VFD/Pump and Low Water Flow Error?

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mirinjesse

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I have had the 2HP VFD installed for 6 months https://www.aquascience.net/downloa..._aquavar_installation_and_troubleshooting.pdf. It’s got a small expansion tank included.

I’m on town water, 50psi, boosting to 70psi and expansion tank is filled to 60 which is 5 below the turn on pressure of 65. Been working fine, then I got irrigation installed and I seem to be having the occasional issue where I get a “lose of prime error” and my pump turns off and has to be reset. I have done some troubleshooting and I believe when I have irrigation on and say take a shower at the same time, my water flow can’t keep up with the required 70psi because the incoming pressure is so low. So I did some testing and ran irrigation without anything else running and it seems to work, but then another time it seemed to get the error, so not sure if it’s just this or if has to do with lower incoming water flow at times as well?

Is there anything I can do, besides lowering the pressure down which kind of defeats the purpose of installing this? Bigger expansion tank so it gives the unit more time to catch-up?
 
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Valveman

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I am sorry you got stuck with one of those expensive VFD systems that are so computerized and complicated that no one can figure out what is going on. All you are doing is pumping water, which is not that complicated and doesn't need a VFD. But having said that, the VFD may not be your problem. Post a model or curve for the pump. That pump might be large enough to boost from 50 PSI to 70 PSI, but may not be large enough when the inlet pressure drops to say 20 PSI. Either the pump is not strong enough to boost from low pressure to high, or the mainline is too small to supply the volume needed for the pump.
 

Reach4

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Put the sprinkler on a timer to water at 3AM, and do not take 3am showers without telling your controller to skip watering?
Put a pressure gauge on the incoming water, during irrigating, to see if the problem is the supply to the house?
Use lower gpm emitters, or run fewer emitters at a time? That would take more zones controlled by your sprinkler controller.
 
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Fitter30

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City water line what pipe size, material, difference in elevation and length feeds the pump? Have s gage on suction of pump?
 
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mirinjesse

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I have a pressure gauge after pump and when pump is off completely (after emptying reserves) it reads 50psi. I can put a gauge before the pump though and come back with that, but I’d assume it should read 50psi as well?

I have this 2AB25HM05 and detailed graphs are here https://cdn.accentuate.io/750031385...-Pressure-System-Datahseet-v1641976001603.pdf

I can try the 3am thing, but it’s weird, I did it once during the day without anything running and it was fine. The second time later in the day it had the issue. I have 5 heads per zone at this point and it’s a dedicated line directly after the pump.
 

mirinjesse

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City water line what pipe size, material, difference in elevation and length feeds the pump? Have s gage on suction of pump?
1.25” looks to be pex incoming into the house and then stepped down to 3/4 PRV (which is turned to highest pressure) and then into 1” in piping to the pipe. Idk what happens after the main as it’s underground to where it connects to city water.
 

Valveman

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That pump has a max pressure of 77 PSI. But it can still do 20 GPM at 70 PSI. So, even if the city pressure drops to zero coming into the pump, it should still make 20 GPM at 70 PSI. However, if any of the line is reduced to 3/4", it will be limited to 10-15 GPM.
 

John Gayewski

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Prv's are rated for a min and max flow. Are you exceeding the max flow rate of the prv? We don't use the size of the prv connections to size them. They are rated from the factory for certain conditions (which can be hard to find without a phone call).
 

Fitter30

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Since the pump curves only list at 0 psi suction need a compound gauge ( reads vacuum and pressure -30" to 30 lbs 2.5" with a valve to keep from screwing up the gauge) on suction of pump. Open valve only with pump running after trying a higher pressure gauge to be sure your less than 30 lbs. Without a suction gauge it's only a guess of pump is doing. That 77 lb discharge is shut off pressure ( discharged valved off @ 60hz). Prv is piped in before the pump? Take it out that's is problem.
 

mirinjesse

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Prv's are rated for a min and max flow. Are you exceeding the max flow rate of the prv? We don't use the size of the prv connections to size them. They are rated from the factory for certain conditions (which can be hard to find without a phone call).

It has a psi range, but not sure this equals flow. Anyway, plan is to remove this PRV this weekend as it seems it could be a point of restriction.
That pump has a max pressure of 77 PSI. But it can still do 20 GPM at 70 PSI. So, even if the city pressure drops to zero coming into the pump, it should still make 20 GPM at 70 PSI. However, if any of the line is reduced to 3/4", it will be limited to 10-15 GPM.

Irrigation used 10GPM per zone. Incoming line is 1.25”, reduced down to 3/4” and then stepped up to 1”/1.25” at the pump itself. This is with the PRV. I am going to redo all of this so it’s only stepped down from 1.25” to 1”, remove the PRV and do additional testing.

Everything that this group has stated, seems to seem that the pump keeping up or creating the pressure shouldn’t be an issue.
Since the pump curves only list at 0 psi suction need a compound gauge ( reads vacuum and pressure -30" to 30 lbs 2.5" with a valve to keep from screwing up the gauge) on suction of pump. Open valve only with pump running after trying a higher pressure gauge to be sure your less than 30 lbs. Without a suction gauge it's only a guess of pump is doing. That 77 lb discharge is shut off pressure ( discharged valved off @ 60hz). Prv is piped in before the pump? Take it out that's is problem.

Going to remove the PRV that is piped from the pipe, I left that in place, but it may be impacting some of the flow given it’s all 3/4 as well.

I will also add a tee for a gauge to check pressure at suction after doing this and report back if my issues still persist to see if there are any other suggestions.
 
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