Let My 1/2 Horsepower Centrifugal Pump Run Dry

[dibbons]

I have a Mexican branded (Rotoplas) little pump we use to suck the city water from the underground cistern in the yard where we store it (water pressure is only available here every other night for a few hours at a time). I was watering last night about 8:00 PM when I got distracted and went inside, starting fixing something to eat, watched a video. About 11:30 PM I went outside and heard a faint humming sound which I thought was coming from the next-door neighbor's property. Then I noticed the yard was flooded and no water pouring from the hose where I had left it. I turned off the pump, disgusted with myself and called it a night.

When I checked the cistern the next morning, I found overnight the city water had arrived for a few hours and filled the cistern about 1/4 full. I primed the pump, crossed my fingers, and turned on the switch. Hardly anything came out at first, but after priming a second time I could see a decent stream of water flowing from the end of the hose.

The pump was not leaking, was not making any noise, did not smell burnt or anything, and it was pumping water. The instruction manual warns not to run this motor dry. Don't know how many minutes it ran dry the night before, it could have been hours. Maybe the newer pumps have sealed bearings or something. Can't explain why it isn't more messed up. Maybe it will fail shortly and just giving its last efforts for the team? Hope not.

 

[Demonracer]

Pull the pump & open it up, it might have scorched the impeller internally due lack of water.

 

[vitamindart]

typically they do not want those run dry because the water cools the seal faces. you can melt the seal seat if its run dry.
if its running and not leaking, you may be ok.

 

[straightlinespeed]

More than likely ceramic seal if its leaking you will need to replace the seal. If not leaking run it as stated. Impellar is fine as it should be brass and doesnt make contact with any surface

 

[MiradaMegaCab]

Perhaps put an electrical PSI or Flow switch on the water discharge line to prevent this from happening again. ?

 

[67Dart273]

^^Good Lord THIS^^ It is pretty simple to protect a pump there are several devices you can buy redi made or build something.

1...Rig a float switch in the cistern, easy. Use low voltage wiring and a relay
2...There are several kinds of protective pressure switches. These typically have a lever or button to bypass the safety so you can get it primed and working. It shuts off at the desired pressure, and drops out the pump if the pump LOSES pressure

 

[pt70]

You should be ok. The water level usually stays about 1/3 up in the casting. And the mist should give enough cooling for a while. I'm guessing you ran out of water at 11:29 PM. Happy thought!