PVC Seacocks ..?

[Maine Sail]

Originally Posted by Gene :^)

Poor installation is not an argument against a material type. Mismatched threads and schedule 40 do not relate to this thread. Any material installed incorrectly can fail.

In that picture it looks like the sched 40 PVC was female threaded and the valve was probably overtightened into it, most likely in an attempt to turn the valve to a desirable, usable position.

Even an engine block can be cracked by over tightening tapered plugs.

White schedule 40 valves with the red handles like you see at home depot can and usually do get stuck and break. They are not comparable to The Hayward valves we are talking about here, which are serviceable and rebuildable.


-----------
Gene :^)
http://www.Strathbelle.com/

Gene,

That was not my installation. That was done by what many consider to be a "reputable" builder. They also used sched 80 mixed with Marelon and I have seen it crack too.

I often use Hayward valves on sanitation systems for a positive shut off at the holding tank. In the case of a burst hose or leak the owner can at least isolate the $hit to the tank with a quarter turn. I pick them up at my local plumbing wholesaler and even with a wholesale account they are not cheap in the 1.5" size.. Only about $10.00 - $15.00 difference between them and the Marelon valves but I get a thread match and it's a fitting that has the potential to sink your boat, just stink your boat..

The "true union" valve is nice because you can tighten the nipples and union end then orient the handle where you need it. With a holding tank and tight access this is a very useful feature and one reason I use "union" sched 80 PVC valves in that application.

Hayward makes a good PVC valve but still I will won't touch them for below waterline use as I have seen far to many examples of cracked PVC on boats. I have also seen plenty of failures of Marelon valve handles, but not a cracked valve or fitting that would have the potential to sink the boat.

As an ABYC installer I really need to follow acceptable safety standards, and try to, but it is not always easy or even doable, especially with Marelon, their utter lack of fitting choices, and their non-standard threads, at least here in the US.

[sailorchic34]

Oh no question at all that PVC valves fail in commercial and industrial applications. Surging and water hammer will take care of it quickly. They are not perfect. Mainly used for chemical compatibility or because they are cheep.


For an aluminum hull, your pretty much limited to plastic valves. Even stainless is a cathode to aluminum and would cause aluminum to rot. The cheep valves you get at the hardware stores really should not be used on a boat. The valves in the photo are higher end 3 part union ball valves and are rebuildable where as the Marelon are not.

I would say that a welded pipe to hull connection offers the same strength as a ABYC seacock, if not a little more. PVC, well really all plastics get brittle over time. Besides operating the handle on every valve every month or so (goes for Marelon too), I might schedule replacement every 3-5 years at haul out, just in case.

I'm betting you have tapered threaded on your standpipes which is why the PVC valves were used.

BTW I do love a well constructed seacock / through hull. My 40 year old tapered lubricated bronze are still in very good condition Its just in this case, no matter what the code says, you've got to use what you can use.

[David M]

It all boils down to how dangerously and inexpensively you want to live. Just because the PVC pipe has not failed does not mean that it won't. It is not one of the stronger materials compared to Marelon or stainless but it is working for you so far.

As far as threading stainless steel valves to welded on pipe nipples, it works fine, this is the standard for doing this and it is also very strong It also passes for USCG inspected commercial passenger vessels. There is no corrosion if you do this correctly, meaning you use Tef-Gel on the threads and use an epoxy barrier coat on the wet side of the pipe nipple where it threads to the stainless steel valve. You never want to thread a bronze valve to aluminum. There is no reaction with threading Marelon to aluminum. Marelon does not conduct electrons. The downside with Marelon is the valves are more likely to stick than with stainless steel valves.

[Tellie]

Originally Posted by Maine Sail

I don't know of a single PVC valve that meets or passes the minimum ABYC/UL/ANSI tests or requirements to meet the definition of a seacock? Perhaps someone can point me to one?

Considering I am replacing some cracked sched 80 PVC fittings this week, that were installed below water, and mated to Marelon valves, that are perfectly fine and did not fail, and I have seen PVC crack before, I simply do not and will not use it if it does not have a Marine UL label on it. Marelon meets the standard as to bronze & stainless fittings that carry the UL Marine Label. Of course on an aluminum boat you want to be mindful of corrosion so that most often rules out metallic fittings. Dupont Zytel, which is what Marelon is, is TOUGH stuff and far stronger than PVC in this application. At a minimum the Marine UL label tells me the product has been tested to a minimum standard for the marine environment, which includes corrosion tests for metallic fittings, and can withstand the 500 pound static load test..

"27.5.4 Seacocks shall be designed and constructed to meet ANSI/UL 1121, Marine Through-Hull Fittings and Sea-Valves.

27.6.1.3 Threads used in seacock installations shall be compatible (eg. NPT to NPT, NPS to NPS)."

I suspect the OP will be fine so long as he is mindful of them but it would not be my choice.....

This was a cracked PVC elbow from a job last summer (between the bucket and cooler). The Marelon valve & thru-hull it was connected to it were perfectly fine. The elbow was split and weeping at the Marelon thru-hull to PVC female threads as it was a thread mismatch and the sched 40 PVC lost the battle. Luckily the elbow was above static when sitting still but it leaked when sailing or under power.. Just some loose stuff in the locker, & a thread mismatch caused it to crack & leak.. I've seen plenty of Marelon valves threaded to NPT bronze, a thread mis-match, and never seen one split...

The picture above is worth a thousand words in relation to the OPs pics. Let a cooler full of ice or even a five gallon bucket half full of water slam against the OPs valve as the boat is tacked and you'll have an opening to the sea in short order. Again, it is not the valve so much as the horrible installation of them both. This is a bad design, ill thought out and built. It does not take an engineer to see the obvious weak link. With all due respect, if one cannot see the engineering nightmare of this install then at the least I'd suggest a dozen or so spare valves or well engineered bilge pump.

[s/v Jedi]

I think most agree to fit Marelon valves and create some protection around them. I wanted to say that the copper pipes need to be sleeved like reported, but also need to be secured in much more spots. At each side of every corner, then at every foot. If you let it like it is, vibration willwork-harden it until it cracks and starts leaking.

cheers,
Nick.

[CarinaPDX]

It seems to me that the one point not made (explicitly) so far is at the heart of the ABYC standard: the 500lb on the inboard end of the nipple + valve is mostly stressing the thru-hull connection at the hull. The longer the length from the skin to the nipple the greater the lever arm on the thru-hull at the skin - in this case the aluminum weld, but often the thin bronze at the bottom of the thru-hull threads. This problem is completely eliminated by flanged thru-hulls bolted through the hull, but can be a bit impractical in many applications (and makes it a lot harder to change valves in the water). Personally I have an aversion to welds as they tend to be brittle and prone to vibration failure; at least the welds in the OP's photos look very substantial. However, the thru-hull on the left in the original photo looks pretty long to me, so that is the one that needs the best protection from a force on the end.

I once had a thru-hull fail as described above - the stem broke from the ball. But the stem was still held firmly in the packing gland, with enough resistance that it felt like I was closing the valve when in fact I was just twisting the stem. It was quite surprising when I opened the engine's cooling system to drain it only to find water spraying out. So just because it looks and feels closed doesn't mean that it is.

[Watercolor]

Re: PVC Seacocks..?
I apologize for coming into the discussion so late, but the topic of marine seacock and thru-hull materials both interests and confuses me. I’ve been playing around with plastics in the marine world for about 10 years now. As I read all the thoughtful comments and opinions, I decided to ask some additional questions. I’d be most appreciative of your answers.

Some of you are willing to accept PVC in a below the waterline thru-hull, the same holds true for other plastics like Marelon. Everyone recognizes the issues with bronze, good and bad. There was also some discussion about ABYC and H-27 thru-hull and seacock standards.

This basic discussion thread seems to re-appear year after year. Like the rest of you, I have my own preferences, like you they’re based on what “information I can find and what I think is important regarding thru-hulls and seacocks.

I propose the following 4 questions. I’m hopeful everyone will find the questions and answers thought provoking and informative.

Question 1. In order of importance (1=most important), list the 5 most important factors you feel need to be included in a seacock and thru-hull standard. Example: corrosion 1, external impact 2, internal pressure 3, etc.)

Question 2. Several people felt that impact resistance, both inside and outside the boat, was an important factor. There was comment about doing a comparison impact test on PVC and Marelon by dropping a sledgehammer on both materials. Being from VT, I know that a good splitting maul or hammer weighs about 8 lbs. So let’s assume each part, i.e. a thru-hull, is placed on a cement slab, the hammer is dropped on each part from, say, 4 feet, and each test drop is identical. As a benchmark, let’s say a malleable bronze thru-hull deforms and is unusable in 8 hits.

What is the minimum number of hits you’d consider for an acceptable thru-hull standard value?

Question 3. Someone presented the Marelon vs. other materials table. The ABYC standard is set at 10,900 psi Tensile Strength (TS) and 505,000 psi Flexural Modulus (FM). Some participants in this thread have seen Marelon break, others suggest protecting the Marelon parts, and others feel the parts are fine as normally installed.

Given the information found in the table and the experiential information the thread participants have provided, would you want to consider raising the values of TS and FM? Is there a number(s) you’d consider or is actual test performance of the parts more importance to you? Or both?

Question 4. Just like metals, every plastic has its weaknesses regarding degradation, in metal it’s called corrosion. For example, H-27 has a test for UV degradation for plastics. Some plastics degrade quickly in UV even when molded with UV inhibitors. All plastics degrade in moisture to varying degrees. The H-27 UV degradation cutoff is when TS or FM of the specific material exceeds 29% of the material’s initial values.

Do you think that a value of 29% maximum degradation for any test is too high, just right, or too low? Is there a % you feel would be acceptable?

Thanks for your input!

[osirissail]

Comments added in red. Some of the questions I feel are not relevant and I doubt that anybody on this forum is set up to do lab tests on the materials in any valid way. I suspect we are all basing our opinions on our own personal experiences in real life and/or on what we have read from other sources on the subject.

Originally Posted by Jedg

Re: PVC Seacocks..? . . . I propose the following 4 questions. I’m hopeful everyone will find the questions and answers thought provoking and informative.

Question 1. In order of importance (1=most important), list the 5 most important factors you feel need to be included in a seacock and thru-hull standard. Example: corrosion 1, external impact 2, internal pressure 3, etc.)

I would suggest that "corrosion" is number one especially since historically seacocks and through-hulls have been made of metal and metal corrodes. "Plastics" (including composite resin products like Marelon) do not corrode but they do wear and debris/dirt does adhere to them which can interfere with the operation of the valve.

The "impact" strength would be next or co-equal factor as seacocks and through-hulls are usually mounted on vertical or other-than-horizontal surfaces in the vessel's bilges. Somebody servicing the engine or something in or around the bilge area may drop something heavy or their foot may slip and they end up impacting the seacock/through-hull in a shear direction. So the importance of the seacock/through-hull to withstand that shock-shear impact and not break off is quite important especially if you are out in the oceans."Internal pressure" which I think you mean pressure in any hose leading from or to the seacock/through-hull is not really relevant as most applications involve gravity flow or low pressure pumping of fluids.

Question 2. Several people felt that impact resistance, both inside and outside the boat, was an important factor. There was comment about doing a comparison impact test on PVC and Marelon by dropping a sledgehammer on both materials. Being from VT, I know that a good splitting maul or hammer weighs about 8 lbs. So let’s assume each part, i.e. a thru-hull, is placed on a cement slab, the hammer is dropped on each part from, say, 4 feet, and each test drop is identical. As a benchmark, let’s say a malleable bronze thru-hull deforms and is unusable in 8 hits.

I think you mis-read the parts about Marelon seacocks breaking - the ball valve part does not break but the handle that controls the ball valve may and does break if forced beyond its limits - which are a lot lower than those of a bronze metal handle. Improper maintenance and lack of exercise and lubrication causes the handle breakage be the seacock Marelon, PVC, or Bronze (metal). Most everything has operating limitations and if you willfully exceed them you can expect failure of the part.

One relevant consideration for PVC valves is the nature of PVC to be "brittle" when stressed at the joint/union with another item such as the through-hull or hose fitting. Again I think this is more a case of using the item outside its design specifications.

What is the minimum number of hits you’d consider for an acceptable thru-hull standard value?

Not relevant.

Question 3. Someone presented the Marelon vs. other materials table. The ABYC standard is set at 10,900 psi Tensile Strength (TS) and 505,000 psi Flexural Modulus (FM). Some participants in this thread have seen Marelon break, others suggest protecting the Marelon parts, and others feel the parts are fine as normally installed.

Given the information found in the table and the experiential information the thread participants have provided, would you want to consider raising the values of TS and FM? Is there a number(s) you’d consider or is actual test performance of the parts more importance to you? Or both?

I think this question is not relevant at all as we as users/consumers do not set the standards - they are set by industry and outfits like ABYC that have the testing equipment. And they balance test results against economic interests and come up with a standard that is "realistic."

Seacocks and through-hulls are purpose built to these standards and function just fine in the real world. Using a product not purposely designed to be a marine seacock or through-hull negates the whole discussion as the product is being used outside its design specifications (e.g., using "garden hose" as plumbing hoses in a marine vessel). Using non-marine products usually is done because of unavailability of marine parts or the cost differential between marine and non-marine parts.

Question 4. Just like metals, every plastic has its weaknesses regarding degradation, in metal it’s called corrosion. For example, H-27 has a test for UV degradation for plastics. Some plastics degrade quickly in UV even when molded with UV inhibitors. All plastics degrade in moisture to varying degrees. The H-27 UV degradation cutoff is when TS or FM of the specific material exceeds 29% of the material’s initial values.

Do you think that a value of 29% maximum degradation for any test is too high, just right, or too low? Is there a % you feel would be acceptable?

Marine Seacocks and through-hulls are usually always installed in bilges or other spaces where "the sun don't shine" so UV degradation is not a relevant factor, IMHO.
. . .

[msponer]

Originally Posted by Jedg

Question 3. Someone presented the Marelon vs. other materials table. The ABYC standard is set at 10,900 psi Tensile Strength (TS) and 505,000 psi Flexural Modulus (FM). Some participants in this thread have seen Marelon break, others suggest protecting the Marelon parts, and others feel the parts are fine as normally installed.

I feel there are huge flaws in the ABYC specifying the material properties. I think it's junk science and engineering, that they probably started with seacocks they want to approve, and then tried to find a scientific sounding justification for including those seacocks and excluding others. In this case, the material properties are a very easy and quick line to draw.

What if we did the same thing for boat hulls? One could arbitrarily pick a minimum tensile strength that excludes fiberglass or cold molded hulls, since aluminum and steel obviously have better numbers. The problem is that is not the whole story-- it's how you design the part and use the materials.

But I can't fault them, since I think ... their charter is fundamentally to make a set of choices and then justify them with something that looks like engineering. And some of these choices, like sea cocks, are so minor that there's no reason to spend a lot of time defining something more precisely. I feel the proper way would be something like you suggest-- tolerance to impact and being stood on. But that is much more work.

For your other questions... They are above me. I have a physics background, which means I can only lightly wave my hands in the direction of mechanical engineering or materials science. I cannot talk or think in their precise terms and know how to define what is "good enough" within that context, especially on the Internet where there is bound to be someone who knows this domain much better than I do. So my idea for a "good enough" sea cock is much more functional: How much would it have to be abused before it would fail completely?

And that was sort of what I was trying to figure out here about PVC and Marelon seacocks.

[sailorchic34]

Just a side note, I checked the hayward valve data sheet and I think they are CPVC which is stronger then PVC. Tensile strength is somewhere around 7500 lbs. A bit better the PVC and somewhat better impact resistance too. Not quite up to yacht standards but not far off either.

BTW I am all for proper flanged seacocks. Thats what I have. The trick is that if the OP has tapered threads on his pipes, which I'm betting he does then his choices are somewhat limited. Try to find a Marelon valve with tapered threads in the USA. Not going to happen.

I'm not totally wild about Marelon valves either. Nylon tends to absorb moisture and swell just a little. Not much but its there. Marelon is glass reinforced nylon. I'm wondering if the hard turning issue with Marelon valves over time and breaking handles might be due, in part, to water absorption.

No matter which valve is used, on the longer pipe risers, I would install supports from a ridged place to firmly anchor and support the pipe and valve.

I really can't recommend stainless valves either on a aluminum hull/pipe. Not in salt water contact anyway. They are strong, But I would fear the aluminum pipe corroding at the threads. No matter what goop you put on the threads you still have metal to metal contact on tapered threads. Stainless / aluminum has about a 0.4V anode index which is high. Max allowable would be 0.15V or less.

Every type of valve has issues in any service. Lordy, I could talk for hours about valves and the good and bad points of each type, material and service used in.

[Talbot]

Thru hull and ball valve material has become a popular issue in Europe recently, with a realisation that most manufacturers are fitting minimal quality fittings that have a life of around 5 years (some considerably less). This has surfaced due to a number of relatively new vessels actually sinking due to their valves failing. Yachting Monthly and Practical Boat Owner have both done quite large articles on this, and the subject continues to rumble, with pressure to improve the standard requirement.

I thought I had marelon, and was very happy about that until I discovered that they were not marelon, but merely PVC. Another item to change at the next haul out where I will have to change 7 thru hulls and valves!

[GordMay]

Greetings and welcome aboard the CF, Jedg.

[daddle]

These type are the best way to go. I've seen them in Monel or some magic metal as well $$$. Flush closing is not just for racers. Close them flush when you leave the boat and you will not find any campers in the hole when you return. None of that ball valve sticking nonsense either.

ForeSpar thru hull fitting

[osirissail]

Originally Posted by sailorchic34

. . . Try to find a Marelon valve with tapered threads in the USA. Not going to happen. . .

Unfortunately, that is not true. See: Boat Marine Plumbing Ball Valve Thru Hull

"All valves sold throughout the U.S.A. have N.P.T. type threads."

Marelon valves and through-hulls marketed in the USA by Forespar, Inc. are made to serve the USA boating market. Therefore in order to sell their stuff they have to be compatible with what is being used in the USA. (For Europe they have different threads on their products to match the European standards.)

See: Boat Marine Plumbing Ball Valve Seacocks

In the USA, Forespar markets three (or four) versions of the Marelon Products - Seacocks (flanged) to be mounted to the hull and then a through hull is inserted through the hull and screwed into the mounted Marelon seacock. The Marelon seacock is made to accept the standard threads of all common through-hulls sold in the USA.

The second version are the "Ball Valves" (the first link above). They are threaded to the standard "National Pipe Thread" (which is a tapered thread - i.e., the more you tighten the fitting the wider the diameter of the threads). This is the type that the OP could use to replace the PVC ball valves - if he wanted to replace them.

The third version are "O.E.M." valves ("93" Series) designed to be incorporated into the original manufacturing of the vessel and are not sold as an "After-market" product, that is, you can get them but the other two versions are easier and more appropriate to be installed in an already built boat - or older boat.

The "fourth" version was available a decade ago but I haven't seen them in the current literature. They were designed to be actually "buried" into the hull during lay-up of the hull. They looked something like the valve "daddle" has in his post #43.

For the OP, there is a somewhat simple solution to his situation and that is to weld to his aluminum hull an aluminum plate (T-shaped) so that it comes up besides the ball valves. Then strap/attach the valves to this "support." Now he had protected the valves from any shear or axial direction shock or other loads that might try to bend the pipe and/or break the valve.

[sailorchic34]

Yes, I checked the Marelon web site before my last post. They indicate that ALL valves they make in the USA are NPT, but they show straight thread fittings. Actually they list the valves are to be used with NPT through holes where I thought all through holes were straight NPS thread. My guess is its a miss print and its really NPS threads. They also offer BSP or british standard pipe thread.


However in any event I finally asked myself the right question. That being whats the best fix.

What I would do is at the next haul out is find either aluminum pipe flanges or better yet have some threaded flange adapters fabricated out of 1/2" aluminum plate. One for each through hole Then get Dielectric kits which include hard rubber gaskets to isolate the metals at the flange surface and bolt holes. This galvanic isolates different metal materials and is standard practice in engineering.

Then you can use any flanged seacock you wish. TADA the best of all worlds, though the most expensive too. It is after all the engineering solution.