Pump size vs tank size

[Traveller]

I have a Grundfos 2 hp convertible jet pump rated at a max. flow of 32 US gpm. It is 20 feet to the water table from the pump intake and I am installing this as a shallow well jet pump, though I may convert to deep well application in an attempt to boost the volume.

How do I calculate the volume of the bladder tank, in order to keep the pump from starting too often? The manufacturer recommends no more than 20 starts per minute.

 

[LLigetfa]

The manufacturer recommends no more than 20 starts per minute.

Wow! Most here advocate no more than one start per every two minutes. Basically more than one minute of run and more than one minute off. There is not enough known by what you posted to calculate tank size but you could eliminate a lot of guesswork by installing a Cycle Stop Valve.

Based on it achieving the 32 GPM spec'd, you want at least 32 gallons of drawdown.

 

[Sponsor]

 

[Reach4]

That is a large pump for a shallow well. Doing irrigation? Long lawn watering sessions? This may be a good match for a CSV, which permits a much smaller pressure tank.

If it is for household use, that could influence your choice.

Quick estimate for just pressure tank is 132 gallons, although more study may find that 120 gallons would be enough.

You would want to find the flow rate at 20 feet, which may be less than 32 GPM. You would like to find the draw down of your tank. Your pump should run for a minute or more to pump the drawdown amount.

 

[Traveller]

Wow! Most here advocate no more than one start per every two minutes. Basically more than one minute of run and more than one minute off. There is not enough known by what you posted to calculate tank size but you could eliminate a lot of guesswork by installing a Cycle Stop Valve.

Based on it achieving the 32 GPM spec'd, you want at least 32 gallons of drawdown.

The cycle stop valve is not an option, as the people I am installing the pump for have never heard of it and therefore, in their minds, it does not exist.

This pump is supplying domestic water to a large shop owned by a logging company here. As a lot of the equipment comes in from the bush caked in mud, the pump also has to supply a 1.5 inch fire hose at their wash rack.

What else would you need to know to calculate the size of the bladder tank?

 

[LLigetfa]

What else would you need to know to calculate the size of the bladder tank?

Size, length, and rise of the pipe. Pressure range. Usage.

WIll the fire hose have a booster pump or rely on the tank pressure?

 

[Reach4]

What else would you need to know to calculate the size of the bladder tank?

Know that you will be calculating the minimum size. If you have the space and money, I don't think there is anything such thing as too big.

Well-x-trol is the leading name in pressure tanks. That is the premium Amtrol brand.
http://www.amtrol.com/support/well_sizing.html has a calculator but it only goes up to 30 GPM. Their WX-350
119 Gallon is the biggest they offer. You can put 2 or more in parallel to get more capacity. I suggest you might consider leaving space and plumbing consideration for 2 tanks, even if you start with one.

The model number of the pump would be important if somebody were to do a detailed calculation using the predicted output of the pump.

 

[Valveman]

The cycle stop valve is not an option, as the people I am installing the pump for have never heard of it and therefore, in their minds, it does not exist.

People had never heard of the “automobile”, “refrigerator”, “air conditioner”, “airplane”, “cotton stripper”, “television”, “computer”, or other new inventions before either. Where would we be today if everyone just said “they never heard of it before so it doesn’t exist”?

I read where only 4% of people think they are below average intelligence. I think it is the other way around.

 

[Traveller]

People had never heard of the “automobile”, “refrigerator”, “air conditioner”, “airplane”, “cotton stripper”, “television”, “computer”, or other new inventions before either. Where would we be today if everyone just said “they never heard of it before so it doesn’t exist”?

I read where only 4% of people think they are below average intelligence. I think it is the other way around.

If you think you can sell them on the idea, I'll introduce them to you.

 

[Valveman]

I have been told I could sell a Snow Cone to an Eskimo. LOL! So it is usually very easy to sell something that people really need, works as advertised, and even comes with a money back guarantee. However, if they are in that 4% or 96%, whichever percentage it is, I have learned that you can't fix stupid.

 

[LLigetfa]

I have learned that you can't fix stupid.

You got that right. Borrowing a quote from Stephen Vizinczey, "Strange as it may seem, no amount of learning can cure stupidity, and formal education positively fortifies it." I have often come across engineers that could not be reasoned with.

 

[Craigpump]

20 starts a minute?

Better have a case of pressure switches on hand......

 

[horacio]

20 starts a minute?

Better have a case of pressure switches on hand......

With the new Franklin DELUXE control boxes seems to me that the pressure switch will last for ever.
Do am I correct or not? Thanks

 

[Valveman]

Deluxe control boxes have been around forever. They just have an extra relay that allows the pressure switch to see a fraction of an amp (coil amperage) instead of full motor amperage. It does help save the pressure switch, but it will still wear out if the pump cycles on/off too much. The pressure switch is the least of your problems though if you have a cycling issue. That extra relay in the deluxe box, the starting capacitor, start relay, the motor, and the bladder in the tank will soon fail as well.

 

[Ballvalve]

He meant 20 starts per HOUR.

 

[Valveman]

He meant 20 starts per HOUR.

Still 480 per day or 175,200 cycles per year.

 

[Ballvalve]

Still 480 per day or 175,200 cycles per year.

Of course, ridiculous. I buy the Square d pressure switches with the 5Hp rating and put them on 1/2 or 1 hp motors. Lasting 20 years if the ants dont get in. But no matter if its a relay or a good switch, the pump is going to get very tired with all those starts

 

[Valveman]

Yeah with that many starts the pressure switch is the least of the problems. And check those GHG2 pressure switch ratings. They are only good to 3HP in single phase. They say only 5HP with three phase, but as long as you have a three phase contactor they can be used for much larger motors as well.

 

[Ballvalve]

Yeah with that many starts the pressure switch is the least of the problems. And check those GHG2 pressure switch ratings. They are only good to 3HP in single phase. They say only 5HP with three phase, but as long as you have a three phase contactor they can be used for much larger motors as well.

Yes, I have a few pump contactor boxes that I bought from Graingers f0r nada. When i have the time and energy, I put them on my properties, and even the basic square D switch then lasts a few million cycles.