Gas pump for pressure tank?

[itinerant]

Hi all,

I am trying to understand if it is possible to use a gasoline powered water pump to fill a pressure tank. I have an off grid camp on a lake in northern Maine. For decades we have used a gasoline pump to fill a 50 gallon tank that sits on a slight hill above the cabin. The pump sits on the shore of the lake, less than 15 vertical feet above the water, and pushes the water another 60 or 70 vertical feet up to the holding tank, which then feeds our sink via gravity. Our pump is a 3.5hp Koshin/Honda: https://www.koshinamerica.com/shopproductdetail.asp?prodID=14

This has worked well, but we recently hooked up a small tankless water heater, and the gravity from the holding tank does not provide sufficient water pressure to activate the heater. I have temporarily fixed this by installing a small 12v RV pump to pressurize the line, run off a car battery, but what I would really like to do is replace the holding tank with a big pressure tank (maybe 86 gallon, which would give me about 26 gallons of drawdown at 20-40 psi). My question is, can a gas pump like the one that I have be used to fill a standard pressure tank? The specs on my pump say that it can manage 42 psi maximum. So in theory, I could put a pressure gauge on the line above the pump, and run the pump until it reaches about 40 psi, and shut it off. Does that make sense? Suggestions appreciated!

 

[WorthFlorida]

Probably not. Pressure tanks are usually set up to run between 30-50 PSi or 40-60-PSI depending on the HP of an electric motor pump. Pressure switches are integrated with the electric motor. When you reach the set pressure, the pressure activated switch shuts off the motor. That cannot be done with a gas powered pump. Tankless water heaters are nice but in this case an old fashion electric water heater may be the simplest solution.

Going with a generator and electric pump might be an alternative but most affordable electric pumps cannot push water that high. There are generators that can run at idle without a load, and then comes up to speed with a load, such as an electric pump. My experience is some motors, a washing machine, could not go into spin mode because of an unregulated power generator. So it is not just getting a generator and electric pump.

 

[Sponsor]

 

[Reach4]

It's close. It may not work as well as your tank 80 ft up.

The specs on my pump say that it can manage 42 psi maximum.

At 0 GPM. 42 PSI is 97 ft of water. 80 ft of water is 34.6 PSI.

 

[itinerant]

To clarify, the holding tank is currently about 80 feet above the water, not above the cabin. It's only about 10 feet above the cabin. The gas pump currently fills the 50 gallon tank in about 10 minutes, which means it's pushing 5 gallons of water 80 feet every minute or so. Does the additional pressure of the bladder/air in the pressure tank mean that the pump wouldn't be able to fill/pressurize the tank? I'm not concerned about the automatic shutoff feature of an electric pump/pressure switch. I'm also not going to use a traditional water heater, for a number of reasons. I guess the question is: if my gas pump is currently pushing 5 gpm up that 80 foot rise, is the additional work required to pressurize a tank going to be too much for it? If so, would a shallow well jet pump positioned on the lake shore even be able to push the water that high AND pressurize the tank (if, for example, I were to run it off a generator)?

Thanks all.

 

[Reach4]

Your current pump is not well matched to delivering 5 GPM or even 10 GPM. You would want a 7 or 10 GPM pump, I think. Your pump is designed for lower pressure high volume. It would be a gross exaggeration to say your pump is like a leaf blower being used to put air in a tire, but you get the idea. The SEH-40H would have been better (but still not that good of a match) than than the SEH-50X for this job. https://www.koshinamerica.com/images/KAC-0116-04.pdf

A submersible pump in the lake pumping into a pressure tank at the cabin would serve you well if it was a 1/2 HP 7 GPM submersible pump I think. Put a flow inducer on it (made from just a few feet of 4 inch PVC or ABS pipe). Put a screen wire cage around the intake to keep out fish and vegetation. I would put a whole house sediment filter after the pressure tank. Honda EU2000i generator is nice and quiet but expensive.

If you want a suction pump, maybe a 1 HP 7 GPM pump would be good. There may be a gasoline powered pump along the same lines. If you are going to use a high volume pump, you should probably switch to bigger pipe from the pump to the house.

 

[itinerant]

Reach4, thank you, that is extremely helpful info, and makes a lot of sense. A submersible pump had occurred to me, and I actually already own one of those Honda gennies, but what about the issue of an electric pump in water that people swim in? Are we assuming that any time the generator is turned on, no one is in the lake near the pump, in case of shock? If so, that seems a little sketchy but totally doable - we don't have any neighbors for 4 miles.

Just to follow up on the suction pump question, when you say a 1 HP 7 GPM pump, does that describe a 'standard' 1 hp shallow well jet pump (like this: http://www.flotecpump.com/ResidentialProduct_fl_hw_jt_FP4150.aspx)? Or are we talking about something more specialized?

Thanks so much for your help!

 

[Reach4]

This would be a good time to use the ground wire connection. You could even power the pump through a GFI if you wanted to be extra-careful.

when you say a 1 HP 7 GPM pump, does that describe a 'standard' 1 hp shallow well jet pump

I was being quite generic. I tried to look for the curves on that pump you used as an example, but I did not find it right away. Jet pumps are not as efficient.

 

[itinerant]

Got it. Thanks again - much appreciated!