The Case of the Overeager Pump


The freshwater division of a municipal water works complained that one of three pumps at a lift station was running constantly, causing the hydrostatic chamber to drain empty. This, in turn, caused the other pumps to come on, and eventually put so much pressure on the system that the pipes burst. The system was only rated for 93 psi, but with the other pumps running the pressure shot up to 130 psi.


The customer had hired an electrician who thought the issue was with the starter, but after replacing the starter the pump would work correctly for a short time, but then return to its hyperactive pumping. If the customer shut down the pump manually the relay would eventually become unstuck and work correctly; but again, this wasn’t a permanent solution.


The ACES Control Systems Investigator called to the scene observed that the relays for Pumps 2 and 3 were 12-volt DC relays rated to 10 amps, and Pump 1 was only rated for .6 amps. The initial amps coming from the starter were well over .6 amps. This caused the contacts on the relay to stick, which in turn caused the pump to run like a five-year-old on a Red Bull rush.


The CSI removed the circuit board to which the relay was attached, and then removed the relay, as well as the terminal strips on either side. He installed a standard 12-volt DC base and relay. To power the components on the board he soldered half of one of the terminal strips to the board, and soldered two wires to the board to deliver power to the relay.

Now Pump 1 switches on and off when it should, and plays nicely with the other pumps.