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Old 31-10-2011, 06:52   #31
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I think it is important at this point to be sure everyone is talking about the same pipe. Their are many types of PVC overall, but the only types to consider for drain pipes are the ones made to be drain pipes. The most common is Schedule 40 which is almost always pure white, is probably in 80% of household drain systems in the US, and is bought in 10' straight sections from nearly any home center or hardware store. It's what I'll use on my boat. Above that is Schedule 80 which is usually dark gray, is stronger and can handle hot water. It's not generally in your home center. It is also sold in 10' straight pieces. This is also called CPVC. Note that PVC and CPVC require different glues - be sure to get the right one.

Then there are other types of PVC. One you will find for domestic water which has a light yellow color. This is thin walled and brittle, but sold in straight pieces. There's also the stuff sold for electrical conduit - light gray and thiner than the white Schedule 40. This stuff would be tempting to use in plumbing but that's not what it is made for. Finally there are the flexible types sold in rolls. Most are soft and easily crushed (like sprinkler pipe) and I'd never put them on a boat. You can also buy thick walled flexible PVC that is sized like and fully compatible with Schedule 40. It glues into all the same fitting and is quite though. However, as Peggie pointed out way above it has zero resistance to permeation, so it is useless on a boat as sanitation hose.

Finally, the other grand assumption here is that the pipe is installed properly. The right glue is used, the joints are properly bedded, nothing is overly stressed, the pipe cuts are made square and clean, etc. There's nothing hard about it but proper techniques must be followed, like anything else.
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Old 31-10-2011, 09:10   #32
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Re: PVC Taboo - Myth or Reality ?

gray conduit PVC would not be a problem. As this fellow says, it is just the colorant and gray conduit PVC not tested under pressure and is the same plastic, so the same glue will work. Not an issue, what kind of pressure will waste sitting in a pipe have in a boat. It just wont be stamped with a marking for proof of use for the intended application. Some of the gray PVC formed pipe bends meant for electrical wires might be more useful, I would use what ever is needed.

Electrical PVC conduit used as drain pipe - InspectionNews - Home Inspection
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Old 31-10-2011, 10:21   #33
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Re: PVC Taboo - Myth or Reality ?

piping 101

PVC (poly vinyl chloride) pipe and fittings used in land side waste systems is thin wall. It's stamped DWV on the outside (drain, waste and vent) Generally only good for 5 psig max. This as used for regular plumbing in homes and light commercial is designed for a max 2 inch pressure. It's a little thin for boat work in my option). Fittings are long radius for gravity plumbing.

PVC pressure pipe comes in SCH 40 and SCH 80 thickness. SCH 40 pvc is rated at something like 70 psig at 100 degrees F. and something like 40 psig at 140 (going by memory here). Fittings are short radius thick wall. Its slightly flexible, but over time (10 years ish) it will out gas a bit and become brittle. Just something to be aware of. Fittings are short radius and Its probably safe to use in boats if proper care is used. Sch. 80 is a thicker wall but is only slightly stronger. Mainly thicker so that when used with some acids and caustics its lifespan is longer


Some of the grey PVC is just colored PVC from china. There is a Grey PVC called Corzan (marked so on the pipe) that has very good chemical properties more like CPVC, but it cost more and needs a hotter (faster) solvent to melt it and join it together. Used in industrial process and for domestic water sometimes. Also good on boats.

CPVC (chlorinated poly vinyl chloride) Has a much higher temperature rating, about 180 degrees F at 100 psig ish and has more flex per given size then PVC. It's superior to PVC from a pressure / temperature standpoint. It generally has a yellow tint to it. Also OK for Boats.

BTW I would never use ABS pipe on a boat (the black plastic pipe). Its a styrene derivative and will dissolve if a solvent is poured down it (like gasoline or nail polish.. So not good... I'm not fond of it for landside projects

I'll not get into PE or PB pipe as these require heat fusion joints and requires special tools to assemble.

Just FYI
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Old 31-10-2011, 10:42   #34
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Re: PVC Taboo - Myth or Reality ?

Ditto for Sailerchic.

As noted the warmer it is the more flexible it is, the other side is true as well. I would not hesitate to use PVC on my boat, in a tropical, or subtropical enviroment, but as noted above in freezing temperatures it is not as flexible, and can be very brittle.


But the hoses can get brittle also.
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Old 31-10-2011, 11:16   #35
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Re: PVC Taboo - Myth or Reality ?

Just my two cents, as pointed out earlier, use schedule 80 (grey dark), not common house pipe schedule 40 (white). Worry not advice from a 77 year old architect.
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Old 03-11-2011, 14:53   #36
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Quote:
Originally Posted by David M
You just don't want to use PVC in situations where if it failed it could sink the boat. PVC is too brittle. A hose you can step on or drop something on it and not break it.
Yea pick a two inch schddule 80 pipe and try to break it!
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Old 03-11-2011, 14:56   #37
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Re: PVC taboo - myth or reality?

Quote:
Originally Posted by peghall View Post
Most large yacht builders do use quite a bit of PVC instead of hose in sanitation system, but it's only recommended for use in long straight runs, which aren't very common in most sailboats <50-60'. A lot of bends require a lot of unions and fittings, all secured with glue pvc cement)...then there's the need to provide shock absorption and protection from flex, which require using about a foot of hose to connect pipe to fixed objects (toilet, tanks, pumps, thru-hulls etc).

Hose, otoh, is pretty easy to install and doesn't need all those glued connections etc. And at least one sanitation hose--Trident 101--is just about bullet proof against odor and isn't THAT much more expensive than PVC.

So yes, there are advantages to hard PVC over hose...and there can be a run or two in which it can work. But in most installations, the disadvantages outweigh the advantages as a total replacement for hose.
So why not use PVC with a piece of really good hose on either end?
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Old 03-11-2011, 20:54   #38
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Re: PVC Taboo - Myth or Reality ?

Yup, it would be almost impossible to have hard PVC pipe be a total replacement for hose. I know I wouldn't be able to do that on my boat and it's not my goal. I'll use the optimal material in each place. For example the exit fitting from my fwd holding tank is a stainless steel smooth nipple with a 1.5" od. Can only put a 1.5" id hose and clamps on that. Also, with the exception of the extremely expensive bronze three way valves all the good plastic ones have barbs to connect to hose, not threaded fittings, nor can they be glued reliably into PVC. So at least short lengths of hose are necessary to transition from one mode to another. You can get PVC bards that glue into the ends of PVC pipe/points.

Moreover for the real bendy places on a boat a hose is the best answer. I like the advice above on how to heat and bend PVC pipe but I personally think of that as going too far when there's perfectly good flexible hose to use in those cases and the extra price is worth the reduced hassle. Just make all your clamps tight!

Here's an update on my project, and a tip, of full replacement of my sanitation pipes throughout my boat. Yesterday I tackled what I knew would be the hardest replacement. It was about 9' of older black rubber hose that ran from a Y valve in the bilge across the boat under a bunch of cabinets and a structural bulkhead up to a deck fitting. I followed a tip in Peggie's book at put coupler on the end on the old hose and connected it to the new hose with the plan to pull the old one through and the new one would follow. The old hose was so snugly in place and pinched by various obstructions that it was impossible to move. After a couple hours of pulling, pushing, twisting, trying to widen holes, etc., I had moved it 6 inches. I just couldn't get enough strength/leverage on the hose end to pull it up and through. The top three feet were in the back of a hanging locker, so I was reaching in and trying to pull up. In my mind I was concocting all sorts of ways to get some sort of lever arm in there, or a jack, or a tackle, etc., to apply leverage. Then the light went off. I opened the deck fitting (the hose was disconnected below), dropped a line in, tied it off to the lowest part of the hose I could reach, and then went topsides and pulled up on the line with my spinnaker halyard on a winch. It took a huge amount of pull but it all started to move and after several trips and resets all nine feet was released. Phew. Everything else will be a lot easier now.
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Old 03-11-2011, 22:51   #39
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Re: PVC Taboo - Myth or Reality ?

Use that PVC, do a good install, do a leak test...If your not a high speed sport fisher pounding around at 23 knots you will make out fine. I think most of the concern is groundless.

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Old 04-11-2011, 10:27   #40
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Re: PVC Taboo - Myth or Reality ?

It is easy to conjure all types of problems that DWV schedule 40 PVC 1120 370 PSI @ 73F pipe can cause in a marine application. But for the many who have actually taken the "cook book and cooked", few problems have occurred, most due to improper gluing.

I installed it extensively in the two boats that I have owned; first a Hunter 30 and now my Silverton 40. Because my Silverton has two heads, one near the bow and one near the stern, my pipe lengths are quite long. I worried about potential flow problems the few 90 degree bends I had to make could cause. So instead of using 90 degree couplings or 2 each 45 degree couplings, I used some sweeps designed for electrical use.

Plumbing codes prohibit mixing electrical pipe with waste lines which I ignored. My boat does not need to comply with state plumbing codes. The sweeps which are smooth 90 degree bends allow fluid passage with no chance for physical obstruction that could result with a sharp 90 degree fitting.

I also installed numerous clean out fittings in case I ever needed to get a snake into the pipe.

And yes, I did need to use some hose, about 6" at the ends of the PVC runs where attachments to both the holding tank and the heads were made. I am well pleased with PVC, it is stink free, durable, should last a life time. PVC pipe also has the benefit of being semi-ridged that waste hose lacks. A long hose run has the potential to form vertical loops or bends that can trap waste. Not so with PVC. Best of all, PVC is affordable!

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Old 04-11-2011, 11:28   #41
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Re: PVC Taboo - Myth or Reality ?

Just to be clear there are different types of PVC pipe, both solid, cored and recycled material with varying uses. To the untrained eye they all look pretty much the same. Use to be you had just straight PVC pipe. Now there is solid and cored pvc as well as recycled PVC and the properties are not always the same. Throw in some plastics made in china and things get a little fuzzy.

PVC-DWV pipe and fittings (sanitary drainage pattern) is not listed for pressure applications, per manufactures data (Charlotte Pipe). PVC Pipe and fittings for cold water is listed for pressure applications. The issue is the fittings. Drainage fittings are designed for gravity "non-pressurized" sanitary systems and are thinner wall then pressure fittings.

For all plastic pipe, the pressure rating is dependent on pipe size and temperature, so working pressure will change with pipe size and temperature. Last Note, Only use pvc pipe for water service. Never use PVC pipe for compressed air piping (which I have seen done). So not good...think balloon popping but with sharp hard bits flying around.

While a bit of thread drift, I would not use PVC for boat pressure water systems. I would recommend PEX as the first chose and CPVC as a distant second. PVC is OK for cold water and will work. However PEX is superior both in material strength and ease of workmanship on a boat.
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Old 04-11-2011, 13:54   #42
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Re: PVC Taboo - Myth or Reality ?

Now SailorChic--- I have high respect for your displayed knowledge. For clarity, I was careful to list the specific type of PVC I referenced........ PVC1120 which is that sold in the big box stores along with plumbing supply stores. The pipe is marked with its 73F pressure rating that I read directly from the 1 1/4" pipe. And I know that you will find my reference to PVC1120 equivalent to D1784.

http://www.harvel.com/downloads/spec...ipe-sch-40.pdf

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Old 04-11-2011, 15:04   #43
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Re: PVC Taboo - Myth or Reality ?

Schedule 40 and 80 PVC pipe have quite high pressure ratings, something in the 100 plus psi. Smaller diameters higher pressure rating but even 2" believe is rated at higher than 100psi. Have had nearly a 1/2 mile of unburied PVC pipe bringing water to our house for 30 years. If glued properly, joints won't leak. Use the primer to etch and clean the surface and then the glue. Our pipe is probably running over 250 PSI because of the 800' drop from the County Meter to our house. It has broken when run over by a car or when a pig steps on a suspended section but not often. Despite the fact that most of the pipe is 3 decades old, the schedule 40 2" pipe is still soldiering on despite laying on the top of a rock wall and the very high pressure.

The ideal solution if you want to use PVC pipe is to use short short hose runs to the fixture with long runs in PVC. ABS is the black drain pipe used in house waste systems. The white PVC drain pipe is usually pretty thin walled and not intended to be used inside a house.

I'd use the household pressure water pipe for doing a pressure water system. It's hot water rated, relatively flexible and designed as an install and forget piping system for water in houses. Of course, you could also use copper for pressure water as well. Don't burn the boat down soldering it, however.
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Old 04-11-2011, 17:04   #44
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Re: PVC Taboo - Myth or Reality ?

Oh no problem with the pipe pressure rating. But PVC-DWV (Drain, waste and vent fittings are not designed to be pressure rated over a small amount. The much heavier wall SCH 40 fittings will hold pressure quite well. My point was to not confuse the two as many times you will find a DWV short ell in with the pressure fittings at the hardware store. Some blonde chic probably tossed it in the wrong bin ;-)..

Yes you can use pvc in hot water, but the rated pressure is derated to 22% at 140 F. CPVC derates to 50% at 140F. Since using engine water can run the water heater temperature to 160F ish, it can be iffy over time on a boat. Least wise on mine anyway...

Copper pipe is fine of course though care must be used when soldering the joints around fiberglass or wood. Plus depending on solder type there could be corrosion / leaching at the joints. I use to be a 100% for cast iron and copper in buildings BTW, but have seen where plastic pipe works better in some cases.

Oh up to 10 years ago PVC pipe was pretty much PVC pipe. Now there is foam core PVC pipe and other types of PVC out on the market which look like regular PVC pipe but may not be pressure rated.
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Old 04-11-2011, 17:33   #45
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Re: PVC Taboo - Myth or Reality ?

My point if I have one is that there are several, well at least four different types of SCH.40 PVC pipe on the market. They are all marked SCH. 40 PVC and all look like PVC pipe. But they are not all rated for pressure. If foam core is marked on the pipe its not. It might hold pressure for a bit, but I would not use it.

Gee if I had a dollar every time I rejected a shop drawing because the pipe did not meet spec for the application, and that it would fail in such in such a way, but it was installed anyway and then did failed, I'd have oh ten dollars or so by now. Oh the price of being Blonde.
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