Seacock and thru-hull Poll

[Lagoon4us]

Engine rooms on commercial (read larger) tend to have a Sea-chest or Manifold this configuration allows for one large inlet with seacock of choice then multiple seacocks leading the raw water supply to its end use.

Maybe in a yacht for raw water supply we may be better having a similar 'central/one point' entry manifolding into the required number of supplies lines each closable seperately at the manifold with its own valve?

The main cock can then be the best of the best with the lesser cocks a more economical replaceable type that is servicable at the very least by shutting the main cock off....

Cheers Frank

[Watercolor]

HOPCAR,

1. As I've said I'm well aware of the problems trying to mate NPT and NPS threads. Groco has tried to get around this problem with it's NPS thru-hulls by taking the cheap way out, cutting/ tapering down the male NPS thread peaks.
2. The appropriate way to create a Groco threaded thru-hull for a ball valve conversion it to use an NPT die on the top 1" of the Groco NPS thru-hull. You will then have an NPT thread EXACTLY the same as the Groco flange.
3. The wall thickness for a plastic Schedule 80 1.5" pipe threaded part (AT THE BOTTOM OF THE THREAD) is approximately .150" and on a bronze fitting possibly less.
4. The "bronze" used by Perko and Spartan and maybe on Groco's best seacocks is not technically bronze. It's leaded red brass or 85-5-5-5 (85% copper, 5% each of zinc, tin and lead.) It's a price compromise material. I'm not saying it's a bad compromise, I've used them in my 50+ years of boating experience with excellent success as have most boaters. The lead simply makes machining (especially the threads) easier and cheaper with virtually no loss in corrosion quality. But it is soft.
5. I would have thought that if you attached a Groco thru-hull (properly machined with the top 1" NPT) to a Groco ball valve the assembly would break at the threads just above the thru-hull retaining nut. If that were the case then I would agree that the Groco flange and Groco valve combination would be stronger. The issue I thought would be simply one of a longer lever arm on the thru-hull combo.
6. However, that wasn't the case. The test showed that the assembly's weakest point was at the FIRST THREAD below the valve.
7. In other words, with the pressure coming from the top of the valve the greatest transmitted pressure was on that top thread just after the point where NPT threaded connection ended. Once that thread valley fractured the valve just sheared away at light speed. The result looked like someone had sawed the thru-hull fitting right below the valve.
8. The question is probably forming in your mind that the Groco flange NPT thread is different. The fact is that all these threads should meet the ASTM standard. If the Groco flange uses a more robust wall thickness than the thru-hull (which I doubt, as it would decrease the flow rate, and there would be a lot of diesels mfg'rs that would be mighty unhappy). The ASTM standard requires 11.5 threads/inch for a 1.5" fitting and 4.8 turns to tight. That leaves you with quite a few NPT threads of weakness on the Groco flange assembly.

I have nothing against Groco, no axe to grind. But, Groco has created two devices, the flange and the combo threaded thru-hull to end run a true seacock. Both products have the same exposed weakness that a true seacock doesn't have. In my mind the bronze seacock wins on safety hands down.

The question I've been trying to raise with anyone interested, is what is an acceptable standard regarding impact on a thru-hull (or Groco flange) ball valve assembly. In a way I'm advocating for the Groco product.

My number of hits question was not meant to be scientific, given the scenario I presented I was looking for boaters to give me a sense of their personnel comfort level. So my question is subjectively, is there a minimum number of hits you'd be comfortable with?

[sdowney717]

So my question is subjectively, is there a minimum number of hits you'd be comfortable with?

Before you go to sea, you should hit all your sea cocks hard to see if they leak or break. Just use a 2lb ball peen hammer and hit on one side then the other a mighty swing. Any failures will then be evident before your away from the dock and sinking.

The thread mismatch issue is not much of a consideration. A little sealer and your fine. Tapered ball valve threads still screw down on straight thru hull threads. Even tapered - tapered connections need pipe sealer as the threads do have tiny misalignments.

I must have excellent thru hulls under my twin raw water engine intake ball valves as when I had them apart they are not wimpy thin like some have mentioned.

I have 2 genuine sea cocks for the the head, inlet and outlet. They are odd design using a rubber cylinder and a compression plate with screw handle.
When I got the boat they were stiff! This was due to NO maintenance by prior owners the last 40 years. They simply needed the rubber plug valves removed and the corrosion in the bores cleaned.

[Blue Stocking]

Originally Posted by sdowney717

Before you go to sea, you should hit all your sea cocks hard to see if they leak or break. Just use a 2lb ball peen hammer and hit on one side then the other a mighty swing. Any failures will then be evident before your away from the dock and sinking.

The thread mismatch issue is not much of a consideration. A little sealer and your fine. Tapered ball valve threads still screw down on straight thru hull threads. Even tapered - tapered connections need pipe sealer as the threads do have tiny misalignments.

I must have excellent thru hulls under my twin raw water engine intake ball valves as when I had them apart they are not wimpy thin like some have mentioned.

I have 2 genuine sea cocks for the the head, inlet and outlet. They are odd design using a rubber cylinder and a compression plate with screw handle.
When I got the boat they were stiff! This was due to NO maintenance by prior owners the last 40 years. They simply needed the rubber plug valves removed and the corrosion in the bores cleaned.

I Have 7 of the Groco tapered rubber cylinder seacocks on my boat. Love them!! 15 yrs old still perfect.
When the T-handle is released the compression on the cylinder is released, and a little water should leak from the end plate.
Every 2 years it takes me about one hour to remove the end plates, wipe the cylinders clean with a soapy rag, dry , grease and re-assemble.
These are NPS sea-cocks with Groco, washer type NPS hose receivers.
No longer made--were not cheap.

[sdowney717]

Thanks now I know what they are. And they are very nice valves.
http://www.kp44.org/ftp/GROCO_Seacocks.pdf

take care on the type of grease used.

Lubrication: Lubrication is not normally required, but
may aid in the easy operion of older valves. Remove
the valve plug and coat lightly with silicon based
waterproof grease. Do not use petroleum based
grease as it will chemically attack the rubber.

I have seen rubber swell up when using oil based greases.

[Blue Stocking]

Originally Posted by sdowney717

Thanks now I know what they are. And they are very nice valves.
http://www.kp44.org/ftp/GROCO_Seacocks.pdf

take care on the type of grease used.


I have seen rubber swell up when using oil based greases.

Yep!!--non petroleum.

[barnakiel]

You guys are all very happy to live in the bronze age!

Imagine here (in the EU) things are not only NPT / NPS mis-matched but also, most of the time, metal mismatched (most everything one can find in an average chandlery here today are chromed brass ball valves).

arghhhhhh and bummer!

;-(

Cheers (?),
barnakiel

[Watercolor]

HOPCAR,

i checked the website where i saw the pull test on the ball valve/thru-hull.

The break wasn't at the top thruhull thread as I remembered it. It was at the bottom thru-hull NPS thread just above where it meets the locking nut.

However, the same hold true for the Groco. There are at least three full threads between the Flange and the valve. The weakest point has nothing to do with an NPS/NPT thread miss match factor or the strength factor related to NPT/NPT thread matches.

There might be a slight difference in overall height of the units that might impact break. but I doubt by much. My suggestion is always sell a seacock, a Groco if you want, when possible. When conditions warrant, ie. space or height then recommend the Groco over a Thru-hull option.

The weakest point is at the exposed threads.

[Badsanta]

I love the Groco Flanged Adapter