What is atmospheric pressure?

As usually spoken of, it is the pressure exerted by the atmosphere on an area of one square inch, or, in other words, it is the weight of a column of air one square inch in cross section. At the sea level this column of air, that is, the earth's atmosphere, is computed to be about forty-five miles deep, giving a pressure of fifteen pounds per square inch.

Why is the atmospheric pressure less at the top of a mountain than at the sea level?

Because the depth of the atmosphere is necessarily less at the top of the mountain.

How does atmospheric pressure affect the boiling of liquids?

The temperature at which a liquid boils, rises as the atmospheric pressure increases. Therefore water will boil at a lower temperature at the top of a mountain than at its base.

How does atmospheric pressure apply particularly in plumbing work?

It applies in pump work, and whenever syphonic action occurs, also on certain devices acting in the manner of the vacuum valve.

Describe the vacuum valve.

The vacuum valve under normal conditions is closed by the pressure of water from within. When a vacuum forms within the vessel to which the valve is attached, the pressure of the atmosphere exerted on the outer face of the valve, forces air into the vessel, thus breaking the vacuum, and preventing disastrous results which might otherwise occur.

What is meant by a pressure of one atmosphere?

A pressure of one atmosphere is a pressure of fifteen pounds. In like manner a pressure of four atmospheres would mean a pressure of sixty pounds, etc.

Country Plumbing - Drainage System Unventilated.

Explain the action of expansion and contraction.

Where heat is applied to a body of a metallic nature, the particles of which the body is composed, increase in size, and the body itself naturally takes up a greater amount of space than when in its normal condition, that is to say, it expands. When the body is subjected to cold, the opposite action takes place, that is, the body contracts. If heat is applied beyond a certain amount, varying with each different metal, the expansion becomes so great that the particles will no longer hold together, and the body is transformed into a liquid state. Expansion and contraction apply to many substances other than metals.

In what important ways do expansion and contraction apply to plumbing work?

In the expansion and contraction of water and air. Circulation, whether in connection with the hot water supply, or heating operations, depends on this principle. All ventilation, including the local venting of water closets, also depends on the same principle.

What provision is made on hot water supply systems for expansion?

In the case of the tank supply system a pipe is carried from the highest point on the hot water supply to the tank, into which the expansion vents itself when sufficiently great to reach this point. On direct supply systems no provision is necessary, for expansion takes place back to the reservoir. On direct pressure work, however, it is usually necessary to use heavier boilers than on tank work.