New Well Pump with Fire Sprinkler

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FarmerGreg

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HI guys.

I am building new (2800 sf home, 2.5 baths) and installing a new well pump. I also have SOME irrigation set up now - only about a acre of dripline. I figure I will irrigate in the evening on a timer. Here is the issue: my state requires fire sprinklers. The sprinkler code requires 260 gallons of water in 10 minutes time (or 26 GPM).

Well specs: 20 GPM well, 202 feet deep, well report says water level is 30 feet.

I am trying to get a straight answer on a good system design.

First, I want to pick the right pump and tank. I would think that I should get a 20 GPM pump - so that I never draw down the water level. That said, what depth should the pump be set at and what HP do I need?

Next, what size tank? And Why?

Next, I would like a CSV. Is this appropriate for me? Where does it go in the whole system?

Finally, I need to make sure this will all work for the sprinkler system design - this all has to get past the code guys. (I want to get the pump NOW and get irrigating while the house build is going on). My hope is that I can rely on (1) the existing tank supply and (2) the 20 GPM incoming water to meet the 26 GPM requirement. In other words, I THINK that I need to have enough tank supply that the 6 GPM that I am losing does not tap me out within the 10 minute requirement. That, to me, means that I would need 60 gallons minimum available in the tank.

Can anyone confirm this thought process - ESPECIALLY with respect to the fire sprinkler.

THANKS
 

Valveman

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You can't really count on pressure tanks to supply extra flow. You have no way of making sure the pressure tanks are full when you need the water. With a 40/60 pressure switch, Murphy's Law says you will always be at 41 PSI when you need the extra water. So there won't be any water in the tanks, and you will only get what the pump can produce.

However, if the pump is set at 200' and the static water level is 30', you have about 250 gallons stored in the well, above the 20 GPM that the well will produce. So a pump could supply 26 GPM for 42 minutes before the output of the well drops to 20 GPM.

You will need a 3HP pump like the Grundfos 25S30-15 to be able to get 26 GPM from 200' and 50 PSI. There is no problem using a 26 GPM pump in a 20 GPM well if you have a CSV. The CSV will turn that pump into a variable flow pump, so you can still run sprinklers or anything at less than 20 GPM without cycling the pump. I would use one of the CSV12560-1 valves and hang it 1 joint (20') down the well. This will vary the pump flow from 3 GPM to 26 GPM, matching the amount being used at the time. It will hold a steady 50 PSI pressure, can be used with a 40/60 pressure switch, and will only need about a 40 gallon size pressure tank.

And since you would have a pump capable of pumping the well dry, I would also add a Cycle Sensor to the electric hook up. The Cycle Sensor will protect the pump if you let out too much water and pump the well dry. It has a built in timer that can be set from 1 to 500 minutes to automatically restart the pump after the well has had time to recover.
 

LLigetfa

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You can't really count on pressure tanks to supply extra flow...
Some fire sprinkler systems use compressed air tanks along with separate water storage tanks where the water tanks are kept full and the compressed air is used to empty them. That is the only way you can count on there being water in reserve.
 

Valveman

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Yeah but with a well that will make 26 GPM for long enough time, storage is not needed. And I don't see how you would keep the water in those type tanks from turning green unless it was used often.
 

VAWellDriller

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Valveman....green water works good on fires.....I see a lot of big commercial fire setups that just sit for years...... one county here makes any new manufacturing business on well water to install a big (like 20-50K gal) storage tank and fire pump onsite..... they just fill it up once and let it sit.

Farmer Greg- This is news to me about residential sprinklers.... it must be a local code because I know they tried to pass this a few years ago statewide and couldn't get it through, what county are you in? Also, what was the drawdown at of the well?... that's crucial to setting up the pump system and may be worthwhile to do a short test and figure it out.
 

FarmerGreg

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Valveman....green water works good on fires.....I see a lot of big commercial fire setups that just sit for years...... one county here makes any new manufacturing business on well water to install a big (like 20-50K gal) storage tank and fire pump onsite..... they just fill it up once and let it sit.

Farmer Greg- This is news to me about residential sprinklers.... it must be a local code because I know they tried to pass this a few years ago statewide and couldn't get it through, what county are you in? Also, what was the drawdown at of the well?... that's crucial to setting up the pump system and may be worthwhile to do a short test and figure it out.


Hi VAWellDriller:

I am in Frederick Maryland. The sprinklers are MD law.
 

DonL

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Hi VAWellDriller:

I am in Frederick Maryland. The sprinklers are MD law.


Is that MD Virginia law ?, Or the Insurance company law, when you have a house loan. ?

I bet Flood insurance is required also ?

Do the math, to see how much water it takes to flood the place, That will tell you the flow you need, for it to REALLY work.


Good Luck.
 
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