Uni-Seal opinions or experience?

[Roger Long]

I know Peggie likes these things for retrofit of larger holding tank vents but I'm trying to figure out if they are the best choice for the new tank I'm having built.

http://www.aquaticeco.com/subcategories/1617/Uniseals/uniseal/0

Peggie appears to be MIA. I hope everything is well.

I'm getting conflicting opinions from piping people I ask. I looked at one at Portland Plastic Pipe and it seems to me they should work fine. Clever design. They would greatly simplify the tank piping and let me make the tank more than an inch deeper. Since capacity is the reason for spending all the money on a custom fitted tank, that's important.

A fellow who builds complex aquarium and aquaculture setups says not to use them on a boat where there is motion and could be pipe movement. Equally "reliable" information says they stay tight up to 15 degree angles.

It's a critical decision. If the Uni-seals leak odor (they will all be in the tank top), I'll have to live with it for months and then re-do the whole thing.

Any experience based opinions greatly appreciated.

 

[bria46]

I wouldn't do it. I think the aquarium guy is correct.

 

[woodster]

if you look at the Todd relocation kit it looks to be a grooping of plastic through hull fittings... makes one wonder if that is good enough for them... then why wouldnt the hub style fittings you are talking about be even better....

regards

woody

 

[Maine Sail]

A fellow who builds complex aquarium and aquaculture setups says not to use them on a boat where there is motion and could be pipe movement. Equally "reliable" information says they stay tight up to 15 degree angles.

Roger,

My gut is that I think you know the answer and Brian in Biddeford has probably given you the most relevant advice, as they make products that go down the road, bump and vibrate like boats do.

Probably would not catch me trying to hold cr@p in my tanks with a GROMMET,.....

 

[Peggie Hall HeadMistress]

My advice:

Have the female threaded tank fittings spin welded into the tank by the tank builder in the sizes and locations you specify . If all the fittings will be on the top of the tank, I don't know why using one type of fitting vs another would have any impact on useable tank depth...'cuz no matter what type of fitting you use, you'd still need a pickup tube inside the tank to the bottom, cut off at about a 25 degree angle.

All that said, as long as all the fittings will be on the top, the Uniseal will work just fine provided the hose coming off it doesn't pull to one side...use 90s or 45s to prevent it. I've used 'em for years...when installed and plumbed correctly, they don't leak. However, even the Aussies (who make the Uniseal) don't recommend using one on a discharge fitting at the bottom of a tank.

As for the Todd relocation kit, you need access to the inside of the tank to use it...and you can buy two dozen Uniseals for the price of one kit.

I dunno who you plan to have build your tank...Triple M Plastics, located in ME Triple M Plastic Products Inc does an excellent job for a decent price. They use PP instead of PE to make welded tanks.

 

[Roger Long]

I don't know why using one type of fitting vs another would have any impact on useable tank depth.

The difference would only be the height of the half couplings welded into the top of the tank and the threaded neck on the elbow. It's less than I thought when I posted now that I look at the fittings.

I'd planned to put a PVC elbow with a Sealand hose adapter on it, a suction tube on the other leg, and just push it all the way through the Uni-Seal. With the elbow pushed right down to the seal, I though I would save more than I would.

I'm planing to have the tank built at Maine Marine Plastics in Biddeford who have done good work for me before. Is there a significant reason to use PP instead of PE?

If the other guys can do flush fittings and MMP can't, it might cause me to switch.

 

[Maine Sail]

All that said, as long as all the fittings will be on the top, the Uniseal will work just fine provided the hose coming off it doesn't pull to one side...use 90s or 45s to prevent it. I've used 'em for years...when installed and plumbed correctly, they don't leak. However, even the Aussies (who make the Uniseal) don't recommend using one on a discharge fitting at the bottom of a tank.

Peggy,

Good info. How fair does the hole in the tank need to be in terms of burr free for the seal to work well etc.? If it seals to 40 PSI why wouldn't they suggest it for a bottom tank location?

I have a FW tank where the vent fitting is cracked due to a PO over tightening it but it is still holding, for now. While admittedly skeptical on using a "grommet" I may consider one of these on the FW tank vent as this tank will not come out of the boat without serious surgery and the opening is too far away to reach it. I would love to weld it but don't know of anyone good who does portable work on these tanks in the location of this tapping...

 

[Tim R.]

I wonder how much pressure or vacuum can be exerted on a holding tank with a clogged vent? I am not sure I would trust anything that is rated at 40psi.

 

[Roger Long]

I am not sure I would trust anything that is rated at 40psi.

Well then, don't ride one of the ferries over to Peaks Island

40 psi is 5760 pounds per square foot which is a 90 foot head of seawater. That's more than the hulls of most small ships are designed for.

My concern is that it's always harder to contain vapor than liquid and, let's face it, "vapor" is the issue here. Some fittings are also more prone to leak at low pressures than high. When I went down to see the "Titanic", the first thing I saw after the sub went in was water seeping in around the windows, a real confidence builder. Fortunately, I had been warned and could deduce enough about the engineering to know that the pressure would seal the several inch thick plastic ports tightly.

I'm setting up a test rig for the Uni-Seal (Yeah, cabin fever) and should have something to report soon.

 

[Roger Long]

why wouldn't they suggest it for a bottom tank location?

Lawyers?

It's actually a very clever grommet. I can easily believe Peggie's good experience with it.

My biggest reason for using them now is that I know, once I get the tank in the boat and start running hoses, I'll find myself thinking that I wished I'd put a fitting there instead of here. It will also be easier to aim elbows in the right direction without over or under tightening. I always worry about stripping plastic.

 

[Roger Long]

My test is underway. Photos here:

http://www.facebook.com/album.php?aid=54034&id=1846284215&l=f0d540cc35

I first tried inserting the PVC elbow in my cobbled together test tank of 3/8" acrylic and a plastic bin epoxied together. I was very unimpressed. My full weight on the elbow wouldn't get it to engage properly and just a slight knock on the side popped it out. I was beginning to wonder if Peggie has been smoking something

I then boiled a pan of water and soaked the fitting in it for a couple of minutes. It worked beautifully after that. I was able to get it out but not easily enough that I think there is any risk with hose connected close to the fitting and the tank properly secured.

This is the test rig:

A suction tube epoxied into the elbow runs close to the bottom of the tank so water poured in the small tube traps air and lets it fill up. The pressure head is about 6 feet, more than the height to the vent in my boat. If there is any slight air leakage, (which would be odor in the boat) the water level will fall. Once the water temperature stabilizes, I'll try wiggling the fitting with some soap solution on it and see if the water level changes.

Before putting the water in, I blew as hard as I could into the tube with soap solution on the fitting and saw no bubbles.

So far: Promising.

Later: Put more soap solution on the fitting and wiggled it much more than it ever should in the boat. Absolutely no sign of leakage. Blew into the hose as hard as I could and did the same thing. Completely tight as far as I can tell.

One result I should have anticipated, now that soap has worked its way down into the joint with the wiggling, the fitting is quite loose and I could probably pop it out easily. Still, nary a soap bubble around the edges.

The advice about not putting them in tank bottoms may be related to not letting the tank contents lubricate the joint.

Unless my tank vent plugs solid and I pump against it, I can't put as much pressure on the joint as I have now.

I decided to pull and wiggle until I did see soap bubbles. The fitting can be moved about 15 degrees before bubbles appear when pushed fully down. Pulling it up about 1/8 inch doesn't cause leaking but reduces the angle it can be moved about 5 degrees. They are surprisingly tolerant.

I probably still am going to go with threaded fittings. These things do appear to work as advertised but even seeing that with my own eyes doesn't dispel the mental image of one of these popping out of a full sewage tank.

 

[Roger Long]

Brian in Biddeford has probably given you the most relevant advice, as they make products that go down the road, bump and vibrate like boats do.

Probably would not catch me trying to hold cr@p in my tanks with a GROMMET

I think their advice is sound for something entirely piped up with PVC. However, with an elbow transitioning immediately to hose and everything properly secured, there is going to be very little stress on the fittings.

I went down this morning and the water level in my tube was actually higher because the basement warmed up a bit. The test soap solution had dried and I tried to pull the fitting straight out. I wasn't strong enough to do it. I couldn't twist it either. It felt as solid as a threaded elbow. By levering it however, to move it at an angle, I was able to break the seal and it came out easily. Big rush of the pressurized air. These things are tight.

As for your second comment, I can not see any engineering or rational reason not to use these fittings as I would be doing. It wouldn't even surprise me to find them more tolerant of unexpected movement than spin welded fitting and plastic elbows which can crack. However, even with this hands on experience, I just can't get over the psychological feeling of not being isolated from the cr@p by a threaded fitting. I thought that would go away with some successful hands on testing but it didn't. At this point, it's strictly emotional though.

A bit later:

10 psi according to the rather low tech gauge on my portable air compressor. This is more than tanks on steel boats are designed for and more than you can ask of a typical plastic holding tank. Fitting didn't move a bit in the Uniseal. Big bang!

It's occurring to me that, if you did have the vent plug and over pressurize the system with enthusiastic pumping, it might be better for a top fitting to blow out than to have the tank fail. I expect most plastic holding tanks would fail before one of these fitting popped out though.

 

[JohnnyMac]

Higher volume mfg uses them

Having worked in the plastic rotomolding business for 20+ years I have seen uniseals and spinwelds used in much more complicated and demanding environments than the holding tank on a boat. RV waste tanks, pond filters seeing 10 psi, water and chemical tanks use these. Uniseals work under the same theory as dapco fittings used for pick up and return tubes in a realm of diesel fuel applications. You just need the proper sized hole saw and scape away any burrs.

 

[Roger Long]

Having worked in the plastic rotomolding business for 20+ years...

Perhaps you can answer some of my questions.

Is it possible to spin weld a fitting nearly flush with the tank top? I'm trying to maximize capacity here. My tank builder wants 1/2 to an inch of fitting above the tank. I'm wondering if I should talk to another tank builder.

Do you know a source for hose barb elbows that can be welded directly into the tank?

I appreciate your advice on the Uniseal. I'm becoming more confident but it's also one of those things I might have to explain to a surveyor who isn't familiar with them if I want to upgrade my insurance. "Hey, you mean those pipes are just stuck in there?!"

 

[Peggie Hall HeadMistress]

Yes it's possible...

In fact, just about every production rotomolded tank mfr except Ronco does spin weld 'em in flush...and Ronco will do it if you ask 'em. But extra 1/2" isn't gonna make enough difference in the tank capacity to matter. I just ran a calculation for a hypothetical 44 gallon tank 17" wide...increasing the width to 17.5 added .3 gallons--just a little over over a quart...not even one flush in a 40 gal.+ tank! It wouldn't even be that much in a smaller tank.

Do you know a source for hose barb elbows that can be welded directly into the tank?

No...and I would recommend doing that if I did.

As for the Uniseal...any surveyor who doesn't know what one is by now shouldn't be surveying boats. SeaLand is even using 'em in their retrofit pickup tube kits!

 

[Roger Long]

Update

I'm going to go with the Uniseals for all tank top fittings. The psychological resistance has faded with time. The simplicity of the piping installation and the flexibility of being able to point elbows in any direction without compromising on thread tightness are just too good to pass up.

 

[Roger Long]

Here is how the fittings will be installed. Note the expansion of the Uniseal with the pipe insertion.

This is the 1" line for the hand pump out. The pipe glued into the elbow will extend almost to the bottom of the tank and be cut off at 20 deg. angle. The shoulder of the elbow will register the proper depths and provide a bit of additional seal. Vent will simply have the pipe cut off about 1/8" below the Uniseal.

The inlet and pump out lines will be done the same way but with the Sealand adapters glued directly in the elbow.

You can also use street elbows which have one leg that is the same size as the pipe but I've decided that having the shoulder to stop the insertion at just the right point and an extra seal surface is better. It's possible to push the street elbows in too far and get past the straight portion which could possible compromise the sealing although I wasn't able to get this to happen in my testing.

 

[Geoff K]

I converted a water tank to a holding tank several years ago. Used a uniseal on the top for the pumpout tube. Used a flanged fitting for the intake and "glued" it with 3M something or other that was new at the time and touted as the only adhesive for rotomolded use. The intake was on the upper side of the tank. (could not run it to the top without leaving low spots.) Neither has leaked and no odors. The tank is under the v birth. If there was an odor we would notice!

Geoff