Pump ‘cycling’ is when the pressure switch of any demand style pump is rapidly turning on and off. Understanding why your pump is doing this is essential to finding a solution to the issue.

Understanding Pressure Switches

To understand why your pump is cycling it is important to understand how a pressure switch works. On the top of all demand style pumps there is a pressure switch. Inside the pressure switch is a small diaphragm connected to an electrical On/Off switch. Once the pressure in the pump head reaches a certain pre-set limit (ex. 60 psi) the diaphragm will inflate and hit the electrical On/Off switch turning your pump off. Once the pressure in the pump goes below the pre-set limit (ex. 60 psi) the diaphragm will deflate turning the pump back on.

Flow vs. Restriction

The flow of your Delavan Pump and your system’s restrictions are the next factors to consider. The flow of your Delavan Pump is written on the label of your pump. For this example, you have a 5 GPM Delavan pump and have it hooked up to nozzles or a spray wand. The nozzle or wand is only able to put 2 GPM, this is the restriction of your system. Your pump always wants to push 5 GPM but the system restriction won’t allow it. This causes your pump’s pressure switch to rapidly turn On/Off. Much like any electrical system, turning your pump On/Off rapidly is causing damage and may cause your pump to prematurely break down.

How do I stop my pump from cycling?

Recognize what is causing the restriction. It could be the size of your nozzles, the wand you are using, a kinked hose in your system, the diameter of the hose, too many 90º fittings. It can be one or a few of these issues. Fixing the restriction and increasing the flow of your system will stop cycling.

If you are using a Sprayer or Wand type system you can easily add a return to tank or “bypass” which will circulate any extra fluid back to the tank. Do this by adding a T-fitting and valve just past the outlet and a hose which will direct any excess flow back to the tank. We have a Youtube video explaining this:

Finally, you can adjust the pressure of where your pressure switch will turn off power to your pump by adjusting the set-screw on top. Follow this link for an explanation of how to do that. Please see ESR-001.