Plastic pipe bending experiment

[Joe Rich]

As you may or may not know, one can bend rigid PVC by heating it.
This is not approved for plumbing (at least on the high pressure
lines) but is acceptable for electrical work. The critical things to
watch here are temperature and kinking of the tubing. With PVC it is
possible to essentially press a small kink out while it is still hot.

I have some semi-rigid black plastic 1/2 inch ID tubing which is
fairly thin walled. I am wanting to use this as the tubing in a
collector. The problem is making the bends so that the tubing fits
nicely. I am wanting to make bends with a radius of about 2 1/2 ".

The OD of the tubing is almost exactly 3/4 inch, which happens to be
the width of a 1-by piece of wood. I cut a radius on a piece of 2 1/2
inch piece of 1-by and then cut two more pieces of wood with a radius
of 3 1/4 inch. I added these two pieces of wood on the outside of 2
1/2 inch radius, one on each side, to form a channel 3/4 inch on a
side.

I then heated the tubing and molded it in the channel. This works
great AS LONG AS THE TUBING IS NOT TOO HOT, otherwise it kinks and
deforms.

Does anyone have any other suggestions?

Joe

[John Allen]

>Does anyone have any other suggestions?

I suggest you test the tubing at the highest temperature you expect the collector to experience. This will be somewhere around 300 F.

A PVC fitting I used on my collector turned to putty one day when my circulation stopped while the sun was shinning. Maybe your PVC is better.

ja

--
John A Allen

[John Allen]

However, maybe the tubing you have would be useful for a heat excchanger. I use Polyethylene for the low pressure glycol loop. I junked the PVC fitting I had there because I'm hoping my storage gets close to 212 F this summer, and when I tested white PVC pipe at 212 it gets very malleable, while the polyethylene does not.

ja

--
John A Allen

[Tony Luck]

On 3/20/07, John Allen <johna...@gmail.com> wrote:
> However, maybe the tubing you have would be useful for a heat excchanger. I
> use Polyethylene for the low pressure glycol loop. I junked the PVC fitting
> I had there because I'm hoping my storage gets close to 212 F this summer,
> and when I tested white PVC pipe at 212 it gets very malleable, while the
> polyethylene does not.

212 F in an unpressurized storage container ... that means you'll have steam
squirting out of the gaps in the insulation ... surely not a good thing from
a variety of perspectives:

1) Evaporation loss from your storage system
2) Humidity/Moisture in your basement.

If you are going to get that hot in the summer, then this is an
area where you'll want to go back to some control circuitry for
the pump so that it will cut out before you get to this temperature
(the lost energy wasn't being stored anyway ... just dispersed by
the steam).

-Tony

[Joe Rich]

I will test by putting it in boiling water and see what happens.
Actually, if this softens the plastic maybe it will work for bending,
also.

I had thought about using this as the heat exchanger. Even then, I
need to be able to reduce the diameter of the loops some, so I have to
figure out some way to "bend" it.

Joe

On Mar 20, 11:34 am, "John Allen" <johnaal...@gmail.com> wrote:
> However, maybe the tubing you have would be useful for a heat excchanger. I
> use Polyethylene for the low pressure glycol loop. I junked the PVC fitting
> I had there because I'm hoping my storage gets close to 212 F this summer,
> and when I tested white PVC pipe at 212 it gets very malleable, while the
> polyethylene does not.
>
> ja
>

> On 3/20/07, John Allen <johnaal...@gmail.com> wrote:
>
>
>
>
>
>
>
> > >Does anyone have any other suggestions?
>
> > I suggest you test the tubing at the highest temperature you expect the
> > collector to experience. This will be somewhere around 300 F.
>
> > A PVC fitting I used on my collector turned to putty one day when my
> > circulation stopped while the sun was shinning. Maybe your PVC is better.
>
> > ja
>

> > On 3/20/07, Joe Rich <RichMan...@gmail.com> wrote:
>
> > > As you may or may not know, one can bend rigid PVC by heating it.
> > > This is not approved for plumbing (at least on the high pressure
> > > lines) but is acceptable for electrical work. The critical things to
> > > watch here are temperature and kinking of the tubing. With PVC it is
> > > possible to essentially press a small kink out while it is still hot.
>
> > > I have some semi-rigid black plastic 1/2 inch ID tubing which is
> > > fairly thin walled. I am wanting to use this as the tubing in a
> > > collector. The problem is making the bends so that the tubing fits
> > > nicely. I am wanting to make bends with a radius of about 2 1/2 ".
>
> > > The OD of the tubing is almost exactly 3/4 inch, which happens to be
> > > the width of a 1-by piece of wood. I cut a radius on a piece of 2 1/2
> > > inch piece of 1-by and then cut two more pieces of wood with a radius
> > > of 3 1/4 inch. I added these two pieces of wood on the outside of 2
> > > 1/2 inch radius, one on each side, to form a channel 3/4 inch on a
> > > side.
>
> > > I then heated the tubing and molded it in the channel. This works
> > > great AS LONG AS THE TUBING IS NOT TOO HOT, otherwise it kinks and
> > > deforms.
>
> > > Does anyone have any other suggestions?
>
> > > Joe
>
> > --
> > John A Allen
>
> --

> John A Allen- Hide quoted text -
>
> - Show quoted text -

[John Allen]

Are to loops currently too big for your hot tub?

ja

--
John A Allen

[Joe Rich]

No, John, the loops would work in the hot tub, but I have sort of
given up on that and convinced wife to let me get rid of it. I
beleive there is too much work fixing leaks.

Just tested the tubing by putting it in boiling water and it stayed
fairly rigid, but would bend using my bending tool. One idea I have
is to fill with the tube with water and then put in a homebrew solar
heater to get the water temperature up (somehow allowing for thermal
expansion), then carefully form into a coil of the proper diameter to
fit in a holding tank. I don't know if this will be good for a
collector. Still thinking.

On Mar 20, 3:40 pm, "John Allen" <johnaal...@gmail.com> wrote:
> Are to loops currently too big for your hot tub?
>
> ja
>

[John Allen]

>Still thinking.

Perhaps for the collector you want to be a test site for the invention you signed a NDA for?

I'm about to go back to testing it here.

BTW,  Polyethylene tubing only cost $9 for a 100 foot coil at Home Depot.

ja

--
John A Allen

[John Allen]

How about 200 F? I've done this before as a candle maker. As long as I float a layer of non-polar fluid on top of the water to stop evaporation, everything is fine.

Truthfully I'm imagining that by the time I get close to boiling, I will do something useful with the large delta t. Worst case is a steam engine/turbine running on R22. (with 65 F ground loop for condensing) 200 - 65 = 135 which is not too shabby.

ja

--
John A Allen

[Timothy]

Hi - I would stick w/ cpr its a better conductor and has a lower fail
rate. t

John Allen wrote:
> How about 200 F? I've done this before as a candle maker. As long as I
> float a layer of non-polar fluid on top of the water to stop
> evaporation, everything is fine.
>
> Truthfully I'm imagining that by the time I get close to boiling, I
> will do something useful with the large delta t. Worst case is a steam
> engine/turbine running on R22. (with 65 F ground loop for condensing)
> 200 - 65 = 135 which is not too shabby.
>
> ja
>

> On 3/20/07, *Tony Luck* <tony...@gmail.com

> <mailto:tony...@gmail.com>> wrote:
>
>
> On 3/20/07, John Allen <johna...@gmail.com

[John Allen]

Actually how about stainless steel tubing for the HX loops?

Anybody have any feel for wha tath would cost? With or without fins?

ja

--
John A Allen

[Joe Rich]

Tim - I agree that copper might be better but much more expensive.
Since this is in a low pressure loop I would think that it would have
a very low failure rate? Joe

On Mar 20, 9:43 pm, Timothy <t...@alvco.com> wrote:
> Hi - I would stick w/ cpr its a better conductor and has a lower fail
> rate. t
>
>
>
> John Allen wrote:
> > How about 200 F? I've done this before as a candle maker. As long as I
> > float a layer of non-polar fluid on top of the water to stop
> > evaporation, everything is fine.
>
> > Truthfully I'm imagining that by the time I get close to boiling, I
> > will do something useful with the large delta t. Worst case is a steam
> > engine/turbine running on R22. (with 65 F ground loop for condensing)
> > 200 - 65 = 135 which is not too shabby.
>
> > ja
>

> > On 3/20/07, *Tony Luck* <tony.l...@gmail.com
> > <mailto:tony.l...@gmail.com>> wrote:
>
> > On 3/20/07, John Allen <johnaal...@gmail.com

> > <mailto:johnaal...@gmail.com>> wrote:
> > > However, maybe the tubing you have would be useful for a heat
> > excchanger. I
> > > use Polyethylene for the low pressure glycol loop. I junked the
> > PVC fitting
> > > I had there because I'm hoping my storage gets close to 212 F
> > this summer,
> > > and when I tested white PVC pipe at 212 it gets very malleable,
> > while the
> > > polyethylene does not.
>
> > 212 F in an unpressurized storage container ... that means you'll
> > have steam
> > squirting out of the gaps in the insulation ... surely not a good
> > thing from
> > a variety of perspectives:
>
> > 1) Evaporation loss from your storage system
> > 2) Humidity/Moisture in your basement.
>
> > If you are going to get that hot in the summer, then this is an
> > area where you'll want to go back to some control circuitry for
> > the pump so that it will cut out before you get to this temperature
> > (the lost energy wasn't being stored anyway ... just dispersed by
> > the steam).
>
> > -Tony
>
> > --

[John Allen]

my 92 year old mom is on deathbed.
so I'll be out of town & off line for awhile.

--
John A Allen

[Timothy]

Joe - The problem with using a polymer is that it cant withstand boiling
temps for long durations. Stagnation due to pump failure, power outage
etc. could turn your system into a steam generator. t