residential fire pump 1

[inspectortx2]

Did an inspection on a condo building that burnt to the ground once from blockage in the main. It was rebuilt and resprinkled it has a residential fire pump is the pump required to have preformance test done annually? It is a 50gpm pump a pitot gauge wont even pic it up and what scale do you use to test it.

 

[TravisMack]

If I recall correctly, NFPA 13R references NFPA 20 for fire pumps, so it would have to meet the criteria of a UL Listed fire pump. Can you choke the test header discharge down to come out through a single 11.2k sprinkler? You could figure out the pitot pressures you need to have with a 0.64" orifice. I know that NFPA 20 has you using a single 1½" hose header valve, but you won't budge the pitot at 25 or 50 gpm with a 1-1/8" play pipe.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[chevy4x4trucks]

With a 50 GPM pump this sounds more like a 13D system. Is this a 2 family condo?

 

[inspectortx2]

nope its a building that has 36 condos i took a fire pump course at oklahoma state university and they didnt teach us how to test cute little pumps like this i have seen bigger jockey pumps. travis i under stand what your saying but how do you do the math on that.

 

[FFP1]

The pertinent question: Is the "residential" pump installed as a dedicated fire pump (i.e. only feeds fire system piping) or is the pump arranged to increase water flow & pressure for both domestic system piping and fire system piping?

 

[inspectortx2]

its a dedicated pump fire line only

 

[stookeyfpe]

A 36 unit condo under the International Codes is a R-1 multi-family dwelling, unless property lines separate each unit and they are separated by 2-hour party walls. If these conditions are not met, NFPA 20 is applicable. If the dwellings are separated by party walls and individually plated, then they are Group R-3 dwellings and regulated by the IRC.

What's the pump's flow and pressure rating?

 

[inspectortx2]

a 50 gpm pump at 70 psi.

 

[TravisMack]

The formula for determining flow from a hydrant is:

Q = 29.83 * c * d^2 * p^.5
Q = flow in gpm
c = outlet coeffient (range from 0.7 - 0.9 for hydrants, 0.97 for UL listed play pipes)
d = outlet diameter in inches
p = pitot psi

Could this same formula be used to figure the pitot pressure required through a ½" orifice or a 0.64" orifice? If the formula is applicable, it would allow you to determine required pitot pressures at your flows. You would have to determine the c for a sprinkler outlet.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[chicopee]

You can test the fire pump by flowing the 2" or 1-1/2 connection at the sprinkler valve by taking pressure readings under now flow and full flow conditions. This test must have been covered at OSU because it was when I took the sprinkler fire course at that same school back in the '80's.

 

[cdafd]

Insp2

Did the original/new have it's own tap at the main

Or was it t off the domestic????

 

[inspectortx2]

chicopee i understand what your saying but reading pressures dont tell me the preformance of the pump for 3 poin or a 5 point testand with the 1 1/2 outlet full blast at 75gpm wont move a pitot gauge. i can get 75psi out of a 75psi1500 gpm pump watching the pressure and the pump not preform when you do a preformance test on it.

 

[inspectortx2]

cdafd it has its own tap at the street but i dont know what it had when it burnt.

 

[SprinklerDesigner2]

"Could this same formula be used to figure the pitot pressure required through a ½" orifice or a 0.64" orifice?"

I don't see why not.

But I wouldn't use a pitot (IMO exploring the center of the stream of a k=11.2 head would be a joke).

Set up a "test header" using a 2" pipe so there is very little friction loss through the pipe itself and at the end have a 2"x3/4" reducing coupling with the k=11.2 orifice sprinkler. Just before the discharge install a 2"x2"x1/2" tee having a 1/2"x1/4" bushing for a test gauge to read residual pressure.

I hear you but the gauge on our "test header" will read less than the discharge gauge on the pump. They should be close but the test header gauge should be less by whatever friction loss is developed through the piping and the difference in elevation.

p=(q/k)^2 and you got it. At 19.9 psi you should have 50 gpm discharging and 75 gpm with 44.8 psi. Ok, use 20 and 45 psi.

The reason you want to see the pipe kept overly large between the sprinkler orifice and test gauge is to keep the k-factor as close to 11.2 as you can.

 

[MGXFP]

""The formula for determining flow from a hydrant is:

Q = 29.83 * c * d^2 * p^.5
Q = flow in gpm
c = outlet coeffient (range from 0.7 - 0.9 for hydrants, 0.97 for UL listed play pipes)
d = outlet diameter in inches
p = pitot psi

Could this same formula be used to figure the pitot pressure required through a ½" orifice or a 0.64" orifice? ""

This is just an iteration of the bernoulli formula. It can be used to find any flow from an orifice if the assumptions are still valid that bernoulli makes. The only trouble I can think of is the outlet coefficient; finding that would be difficult for flowing one sprinkler versus a fire hydrant where lots of testing has been done to find the empirical coefficients. Bernoulli is theoretical so some adjustment should be made.

 

[inspectortx2]

THANK YOU sprinkler designer 2 your post was valuable just what i needed

 

[pipesnpumps]

I agree SD2's Idea sounds like the ticket. Any friction losses are going lower the pressure making results conservative. I do wonder how well the stream is going to stagnate it's velocity pressure into a tee, you might try the opposite. Put a tee upstream of the orifice, with the gauge on the opposite side of the tee.. This would be just like testing a hydrant without a pitot, and you will probably get closer to the real stagnation pressure since there won't be alot of splashing and don't have to get the distance downstream exactly right.

Real world knowledge doesn't fall out of the sky on a parachute, but rather is gained in small increments during moments of panic or curiosity.

 

[SprinklerDesigner2]

"Could this same formula be used to figure the pitot pressure required through a ½" orifice or a 0.64" orifice?"

Yes but remember the discharge coefficients of sprinkler heads vary between 0.7 and 0.8.

I would run a 2" test header, at 75 gpm the friction loss through the pipe would only be 0.06/foot which with only 1' of 2" between the gauge and 2"x3/4" reducing coupling with orifice would have negligible effect on the k-factor of the entire assembly.

From the pump I would run the entire test header line in 2" with the gate valve as close to the fire pump as possible so as to hopefully have 5' of straight pipe to the discharge. Just before I got to the wall I would fix the 2"x2"x1/2" tee (or simply use a welded outlet) to fix my gauge which would take a 1/2"x1/4" bushing, short 1/4" galvanized nipple and plugged 3-way 1/4" globe valve. From this point, knowing the k-factor of the orifice, it is easy to accurately calculate the discharge without having to use a pitot tube which I think would be a real problem with such a small orifice.

The 5' of straight pipe would be necessary (this is just my opinion based on nothing) to minimize the turbulence that might result in inaccurate readings or the gauge "jumping around".

In addition I would fix a sign clearly stating he discharge orifice size and k-factor to help any inspectors coming after you.

 

[inspectortx2]

the header is run in 1 1/2 and its right at the pump but it will work the same as 2"

 

[SprinklerDesigner2]

"the header is run in 1 1/2 and its right at the pump but it will work the same as 2 inch"

Probably not enough difference to get really excited about.

Assume a 1 1/2" test header with k-11.2 orifice. There is 5 linear feet of 1 1/2" pipe between the gauge and orifice in addition to one (1) 1 1/2" O.S.&Y. valve and two (2) 1 1/2" elbows.

Not only that but the test header is 3'-0" higher than the gauge used to read the discharge pressure. Perhaps the discharge gauge on the pump which if used would introduce even more error.

With 5' of pipe, two elbows and gate there is a total equivalent length of 14' of pipe. Using a C-value of 140 (new pipe and I know this throws off the equivalent fitting length but will use 14' because it is "best case") flowing 75 gpm there develops a friction loss of 2.0 psi which is not insignificant. Add to this the 1.3 psi required to compensate for elevation and for 75 gpm the gauge needs to show 48 psi and not 45. No one reads tenths of a pound we're lucky to get to the closes 1 pound increment.

If it were me I would want to see the gauge at 48 then assume we had 75 gpm flowing.

Guess the point I am making is we need to be conservative. We are not testing to see if something will do xyz we're testing to see if it will at least do xyz. There is a difference.

I remember reading an magazine article about C-Values in newly laid PVC water main. They had tests from all over the country there must have been three dozen and not one had an actual measured C-Value higher than 145 and most were around 135 and and some as low as 130 which is not insignificant over a substantial length.