Air Release Valves: 2" force main to atmosphere

[mikewags]

I have a well pump that connects to a 2" HDPE pipe at the pitless adapter. The 2" pipe is approximately 1500 feet long. From the well (elevation 640 feet) there is a high point 150 feet downstream (elevation 642 feet). 600 feet downstream of the high point is a low (elevation 638). 500 feet from the low is another high point (elevation 645 feet). 250 downstream is a manhole to which the pipe daylights to atmosphere (elevation 634 feet).
Is an air release valve needed in this situation? The well pump may run continuously for long periods of time, as it is a dewatering well.
Thanks for your help!

 

[bimr]

Usually a well have an air release valve. A well usually drains back into the aquifer on shutdown. On startup, the air service valve discharges the air that is in the well column pipe. If you do not have an air release valve, on startup, the well pump will be starting against the pressure of the water column. On a deep well, this may be considerable pressure.

Since your well is probably shallow, you may be able to get by without this valve.

Since this is a dewatering well, you probably do not need air release valves. However, you need to make sure that the velocity in the pipeline is a minimum of approximately 4 ft/sec. That velocity will push out any air bubbles in the pipeline. If you do not keep the velocity to at least 4 ft/sec, then the pipeline may get air bound because the water flow is not high enough to force the air bubbles down the pipeline.