Passing the tests for NICET III at four years total experience is pretty good.

When you say training in school was it general education or directly related to fire protection and sprinkler in particular?

 

I have an associates in engineering technology (drafting and design, 2007) and I'm completing my 4 year engineering degree (civil, 2010).

   

I started my career in sprinklers in 1976 when nearly everything was pipe schedule and the few calculated systems we had were done by hand.

Done well over the years but getting a degree, even if only a two year degree, is something I regret not doing. Maybe when I retire.

The best NICET study guide I've seen was the one published by the NFSA.

You know a degree is for many only a certificate of attendance.  I've worked with legions of educated idiots. Of the truly wealthy I know (balance sheet wealthy), about half have only a high school education.

Of course I'm not against education and my associates was a great program.  I know how to do most any drafting, use descriptive geometry, and figure out most any drafting/design software.  The process piping classes were especially helpful in fire sprinkler layout (even though they were geared more for the petroleum industry).

I've been using Gagnon's Design of Water Based Fire Protection Systems for study, especially hydraulic calculations.  Also on loan I have some other study guides, but they're of varying usefulness.  Calculating trees is easy enough and I was glad to learn of the method of using a K factor for a typical branch line to speed the process along. Loops are a headache but doable with enough time and grids.... well I can do a grid but would prefer to let the computer tackle that one!  I'm experienced enough to know if my answer is reasonable and to evaluate that flows through grid piping makes sense.

I would like to ask: do most calculations by hand truncate values instead of rounding them?  I've seen both and I'm not sure which is most correct.  Typically I'll round up pressures and flows to three decimals and sometimes this can add significantly to a residual pressure at the base of the riser.

I would like to ask: do most calculations by hand truncate values instead of rounding them?

Doing them by hand you round them to the nearst 10th.

We're not building swiss watches and sprinkler heads are not all equal even if they came out of the same box.  If you actually measured each individual head out of a box you might find one with a k-factor of 5.7 and the next at 5.5 and the next at 5.6 then one at 5.5.  They aren't perfect.

We're not calculating what a system will do our calculations show it will at least do that.  Newly installed black steel pipe has a c-value of around 140 but we use 120 simulating what the internal condition of that pipe mgiht be in 20, 30 or 40 years.

The oldest system I ever dug into was one at a wire assembly plant installed in 1914 and I was shocked to see the internal condition of pipe was such that it looked like it was installed yesterday.  I've torn into systems that were 10 years old and they were a mess with corrosion and I bet the c-value wasn't 90.  It's a guess.

It really is irrelvant that a 1" pipe has a friction loss of 0.324 psi per ft... the 24 really doesn't mean anything and if you actually lab tested a section I am willing to bet your answer would be anything but 0.324 psi

When I was doing them by hand we bumped the actual number back and forth to the nearest 10th. Close enough.

Do you know you can figure the loss through a loop by using a piece of N^1.85 paper?  I'll be glad to show you if you want.
 

As is in any engineering its a crapshoot.  I had a water guy tell me a hydrant would flow a certain amount and I called his bluff given that, statistically, I know a fire hydrant has a K factor of around 150 to 160 and sure enough the real flows correlated with a similar K factor and nowhere near his surest estimate (the math didn't make sense) because I knew the pressures in the area.

I seem to recall reading a thread between you and stookyfpe about such a method and I wasn't able to figure it out.  If you wouldn't mind explaining a bit I think that would be great.

Thanks for your help on the calculation rounding, that makes it much easier.  I always thought the three decimal places was silly in that the high precision was irrelevant.

Yeah, the three place rounding is really ridiculous and the only reason it is shown on reports is computers make it easy to do.

Of course k-factors on hydrants can vary a lot, just like they can vary between individual sprinkler heads, but I seem to remember a factory mutual book I had that placed the k-factor at 148 (call it 150 I suppose) for a 5 1/4" hydrant barrel having a 2 1/2" outlet.

Assume the k-factor is 148.

p=(q/k)^2

If a hydrant is flowing 1150 gpm the residual pressure in the line should be (1150/150)^.5 or 58.8 psi.  Works the same as with a sprinkler head.

Check sometime, if you have a residual pressure of say 40 psi the test hydrant (the test hydrant being the hydrant where the static and residual pressure is obtained) should have a discharge of around 948 gpm. but this is assuming very little friction loss between the test hydrant and flowing hydrant.

Let's take hydrant A and B

--------A-------------B

Flow direction-->>>>

Let's assume 500' of 8" DR18 between hydrant A and B and as shown it is a dead end line.

You obtain a flow of 1200 gpm from hydrant B.

What should you expect your residual pressure to be at hydrant A?

I would expect 64.0+4.5=68.5 psi. At 1200 gpm the friction loss between A and B is 4.5 psi.

What if you had 1,000 feet of 6" DR18 between A and B and obtained a flow of 885 gpm?

I would expect 34.8+19.0=53.8 psi. At 885 gpm the friction loss between A and B is 19.0 psi.

These calculations are aren't worth a whole lot in and of themselves but it is a good way to "sense" something wrong.  In the first example if you had a 70 psi residual but obtained only a 780 gpm flow I would think there's a problem the line can't be 8" or a valve is shut or maybe some old bad pipe or blockage.  To be it would be enough to suspect not all is as it should be causing me to investigate further.

I've been doing this for 35 years and I've had my share of problems; running into beams, missing duct on a drawing, misreading a steel drawing and once I miss-counted some bays but all these things were relatively simple to correct.  I make a mistake somewhere on just about every job.

But the few jobs that really made my hair stand up on the back of my head the problem could always be traced to a bad water supply.
 

I'd also like to share a few test-taking points I've picked up through the years of not only NICET certification, but other certification exams I've taken in various disciplines.

1. Read each question at least twice.  Often times writers will phrase questions in a manner requiring a complete understanding and a quick reading can lead one to a wrong conclusion.

2. Pick the low-hanging fruit first.  Scanning through an element and answering questions one knows immediately can save time for the entire element.  This method allows for better use of time when the test taker can visually estimate how many questions are left.

Been studying 2+ hours every night; its amazing what one can learn simply by studying the nfpa along with paper and pencil.

Back to calculations; using the tables in 22.4.1.1, I can use the hazen williams equation to determine friction loss through fittings and pipe, then if a C factor of 100 is used (in the equation) I also need to use the C value multiplier found in table 22.4.3.2?  This seems to result in lower friction loss through rougher pipe.

I'm also a bit confused about total pressure.  I understand normal pressure in engineering is pressure exerted orthogonal to a surface i.e. a box sitting on the floor exerts normal pressure on the floor.  I understand how to calculate velocity pressure; but if my memory is correct it is rarely used.

Thank you SprinklerDesigner2 for all your help.

I survived the exam thanks to your input.