PVC Seacocks ..?

[sailorchic34]

Hum OK it may be that the Marelon valves are NPT. BTW NPT is national pipe taper, not national pipe thread, though most people use the later.

This worries me a little. You can join a NPT valve to a NPS thru hull fitting. It however only has about 4 threads engaged which is not that strong. It seems tight but its a rather weak connection. Not really something I would want

There may be a NPT thru hull fittings made, but I've not found one yet. The ones at WM and other marine stores are NPS or straight pipe threads. Least wise the ones I've seen.

So to the OP looks like you could use a Marelon valve on your pipe risers. Now I'm worried about the people with NPS thru hulls with Marelon npt valves.

[s/v Jedi]

The Marelon valves are NPT. The Marelon seacocks (flanged valves) are NPS. Tada...!!

ciao!
Nick.

[sailorchic34]

Hum... In doing a little checking it seems that all the inline ball valves sold for marine use are NPT, Apollo, Marelon, etc all have tapered threads (in the US, BTW). Yet all the thru hull fittings I've seen are NTS or straight threads. Straight threads are used as its easy to cut down the threads to work with different hull thicknesses.

I had no idea it had become common practice to use mismatched threads. Even some boat manufactures do it as standard practice. That is scarry. It may work because the pressures seen in thru hull service is not much. But it is a rather weak connection in a location where it should not be.

Gee the only way I would use a inline valve at a thru hull is with a groco (or equal) flange adaptor. That has NPS on the water side and NPT on the valve side. That is assuming the hull is NOT aluminum where other things need to be considered.

Oh you could use whats called a combination thread thru hull, which has the first few threads cut down. Groco makes one. But its not normally stocked at the local marine supply houses. Nor is it a true NPT thread. But it better then nothing.

While I'm drifting a little, I'll note that most of the apollo valves in the stores have a chrome plated ball. The chrome will not last in a salt water environment and the ball will pit. Cobranco / apollo does make a valve with a stainless steel ball, but again its not normally stocked at the local level.

Just fyi

[Maine Sail]

Originally Posted by sailorchic34

Hum... In doing a little checking it seems that all the inline ball valves sold for marine use are NPT, Apollo, Marelon, etc all have tapered threads (in the US, BTW).

NPT has been the standard in the US for valves for a long time. Early on I recall the RC Marine/Forespar valves were a straight thread (NPS) and they're now NPT just like the bronze and stainless ball valves..

Originally Posted by sailorchic34

Yet all the thru hull fittings I've seen are NTS or straight threads. Straight threads are used as its easy to cut down the threads to work with different hull thicknesses.

And to thread it into a flanged seacock.

Originally Posted by sailorchic34

I had no idea it had become common practice to use mismatched threads. Even some boat manufactures do it as standard practice.

Often times US boat builders, building to ABYC standards, will use a "combination" threaded thru-hull. This is a Band-Aid at best but I suppose might qualify as a "thread match". Technically it is not a thread match because a "combination thread" only shaves the peaks off the first few threads of a NPS thru-hull. The valleys are still the same depth because the wall thickness is simply not sufficient to cut a true tapered thread into, and not compromise the thru-hull strength.

Originally Posted by sailorchic34

That is scarry. It may work because the pressures seen in thru hull service is not much. But it is a rather weak connection in a location where it should not be.

NPS to NPT / NPT to NPT


Yes it is scary and this is why the ABYC suggests that threads must be "matched"...

Originally Posted by sailorchic34

Gee the only way I would use a inline valve at a thru hull is with a groco (or equal) flange adaptor. That has NPS on the water side and NPT on the valve side.

The flanged adapter is a great product. I install a lot of them and have been since they hit the market. They also make future valve changes a 5 minute job instead of a haul out. I've been bugging Forespar to make one to solve the broken handle issues. Would be a LOT easier than spinning a thru-hull while trying to get a Marelon valve off that has a broken handle.

Originally Posted by sailorchic34

Oh you could use whats called a combination thread thru hull, which has the first few threads cut down. Groco makes one. But its not normally stocked at the local marine supply houses. Nor is it a true NPT thread. But it better then nothing.

]

Yes better than nothing BUT you can't cut it down or you lose the "shaved threads".. This adds to lever height and can make for an awfully tall lever arm to snap a thru-hull.

A"Band-Aid" / budget approach..

Originally Posted by sailorchic34

While I'm drifting a little, I'll note that most of the apollo valves in the stores have a chrome plated ball. The chrome will not last in a salt water environment and the ball will pit. Cobranco / apollo does make a valve with a stainless steel ball, but again its not normally stocked at the local level.

Just fyi

Hamilton Marine stocks both combination thread thru-hulls and valves with SS balls. Jeez thanks for letting me know chromed balls will not last.. I have lots of customers with 17-25 year old ball valves. A lot of these were made by Apollo/Conbraco and a chromed red brass balls or chromed bronze balls. They still work.. On our own boat I have two 13 year old Apollo valves with chromed balls still performing perfectly and the rest are all Groco, again with chromed balls all performing perfectly.

This was a five year old Groco I had removed couple of years ago... Looks pretty good to me for five years of service in salt water..


Even if a chromed ball were to start turning hard I would simply thread it off the flanged adapter and put a new one on. About 10 minutes and 40 something dollars for a 1" valve. Beats twisting a thru-hull, breaking the seal then having to remove, clean and re-bed it....

As s side note I have not seen a Marelon valve snap. I have seen handles break off Marelon and yellow brass literally crumble but goo quality Marine UL valves are pretty darn reliable.. Heck I have some customers with 40+ year old tapered cone 85-5-5-5 bronze seacocks still going and still performing like new at 40+ years!!!

[sailorchic34]

Yes agree with everything you say. OH agree, NPT standard has been around forever. I had a apollo valve fail in a previous boat where the chrome was flaking off and the stem was shot.. I've also seen ball valves fail in regular land side plumbing systems. Mainly where someone is using a mix of steel and copper pipe.

BTW despite being blonde, I've about 33 years experience designing hydronic, plumbing and process piping, etc., etc. systems for projects all over the world. Plus a wee bit of utility plant (chilled water and steam) design, up to 12,000 ton capacity which is fair size.

Yes its the valve handle on the forespar valve that tends to bind and snap off.

With you 100 percent on the threads matching. Though I checked the web sites of WM and Defender and they offer NPT inline ball valves and NPS thru holes. Its not widely known by boaters that the NPT valves are not quite compatible with the NPS thru holes..

Oh I have the 40 year old taper plug sea cocks on my little boat... Great valves.

[Watercolor]

@font-face { font-family: "Arial"; }@font-face { font-family: "Cambria"; }p.MsoNormal, li.MsoNormal, div.MsoNormal { margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: "Times New Roman"; }div.Section1 { page: Section1; } I believe the Marelon seacock and ball valve threads are, in the US, now standardized as either NPT (National Pipe Tapered) or NPS (National Pipe Standard). The Marelon ball valves are generally NPT at both ends. The Marelon seacocks are NPS at the through-hull end and NPT at the hose end. Older Marelon and RC Marine valves (Forespar bought the RC seacocks and valves years ago) are on the through-hull side standard threads and on the hose side BSP (British Standard Pipe) threads since RC Marine was from New Zeeland.

Regarding the joining of NPS and NPT threads, I think Maine Sail’s visual is excellent. However, here’s a heads up, unless I missed it and someone’s beaten me to the punch.

1. NPS threads are the same, on a 1.5” NPS thread every thread is or should be the same the same tooth pitch, diameter, # of threads per inch, etc.
2. The ASTM Standard F1498 00 for thermoplastic NPT pipe threads sets the number of turns, hand tight at 4.8 turns. That’s not only for sealing, but for structural continuity.
3. Maine Sail pictorial shows only half of the conflict between NPT and NPS. His pictures show the easier to notice male NPS thread into a female NPT thread. If the threads are reasonably close to the ASTM standards you’ll see exactly what the picture shows, only a two complete thread match.
However, threading an NPT male thread into a female NPS thread is less visible . The male NPT pipe will screw in until it finds the thread that exceeds the diameter of the NPS female connector. So you will find it easy to screw these to parts together (easily 5 full turns in), however, you probably have less than two threads in real contact. The smaller diameter threads are not sealing or locking the components together.

If you find the newer NPT threaded Marelon ball valves harder to thread or that they seem to leak, there is a reason for that. Nylon (plain or glass filled) like Duponts Zytel (Marelon) has a particular molding characteristic, it is what is called “dimensionally unstable.” All this means is that it shrinks a lot in the molding process. This issue is solved generally by simply making the molds larger to accommodate the shrink. However, on the Marelon ball valve because of the nut shape on the top and bottom the threads are by nature uneven. The problem is the significant different in thickness between the nut peak and the nut flat makes hole diameter at the peaks significantly larger than the flats. Nylon in the right environment is cheap and strong but not precise. I found this out the hard way.

I hope this is of some help.

Also, I want to thank those who responded to my questions. Those who missed them I hope you’ll give them a try.

[osirissail]

Originally Posted by Maine Sail

. . . The flanged adapter is a great product. I install a lot of them and have been since they hit the market. They also make future valve changes a 5 minute job instead of a haul out. I've been bugging Forespar to make one to solve the broken handle issues. Would be a LOT easier than spinning a thru-hull while trying to get a Marelon valve off that has a broken handle. . .

Why would you dismount (remove the through-hull) of a flanged Marelon Seacock for a broken handle?

The Marelon flanged seacocks come in 3 parts, base, ball and body (not counting the hose adaptor).

In the case of a broken handle you can replace the handle by removing the screw under the label. In the case of a broken ball stem you can remove the interior hose/adaptor and unscrew the body off the flanged base. Then replace the ball or replace the whole body and ball. The hull mounted flanged base and through-hull are never touched.

Of course periodic maintenance will eliminate the problem of broken handles. Buried in the Forespar Marelon library is the information that the recommended lubricant is PFTE waterproof grease. The procedure they suggest is to close the valve; remove the hose adaptor or just the hose and use a long handled artist's brush to paint the ball with PFTE lubricant. Then exercise the valve after replacing the hose, etc. Below is an example of such a grease.

To free a stuck Marelon seacock all you have to do is use two spanners to "unthread" the body from the base about an 1/8th rotation and then exercise the ball and lubricate it. After lubrication you can tighten the body/base again.

- - - - -
I would agree with sailorchic34 that "chromed" balls in ball valves are a high potential for being "eaten" or surface pitted in a salt water environment - - unless they are also maintained and lubricated frequently.

[Maine Sail]

Originally Posted by osirissail

Why would you dismount (remove the through-hull) of a flanged Marelon Seacock for a broken handle?

The Marelon flanged seacocks come in 3 parts, base, ball and body (not counting the hose adaptor).

In the case of a broken handle you can replace the handle by removing the screw under the label. In the case of a broken ball stem you can remove the interior hose/adaptor and unscrew the body off the flanged base. Then replace the ball or replace the whole body and ball. The hull mounted flanged base and through-hull are never touched.

Many of the Marelon tri-flange seacocks have locking retainer pins. You've un-threaded these..?



Also I've tried to remove a few that did not have a pin, some smaller size don't, and the glue they were put together with ruined the threads making the valves/flange junk. Don't know what the adhesive was but it was tenacious stuff.

Others, without pins, seemingly have no adhesive and come apart easily. No way to know what it was put together with so in-water I am not about to try that. Out of water there's nothing to lose. They have also made multiple changes to these valves over the years so I would not feel entirely comfortable putting a new valve body onto an older base for fear that specs may have changed slightly.

These are the types of handle failures I often see. It is the stem that often fails not the handle... Later valves have a different designed ball stem and are less prone to failure..


But the real answer to your quote of mine was that I was not referring to their flanged seacocks but rather their valves stuck directly to their thru-hull fittings. Many boats I work on have a Marelon valve threaded to a Marelon thru-hull fitting. More often then not, just happened to me last week on a mid eighties Ericson, when removing a valve you spin the thru-hull and then need to re-bed it.

I'd still love to see Forespar come out with a true flanged adapter as their valves cost less money to replace than their flanged seacocks. I'd also know they were meant to come apart & not be left wondering if they have a locking pin or some NASA strength adhesive in there...

[s/v Jedi]

Osiris is dead on. There is no mismatch between the Marelon seacick and thru-hull fitting.

Also, I have seen regular ball valves (Marelon) that could be taken apart like the flanged seacocks.

cheers,
Nick.

[s/v Jedi]

Originally Posted by Maine Sail

It's called a locking pin and many of the Marelon tri-flange seacocks have them. You've really un-threaded these..?

Also I tried to remove one that did not have a pin and the glue it was put together with ruined the threads making the valve junk.

I am starting to rhink they sell different versions in different parts of he world?

I first noticed the parts of the seacock when I couldn't turn the handle after install. It had turned very easy just before install. I had tightened the valve-parts too much during mounting it on the hru-hull fitting. I could just take them apart, there was a rubber O-ring, no glue. I buy these either in South Florida or the Caribbean.

cheers,
Nick.

[Maine Sail]

Originally Posted by s/v Jedi

I am starting to rhink they sell different versions in different parts of he world?

I first noticed the parts of the seacock when I couldn't turn the handle after install. It had turned very easy just before install. I had tightened the valve-parts too much during mounting it on the hru-hull fitting. I could just take them apart, there was a rubber O-ring, no glue. I buy these either in South Florida or the Caribbean.

cheers,
Nick.

They probably do. I have seen many iterations of Marelon valves over the years, got a box full in my barn. They seem to be pretty stable now but for a while there were seemingly quite a few changes.

Problem for me is that I work on boats that still have RC valves that fail and later Forespar valves that fail both old and new style though less new style so I don;t really want to try and "mix-n-match" with new stock for fear they might not be 100% perfectly compatible.

Had done a couple of "spin offs" on the tri-flanges then got a few that would not spin off and discovered the pin and adhesives. Now days they have a mix of some with pin some without. So hard to keep up... Just give me a good old tapered cone or Groco flanged adapter and any UL Marine NPT valve and I am good to go.

That said the series 93 valves are great valves but the thru-hull is specific to the OEM valve series. This is why they rarely sell them through the retail channel for fear someone might try and use a standard NPS thru-hull in one...

[osirissail]

I must admit that my Marelon seacocks are more than a decade old and do not have any "locking pin" nor are they "glued." I will have to examine carefully what is currently on the shelves these days.

If the current models do have "pins" or are "glued" I will certainly never buy them again or find a way to extract the pin. Even the metal seacocks and ball valves I have seen on the shelves can be disassembled. "Pins" seem to me to be a stupid idea since more than a few "stupid" people twist the handles off the valves because they never service the valves (which is unfortunately quite a common thing).

Also If they keep changing the spec's and don't keep or make available "parts" for older versions then I see a return to the metal valves as the most viable alternative. More than a few companies have "improved" themselves out of business.

As to threads - my research has found that "NPT" is classification of a thread form (pitch, tpi, etc.). The term "NPT" is also commonly used to denote a tapered NPT thread - 1° 47'. "NPSM" is NPT thread form but with straight (not tapered) threads. "NPSM" (National Pipe Straight Mechanical) is often shortened to "NPS." NPT tapered relies on an interference fit caused by the taper to eliminate fluid leakage, while NPSM (NPS) relies on a "mechanical" seal using a seat or O-ring to prevent leakage.

[Watercolor]

@font-face { font-family: "Arial"; }@font-face { font-family: "Cambria"; }p.MsoNormal, li.MsoNormal, div.MsoNormal { margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: "Times New Roman"; }p.MsoPlainText, li.MsoPlainText, div.MsoPlainText { margin: 0in 0in 0.0001pt; font-size: 10.5pt; font-family: "Times New Roman"; }span.PlainTextChar { font-family: Courier; }div.Section1 { page: Section1; } I believe the Marelon seacock and ball valve threads are, in the US, now standardized as either NPT (National Pipe Tapered) or NPS (National Pipe Standard). The Marelon ball valves are generally NPT at both ends. The Marelon seacocks are NPS at the through-hull end and NPT at the hose end. Older Marelon and RC Marine valves (Forespar bought the RC seacocks and valves years ago) are on the through-hull side standard threads and on the hose side BSP (British Standard Pipe) threads since RC Marine was from New Zeeland.

Regarding the joining of NPS and NPT threads, I think Maine Sail’s visual is excellent. However, here’s a heads up, unless I missed it and someone’s beaten me to the punch.

1. NPS threads are the same, on a 1.5” NPS thread every thread is or should be the same the same tooth pitch, diameter, # of threads per inch, etc.
2. The ASTM Standard F1498 00 for thermoplastic NPT pipe threads sets the number of turns, hand tight at 4.8 turns. That’s not only for sealing, but for structural continuity.
3. Maine Sail pictorial shows only half of the conflict between NPT and NPS. His pictures show the easier to notice male NPS thread into a female NPT thread. If the threads are reasonably close to the ASTM standards you’ll see exactly what the picture shows, only a two complete thread match.
However, threading an NPT male thread into a female NPS thread is less visible . The male NPT pipe will screw in until it finds the thread that exceeds the diameter of the NPS female connector. So you will find it easy to screw these to parts together (easily 5 full turns in), however, you probably have less than two threads in real contact. The smaller diameter threads are not sealing or locking the components together.

If you find the newer NPT threaded Marelon ball valves harder to thread or that they seem to leak, there is a reason for that. Nylon (plain or glass filled) like Duponts Zytel (Marelon) has a particular molding characteristic, it is what is called “dimensionally unstable.” All this means is that it shrinks a lot in the molding process. This issue is solved generally by simply making the molds larger to accommodate the shrink. However, on the Marelon ball valve because of the nut shape on the top and bottom the threads are by nature uneven. The problem is the significant different in thickness between the nut peak and the nut flat makes hole diameter at the peaks significantly larger than the flats. Nylon in the right environment is cheap and strong but not precise. I found this out the hard way.

I hope this is of some help.

Also, I want to thank those who responded to my questions. Those who missed them I hope you’ll give them a try.

[Maine Sail]

Originally Posted by osirissail

If the current models do have "pins" or are "glued" I will certainly never buy them again or find a way to extract the pin. Even the metal seacocks and ball valves I have seen on the shelves can be disassembled. "Pins" seem to me to be a stupid idea since more than a few "stupid" people twist the handles off the valves because they never service the valves (which is unfortunately quite a common thing).

.

I guess count me as a "stupid people" even though my own valves were ALWAYS lube and I still have had three handle failures on boats I've personally owned.

All three of these valves were the old style when they had problems with out of round balls and a weaker stem design. Even lubed and perfectly clean they never turned as they should have. Lube didn't fix it but feel free to continue with your misguided insults if you want..... If two design flaws, out of round balls and a weak stem, that were later changed & addressed to minimizes failures, makes me a stupid people, well, I guess I'll live with that....

The pictured valve came off a customers boat and when I yanked it there was still a good shiny gloss of grease on both the top and bottom of the ball and he had been maintaining them using an artists brush and Lanocoat every spring. They now sell Marelube but back then they recommended Lanocoat.

[osirissail]

Don't get your feathers in a fluff - I was not insulting you but making the point that all too many people are too busy with other things to keep up with all the "supposed to do . . ." maintenance involved in boats or for that matter many other things.

Everybody, myself included, gets in a hurry and can force the handle beyond its break strength or at least is tempted to do that. On seacocks without pins you can unscrew the base and body so things are very loose. If the handle still refuses to move, breaking it off won't solve anything - replacing the valve will solve the problem. This is one of the areas where the rule "just get a bigger hammer" doesn't work very well.