steam from the heater through to the tender, which gives temporary relief. If any of the pump-valves are stuck up, and can not be got back to their seats by blowing water and steam through them, the engineer will take a soft hammer, and tap the seats lightly, with good prospects of remedying the defect. In case no improvement can be effected in that way, and there is no other feeding-medium to rely upon, the engineer can take down the top or bottom chamber in a few minutes to remove any impurities that may be keeping the pump from working. He will then be likely to find a piece of packing that has passed through the pump, bushing, or some other foreign substance, jammed between the cage and the valve, keeping the latter immovable. Or the trouble may be a broken valve or cage, which will render the pump useless till repaired.