Calculating Pressure Drop

In Kentucky, water systems have to supply water to various elevations. This can be a very challenging task. Whether it is delivering water to a house in a valley or a house on a hill, knowing the pressure is essential, according to the regulations, and assuring that the minimum pressures are successfully being reached is very important. Also, multi-level houses or houses with bathrooms in the basement are common. In the following math problems, let’s see if the mandatory 20 psi of delivered pressure is being met.

An 8-inch main is being tapped for a service line. The pressure at the meter is 72 psi. The two-story house with 14-foot ceilings sits on a hill and has an upstairs bathroom. The meter is at an elevation of 276 feet, and the house sits at an elevation of 335 feet. What is the pressure delivered to the upstairs bathroom from the meter?

Difference in Elevation
276 ft – (335 ft + 14 ft)
(276 ft – 349 ft) = -73 ft

Pressure Drop
-73 x .433 = -31.61 psi

Pressure Delivered to the Upstairs Bathroom
72 psi – 31.61 psi
40.39 psi

It meets the requirement of 20 psi of delivered pressure.

Check out the Test Your Knowledge––Calculating Pressure Drop post for additional practice problems.

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