I am helping define real world use cases for pipe modeling software (mostly to be used for commercial DWV detailing), and I need to know if there is any reference material available on how back-to-back 45 deg. elbow (1/8 bend) joints can actually be used, specifically to connect double offset (or rolling offset) piping conditions. If this method is still used and hasn't generally fallen out of favor (like using a 60 deg. elbow (1/6 bend) into a wye rolled 45 degrees, has) I'd like to know what angle ranges can be solved, and if out of the infinite possible angle combinations, are there any known/commonly encountered angle conditions it solves? E.g. whenever you have a 45 horizontal and 60 vertical drop-in, two 45 elbows at x & y degrees will connect that condition.

Also, I know that pipe deflection at joints allows room for play/fudging it - I believe 6 degrees of deflection for glued joints like PVC & ABS, and 13 degrees for hub & spigot and no-hub. Because I am looking to solve this programmatically and computing can work out exact numbers, I don't believe deflection is material to this discussion. I.e. if computing couldn't resolve exact numbers, then deflection could make up for the difference. If you believe I am wrong, that deflection still matters for whatever reason, please counter.

The simplest 45/45 connection is a straight 180 (zero angle deflection) which yields an S-turn to offset a pipe run continuing in the same direction. What do all the rest solve, if this method is even used? Below are several I created in the software to give a visual idea of what I mean.






Edited 5 times.

theoretically deflection is not supposed to happen.
as a practical matter is does happen.
so i guess your drawings should not incorporate deflection.

having said that.. there would be times when 2 fittings will not give you the needed change of direction so a 3rd would have to be added.

also keep in mind that some codes (Mass is one) do not allow PVC nor ABS on commercial applications.

I have used two 45s to make a 90 degree turn when there is also an small elevation difference. In other words it is not a horizontal 90, but the upstream 45 is rolled down a little, followed by a short piece of interconnecting pipe, then the downstream 90 is rolled up a little, the result is a 90 degree turn with an elevation offset.

Thanks Packy.