# How Different is the 2016 NCEES Practice test from the 2011 one?



## caley89 (Dec 6, 2016)

I see that they have a new one listed, copyright November 2016. Anyone have both and compare?


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## Audi Driver P.E. (Dec 6, 2016)

I suspect the new one is aligned to the new test format that essentially does away with breadth questions.


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## Audi Driver P.E. (Dec 6, 2016)

Well, I said the above without even looking at their site, and from their description of the new booklet:

"Some new questions have been added to represent the revised exam specifications, but most are the same great questions reused from previous editions and selected by the engineers who write the actual exam. "


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## MechanicalApril17 (Dec 7, 2016)

The booklet contains exam spec before the exam. It's updated to reflect revised specification.


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## Nevill24 (Jan 4, 2017)

Notice this thread. See my post here...

http://engineerboards.com/index.php?/topic/24508-how-i-passed-the-thermal-fluid-pe-exam/&amp;do=findComment&amp;comment=7404137


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## aakrusen (Jan 5, 2017)

I'm bought the new book when I registered for the exam (saved a few bucks that way).  I took a quick look through it (I bought the Mechanical Systems and Materials) and I saw 28 new questions.  The questions are in a different order than the 2011 book, so it threw me off at first.  Even if I mistook a few for new, there's easily 25% new questions in the book.  If the book goes for $40, you're spending about $25-$30 for new questions.  To me it's worth it, YMMV.


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## aakrusen (Jan 6, 2017)

aakrusen said:


> I'm bought the new book when I registered for the exam (saved a few bucks that way).  I took a quick look through it (I bought the Mechanical Systems and Materials) and I saw 28 new questions.  The questions are in a different order than the 2011 book, so it threw me off at first.  Even if I mistook a few for new, there's easily 25% new questions in the book.  If the book goes for $40, you're spending about $25-$30 for new questions.  To me it's worth it, YMMV.


I meant to say that I bought the Machine Design and Materials book, not the MSM book.  MSM is what they called it before 2017.


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## aakrusen (Jan 21, 2017)

Just wanted to point out that I have found several errors in the book.  Most of the errors are in the answers for the problems.  The incorrectly show how to answer the question and the answer they get doesn't jive with the way they show how to do it.  This may cause frustration for those that are not as familiar with the content (meaning those types of problems) and may require additional research while trying to learn the material.


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## amats42 (Apr 6, 2017)

aakrusen said:


> Just wanted to point out that I have found several errors in the book.  Most of the errors are in the answers for the problems.  The incorrectly show how to answer the question and the answer they get doesn't jive with the way they show how to do it.  This may cause frustration for those that are not as familiar with the content (meaning those types of problems) and may require additional research while trying to learn the material.


Would you mind pointing out which problems are solved incorrectly? The only mistake I have found thus far is that they solved the problem as I have and arrived at the same answer but selected the wrong letter (problem 515).


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## amats42 (Apr 6, 2017)

Sorry, I can't find an edit button. I realized you were talking about a different exam.

The only error I found in the TFS 2016 exam was problem 515. My mistake.


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## Nevill24 (Apr 7, 2017)

What do you guys think about problem 124?  I think 3 pumps is much closer to about 55 ft (~167 gpm on pump curve*3= 500 gpm and intersects system curve at around 55 ft of head) which isn't close to the choices available. In any cause it is clearly below 65 ft, but clearly above 38 ft.


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## amats42 (Apr 18, 2017)

This was excellently answered by Audi on this other post, but I wanted to add here in case someone only clicks on this thread.

The solution appears to me to be correct. I get 65-70 ft estimating off of the diagram with a ruler (3xdistance measured to the intersection). I'm also not sure how you got ~167 GPM as the intersection occurs ~230 GPM. 3x230 = 690 GPM


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## Nevill24 (Apr 18, 2017)

Pump in parallel you sum the flow while head remains constant. Then where the system curve intersects the sum of the parallel pump curves you get your operating point. 3 pumps in parallel @ 230*3=690 GPM the pump provides 35 ft of head not 65-70 ft.

I didn't use a ruler but eyeballing 65 ft on the system curve I get about 600 GPM. Divide this by number of pumps (3) I get 200 gpm required by a single pump at 65ft head. The single pump curve is clearly lower than 200 gpm. 

167 gpm is where the combined 3 parallel pump curve intersects the system curve.


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## Nevill24 (Apr 18, 2017)

167 gpm is where the combined 3 parallel pump curve intersects the system curve.

By the statement above I mean 167 gpm each which multiplied by 3 gives total flow of 500 gpm and intersects at 55 ft head on system curve

Essentially 1 pump 167gpm 55 ft head, 3 pumps in parallel 500 gpm 55 ft head, system curve 500 gpm @55 ft of head therefore new operating point is 500 gpm 55 ft head. Sorry I'm writing this from my phone so hopefully this makes sense


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## Nevill24 (Apr 18, 2017)

Here's a illustration that should help clarify things...


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## Nevill24 (Apr 18, 2017)

Sorry really struggling on this...hopefully that will be out of my system come Friday! See attached


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## Audi Driver P.E. (Apr 18, 2017)

Nevill24 said:


> Pump in parallel you sum the flow while head remains constant. Then where the system curve intersects the sum of the parallel pump curves you get your operating point. 3 pumps in parallel @ 230*3=690 GPM the pump provides 35 ft of head not 65-70 ft.
> 
> I didn't use a ruler but eyeballing 65 ft on the system curve I get about 600 GPM. Divide this by number of pumps (3) I get 200 gpm required by a single pump at 65ft head. The single pump curve is clearly lower than 200 gpm.
> 
> 167 gpm is where the combined 3 parallel pump curve intersects the system curve.


First of all, there are no units on the flow, so that should be a clue to you that this is a logic problem and not one where you need to find a hard and fast solution.

Second, as I noted in the other post, for a SINGLE pump, you have about 38ft of head where the pump curve intersects the system curve.  Adding pumps is NOT going to move you backward on the system curve to any point lower than that.  In fact, it does the opposite.  So, as you add pumps and flow, you actually DO move up in head because of the shape of the system curve given.

The only logical choice given the answers provided is 65 ft. Why? Because 38 ft. is the head for one pump, not three. 30 ft is moving the wrong direction on the system curve, and 210 ft is not achievable with the pumps in the scenario.  65 ft may not be the exact answer given the curve they provided, but they are NEVER asking for the exact answer, only the CLOSEST answer.


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## Nevill24 (Apr 18, 2017)

I don't disagree with anything your saying Audi. I took the practice exam and selected 65ft for the reasons you point out. That said, I just feel it is a poor choice provided by NCEES. Only way you go above the pump curve like that is with an oversized impeller, clearances are tightened, VFD, etc changes are made to the original pump. Obviously since others have posted this problem within the forums I'm not the only one that sees issues with it.

Once again 65 ft is the best choice, but in my opinion a poor one. I think it's worth discussing so people understand such as amats believing the pump curve would intersects the system curve at 690 gpm. If say 55 ft was given as a choice in place of say 210 ft he would have chosen the wrong one (see my graph showing actual intersection).


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## Audi Driver P.E. (Apr 18, 2017)

Go over the pump curves?  I don't think you're fully grasping parallel flow.  Either that or you're not looking at the graph close enough...  and you may not be.  For example, I don't get where you come up with 167 for flow and 55 ft of head on the single pump graph that is given.  The values at the intersection of the pump and system curve are closer to 38 and 230.  And the chart you provided here doesn't quite jive with the one given either.  In any case, the solution chart they plotted and provide in the answer is pretty accurate for the assumptions you have to make to solve this problem.

The only ACTUAL issues with this problem is that there is not a very good way to come up with the exact 65 ft figure, given the plot you're given.  As I noted that is the answer because it's still below the max pump head and is higher than the other two answers that are also disqualified purely by using logic.  Really it's between 210 and 65, but 210 is way out of range because it's above what the weakest pump can produce (75 ft)... by a factor of at least two.


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## Nevill24 (Apr 18, 2017)

You must be looking at the graph incorrectly.  See below. Do you not agree that the flow for 3 pumps in parallel triples that of a single pump at a given head?  Look at the uploaded image of the curves given on the practice exam.  The graph i have in my post above is just taking the data from the curves given on the practice exam and plotting it in excel with the parallel pump curve and if you look closely you can see that the intersection is around 520 gpm and 55 ft head.


Head


Flow 1 pump


Flow 3 pumps


70


0


0


65


100


300


45


200


600


0


300


900

And "go over the pump curve" by that i mean you are given a design pump curve that is tested at the factory.  Any way to operated above the curve is if changes are made (e.g. impeller sizes, motor speed, tighter clearances, etc).  Only way you operate below the curve is intentionally due to VFDs or loss of efficiency (opened up clearances, worn impeller, cavitation, etc.)


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## amats42 (Apr 18, 2017)

Excuse the crude adobe job, but this was my method. There is no way that I can see that the head won't increase.

View attachment tyKTLBp.pdf


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## Nevill24 (Apr 18, 2017)

Forgot to add.  So if you see that the operating point of 3 pumps in parallel is 500-520 units (lets gpm as you pointed out its unit less).  If you were to measure the flow at the discharge header on 3 pumps you would measure the 500-520 gpm.  What would you measure if you took a flow measurement directly at the discharge of each pump? 500 to 520 divided by 3 so ~170 GPM which is where I get the 167 GPM.


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## amats42 (Apr 18, 2017)

Nevill24 said:


> Forgot to add.  So if you see that the operating point of 3 pumps in parallel is 500-520 units (lets gpm as you pointed out its unit less).  If you were to measure the flow at the discharge header on 3 pumps you would measure the 500-520 gpm.  What would you measure if you took a flow measurement directly at the discharge of each pump? 500 to 520 divided by 3 so ~170 GPM which is where I get the 167 GPM.


From engineering toolbox:


Pumps in Parallel - Flow Rate Added


When two or more pumps are arranged in parallel their resulting performance curve is obtained by *adding the pumps flowrates* at the same head as indicated in the figure below.







Centrifugal pumps in parallel are used to overcome larger volume flows than one pump can handle alone.


for two identical pumps in parallel and the head kept constant - the flowrate doubles compared to a single pump as indicated with *point 2*

Note that for two pumps with equal performance curves running in parallel


*the head for each pump equals the head at point 3*

*the flow for each pump equals half the flow at point 3*


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## Nevill24 (Apr 18, 2017)

amats42 said:


> From engineering toolbox:
> 
> 
> Pumps in Parallel - Flow Rate Added
> ...


That's exactly what I am doing!  The flow does not triple because it most follow the system curve!.  You tripled the flow and found where it intersected the y-axis for head.  This assumes there is absolutely no friction and the system curve is flat.  See below it's kind of sloppy, but hopefully it makes some sense.


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## amats42 (Apr 18, 2017)

I see what you're saying now. Hammering through questions I didn't question it and just took 3x the flow rate and moved on. I didn't look too closely at what a properly plotted 3xQ would look like.

I'm afraid I'm not any help, then. Perhaps you can report it to NCEES and hope to save future engineers the headache if they verify the graphs (unless I'm also now missing something!).


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## Nevill24 (Apr 18, 2017)

amats42 said:


> I see what you're saying now. Hammering through questions I didn't question it and just took 3x the flow rate and moved on. I didn't look too closely at what a properly plotted 3xQ would look like.
> 
> I'm afraid I'm not any help, then. Perhaps you can report it to NCEES and hope to save future engineers the headache if they verify the graphs (unless I'm also now missing something!).


Well it doesn't change the answer that would be selected as Audi points out using logic 65 ft is really the only thing that is event remotely feasible.   Personally I just thought it was a bit wacky of a best choice and while Audi may think I'm crazy at least I'm not the only one that is!


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## amats42 (Apr 18, 2017)

No, I definitely agree. I don't work with pump sizing so I just had it in my head that parallel means 3xQ and sped through it. Seeing the "correct" answer when going over the solutions cemented that false method in my head and I was happy (didn't think I needed to look back over curve material). Turns out I could use more review because I was making an easy mistake.


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## Audi Driver P.E. (Apr 18, 2017)

Ok, at least I see where you're coming from now.  There is still some problem with your methodology, but there are two things going on here.  One,you're looking at the wrong operating point, from which to basis your calculation/plot.  You need to look at the intersection of the pump curve and the system curve.  That point is at roughly 38 ft and 230.  Your point on the green line is sort of pulled out of thin air... you did not move from point 1 to point 2 on the engineers edge chart, you did something else to arrive at your 55 ft /170 flow point. You have the final point on your pink line plotted correctly, but there should be a point on it that corresponds with 38 ft and 3 * 230= 690 (which is one of the only other points you can really plot with any accuracy).  That point is obviously NOT the capacity for the three pump system because you need to move back up your pink line to the system curve.  IF you've plotted your pink line correctly, at that intersection you should be approx 60 ft or so (by my reckoning).  It appears to me, you've drawn your pink line a bit too flat.  Even if your pink line is dead on the answer is still the same, yes?

The second thing that is compounding the confusion in this, is that they changed the provided pump/system curve from what was provided for the 2011 exam, but not the answers.  Rightfully so (for the plot anyway), because you had to do a lot more guessing out to the 690 point because the plot of the system curve is too short in that exam booklet.  When they made the new graph for this booklet, they altered the system curve so that it isn't as steep as what they provided before.  So, It's suggesting a bit lower value than what was more obvious in the other booklet.  Here is a photo of the original pump plot:


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## Nevill24 (Apr 18, 2017)

Ahhh ha...That's a completely different system curve than what is included on the 2016 practice exam.  Hopefully that is what you have been basing everything off of. Go back and look at the curves we have posted and you will see the difference.


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## Nevill24 (Apr 18, 2017)

OK I didn't notice in your last post that you acknowledged the difference...But taking that pump curve which is completely different than the 2016 practice exam using the method that I say is correct you get guess it...65ft.  My guess is NCEES expanded the plot, changed the system curve, but did forgot to change the options?  

Going back to the 2016 exam curve. I am looking exactly at the intersection pump of the parallel pump curve and the system curve.  That's how I am getting the ~170 gpm and ~55 ft of head.  The basis of my calculations/plot is using the single pump curve and creating a parallel pump curve by multiplying the flow at each point of head by 3.  Then plot the system curve and where the system curve intersects the parallel curve is where the system will operate.

The existing operating point of 38 ft and 230 IS taken into consideration in the combined parallel pump curve.  At 38 ft of head the parallel system creates 690 gpm (230+230+230).  At 0 feet of head 900 gpm (300+300+300).  At ~45 ft of head 600 gpm (200+200+200).  At ~65 ft of head  300 gpm (100+100+100). and so on. If you keep doing this you get at ~55 ft of head ~510 GPM (170+170+170).


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## Audi Driver P.E. (Apr 18, 2017)

Gotcha.  That approach is entirely correct.


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## Nevill24 (Apr 18, 2017)

Plotted everything in excel which hopefully will clarify anything for anyone that is interested down the road.  I just did smooth lines so it stands out better, but for more accuracy you can do a trend line....Thankfully we will not have to do this on the actual exam!  

View attachment Parallel Pump Problem.xlsx


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## amats42 (Apr 19, 2017)

Thanks y'all for the detailed responses. I definitely think it's worth bringing this up to NCEES. Like I said, if it wasn't for this thread I wouldn't have questioned my very wrong methodology. Well done!


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## spacebanjo (Apr 19, 2017)

I had the same question on this problem. 



I believe it is an error and reported it to NCEES early this week.


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## Audi Driver P.E. (Apr 19, 2017)

To be clear: there is no error.  I don't believe there is anything they will or even should fix.  The question is a LOGIC question that is answered in a minute or less depending on how fast you can read.


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