Need Advice

[deicer]

Hi I recently ahd a new irrigation system installed. I needed a booster pump so the irrigation contractor recommended a Grundfos MQ pump which I installed on the irrigation line only. This runs the irrigation system well. Now the pump sucks the water form the house side of my system. Only a trickle of water or none or even sucking air back into the system. The irrigation system runs at night. I need some water in the house at night with three children.

Some details. City Water 3/4" line onto the house. Static pressue 50psi. Poor GPM inot the house but the pump dosen't run dry. The line to the irrigation system tees right after the meter and before the
PRV. I put a check valve on the house side of the system. This helped a little with sucking air back into the system. The irragation line has a backflow preventer.

Would a pressure tank on the house side of the system give me water in the house while the pump is running for things like flushing toliets and getting a drink of water at night? I would like to avoid another pump. Thanks.

 

[Bob NH]

The plumber didn't do any plumbing engineering for you.

The Grundfos MQ 3/4 HP will pump more than 16 GPM at flooded suction condition (zero inlet pressure; no lift). That is probably more than your 3/4 inch line can provide.

Here is the simplest solution for you.

Make a connection between the discharge of your pump and the HOUSE side of your new check valve.

Draw the picture and you will see that the pump will provide pressure to the house when the pump is running. When the pump is not running, the flow will go through the pump or the check valve. At your household flows you should not have a problem with the pump spinning. It shouldn't hurt it to spin a little.

If the pressure is too high for the house, then insert a small (1/2") pressure regulator in that connection. If the pump only runs when the irrigation valves are open, then you shouldn't have a problem.

You could put a tank after the check valve, instead of the crossover. It would have to be large enough to supply all of your needs while the pump is running.

Pulling a water line below atmospheric pressure creates a hazardous condition. It can suck polluted water in through a leak. If you want to see the effect, Google "holy cross football hepatitis".

 

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[deicer]

Thanks for the reply. Would I also have to move the doublecheckvalve backflow preventer downstream from the discharge of the pump but before the crossover? When you say the pump will spin a little I think you mean by the flow of the water and but won't the flow switch make the pump come on even with the normal house hold flow?

 

[Bob NH]

I was not aware that there was a flow switch.

If you set the pressure on a regulator in the crossover at less than the municipal operating pressure (set it at 30 psi if the municipal water supply is 50 psi), then the regulator will close when the pump isn't running. The regulator will open when the pump is running and sucks the pressure down so the irrigation pump will maintain the set pressure in your house. That will solve the spinning and flow switch problem.

A Watts 263AB, Grainger Stock Number 2A645, is a 1/2" water pressure regulator that can be adjusted over a range of 3 to 50 psi and accepts up to 300 psi inlet pressure. My last-years catalog price is $37.85. Put that in the bypass and set it at about 30 psi. Get a 100 psi gauge (Grainger stock 5WZ19, $3.21) to set the regulator.

You will need to set the regulator when the irrigation booster is running, because otherwise the downstream pressure will be greater than 30 psi.

Your check valve creates a closed system. You should be adding an expansion tank (Grainger 4UN99, $56.30), or you can drill a 1/16 hole in the check valve poppet to let the backpressure escape. That hole will have little effect on your irrigation pump capacity.