Science of Water : Concepts and Applications

Water Hydraulics 51
√ Important Point: 1 ft of water = 0.433 psi.
With the above information, feet of head can be converted into pounds per square inch by multiplying
the feet of head times 0.433 psi/ft.
Example 3.5
Problem:
A tank is mounted at a height of 90 ft. Find the pressure at the bottom of the tank.
Solution:
90ft 0.433psi/ft 39psi
(rounded)
√ Note: To convert pounds per square inch into feet, you would divide the pounds per square inch
by 0.433 psi/ft.
Example 3.6
Problem:
Find the height of water in a tank if the pressure at the bottom of the tank is 22 psi.
Solution:
22psi
Height (ft) 51ft
(rounded)
0.433psi/ft
√ Important Point: One of the problems encountered in a hydraulic system is storing the liquid.
Unlike air, which is readily compressible and is capable of being stored in large quantities in
relatively small containers, a liquid such as water cannot be compressed. Therefore, it is not
possible to store a large amount of water in a small tank—62.4 lb of water occupies a volume of
1 ft 3 , regardless of the pressure applied to it.
HYDROSTATIC PRESSURE
Figure 3.2 shows a number of differently shaped, connected, open containers of water. Note that the
water level is the same in each container, regardless of the shape or size of the container. This occurs
because pressure is developed, within water (or any other liquid), by the weight of the water above.
If the water level in any one container were to be momentarily higher than that in any of the other
FIGURE 3.2 Hydrostatic pressure.
Liquid
level
T