What size pump?

[jdz]

i am installing a tank 120’ below my house and pumping water from there. I am running a 60/80 switch and using 650’ of 1.5” poly pipe. I think I calculated TDH to be roughly 285’, if I understand how to do it??? I am hoping to use a 25 gpm pump for irrigation plus my house water needs. What horsepower pump do I need? I was looking at the Franklin site and I seen a 1.5 hp 25 gpm pump but the TDH for that was 200’.

Another question I had was about the stages in the pump. I know what they are, I just don’t know what the purpose is to have more or less stages in a pump. Does having more stages increase the pressure a pump can produce?

 

[Reach4]

i am installing a tank 120’ below my house and pumping water from there. I am running a 60/80 switch and using 650’ of 1.5” poly pipe. I think I calculated TDH to be roughly 285’, if I understand how to do it??? I am hoping to use a 25 gpm pump for irrigation plus my house water needs. What horsepower pump do I need? I was looking at the Franklin site and I seen a 1.5 hp 25 gpm pump but the TDH for that was 200’.

Where is that 60/80 switch going to be -- at the tank or at the house? If at the house, I am thinking 3HP. If at the tank, then the 1.5 HP seems about right at first glance.

Another question I had was about the stages in the pump. I know what they are, I just don’t know what the purpose is to have more or less stages in a pump. Does having more stages increase the pressure a pump can produce?

Yes.

 

[Sponsor]

 

[jdz]

The pressure switch will be at the house.

 

[Boycedrilling]

The design of a single impeller or stage At a set rpm, determines the gpm. I.E., is the impeller is 1/2” thick or 3/4” thick. The number of impellers or stages determines the total head that the pump will produce. A 14 stage pump will produce 2 times the head of a 7 stage pump if they both have the same impellers.

the combination of gpm and tdh, determines the horsepower required to operate the pump. If you double the gpm at the same tdh, you’ve doubled the horsepower required. If you double the tdh, at the same gpm, you’ve doubled the horsepower required.

Also changing the pumps rotation speed, changes both the gpm and the tdh, but not by the same percentage.

 

[Valveman]

The pressure tank and pressure switch must be close together. You can't have the tank 120' below the switch. So, if the switch is down by the tank it will need to be set for 90/110 to get and average of 50 PSI at the house. But if the switch and tank are at the house you only need a 40/60 switch to get an average of 50 PSI. A 2HP, 25 GPM pump can get you 25 GPM from 235' of head.

 

[LLigetfa]

I'm guessing the mentioned tank is a storage tank not a pressure tank.

 

[Reach4]

Here is my try at a TDH:
2.31 ft/psi factor
16.74 psi dynamic 650 ft pipe 25 gpm (1)
3.348 psi 20% dynamic compensation curves, fittings, whatever. (2)
20.088 psi dynamic total
46.40328 dynamic head ft


120 static head ft


60 PSI design ( ok for flow less than 25 gpm at 80 psi) (3)
138.6 Pressure head


305 TDH, sum of dynamic, static, pressure head

notes:

1. http://www.pressure-drop.com/Online-Calculator/ 650 ft using 0.03mm roughness which was over-pessimistic. Presumed straight pipe, used 1.5 nominal diameter instead of actual ID.
2. Used pessimistic 20% of dynamic head for fittings, angles, whatever.
3. Instead of using 70 psi (average of 60 and 80), I thought that the 25 gpm at 60 psi was quite sufficient. As the pressure rises, it would be ok for some drop in flow rate.

 

[jdz]

The pressure tank and switch will both be 120 feet above the pump which will be in a storage tank. I don’t see a purpose of putting the pressure controls down at the storage tank.

 

[jdz]

The pressure tank and pressure switch must be close together. You can't have the tank 120' below the switch. So, if the switch is down by the tank it will need to be set for 90/110 to get and average of 50 PSI at the house. But if the switch and tank are at the house you only need a 40/60 switch to get an average of 50 PSI. A 2HP, 25 GPM pump can get you 25 GPM from 235' of head.

The switch will be by the tank, near the house. I am not looking for 50 psi at the house. I currently have my switch set to 55-75 but I am going to change it to 60-80. I prefer more pressure.

 

[jdz]

The design of a single impeller or stage At a set rpm, determines the gpm. I.E., is the impeller is 1/2” thick or 3/4” thick. The number of impellers or stages determines the total head that the pump will produce. A 14 stage pump will produce 2 times the head of a 7 stage pump if they both have the same impellers.

the combination of gpm and tdh, determines the horsepower required to operate the pump. If you double the gpm at the same tdh, you’ve doubled the horsepower required. If you double the tdh, at the same gpm, you’ve doubled the horsepower required.

Also changing the pumps rotation speed, changes both the gpm and the tdh, but not by the same percentage.

I believe the pump I originally referenced was a 1.5hp 8 stage pump rated for 25gpm at 200 ft of head. If I understand you correctly, I would still be able to use a 1.5hp motor if there were 12 stages in the pump and I had 300 ft of head to overcome?

 

[VAWellDriller]

You can use a 1.5HP with more stages to get the head, but you won't get the flow. There is a required amount of HP to do a required amount of work; (which would be expressed as a combination of flow and head)......then you have to factor in efficiency of the pump you have picked. Your flow and head requirements cannot be met with any 1.5HP pump/motor combination. You can either give up something, or increase pump/motor size. I haven't looked but I think it was mentioned above that a 3HP is probably required to meet your specifications.

 

[jdz]

You can use a 1.5HP with more stages to get the head, but you won't get the flow. There is a required amount of HP to do a required amount of work; (which would be expressed as a combination of flow and head)......then you have to factor in efficiency of the pump you have picked. Your flow and head requirements cannot be met with any 1.5HP pump/motor combination. You can either give up something, or increase pump/motor size. I haven't looked but I think it was mentioned above that a 3HP is probably required to meet your specifications.

That’s not what I wanted to hear, I have all the controls and a pumptec for a 1.5 motor from a previous well. I figured that would be the case though.

 

[Reach4]

The pressure tank and switch will both be 120 feet above the pump which will be in a storage tank. I don’t see a purpose of putting the pressure controls down at the storage tank.

Putting those at the house, as you plan, is best.

Some people have power available at the well, and like the idea of having the pressure tank in the well house for space reasons. They have to run much higher pressures at the pressure tank, and that can require special pressure switches and pressure tanks.

Most house do quite nicely with 7 or 1o gpm pumps. That is a lot less hp for a given rise.

A 10 to 13 gpm 1.5 hp would fit. You could perhaps run lower gpm irrigation longer or have more zones.