Go With The Flow!
If you have ever dealt with small KNF diagram fluid pumps, you may have had the frustration of a pump that seems to run but does not actually pump and fluid. But fear not, as we have a simple little trick that will help fix this problem for most instances. However, before I get to the trick, let’s first understand the problem. These micro diaphragm pumps have very small valves inside that direct flow thru the pump. These valves are intended to be submersed (“wet”) at all times, thus resulting in them being very easily prone to drying out and getting stuck. The common symptoms of this problem would be the apparent normal operation of the pump and motor (you can hear and see the pump motor spinning), but no fluid flow is occurring.
So let’s now get the good stuff, my simple little fix. The tools you will need are a plastic syringe (with Luer lock tip), a ¼” Luer lock barbed fitting, length of 1/8” ID plastic tubing, and a 1/8” tubing ferrule and nut (for connection to KNF pump in my example).
Now, fill the syringe up with DI water and connect to the KNF pump. Please be sure to attach the syringe to the inlet side of the pump (as shown below).
You now want to energize the pump, and send a command signal to run at least 50% of maximum rated flow rate. With the pump motoring spinning, slowly squeeze the syringe and inject DI water into the pump. This will re-moisten the valves and push fluid thru the pump to restore proper pumping action.
And that’s it. Your once “bad pump” is now restored and working like a champ.