View Full Version : Bulkhead to PVC Threaded Connection

09/17/2017, 05:46 PM
OK, I am finally busy trying to get my 10' tank set up. *There are a number of 1.5" bulkheads in the plumbing, which I bought at a quality plumbing store here in New Zealand, together with male threaded adapters going to PVC pipe. I glued the pipe to the male threaded adapter with PVC cement - no worries. *The bulkheads are made in New Zealand and Hansen brand, but they are basically indistinguishable from what I used previously in the USA. The bulkheads themselves are also perfectly tight. *It's the bulkhead to adapter threaded connection I am having trouble with. *For the life of me, I don't seem to be able to get it drip free. *I've spend days of reading on the Internet - make it tight, don't over-tighten, use Teflon Tape, use the good thicker Teflon Tape...

I've tried it all, but drip, drip, drip. *Has anybody had any luck with these connections short of gluing them together?* I would really like to be able to pull this apart for maintenance when necessary, but if nothing else works, I guess I'll just have to glue them together and make do. *Maybe if I put Silicone on the threaded connection before screwing it together, I might even be able to pull it apart again. The last thing I need is my wife finding a puddle on the new laminate flooring I just put down!

Thanks for any advice!

09/17/2017, 05:58 PM
You should never use teflon tape on threaded plastic connections..
Its for metallic threads only..

threaded PVC connections should be made with a non-hardening thread sealant (paste) specifically designed for threaded connections...
its possible that the overtightening has already damaged the connections but getting the proper thread sealant is the first step..

I have no idea what brands are available in New Zealand though but if you pay for my plane trip and set me up with a bed to sleep I would be happy to come to the store with you and source the proper stuff :thumbsup:

And its very easy to overtighten with threaded fittings.. It doesn't take much when done properly to get it leak free..

Vinny Kreyling
09/17/2017, 06:34 PM
Someone in the know @ MACNA in NOLA did say that he uses a dab of silicone on pvc threads.
When I did maintenance we did it too.

09/17/2017, 06:53 PM
Bulkheads are being used on cylindrical tanks? You sure the leak is from the threads?

09/17/2017, 06:54 PM
Can you show us what those pieces look like unassembled? It's hard to tell what is what. I don't see any threads, and it looks like what must be the threaded fittings are both completely bottomed out. That should never happen, the threads are tapered and should lock tight way before they're bottomed out.

All bulkheads come with threaded outsides, for the nuts - those are straight threads and should not be used with plumbing fittings. Sometimes, people try to thread female plumbing fittings on them and end up with threads like this, so I figured it would be worth mentioning, since I can't really decipher the photo (at least not on my phone).

09/17/2017, 06:56 PM
Bulkheads are being used on cylindrical tanks? You sure the leak is from the threads?

That's a good point. A curved surface calls for a uniseal, not a bulkhead.

Another thought - bulkheads should be assembled with the gasket under the flange, regardless of which side of the bulkhead (flange or nut) is on the outside. Sometimes, people put the gasket under the nut, which basically leaves a path for water to leak (between the flange and the tank wall, then out between the nut threads).

09/18/2017, 01:00 AM
Thanks for all the feedback. Much appreciated.

Well, I guess the take home message here is that I need to get myself some suitable paste, and it seems I will have to order it from the US, because even professional plumbing supply stores have never heard about the stuff. They use Teflon tape, and as you guys have said, that just doesn't cut it.

The problem is that I need to be able to connect and disconnect these things more than once, but it could well be that I ruined the bulkheads I practiced on via a combination of tape use (maybe too much) and over tightening. I started of just hand tight, but when that still dripped, I tightened it a bit more. Never more than a few degrees past hand tight, but maybe that's too much already.

Regarding the bulkheads in the rain barrels, I was super worried about that. Frankly, I didn't think this would work at all, but it's been tight every time I installed it, because the plastic in the barrel is quite soft, and pulls flat as soon as you tighten the nut of the bulkhead just a little. You don't have to crank it. By the way, these bulkheads come with two gasket - one for under the nut and one for under the flange. Also, I am using the female end of the bulkhead with a male adapter, but the male end of the bulkhead has exactly the same thread as the adapter, so I am pretty sure I could have worked it the other way around also, but I didn't.

PS: I just checked and no seller on Amazon is willing to sell pipe sealing paste to New Zealand, and the folks on eBay want $50 in shipping for a $5 tube. I think I am going to try acrylic caulking first, and if that doesn't work some silicone might do the trick. If all that fails, somebody on eBay is going to become rich :wave:

09/18/2017, 02:22 AM
Tape should make a seal, even if its not 'correct'. I think the problem is as was pointed out that those fittings are bottoming out (and still not sealing) so its either taper to straight threads or a mix of metric/imperial threads or something like that that is the root of the issue. It could be that those bulkheads are designed for a face seal on the mating fitting with as wide a shoulder as it has.

Numbers off the bulkheads/fittings should label them pretty clearly... I think i see a 40mm on the bulkhead, but nothing else. Who makes it?

09/18/2017, 03:11 AM
The bulkheads are made here in New Zealand by Hansen:


Just looking at their site, they actually recommend a sealing paste: Loctite 5331.

I went to what the local aquarium club considers the best plumbing store here in Auckland, bought the bulkheads, and asked them for the matching threaded fittings. I specifically asked them for paste, and they acted like they did not know such a thing exists. Seems like I bumped into an incompetent sales person. Better see where I can get Loctite 5331!

09/18/2017, 04:40 AM
Wow, that is a REALLY short male fitting. Is that the only style available?

Maybe it's time you brought your fittings in to a reputable plumbing supply shop and asked for help. I'm wondering if there is some difference in conventions there.

I agree with Gorgok - tape can easily create a seal. It's just not the best, and it's easy to overtighten a taped joint, but it doesn't seem like that's what is happening here. Overtightening is bad because it causes cracking, and if those were cracked I think you'd know it.

You mentioned being able to disassemble. Threaded fittings aren't really meant for service disassembly. That's what a union is for.

You also mentioned putting caulk or silicone in the threads. While it might seal things, it'll also basically ruin any chance of disassembly. Pipe dope (teflon paste) is really what's best for those fittings. I'm surprised you can't find it. Might be a naming convention, if they call it something different there.

Is there a local hobbyist forum in NZ you could get help from?

09/18/2017, 04:49 AM
Get slip bulkheads and add a union in the middle of the pipe..
Thats a better solution vs threaded fittings anyways..

09/18/2017, 06:06 AM
I agree, if that is an option. IMHO threaded fittings really have no place in this hobby except when you are forced to use them (ie pumps or other equipment that comes with threaded fittings).

09/18/2017, 07:11 AM
I should have recommended that from the start.. I admit to being guilty of just skimming your post and missed the details first time around..

09/18/2017, 07:40 AM
^^^What all of them have said^^^

It almost looks to me like there could be a gasket (missing?) on the inside of the female end on the bulkhead as well - much like a garden hose fitting. I really can't think of another reason the male PVC fitting would sit so deep otherwise.

Vinny Kreyling
09/18/2017, 07:57 AM
I would not use the gasket under the nut, just on the other flange.
A union is best to separate the units as all have mentioned.