The boiler feed is taken from the hot well either by the feed pump or by injectors, as the case may be.
In case the boiler feed should stop working, however, the hot well is provided with a pipe of large diameter, and called the overboard discharge pipe, so that the water of condensation may not accumulate a pressure in the hot well if the boiler feed ceases.
This overboard discharge pipe is provided with a weighted valve (placed at the side of the ship), which is constructed after the manner of a safety valve, relieving the hot well of pressure if the water accumulates, and preventing the sea water from entering the hot well.
To prevent loss of fresh water, the exhaust steam from the various engines and pumps (if any) about the ship passes to the condenser and is pumped into the hot well.
In some cases, however, a separate and independent condenser is used for the smaller engines about the ship.
An independent condenser is one whose air pump and circulating pump are not worked from the main engine, and can therefore be operated when the main engine is standing still.
If the main condenser is independent, it may be started so as to form a vacuum before the main engine is started, and thus obviate the use of the starting valve on the low pressure cylinder except to warm the cylinder before starting.
Feed water for the boilers when the engine is standing is obtained by a pipe from the bottom of the condenser, so that the water of condensation of steam blown through the engine cylinders, and from the exhausts from the smaller engines about the ship, may be pumped or forced direct from the bottom of the condenser to the boiler.
This feed from the bottom of the condenser is necessary when the air pump is not working, and the water of condensation is not pumped into the hot well.
If the water thus obtained is not enough to keep the boilers supplied, an auxiliary or salt water feed admits extra water from the circulating water to the inside of the condenser to supply the deficiency.