Pump supply lines: To drain or not to drain?

November 23, 2022

By Sara Heger, Ph.D.

The answer to whether you need to drain pump supply lines depends on where you live. If you live in an area that does not typically have frozen ground, the use of a check valve is common. A check valve is included in the discharge assembly to prevent drain-back through the pump after a dosing event. Drain-back through the pump may cause bearings to wear out more quickly, shortening pump life. This would typically be an issue if the pump was turning on while drainback is occurring (which is not common). In this case, a vent hole (air release) must be provided between the pump and the check valve to prevent air lock of the pump.

In discharge assemblies for colder areas, a weep hole may be added to empty the piping and prevent freezing and limit the backflow through the pump. Typically, some of the effluent will also drain back through the pump and generally is not an issue unless the pump turns on during drainback. 

Be sure the pipe is well supported and bedded to prevent a bow from forming and draining back to the tank. The weep hole is typically 1⁄4-inch perforation drilled on the bottom of the pipe in the discharge assembly to assure that the supply pipe will drain. The other option is burying the supply line beneath frost depths.

Pumping downhill?

If the discharge point is at an elevation lower than the pump-off elevation, an anti-siphon device must be provided. Methods to implement an anti-siphon device include the following:

  • A drain hole used to allow drain-back to the tank can also serve as an anti-siphon device.
  • A check valve installed in a reversed orientation at the highest point in the discharge pipe. When the pump activates, the valve closes. When the pump deactivates, the valve opens and breaks the siphon.  
  • A "spit tube" installed at the highest point in the assembly. The open tube breaks the siphon when the pump deactivates. A spit tube may also serve as a sampling port.