Today I'm going through an all systems check on my new TT. Hooked up water, made sure plumbing worked, hot water heater, etc. I put some water in the fresh tank (found a leak at the drain valve area, appears to be hairline crack on the tank) Anyway, ran the water pump all was fine. Here is where I messed up. I drained the fresh water and left the water pump switch on by accident. Realized I left it on 6-7 hours later. I heard it humming and said ****! Here is what confuses me.... Why would the pump hum when there was no call for water? It didn't have the loud pulsating chatter when it pumps, just a quiet purr. During my testing, turn on faucet and pumped activated. Shut off faucet and pump went quiet. I don't know why it was humming when there was no call for water. I put water in the tank and tested it again and it worked. How much damage do you guys think I did to pump?

If it's working, it ain't broke....enjoy the trip./...Dennis

If it works now, you probably just shortened it's life. The pump runs until it establishes water pressure in the lines. If there is no water in the tank, it can't establish water pressure, so it continues to run. Under normal conditions, it establishes pressure as soon as you turn off the faucet. Turn on the faucet and the pump runs trying to establish pressure.

The pump failed to prime, therefore was not creating pressure in the system, not even air pressure. The pump relies on water to cool itself. Odd that it ran for so long... Only way to know what, if any damage, is to run it again with water. Sounds like it worked, so I would continue to keep karma in my favour...

I don't believe you've done any damage at all to the pump. The reason it was humming was that it didn't have enough water to pump up to pressure. It was trying to pressurize the lines, and all it was drawing was air.

TucsonJim wrote:I don't believe you've done any damage at all to the pump. The reason it was humming was that it didn't have enough water to pump up to pressure. It was trying to pressurize the lines, and all it was drawing was air.Won't continuously drawing air damage the pump? Burn it up so to speak?

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Executive45
Explorer III
May 05, 2014
If it's working, it ain't broke....enjoy the trip./...Dennis
Water-Bug
Explorer
May 05, 2014
If it works now, you probably just shortened it's life. The pump runs until it establishes water pressure in the lines. If there is no water in the tank, it can't establish water pressure, so it continues to run. Under normal conditions, it establishes pressure as soon as you turn off the faucet. Turn on the faucet and the pump runs trying to establish pressure.
danager
Explorer
May 05, 2014
The pump failed to prime, therefore was not creating pressure in the system, not even air pressure. The pump relies on water to cool itself. Odd that it ran for so long... Only way to know what, if any damage, is to run it again with water.

Sounds like it worked, so I would continue to keep karma in my favour...
TucsonJim
Explorer II
May 05, 2014
I don't believe you've done any damage at all to the pump. The reason it was humming was that it didn't have enough water to pump up to pressure. It was trying to pressurize the lines, and all it was drawing was air.
Tacswa3
Explorer
May 05, 2014
TucsonJim wrote:
I don't believe you've done any damage at all to the pump. The reason it was humming was that it didn't have enough water to pump up to pressure. It was trying to pressurize the lines, and all it was drawing was air.

Won't continuously drawing air damage the pump? Burn it up so to speak?
Tacswa3
Explorer
May 05, 2014
Good news, Found the manufacture spec sheet on the pump. Apparently its a dry running pump and is able to run dry without damage. Sweet
TucsonJim
Explorer II
May 05, 2014
Yeah, I know from first hand experience. My brother came to visit and used the RV. One morning I was walking by it and heard the pump. I asked him how long it had been going on. He said a couple of days!
cochise49
Explorer
May 05, 2014
Were me...I'd find a sale on water pumps and keep a fresh one on hand. I do that anyway. Even if you need a technician to install it you won't have to wait for the part to come in. I can get anything in two days from Amazon or CW. Businesses seem to need a week or more.
wa8yxm
Explorer III
May 05, 2014
Why would the pump HUM if there is no call for water? Well, this is an easy one, The pump is controlled by a pressure switch, I will round shamlessely and say that it wants to see 50 PSI, if it sees 40 PSI, OR LESS it turns on and pumps. It will pump air if there is nothing else to pump but due to the design of the pump it can not compress AIR to 50 PSI shut off, so it will run, as long as the batteries hold out.

(Water does not compress, what compresses is the air cushion in the water heater, Thus providing the back pressure needed to shut it off.. If you really need to understand why it works I can explain but ... Well, enough typing already for one post.

Thus the pump keeps running and running...

Now the good news: Most all RV water pumps have no problem running dry for hours on end,, Does not harm them.
Tacswa3
Explorer
May 05, 2014
wa8yxm wrote:
Why would the pump HUM if there is no call for water? Well, this is an easy one, The pump is controlled by a pressure switch, I will round shamlessely and say that it wants to see 50 PSI, if it sees 40 PSI, OR LESS it turns on and pumps. It will pump air if there is nothing else to pump but due to the design of the pump it can not compress AIR to 50 PSI shut off, so it will run, as long as the batteries hold out.

(Water does not compress, what compresses is the air cushion in the water heater, Thus providing the back pressure needed to shut it off.. If you really need to understand why it works I can explain but ... Well, enough typing already for one post.

Thus the pump keeps running and running...

Now the good news: Most all RV water pumps have no problem running

dry for hours on end,, Does not harm them.

Thanks! I appreciate the explanation, makes sense.

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