12-volt water pump advice

[JimandLou]

Looking for a good, reliable 12 volt water pump for our off grid cabin (toilet, shower, sink).  We're at 7300 feet. Pump inlet pressure via gravity flow thorugh 1 inch pipe from cistern is 15 psi and 2 gpm.   Horizontal run from pump to cabin is about 30 feet, total lift about 20 feet.  We'd like about 4 gpm and 40 psi minimum.  Have tried a Flojet VSD advertised at 4.5 and 45, but it only puts out 22 psi (great flow, though).  Then tried a Flojet Triplex 3526 advertised at 2.9 and 50.  Worked great for 5 minutes, then motor burned out.  Water is crystal clear.  Battery voltage 12.7, followed all installation instructions.  Where'd we go wrong?

[thirteen]

Not sure of your system but do you have a water filter before the pump?  I put one in and the bleed vlave on the filter leaked some air and I had a hard time getting preasure to stablize. Some pumps have a setting that is adjustable for preasure for different aplications. Your lift might be more than the pump can handle. It maybe trying to pull more water up than can be supplied thus starving the pump.  In turn possibly burning the pump. I'm sure you cheated but kind of a long shot are your shutoff valves fully open. Do you know what was the preasure before the pump burned out. Maybe you had a bad pump I would call Flowjet they may be able to give you some information,  Just some ideas.

[thirteen]

checked not cheated HA HA I caught it afterward

[stephent]

I'd say your pumping more then the feed system can deliver.

Use a reserve tank (air bladder style) between the pump and cistern to help keep the volume up to the pump. Probably 30 to 40 gallon capacity.

[Nando]

You already have some pressure and just to increase the pressure to 40 PSI and 4 GPM You need 48 watts of energy at 100 % efficiency, for 50 %over all, You will need 100 watts.

Motor burn out can be caused by a locked rotor or too high friction due to debris in the water.

You are not clear with the whole system, one needs to remember that the only person that knows the system is You (or am I wrong here ?.).

Give an accurate detailed description step by step to see what is going on, this way a possible realistic suggestion can be given.

Something is wrong with your statement :

>Pump inlet pressure via gravity flow through 1 inch pipe from cistern is 15 psi and 2 gpm.

Can You accurately tell us if you have the water volume and the pressure at the same time, or is the pressure static at zero water flow and the volume of 2 GPM when the pipe is in full flow fully open ?,

Because 15 PSI is 10.6 meter head, that with 1 inch pipe, the open pipe flow for such short distance would be 7.2 liter/sec or around 115 GPM.

How old is the pipe in the system ?.

Is the water clear with out any sediments that may place or glue "Cholesterol" on the pipe walls ?.

If the pipe is clogged the pumps may be fighting a restricted flow causing over heating and motor burn out.

Nando

[Volvo farmer]

Good advice.

I just went from an on-demand 3/4 HP jet pump (no pressure tank) to an 80 gallon pressure tank and a Shurflo 2088 series on 115V. They make them for 12V too. My energy consumption dropped by almost a degree of magnitude for water pumping. Some of the 2088s are rated at 3.3 GPM. Mine runs about 20psi to 35 or so on the pressure tank, though I think the pressure is adjustable up to 45 or so. I've had the thing come on when I'm in the shower and the pressure definitely rises while it is on, I think the showerhead is rated at 2.6GPM at about 50 PSI.

I don't know what you're water requirements are but for one fixture at a time, this little Shurflow has been fine so far. I think the Flowjet pumps are a similar design so perhaps you are asking too much from the little pump?

[thirteen]

you may try back flushing the system to clear the pipe.  A little dirt in the  pipe will cause problems of supply.

[desertcoyote]

I have been through a pile of pumps. my latest is a 24V piston pump with leather rings feeding a pressure tank. So far so good. I really like the fact that the motor runs at 1800 rather than the normal 3600 rpm. runs quite too. according to the manual it is fairly tolerant of dirt or rust in the supply. It has only been a couple of months though. got around 5-years out of the 24V sureflow type. pump seals, brushes, and commutators get old. AC centrifugal pumps work, but are disgusting power dipping hogs. hopefully the 20 year thing works this time.

[JimandLou]

Thanks everyone for your thoughts.  To clarify, gravity flow from our 3600 gallon cistern is 2 gpm at 15 psi. When valve is fully open, flow is about 4 gpm, but pressure drops to about 5 psi.  System is new and water is clean.  No filter between cistern & pump.  We'll contact Flojet to see if we're asking too much from their pumps.  If so, we'll check into your suggestions.  Thanks again.

[mungewell]

Any update on this?

I'm currently looking at using the Flojet in a similar manner, but from 24V supply.

Simon.

[mungewell]

Follow up for future 'searchers'.

I did indeed purchase/install a Flojet R4525-743 (auto 12/24V, 4.5GPM), it is working but not perfectly. Once the household plumbing was connected the back pressure of all the pipes cause it the flow to pulse, I think some adjustment of the Pex piping is required.

Another note, forgot to isolate pump when equalisating battery this weekend. My wife came down to complain that the water wasn't working. 1/2 hour of concern whilst we waited for equalisation to finish before we found out that the pump survived.... must have auto-protected.

Will remember to isolate next time, just in case.

Simon.

[bridget]

We have a  12v NEMO pump, diaphram pump, it gives about 2 gpm with 40 feet of head. they come in 24v as well, we've had it in place for about 6 years, mostly for gardening at this point but hooking it up for household supply this year. We plan to have a storage tank and a flojet in line to suply the house with more pressure.

[mungewell]

And another comment about this scheme; some time in the last week the pump managed to freeze. We were away and temp dropped to -27'C, I guess the lack of usage (and therefore heat generation) contributed....

Just a caution to anyone else. I intend to rig up some thermostat controlled heating to prevent this happening again.

Simon.