NCEES HVAC&R Practice test questions 38

[bkuhn]

I'm looking for help understanding the NCEES solution for Question 38 of the HVAC&R practice test.  the question is below and i've attached my solution. 

#38 A proposed piping and pumping system has 20-PSIG pump inlet pressure, and the piping discharges to atmosphere 160 ft above the pump. If the piping friction loss is 20 ft of head, the minimum pressure rating (psi) of the piping system is most nearly:

I used Bernoulli to solve, with the understanding that Poutlet=0PSIG. Why does NCEES add the 20PSIG inlet pressure to the maximum pressure in the system? What am I missing? Any help clearing this up in my mind will be greatly appreciated.

 

[MikeGlass1969]

Can you please post the problem from the book so we can be sure the information is correct?

Thanks

 

[bkuhn]

here is the problem.

 

[MikeGlass1969]

I do agree with your solution.  However,  You could have just done P1 at the pump discharge and P2 the outlet of the pipe.  Just a quicker way to the solution.

Mike

 

[bkuhn]

I do agree with your solution.  However,  You could have just done P1 at the pump discharge and P2 the outlet of the pipe.  Just a quicker way to the solution.

Mike

That is how I originally solved the problem: max pressure will be at the pump discharge so Pmax=P1+pump head.  However, after I saw it was wrong, I worked it from the pump inlet to the discharge, but nothing changed.