System not maintaining pressure after water runs out in storage tank

[thelinuxfan]

Hello! I have a Grundfos booster pump that connects to two storage tanks. Every once in awhile, someone leaves water running and the storage tank runs out of water. When this happens, the system will not pressurize until the water level in the storage tank reaches the pressure gauge. If I power cycle the pump, it will work but cannot maintain the pressure. The system works until the water is below the outlet of the tank, but we have to wait until it reaches the gauge.

Why does the system need to be at such a high level to work? We have to wait until there are nearly 300 gallons in the tank to work when it works with only < 50 gallons before it runs out. I am sure gravity has a role somewhere in this issue.

Even if I can't resolve it, I'd like to understand why the problem exists.

I am not home right now. My wife let me know it occurred, but I have some pictures saved. The first picture is where the gauge is located. That line goes into the pex you can see in the next picture near the water softener.
Thanks!

 

[Valveman]

Do you have a low level cut off float switch in the storage tank? What kind of booster pump is it?

 

[Sponsor]

 

[thelinuxfan]

It is this pump: Grundfos 22 BMQE 10C-190. I do not have a float switch in the storage tank for the booster pump, just for the well pump.

 

[Reach4]

Pressure drop after the storage tank runs dry should be expected, don't you think?

In filling a cistern, a pump-up float switch, as you have, controls the well pump. A pump-down float switch can be added to inhibit the pressure pump when the cistern runs dry.

 

[Bannerman]

Suggest posting a photo showing the location of the pump in relation to the bottom connections on the storage tanks.

I suspect your pump is located above floor level, possibly similar to the pressure gauge elevation. If so, I expect the pump is loosing prime when the tank level is low, but once the water level in the tanks rise again above the gauge elevation, water is then flowing by gravity to the pump inlet, thereby restoring prime between the tanks and pump inlet.

 

[Valveman]

It is this pump: Grundfos 22 BMQE 10C-190. I do not have a float switch in the storage tank for the booster pump, just for the well pump.

Oh OK...a submersible in a can type pump. Very familiar with those. There are places in the can that trap air and need flow through before it will prime the pump. Best to not let it run dry. Adding the pump down float switch to shut it off before it sucks air would be a good idea. May also need a relay to open both legs to the CU301 controller, as cutting only one leg may damage the VFD.

BTW that pump will work great with a Cycle Stop Valve. When you get tired of the problems and expense of the CU301 VFD thing,, it can be replaced with a regular pressure switch and a CSV1A can make the constant pressure you want.

 

[Valveman]

Could also just put the submersible in the cistern as those cans are expensive.

 

[Fitter30]

It is a booster pump it's not made to pull water needs a little back pressure to start to build pressure.

 

[thelinuxfan]

That kind of makes sense, but it works when there is only 30 gallons in the tank. It is only when the water drops below the outlet that it has to make it back to the gauge level which is around 300 gallons.

Say there is 280 (or 140 in both tanks) gallons and it is half an inch below the gauge, it will not work. Why does it need that last 1/2 in to work? Why does it work where there is only 30 gallons but hasn't been ran dry? As I originally stated, I assumed gravity and pressure is part of the problem.

Is there anyway to prime the system to get it to work again? It sucks when we lose water for over 12 hours.

 

[Fitter30]

What are using to maintain level in the storage tanks.280 gallons of storage how long does it take to refill?

 

[Bannerman]

Why does it need that last 1/2 in to work? Why does it work where there is only 30 gallons but hasn't been ran dry?

Answered in the prior replies.

 

[thelinuxfan]

What are using to maintain level in the storage tanks.280 gallons of storage how long does it take to refill?

There are 2 300 gallon tanks. It takes probably 10 hours to fill. Unfortunately, it will rune dry. There isn't a float for the booster pump.

 

[thelinuxfan]

Could also just put the submersible in the cistern as those cans are expensive.

View attachment 98493

Yes. I am sure we could modify it for this, but it wouldn't be cheap.

 

[thelinuxfan]

Suggest posting a photo showing the location of the pump in relation to the bottom connections on the storage tanks.

I suspect your pump is located above floor level, possibly similar to the pressure gauge elevation. If so, I expect the pump is loosing prime when the tank level is low, but once the water level in the tanks rise again above the gauge elevation, water is then flowing by gravity to the pump inlet, thereby restoring prime between the tanks and pump inlet.

It is on the ground flush with the outlet of the storage tank. I am sure it is losing prime when the level drops below outlet; however, it still won't supply pressure until the water level is at the gauge which is about 3 ft above the pump. Here is a better picture.

 

[Fitter30]

2.31 ' = 1 lb of pressure doesn't matter what size pipe.

 

[thelinuxfan]

Answered in the prior replies.

I don't think it was answered. I didn't have a great picture of the pump on the floor as it was hard to see in the first photo. The inlet of the pump might be dry for a very brief time when it initially runs dry and then the well pump will fill it within minutes, but the pump won't maintain pressure until the tank is above the gauge which takes many hours to fill. During this time, the inlet will have hundreds of gallons of water above it. I will turn off the valve to second tank to restore pressure quicker.

I apologize if I am missing something really obvious.

We have nine people in our house and we never run out of water showering, dishes, laundry, etc. The well pump has no problem keeping up with that, it is really only when water is accidentally left on on a spigot or the kids play in the in the water for too long.

 

[thelinuxfan]

2.31 ' = 1 lb of pressure doesn't matter what size pipe.

I am not sure what this is in reference to. I don't think I was saying there would be more or less pressure in a pipe. If this is in reference to me saying won't supply pressure, I mean when the inlet of the pump has water, it will not bring the system to pressure. It will run for 30 seconds or so and stop because it can't maintain pressure.

 

[Valveman]

Oh OK...a submersible in a can type pump. Very familiar with those. There are places in the can that trap air and need flow through before it will prime the pump. Best to not let it run dry. Adding the pump down float switch to shut it off before it sucks air would be a good idea. May also need a relay to open both legs to the CU301 controller, as cutting only one leg may damage the VFD.

BTW that pump will work great with a Cycle Stop Valve. When you get tired of the problems and expense of the CU301 VFD thing,, it can be replaced with a regular pressure switch and a CSV1A can make the constant pressure you want.

Maybe I can say this a different way. after that type pump runs dry, the pump doesn't need to be primed, the can needs to be flooded. There are places in the top of the can that trap air and make it hard to flood until there is some kind of flow, which can't happen until the pump is drawing water. It is not like priming a centrifugal or jet pump.

Easiest to put a pump down float switch above the intake for the pump and shut the pump off before the can is sucked dry.

You might also be able to tap the top of the can and add an air relief valve.