NECEES Mechanical PE Reference Manual Released

[Ramnares P.E.]

Apologies @YW55, you are correct that equation is the Wahl factor.  The equation in the NCEES manual is the Bergstrasser factor which is a simplified version of the Wahl factor.  

Essentially Shigley says that since the results of the two equations typically differ by 1%, the Bergstrasser (NCEES equation) is preferred.

 

[YW55]

Apologies @YW55, you are correct that equation is the Wahl factor.  The equation in the NCEES manual is the Bergstrasser factor which is a simplified version of the Wahl factor.  

Essentially Shigley says that since the results of the two equations typically differ by 1%, the Bergstrasser (NCEES equation) is preferred.

According to the following link the max difference can be up to 7.5%? I think I'll stick to Wahl factor since the time saved is insignificant.

https://www.chegg.com/homework-help/shigley-s-mechanical-engineering-design-9th-edition-chapter-10-solutions-9780073529288

 

[Ramnares P.E.]

Those are theoretical problems for students so not sure that 7.5% is valid.  I presume Shigley's statement regarding 1% is from industry experience.  

 

[MattW]

I was looking at the Affinity Laws and page 228 and a couple don't seem to agree with the MERM.  For Q the MERM has the D term to the 3rd power where it is to the first power in the handbook.  For Hp the MERM has the D term to the 5th power where it is to the first power in the handbook.  Those seem wrong to me but I am just starting my studying so I may be missing something.



Also, I cannot fine errata for this handbook.  Is it available on-line somewhere?

 

[Dr. Barber]

...I cannot fine errata for this handbook.  Is it available on-line somewhere?

There is no errata.

I’ve been reporting to NCEES all the typos I’ve listed in this thread. I always get an email saying this [emphasis mine].

”Thank you for your input. I will forward your questions and concerns to the committee responsible for creating and revising the PE Mechanical Exam Reference Handbook. If there are issues found with the publication, changes will be made on the next version. NCEES does not publish errata since the handbook is revised frequently. If no changes occur as a result of reviewing your concerns and questions, no further action will be taken.”

So if it still says “version 1.0” on the cover, none of the typos have been addressed.

 

[Vel2018]

I actually think this might force NCEES to water down the questions. Who really knows...

Hmmmm..I don't think so..You really don't need those huge diagrams. 

What I would suggest is that, during the course of your study, try using the reference material with your desktop! That sucks but it will greatly help you prep for the CBT.

 

[ChooChooEngineer_PE]

Hmmmm..I don't think so..You really don't need those huge diagrams. 

What I would suggest is that, during the course of your study, try using the reference material with your desktop! That sucks but it will greatly help you prep for the CBT.

Gotta get that CTRL-F training down when you use the CBT version

 

[Audi Driver P.E.]

I was looking at the Affinity Laws and page 228 and a couple don't seem to agree with the MERM.  For Q the MERM has the D term to the 3rd power where it is to the first power in the handbook.  For Hp the MERM has the D term to the 5th power where it is to the first power in the handbook.  Those seem wrong to me but I am just starting my studying so I may be missing something.

View attachment 12884

Also, I cannot fine errata for this handbook.  Is it available on-line somewhere?

I'm not seeing the issue. The MERM 13th Ed. p.18-19 agrees with this table.

 

[Dr. Barber]

I'm not seeing the issue. The MERM 13th Ed. p.18-19 agrees with this table.

Equations 18-45, and 18-47 of MERM13 are valid when you reduce the diameter by trimming the impeller. 

The relationships for changes within a family of geometrically similar pumps are different (I guess trimming the impeller makes the new pump not "geometrically similar" as the original)

Consider Equation 18-52 and set n1=n2 (same speed for both pumps), the result is Q2 = Q1 (D2/D1)^3, which is NOT equation 18-45.

Consider Equation 18-53 and set n1=n2 (same speed for both pumps), the result is P2 = P1 (D2/D1)^5, which is NOT equation 18-47.

This is also done in Fluids textbooks. Here is a screenshot of the book by Munson, Young and Okiishi.

I guess the take-away message is to be careful and make sure to know how is the impeller diameter changing: Is it being trimmed? or is it being replaced by a smaller one, but geometrically similar? The equations can be quite different. 

 

[Audi Driver P.E.]

Equations 18-45, and 18-47 of MERM13 are valid when you reduce the diameter by trimming the impeller. 

The relationships for changes within a family of geometrically similar pumps are different (I guess trimming the impeller makes the new pump not "geometrically similar" as the original)

Consider Equation 18-52 and set n1=n2 (same speed for both pumps), the result is Q2 = Q1 (D2/D1)^3, which is NOT equation 18-45.

Consider Equation 18-53 and set n1=n2 (same speed for both pumps), the result is P2 = P1 (D2/D1)^5, which is NOT equation 18-47.

This is also done in Fluids textbooks. Here is a screenshot of the book by Munson, Young and Okiishi.

I guess the take-away message is to be careful and make sure to know how is the impeller diameter changing: Is it being trimmed? or is it being replaced by a smaller one, but geometrically similar? The equations can be quite different. 

View attachment 12957

Equations 18.49 thru 18.54 are Pump Similarity laws, not Pump Affinity laws. The Handbook table being discussed shows equations for Pump Affinity laws. And the table is correct.

 

[Dr. Barber]

Equations 18.49 thru 18.54 are Pump Similarity laws, not Pump Affinity laws. The Handbook table being discussed shows equations for Pump Affinity laws. And the table is correct.

Agreed. I haven’t said they’re wrong.

I guess I was “thinking out loud” and figuring out when to use similarity and when to use affinity. Still not clear.

 

[Audi Driver P.E.]

Agreed. I haven’t said they’re wrong.

I guess I was “thinking out loud” and figuring out when to use similarity and when to use affinity. Still not clear.

Knowing when to use the similarity laws vice affinity laws is important for the exam, to be sure. Generally speaking if you have more than 1 parameter changing at a time (propeller diameter and shaft speed, for example) you need to use the similarity laws.

Note: the MERM seems to suggest the word "homologous" is something to key on. I wouldn't bet on that for the PE exam, but it is applicable.

 

[Dr. Barber]

Knowing when to use the similarity laws vice affinity laws is important for the exam, to be sure. Generally speaking if you have more than 1 parameter changing at a time (propeller diameter and shaft speed, for example) you need to use the similarity laws.

Note: the MERM seems to suggest the word "homologous" is something to key on. I wouldn't bet on that for the PE exam, but it is applicable.

Some more clarification:

https://www.eng-tips.com/viewthread.cfm?qid=89032

 

[Atf TX]

Anyone taking the October 2019 exam, this would be a handy reference book that you could use, in addition to other resources. 

 

[Audi Driver P.E.]

Anyone taking the October 2019 exam, this would be a handy reference book that you could use, in addition to other resources. 

If you correct all the errors in it, yes.

 

[Mechanical Ryan]

500 plus pages hehehe 

 

[YW55]

Anyone taking the October 2019 exam, this would be a handy reference book that you could use, in addition to other resources. 

Used it for my April 2019 MDM exam and passed. You just have to practice with it and all the errors will come up and you can correct it. Think of it as a treasure hunt.

 

[cjcarter]

I went over the reference manual, having taken the October 2019 pe exam, i am convinced that NCEES will be changing the type of questions asked for the CBT style exam due to some of the 2019 October exam questions not being covered by the reference manual. Besides the computer glitches ( the screen may freeze or load slowly while scrolling down) and using a marker on a plastic pad, the CBT style exams should be easier. I don’t think they can ask a question outside the reference manual. You can use that to your advantage. 

 

[TX_PE_Oct19]

I went over the reference manual, having taken the October 2019 pe exam, i am convinced that NCEES will be changing the type of questions asked for the CBT style exam due to some of the 2019 October exam questions not being covered by the reference manual. Besides the computer glitches ( the screen may freeze or load slowly while scrolling down) and using a marker on a plastic pad, the CBT style exams should be easier. I don’t think they can ask a question outside the reference manual. You can use that to your advantage. 

True. However they may ask questions outside the reference manual. It clearly stated on the front page of the manual that It may not be sufficient to solve all the questions. So basically they still CAN/MAY ask anything they want and no one can argue with it. Sorry...

 

[cjcarter]

True. However they may ask questions outside the reference manual. It clearly stated on the front page of the manual that It may not be sufficient to solve all the questions. So basically they still CAN/MAY ask anything they want and no one can argue with it. Sorry...

Asking questions outside of the reference manual WAS only valid for the April 2019 and October 2019 exams as shown below; 

Using the Handbook for the April and October 2019 Paper Exams
The Principles and Practice of Engineering (PE) Mechanical exam is an open-book pencil-and-paper exam through October
2019. The PE Mechanical Reference Handbook is a reference you may use on exam day. It contains charts, formulas, tables, and
other information that may help you answer questions on the PE Mechanical exam. However, it does not contain all information
required to answer every question; theories, conversions, formulas, and definitions that examinees are expected to know have
not been included.
This PE Mechanical Reference Handbook is intended solely for use on the NCEES PE Mechanical exam. You may bring your
personal copy of the Handbook into the exam room as long as it is bound and remains bound according to the policies in the
NCEES Examinee Guide. Additional references that adhere to policies in the Examinee Guide are allowed in the exam room for
the April and October 2019 exam.

If you read it that is the case only for the April and October 2019 Paper exams.

For the computer based exam it says the following; 

Using the Handbook for the April 2020 Computer-Based Exam
Beginning in April 2020, the PE Mechanical exam will be computer-based, and the PE Mechanical Reference Handbook will
be the only resource material you may use during the exam. Reviewing it before exam day will help you become familiar with
reference information provided. You will not be allowed to bring a copy of the Handbook into the exam room. Instead, the
computer-based exam will include a PDF version of the Handbook for your use. The PE Mechanical Reference Handbook is
intended solely for use on the NCEES PE Mechanical exam.