Sample question about psi

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    Brandon Estes (Edited )

    1) It's Kaplan - you should already be skeptical.  But more importantly, 2) it assumes a bottom-feed (up-feed) system instead of a top-feed (down-feed or gravity-feed) system, although there is no mention of that in the question.  You have to convert the height of the building to psi which is seems like you already know how to do.  This is obviously an easy task/calculation so count on NCRAB to pull some type of trickery and overly-complicate the question.  Also, a great tid-bit to remember is that 1' = 0.433 psi so keep your units in check.  2.3' = 1 psi whereas 1' = 0.433 psi. 

    Some systems provide pressure from the public water main such as residential and low-rise commercial; other systems use pumps separate from the public main to pump water to a rooftop storage tank where the weight of the water/gravity provides the pressure.  (Other systems simply use a pump in the basement to provide pressure beyond what the municipality provides, but I have not encountered that in my studies or on PPD/PDD.)

    From my experience and hearing from others, Kaplan (now Brightwood) isn't the best material from which to study.  However, the typos, grammatical errors, and  questions that you will never encounter in practice offered by Kaplan are perfect preparation for the ARE exams questions.  Be sure to read about up-feed and down-feed systems.  Also be sure to know your stack diagrams (vent stack and stack vent are different - stack vents penetrate the roof) and difference between building drain, lateral, and public sewer.  Good luck.

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    Michael Ermann

    This concept trips everyone up. Know that while every 2.3 higher you store the water in a down-feed system (like a tank on the roof) creates one extra psi at the fixture (sounds like this part is intuitive to you). . . it is also true that every extra psi in an up-feed system (like from an underground municipal system) is able to push the column of water 2.3 extra feet higher into the building (sounds like this part is less intuitive). So, in this case, your fixture is 120 feet in the air, so you need 120/2.3=52.2 psi to push the water to the height of the fixture. But the fixture itself requires 15 psi to work properly (just pushing the water up to that height might not allow the tank to fill properly; we need extra pressure for that). So the line into the building requires the following pressure: 52.2 (to lift the water 120 feet) plus 15 (to operate the fixture) equals 67.2psi.—Michael Ermann, Amber Book creator

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    Robin Tannenbaum

    Thank you both!  I agree that the question is worded poorly and implies it wants an answer for the bottom floor and in fact wants one for the top.  I have a plethora of 4.0 materials that I like to intersperse with the 5.0 primary sources for studying but I do need to be careful.

    Brandon - Luckily I think that NCARB gives at least part of that formula so I am set to do the inverse math. I'm all over the vents and get the difference between the big two but once we get into branch v. circuit v. back v. loop it all gets a little hazy.  Also on tonight's plumbing focus - valves!

    Michael - I did your videos last year for PPD (and my first attempt at PDD) - they were awesome. Just found two practice questions on this topic in the book.  Got 'em both!

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