Question on swept and mitre bends

[Ask1122]

Hi all, i was wondering why do we use swept and mitre bends instead of just normal elbows?

The change in radius in swept bends can increase or decrease the pressure depending on the orientation. I understand that it can be used to connect pipes in different sizes. But why do it at a bend (flow will be disturbed by both the bend and the change in radius)? Wouldn't it be better to just use a reducer or something?

And for mitre bends, i don't understand why one would even use it? What benefits does it give? Because it does the same thing as elbow, and worse of all, it have a shape 'kink' at the corner which disturbs the flow? So why use it??

Thanks all!

 

[FredGarvin]

Mitre bends can be easier for some people to fabricate since all you really need is a straight cut and a weld. The drops are worse in them but everything is a tradeoff. I have only seen mitres in a few installations. I think most people today have the abilities to make what they need from bends and fittings.

A swept bend is pretty nice to use. They are by far the best in terms of pressure drop and are not that difficult to make. Plus it makes sense to put the diameter change in a spot where the flow is already pretty much non uniform. It helps to save as much straight run piping for flow normalization prior to going into things like flow meters, heat exchangers, etc...

Fittings are convenient, but they are pricey and require more work to install usually. Plus you have to have more loose parts lying around, etc... I personally use fittings sparingly when I have to do such things mostly because, if there is going to be a leak, it's going to be at a fitting.