Static pressure is the pressure when water is motionless. In a closed level piping system the static pressure is the same at every point. There are two way to create static pressure, by elevating water in tanks and reservoirs above where the water is needed and by utilizing a pump. Pumps can be used to increase or boost the pressure.
Working pressure is pressure at any point in the sprinkler system when water is moving through the sprinkler system. Working pressure is always less than static pressure because the movement of water through a sprinkler pipe always results in a loss of pressure due to friction.
Pressure loss (friction loss) is equal to static pressure minus working pressure.
Even though the water that is running through the water main in your particular city is probably never at rest, commonly it will be referred to as static pressure. Pressure in the city main will vary depending on demand. This is important to you because it may be necessary to water your yard at times of the day or night when demands on the city supply is lower.
As the flow of water increases, so does the friction and the resulting loss of pressure. In summary, when water demand from the city is at its highest, the pressure will be at its lowest.
Friction loss, loss of pressure, pressure drop, and pressure loss all mean the same thing. The more water that is being forced through a sprinkler system, the higher the flow velocity, and the higher the friction loss.
Friction loss is one of the most important factors when designing or troubleshooting a sprinkler system. I will discuss this topic in much more detail in upcoming posts.
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