A question we will get from time to time is “how do I know that my solar pump is running?”  There are several answers to this question so we will cover one way to know if the pump is operating properly.  When you look at it all a pump does is create a pressure differential across itself.  The pump (if working properly) will have lower pressure before the pump and higher pressure after the pump.  This pressure differential causes fluid to flow away from the higher pressure region towards the lower pressure region.  On a closed loop glycol system (or other hydronic systems) you should have the following components in addition to the pump: an expansion tank and a pressure gauge.  A properly designed system will place the expansion tank immediately prior to the inlet to the pump.  The expansion tank serves as the zero pressure change point of the hydraulic loop.  Since the expansion tank doesn’t see pressure change as flow is generated the only way for the pump to do its job (creating a pressure differential) is for the pump to create an increase in pressure on the outlet side of the pump.

This pressure increase on the outlet side of the pump can be easily observed by watching the pressure gauge when the pump is turned on and off.  Watch this video to get a better sense of what you are looking for.  The higher the head of the pump the larger the pressure spike you will see when the pump is turned on.