PVC at odd angles

[Steve Roylance]

What do you do if you need PVC (I'm working with 2" DWV for a bathtub) to make an angle smaller than you can buy a fitting? Is it OK to warm and bend it? Is there some other technique?

[LazyPup]

PVC must not be heated, bent or stressed in any manner.

In order to insure that DWV fittings will not be confused with pressure fittings DWV fittings are listed by a fraction of a circle while pressure fittings are listed by the degree of the angle.

To determine the angle of a DWV fitting divide 360deg by the fraction:
I.E.
1/4 bend = 90deg. (360 / 4 = 90)
1/8 bend = 45 deg. (360 / 8 = 45)
1/16 bend = 22.5 deg. (360 / 16 = 22.5)


If you end up with an odd bend one of your pipes is either too long or too short and the length must be corrected accordingly.

To mathematically compute the length of an offset begin by visualizing it as a triangle. (SEE ILLUSTRATION BELOW)

In all cases the sum of all the angles will equal 180 degress and one angle will always be 90 deg. therefore if you have a 1/8th bend (45deg DWV fitting) on one end of the offset the opposite end would be:

180 - (90 + 45) = 180 - 135 = 45 deg.

If you have a 1/16 bend (22.5 DWV fitting) on one end the opposite end would require:

180 - (90 + 22.5)=
180 - 112.5 = 67.5 deg.

There is no 67.5 deg fitting so we combine a 1/8th bend (45 deg) and a 1/16 bend (22.5deg) ...45 + 22.5 = 67.5 deg.

We can then compute the length of the offset from the Pythegorian Therum for a triange.

The Hypotaneue equals the square root of Side A squared plus Side B squared.

Once we know the hypotaneus of the triangle we must then deduct the fitting allowance.

The fitting allowance is the overal distance from the center of the fitting to the base of the hub.

once we know the hypotaneus of the triangle and deduct the total combined fitting allowance for all fittings on both ends of the offset, the resultant is the length of the offset pipe.

[kactuskid]

Wow LazyPup, Very cool. Thanks for the lesson, that was GReat

[Steve Roylance]

Let me post a couple pictures of what I'm dealing with and maybe you have some specific advice. My options are limited by the tight space and short distances.

Here's a picture of the general area. Previously there was a tangled mess of threaded galvanized pipe (original to the house I think) and some ABS that had been added. I had to expand a couple of the joist notches because the previous abs run that was there ran uphill. I'm planning on reinforcing those joists when I have the ceiling underneath open.


This is what I need to work back to. I used the oakum/expoy putty technique I read about here (thanks lazypup) to fix 2" PVC into that hub.

[LazyPup]

Coming off your cast iron it appears to be an 1/8th bend. You can use a second 1/8th bend turning in the opposite direction to create a running offset that should bring you inline with the Tee at the vent. It appears as if you will have about an inch between the two 1/8bends. If it is a really short offset you can use a Street "1/8th bend" connected directly into the hub of the existing 1/8th bend.

(Street fittings have a female hub on one end and a male fitting on the other end.)

From the vent Tee continue on until you are at right angles with the line from the tub drain, install a 1/4 bend at the corner.

If you will have an access to the drain fittings under the tub you can install a trap adapter and a common slip joint type waste & overflow kit on the tub. If you do not have an access and it will be a concealed location you will need a glue in type P-trap and waste & overflow kit.

[Steve Roylance]

That 1/8th bend is part of what I set into the hub. It's there in an attempt to straighten out the angle I'm working on. The pictures I took didn't quite describe the situation, so let me try a different one


I'll think about it some more, maybe there's a way I can get what I need with standard bends, but I haven't been able to think of a way yet.

I really appreciate the time you've taken to help me out lazypup.

[LazyPup]

Steve,,you are trying to connect the bend fitting at the base of the stack to the Tee fitting at the fernco. That would be a running offset.

To create a running offset, whatever angle you use on one end will be the same on the opposite end to return to a straight run. The flatter the angle the longer the run of the offset.




Not meaning to cause you additional problems but in the background of the photo you have a veritical riser with an S-Trap on it. S-Traps are no longer permitted.

You can easily convert it to a P-trap...

[Steve Roylance]

I've been away from this a while. I understand about the running offset, but you can see in the picture that the main horizontal is running at a shallow angle relative to the joists. I think I need the pipe to be running parallel to the joists so that I can use a 90 degree elbow onto the pipe that runs perpendicular to the joists towards the tub.

Also, a somewhat related question, the gasket fittings require "60 inch pounds" of torque. I don't have any torque wrench or other torque measuring tool. Can I estimate the required torque? I don't even know what '60 inch pounds' would 'feel' like estimating by hand.

[LazyPup]

I think i have a solution for you but I would need a couple more dimensions to work it out.

What is the total lenght of the 1-1/2" pipe from the cast iron to the Tub Trap?

How much vertical clearance do you have from the top of the PVC at the cast iron connection to the finished floor?

When the 1-1/2" makes the 90 deg turn toward the tub trap, will that section be concealed beneath the tub?

[Steve Roylance]

I really appreciate the time your giving me here LazyPup.

I'm doing most of this in 2 inch, I thought tub/shower drains had to be 2 inch. The section that is 1+1/2 is just the short bit to the galvanized vent.

I have about 3 inches vertical clearance from teh top of the PVC attached to the cast iron hub to the _bottom_ of the subfloor. I expect that the floor with be about 2 inches thick (3/4 current pine planks, 3/4 for a new layer of plywood and 1/2 for cermaic tile).

From the hub to the joist cut is 24 inches parellel to the joists. The joist cut is about 5+1/2 inches wide. I'm not sure yet exactly where the tub trap will be. I'm planning on cutting that section long and working out the whole drain/trap assemby from underneath after the tub is installed. I think the distance along the joist cut will be about 42 inches.

the fernco fittings have some give to them, would it be permissible to use one of those to straighten the run out? I don't have any good way to measure, but I think the angle I need is less than 10 degrees.

[LazyPup]

This is going to be tighter than a scotchmans wallet but I think I have you a working solution.

A shower stall is required to have a 2" drain line but a tub/shower only requires an 1-1/2" line.

The estimated overall run is 24" + 42" = 66" (5.5')

1-1/2 must have a 1/4" per foot pitch so the pitch allowance from the cast to the trap is 5.5 (5 x 1/4)+1/8 = 1-3/8"

You currently have 3" vertical clearance with the 2" pipe therefore dropping the pipe to 1-1/2" will drop the top of the pipe about 1/8" leaving about 3-1/8" vertical from the top of the pipe to the underside of the subfloor.

Subtrating the pitch allowance from the vertical clearance we get 3-1/8 - 1-3/8 = 1-3/4"

You will need two 1-1/2 street 1/4 bends and a 2 x 1-1/2 bushing.

On the open end of the PVC from the cast install the 2 x 1-1/2 reducer bushing then install an 1-1/2" street 1/4 bend turning vertical. You can then install the second 1-1/2 street 1/4 bend at any infinite angle to return your run to the desired angle.

[Steve Roylance]

I see... that would be really tight. The tee off to the vent wouldn't be anywhere near 45 degrees, is that 'negotiable'?

The fernco would be easier, but I want to do this right.

[LazyPup]

An easier and better solution would be to remove the 90 on the vent, then run the vent straight though the joists and tie in on the line to the tub. This would put the vent closer to the trap.

[Steve Roylance]

The tee+45 degree bend to connect to the vent takes up the whole 3 inch vertical clearance.

[LazyPup]

If you remove the galvanized 90 off the vent and run it strraight through the joists it should come out at about the same elevation as the drain line at the tie in point.