Pipe bending help?

[Matthew Piper]

hello. i'm new here, and new to plumbing.
for my course i have been asked to work out the exact length of a 45/135 degree bend in 22mm copper. and do not have a clue how to work it out.
i've been given 2 measurements : 275 and 300 each side of the 135 bend. whats the total length of pipe?

 

[WHPES]

Your straight lengths are 275 and 300 as you state. 45 degrees is 1/8 of a full rotation therefore the section of the bend is (1/8) x 2 x pi x r where r is the central radius of the pipe bender specific to the bender.

 

[fuzzy]

bend an oversized pipe and cut to length

 

[WHPES]

Yes I know thats what everyone does in the field but students have to know how to calculate pipe lengths.

The radius is sometimes marked on your pipe bender. This radius and hence the overall length of pipe will be specific to your make of pipe bender, but there is proabably a standard value that the college will give you for doing calculations.

The colleges sometimes refer to something called "gain". This is the difference between the length for the straight sides and curved segment, and the linear measurements to where straight lines continued from the straight sides bisect. Basically when pulling a bend, the pipe "cuts the corner" and this value is the difference.

Don't worry, you won't need to make single sections of complex bends in different planes in real life (unless you are doing heavy gauge steel). The only trades who do this are the car exhaust fitters.

 

[REDSAW]

elbows m8 elbows.

 

[WHPES]

From a fluid mechanics point of view, slow bends are always preferable to elbows as greater hydraulic resistance is encountered the sharper the bend. The friction losses to head are hence greater.

See description:

Simulate hydraulic resistance in pipe bend - Simulink

As regards to bending, we work on the assumption that the plastic deformation is equal in compression and expansion and hence take the centre line of the pipe as the neutral, undeformed plane.

 

[bobble]

Bend radius (on the neutral axis / midline ) is usually 4x tube dia, for copper, but benders vary from model to model.

 

[Gray0689]

From a fluid mechanics point of view, slow bends are always preferable to elbows as greater hydraulic resistance is encountered the sharper the bend. The friction losses to head are hence greater.

See description:

Simulate hydraulic resistance in pipe bend - Simulink

As regards to bending, we work on the assumption that the plastic deformation is equal in compression and expansion and hence take the centre line of the pipe as the neutral, undeformed plane.

And it looks better and shows a bit of skill

 

[richardd]

what a load of bull you will never use these calculations on site. So why teach them

 

[stevetheplumber]

what a load of bull you will never use these calculations on site. So why teach them

i agree theyd be better of teaching some use full stuff most boys who go into the building trade tend to be practical rather than theory boys theve struggled at school to keep up with maths and science then the go to colledge and get more useless theory stuff slung at them
i spent half my time at college doing back gutters in lead ally and neualite and pulling 4 inch nends despite roofing having already become a seperate trade and 4 inch lead being obsolete in this age of infomation interchange youd hope the college would have caught up

 

[tamz]

I agree with Richard and Steve here. In the real world no one would ever have use for these calculations so they are irrelevant. Plumbing is not precision engineering.
I've also noticed they make the students pipe stuff up in MI. Another handy thing that 99% will never see again but i suppose the skills are handy.

Neuralite.....now i quite liked that, except for the blisters

 

[HoodedClaw]

I was taught BillP's bending methon on the C&G course
http://www.diyfaq.org.uk/plumbing/Pipe%20Bending%20(BillP).pdf

Gave an accurate position bend every time and you can calculate total length from it.

 

[Dannypipe]

I pull all my bends by eye...and I would say a good 17% of them fit perfectly everytime! LOL

I remember learning all this crap in college. Just get through it and get your qualification, then do what we all do, and bend it too long and throw the off cuts in a scrap pile. Time is money.

 

[Tong]

I think it means that the 275 & 300 are the lengths of the arc of the inside and outside of the bend respectively .. the inner part of the pipe compresses and the outer part stretches to form the bend .. so a quick answer is 300-275 = 25/2= 12.5 so the centre line arc and length to be allowed for the bend would be - 287.5 !

 

[tweakyboy]

http://www.diyfaq.org.uk/plumbing/Pipe Bending (BillP).pdf

Hope this is what you are looking for, seems like a good guide for newbies.

 

[Scottley]

I bought my benders in about 2001 and since then i have been ok with them. However after looking at that link above my life will be easier from now on for sure!

Thatnks guys

 

[Unregistered]

Pipe 'Gain' is 1.5 times the diameter of the pipe used...
15mm pipe = 15*1.5=22.5mm to the centre of the pipe! Usually rounded up to 23mm
Its in the Foot notes of the study guides (sides of pages)
Hope this helps, took me time to find it too

 

[Atouchofgas]

After 5yrs I suspect he's probably worked it out

 

[Dotty]

This is starting to annoy me.