* * *
It takes less power to feed into the bottom of a tank than it does into the top, on account of the weight of water in the tank. The bottom of the tank holds up all the water except the column directly over the opening of the delivery pipe, so that the additional pressure on the pump is due only to the depth of water in the tank, not to the size of the body, and it is impossible to feed into the top without increasing the height of the column fully as much. It makes no difference whether the height is due to the depth of the water inside the tank or an additional length of pipe outside.
* * *
The duty of the air pump is solely to get rid of the water and air in the condenser. It adds to the efficiency of the condensing apparatus, and renders its operation continuous; its valve being thrown by the action of its own piston, it must complete its stroke in length whether the piston is moving in air, water or vapor.
Pumps should be kept clean internally and externally. In order to keep a pump clean internally it must be inspected and oiled internally at regular intervals the same as it is externally.
* * *
When pumps fail to work properly the difficulty is generally located in one of three places, viz.: the water end, the steam end or the suction pipe.
* * *
The several parts of the valve gear of a single cylinder pump should be marked when the pump works properly, then any trouble due to the slipping of the collars or tappets can readily be remedied; if the nuts and set screws are kept tight, derangements occur only at long intervals.