Expansion Joint Friction Loss

[Clymber]

I am looking for data on friction loss across elastomeric/rubber expansion joints. Specifically, I have a 6" to 3" reducing joint at a pump inlet. Looking at the profile, I would expect a fair amount of loss.

Does anyone know where I can find rough data for this?

Thanks in advance.

 

[BobPE]

Bleacher:

What does the section look like? I am assuming ringed or ridged? I have several emperical solutions for these types of fittings. The loss won't be as much as you think and is still a minor loss, but you are right in accounting for it.

BobPE

 

[Clymber]

Bob,
Thanks for the quick reply.

Yes, the joint is ringed. It is flanged on both ends, with two ringed sections as it narrows from 6" to 3".

 

[StressGuy]

I'd say that if your available head is critically low enough that the pressure drop across a rubber expansion joint is going to lead to cavitation, then you've got much bigger issues than the joint. The head loss across that joint isn't going to amount to very much, I'd expect. Edward L. Klein
Pipe Stress Engineer
Houston, Texas

All opinions expressed here are my own and not my company's.

 

[Clymber]

...I'm not really in a critical situation. However, I've never seen data for that type of fitting and I'm curious as to it's effects.

 

[BobPE]

Bleacher:

A reducing flexible coupling as well....YIKES....., I only have a non reducing flexible hose equation. You would think that because there are rings protruding into the flow stream in the flexible hose that it would add a lot of headloss. What happens is that as you apply pressure the diameter increases from expansion and negates a lot of what the wires do to the flow. In suction service, it may go to vacuum and decrease the diameter, then you will have an interesting problem.....

Sorry, if you want the pipe formula let me know...

BobPE