1/2hp to 5hp jockey pump 2

[sparky9]

I designed fire protection for an addition to a large civic center facility. Existing diesel and electric pumps were adequate for the additional sq ft added. I was informed by the FP contractor that it took too long to recharge the system with the current 1/2hp jockey pump. They have recommended a 5hp jockey pump. Jockey pumps to maintain pressure for leaks and pressure variences are the primary responsibility isn't it? Who cares how long it takes to recharge the system as long as it hold the correct pressure? Correct me if I am wrong! I have also found the facility is without coverage to a certain area to do the planned impairment and a 2 1/2" line was cut and capped until other demo work was completed. Would this effect recharge time. thanks for your advice

 

[stookeyfpe]

Sparky:

What is too long? A jockey pump (i never liked the term) is a pressure maintenance pump. Your system is not hydrodynamic -- it is static. I think you have a sprinkler contractor feeding you a line of horses____t.

I can't respond to problem two without more information.

 

[gouveia]

Technically you are correct that a 1/2 hp jockey is probably adequate depending upon your pressure requirements. I personally think that too large of a jockey pump is bad since when you open an inspector's test, the jockey pump just keeps up. And the fire pump never starts.

Never quite comfortable with it, but I have seen systems filled up and then had the fire pump turned on to pressurize up the system fast. Too much water hammer in most cases in my opinion, but it was not my system.


FROM NFPA 20 (2003 edition)

5.24.1 Pressure maintenance pumps shall have rated capacities not less than any normal leakage rate.

A.5.24 Pressure maintenance (jockey or make-up) pumps should be used where it is desirable to maintain a uniform or relatively high pressure on the fire protection system. A jockey pump should be sized to make up the allowable leakage rate within 10 minutes or 3.8 L/min (1 gpm), whichever is larger.

 

[sprinklerdesigner]

Except in some very large old underground systems I can't imagine anyting more then 1/2 HP being required.

I've never met an owner or occupant who would tolerate "visible leakage" that would be of such a quantity even a small jockey pump wouldn't be able to keep up with.

I wouldn't be concerned with "water hammer" just contemplate what happens every time a dry pipe system trips.

About 15 years ago we were demolishing some large systems in a building owned by Owens Illinois. System had a large 2000 gpm @125 psi fire pump taking suction from a ground storage tank all of which was being removed.

At churn with the tank full (20' high so we got an extra 8 psi there) we developed a churn pressure of around 160 psi.

It was a lump sum contract and since everything was going to the scrap yard I spent the day with the guys in the field "trying" to "break something".

It was great deal of fun.

I wanted to see something "blow apart" and couldn't get it to do it. We tried everything even going so far as to drain a large system then manually operating the fire pump. We tried everything we could think of to destroy the system but just couldn't do it.

Not saying I wouldn't be a little concerned if we were dealing with a large (say a mile or better) undergound system with dead ends but that is something a little different from an overhead system but then again think of the old dry pipe system at the end of an old yard main.

 

[LCREP]

Oh stuff happens all the time and we get to pay for it!

Check out this case study, how many fire pumps do you see churning too high??

http://fpemag.com/archives/article.asp?issue_id=13&i=66