Simple Loop - Hardy Cross

[MechEng2007]

I have a Hardy Cross example I am trying to solve as practice for the NICET test.

The link below is a picture of the loop. Total fittings are 4 elbows and 2 tees. I set a flow of 250 gpm at a minimum pressure of 7 psi at node Z. Node A is the supply with 50, 40, 1,000 set as the static, residual, and gpm, respectively. All pipe is Sch. 10 and everything is at the same elevation.

My problem is that HydraCalc gives me a flow of 182.642 gpm in segment ED and 67.356 gpm in segment QE. My hand-worked Hardy Cross Analysis gives me 194.95 gpm in ED and 55.05 in segment QE.

What do your calc programs give you in these two segments? Thanks in advance for the help.

 

[TravisMack]

I use AutoSprink for my drawings. AutoSprink gives a flow of 182.83 down one leg and 67.17 down the other leg.

Remember, these carry calculations out to something like 7 decimal places. It only prints out to 2 decimal places. I don't know if that would be enough to throw you off that much. It has been a few years since I did a HC analysis of a loop by hand. Actually, last time was during my NICET test.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[TravisMack]

Just a thought. Since you are using Sch 10, are you adjusting the equivalent length of your fittings for Sch 10. They are given in tables as Sch 40 equivalent length. This could account for some of your differences.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[MGXFP]

I echo Travis Mack. Per 22.4.3.1.3.1 you should divide the actual ID by the sch. 40 ID and raise the quotient to the 4.87 power to get your adjustment factor for fittings.

In my experience rounding to the nearest tenth is about the same as the nearest thousandth when you arrive at the source.

Good luck on your exam!

 

[MechEng2007]

I had not that about that Travis. Thank you. I will check my fitting take-outs.