Water Pressures : Water is composed of two gases , hydrogen and oxygen , in the ratio of two volumes of the former to one of the latter .

In the English System of measure , water boils under atmospheric pressure at 212 degrees F . and freezes at 32 degrees F.

Its greatest density is 62.425 pounds per cubic foot , at 39.1 degrees F . In metric SI measure water boils under atmospheric pressure at 100 degrees C (Celsius) and freezes at 0 degrees C . Its density is equal to one kilogram per liter , where one liter is one cubic decimeter.also in metric SI , pressure is given in pascals (Pa) or the equivalent Newton per square meter .

For higher temperatures , the pressure slightly decreases in the proportion weight of water per cubic foot at different temperatures.

The pressure per square inch is equal in all directions , downwards , upwards and sideways. Water can be compressed only in a very slight degree , the compressibility being so slight that even at the depth of a mile , a cubic foot of water weighs only about one – half pound more than at the surface .

The amount of water that will flow through a pipe in a given time are approximate . The formula below will give results within 5 or 10 per cent of actual results , if applied to pipe lines carefully laid and in a fair condition.

In which :

V = approximate mean velocity in feet per second ,

C = coefficient from the accompanying table ,

D = diameter of pipe in feet ,

h = total head in feet ,

L = total length of pipe line in feet.

Example : A pipe line 1 mile longs , 12 inches in diameter , discharges water under a head of 100 feet . Find the velocity and quantity of discharge.

From the table , the coefficient C is found to be 48 for a pipe 1 foot in diameter ,

Hence :

To find the discharge in cubic feet per second , multiply the velocity found by the area of cross – section of the pie in square feet :