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Old 22-12-2011, 18:12   #1
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PVC Seacocks ..?




The thru-hulls on my aluminum boat are PVC valves screwed onto aluminum pipes that are welded to the hull.

I have read that Marelon valves are the AAA++ Super Technology. The Forespar website says that Marelon is a lot stronger than PVC. I'm not sure strength is important in this installation, since the standpipes are protecting them from anything from the outside.

If this is critical, I will of course replace them with the A+ super technology valves. But the boat is ~14 years old and has not sunk. So I am not certain that leaving these valves as is is some elaborate suicide ritual.

Do you guys have any thoughts or experiences with PVC valves?
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Old 22-12-2011, 19:48   #2
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Those are schedule 80 PVC and good ones at that. Easy to replace too since they are double union and the center is like a cartridge. Those valves can even fit a pneumatic or electric actuator for remote open close. Also the handles come right off to make them semi tamper resistant.

I use those all day long at work, never thought about using them on a boat, but maybe? I don't think I would change anything, I would just carry some spares.

You can get replacements or parts easily through McMaster.com

Not that you would but the center cartridge can also be swapped for a check valve, or y valve, same size mix and match stuff.
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Old 22-12-2011, 20:11   #3
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Forgot to mention, I have never seen a broken one at work and the gorillas are rough on them.

A strap wrench or two is the key to working with these.

And they can be adjusted if the ball ever leaks. Pull the cartridge out and see that on one end the seat can be adjusted, the arrow on the label points to the adjustable end. If you install them in the right orientation you can adjust them by undoing the inside side and have the valve still holding water on the outside side.
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Old 22-12-2011, 20:17   #4
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Re: PVC Seacocks..?

The concern on a vessel is breaking a seacock and then the vessel sinks. So the standards are set such that side impacts or pressure on the seacock will not break it. For instance, if you are working in the area and step on the seacock with your foot to get out of the area - you might just fracture or break-off the seacock unless it is built to "take it."
- - Marelon and bronze seacocks in combination with through-hulls and "mounting pads" are the typical components for a vessel. You can get the "technical" specifications from ABYC or just use common sense and make sure each component is capable of withstanding that impact or excessive side load without breaking.
- - Personal opinion - PVC valves and through-hulls do not qualify as strong enough. If your boat is insured then ABYC standards should be followed or you might not be covered as you expected. Land based/designed equipment looks good and may be as strong, but are they certified for marine vessels?
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Old 22-12-2011, 21:09   #5
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Re: PVC Seacocks..?

ABYC "Seacocks, Thru-Hull Fittings and Drain Plugs" Standard H-27 says

27.4.4.2 In line ball valve - A seacock designed to be supported entirely by the through-hull fitting.

27.6.1 A seacock shall be securely mounted so that the assembly will withstand a 500pound (227Kg) static force applied for 30 seconds to the inboard end of the assembly, without the assembly failing to stop the ingress of water.

It never occurred to me until this was raised but Marelon fittings contain carbon. Carbon is cathodic to aluminum. I'm not sure if the nylon in the fitting insulates the carbon but I'd research this carefully before I put Marelon fittings in contact with an aluminum hull.

I routinely apply foot pressure to throughull and seacocks in my surveys
with the exception of Marelon fittings under 2" ID. they break too easily.

I would have no issue with the installation shown in the OP's photos in any survey I performed.
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Old 22-12-2011, 21:15   #6
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Re: PVC Seacocks..?

Article on seacocks.
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Old 23-12-2011, 04:58   #7
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Re: PVC Seacocks..?

I might be a bit concerned about these ball valves used. The valve itself might be OK but the mounting is in my opinion vulnerable. The weak link is the valves threads screwed to the aluminum nipple. This valve could not take the side load a good marine thru hull is designed for.

But even more of a concern for me in the first picture would be what I assume to be electrical wiring just a few inches above the valves. That wouldn't pass a residential electrical inspection much less on a boat. Look at that edge on the aluminum angle bar. If that wasn't a big concern on a survey report I'd want my money back. Who built this boat?
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Old 23-12-2011, 06:22   #8
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Re: PVC Seacocks..?

My boat has a similar construction, but the aluminium pipes extend a bit a above the waterline. The aluminim pipes on your boat are different lengths, any chance the seacocks are above the waterline ? It si a bit hard to tell from the photo.

I agree with Tellie about the electrics, also be careful with the copper pipe if there is any chance of it touching the hull it needs insulation.
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Old 23-12-2011, 07:11   #9
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Re: PVC Seacocks..?

Wow, there are some sharp-eyed folks on this forum! I missed the copper pipes and then the really unacceptable electrical wiring in the first photo. But I get the impression the boat is still being constructed as their are wooden spacer blocks in the second photo.

Although things, especially plastics, are always improving, I am still not happy with the use of those PVC seacocks. In my experience PVC valves tend to be quite "brittle." Especially when they are threaded onto a metal pipe with NPT threads. The PVC plastic is under serious stress and frequently fractures.

From the Marelon spec sheets their "marine seavalve is made of MARELON®, a glass reinforced nylon composite." To me this means a greater ability to absorb attachment stresses than brittle PVC.

There was a rumor about the E.U. not allowing Marelon on aluminum boats, but I cannot find any authoritative links on the subject so it seems to be just a rumor. But anyway, why not use stainless steel ball valves which are easily available - I see them on boat store shelves in all the French Islands and elsewhere.
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Old 23-12-2011, 08:09   #10
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Re: PVC Seacocks..?

In my experience PVC is both tough and amazingly fragile. It is apparently brittle under duress. It looks like your thruhulls may be above the normal waterline. Is that so?

I would not use PVC in any place where it may receive an impact. Like those places in your pictures. Go with the accepted standards.
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Old 23-12-2011, 16:18   #11
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Re: PVC Seacocks..?

I forgot to paste this graphic to my post #9. It shows the comparative properties of all the different seacock materials. What is of special interest is the notes down on the bottom left side where the "minimum tensil strength " and "flexural modulus" are given. PVC is "substandard" according to this chart. Which I believe translates to the problem that PVC "breaks" too easy. It seems only "polypropylene" is worse.
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Old 23-12-2011, 20:15   #12
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Re: PVC Seacocks..?

Quote:
Originally Posted by osirissail View Post
I forgot to paste this graphic to my post #9. It shows the comparative properties of all the different seacock materials. What is of special interest is the notes down on the bottom left side where the "minimum tensil strength " and "flexural modulus" are given. PVC is "substandard" according to this chart. Which I believe translates to the problem that PVC "breaks" too easy. It seems only "polypropylene" is worse.
Orisail thanks for the back up info on why PVC is substandard. I will have to question it though. It says PVC but does not say what schedule it is. I have seen pipe called PVC schedule 40 that I refer to as thin wall and another that is thick wall. The difference in pressure between the two is substantial. I don't know if schedule 80 has that same distinction. I think that Sailorchic might be able to give us a better idea because she is an engineer who has designed many plumbing systems. I know that Schedule 80 is pretty hard to break.
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Old 23-12-2011, 20:35   #13
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Re: PVC Seacocks..?

I believe the Schedule 40/80 applies to PVC pipe and joints not valve-type fittings. I have never seen any "second" version of ball valves, etc. From the photo below the NPT threaded parts seem to have rather thin walls. To me the problem is more of the "brittleness" of the PVC plastic rather than its static strength. Here is a link to what looks like the same type the OP's photos. See: Product Listing PVC-BallValves-TrueUnion

In another link the spec's denote "Sched 80" - so I don't think Sched 40 is available. See: 772 PVC Ball Valve - True Union - Solvent or Threaded

I guess the only "sure" way to find out is to get both a PVC valve and a Marelon valve and put then on a concrete pad and smack them with a sledge hammer and see which one (or neither) shatters.

The Marelon (3rd photo) has a seriously thick wall surrounding the female thread. But maybe the PVC's were installed in the OP's case as the 1" version of the Marelon ball valve costs about US$101 versus the PVC valves cost of US$30.
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Old 23-12-2011, 22:52   #14
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None of those valves pictured are the same. The valves on the OP's boat are Hayward brand and very high quality. If it were my boat I would not change the valves. Instead I would suggest putting the effort towards changing those copper lines to PEX (assuming they are water lines). Any copper touching aluminum will lead to problems. If they are fuel lines maybe look into rubber lines or better support and insulation.

http://www.haywardflowcontrol.com/pr...01_11506_Y.htm

These are not the cheap white schedule 40 valves they sell at Home Depot.

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Old 23-12-2011, 23:34   #15
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Re: PVC Seacocks..?

I think the PVC valves used are probably adequate, at least as strong as the Marelon valves and has a high pressure rating. My only question is the threads on the thruhull / pipe.

The PVC Valve will have tapered NPT (standard plumbing) threads. Most thruhulls have straight threads. I can't tell if the thru hull pipe is custom or not, that is was it cut with a tapered thread or straight thread. That's the IMPORTANT consideration.

If it does have straight cut threads, then I would replace the valve ASAP as the thread engagement may only be a few threads deep. If it has tapered threads then its equal to the Marelon valve in strength/pressure rating and good enough.

Because the pipe is welded to the hull you don't need the normal flange/seacock and would never use a bronze valve on an aluminum hull, as aluminum is an anode to bronze.
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