Criteria for selecting pump

[madhattie]

I have a low yielding well (3 gpm) with 6 inch PVC casing. We have a seasonal fluctuation of about 15 feet in our static water level. The pump setting depth and water level measurements tell me that the amount of reserve water in the casing will be about 50 gallons during our dry season (fall/winter) and about 78 gallons during spring/summer.

When looking at the criteria for pump selection should I use the low-50 gal basis for calculating which pump to get?

 

[Reach4]

I would think you might use the midpoint if you need a single number. If the available flow slows as you are about to run out of water, I don't see that as a problem. Pumps are only available in certain sizes.

Are you thinking 7 GPM pump? Are you going to use a backwashing iron filter or other higher flow load?

You would probably do well to use a device, such as Cycle Sensor, to shut down the pump for a while if you run out of water.

You could also consider running a tube, open at the bottom, down with your wiring. You blow air into it from up top, and from the pressure it can maintain, you know the current water depth.

 

[Sponsor]

 

[madhattie]

Are you thinking 7 GPM pump? Are you going to use a backwashing iron filter or other higher flow load?

I don't know yet whether we will need a backwash filter. Just recently bought the property and the pump was defunct. There was no filter on the existing system.

I like the Grundfos 5SQ-140 - 1/2 HP 5 gal per minute (flow range of 1.5 - 7.5 gal per minute). But, I may need the Grundfos 5SQ-180, depending on whether I calculate TDH at low water level or mid range of the fluctuating water level. Here are my calculations:

Total Dynamic Head = 190.28 @ 51’ static water level
Total Dynamic Head = 179.28 @ 40’ static water level
(pump performance curves attached)

Thank you for any assistance in clarifying this for me.

 

[Reach4]

How deep is your well, and what is the pump setting depth?

With a 6 inch casing, I would not be looking at an SQ pump. I would rather have a 4 inch pump that runs about 3500 RPM than a 3 inch pump running over 10,000 RPM.

Is the inside of the toilet tank rust-red?

 

[madhattie]

How deep is your well, and what is the pump setting depth?

The well is 110' deep and we will be setting the pump at 90'. Static water level is 51' during dry season and 35' during wet season. I measured those levels since pulling the old pump. The original well driller's report in 1986 identified 3 gal per minute flow rate, static water level at 30' and a "stabilized measured pumping water level" at 70'.
And no, there is no rust stain anywhere in the house fixtures.

 

[Reach4]

20 ft is a common distance to set the pump from the bottom. That leaves space to let sediment sit that does not get sucked up. However in the case of a well that may run dry, setting it deeper can be good.

Of the 2 choices you named, the 05SQ05-180 wound be the better choice.

With the SQ, I think you only get the top part of the curve you posted. With the SQE you also need to have the controller to bring the pump down to a lower RPM. That adds more complexity and cost.

Instead I would tend to use a 4-inch pump. The 1/3 HP pump would be OK for a 30/50 PSI and maybe a 40/60 system, and the 1/2 could be used with a 40/60 or even 50/70 PSI setting.
You would use a 44 gallon pressure tank, or you could use a CSV with a smaller tank.

 

[madhattie]

20 ft is a common distance to set the pump from the bottom. That leaves space to let sediment sit that does not get sucked up. However in the case of a well that may run dry, setting it deeper can be good.

My reasons for preferring the Grundfos are:
1) Frequent power outages and need to occasionally run the well on a generator
2) Future likelihood of installing off-grid solar electric. I could then get the controller for the pump. I've already had long go-rounds with the POS utility company about their service and smart meter. They don't allow opt-outs from their meter and I have EHS. So actually, we are outfitting the house systems for lowest possible electric needs (wood heat, propane kitchen stove, propane water heater, etc) in anticipation of using a solar system.

 

[Reach4]

The Grundfos SQFlex can run on AC or DC. http://us.grundfos.com/products/find-product/sqflex.html

The Simple Pump would let you back up an electric pump with a hand pump. http://www.simplepump.com/

 

[madhattie]

The Grundfos SQFlex can run on AC or DC. http://us.grundfos.com/products/find-product/sqflex.html/

I've looked at the SQFlex and we have eliminated using solar DC to run a pump set at 90'. It is my understanding that DC power has a limit of 40' max for the electric line.

If the 180 model Grundfos SQ is suitable for our needs, then the only remaining question I have is whether to get the 230V or 115V version of the pump. I think using it with the controller might require 230V. I plan to call Grundfos tomorrow (Monday) to get more details.

 

[Reach4]

It is my understanding that DC power has a limit of 40' max for the electric line.

Where did you pick that up? Not reasonable.

 

[Reach4]

230 volts would draw half as much current. On the other hand, the little Honda EU2000i can provide 120.

 

[Valveman]

Like Reach said set the pump as deep as you can. Use a 4" flow inducer shroud to keep the motor cool. And even running from a generator or inverter the regular 4" pump like the 7S05 will work fine and last longer. The Cycle Sensor will shut the pump off if you run it too long and pump the well dry.

 

[madhattie]

Where did you pick that up? Not reasonable.

When I was getting a quote from a solar well pump company they told me that was the limit for the DC powered route. Perhaps they were just talking about their DC powered pump?

 

[madhattie]

Like Reach said set the pump as deep as you can. Use a 4" flow inducer shroud to keep the motor cool. And even running from a generator or inverter the regular 4" pump like the 7S05 will work fine and last longer. The Cycle Sensor will shut the pump off if you run it too long and pump the well dry.

Regular 4" pump like the 7S05? I have no information about that pump. Guess I'll need to check it out. Why do you say it will last longer?

I already purchased the cycle sensor. Very sensible unit.

 

[Valveman]

Regular 4" pumps spin 3450 RPM. The SQ spins 10,700 RPM. From Grudfos' own engineering manual it states that doubling the RPM of a pump will quadruple the wear rate. Should be a no brainer.

 

[madhattie]

Regular 4" pumps spin 3450 RPM. The SQ spins 10,700 RPM. From Grudfos' own engineering manual it states that doubling the RPM of a pump will quadruple the wear rate. Should be a no brainer.

Zing.... right to the point. Thank you so much.