How many barbs?

[Roper]

I just plumbed my new waste tank. I used Trident 101 (black) 1-1/2" sanitation hose. Following the advice in this column I lubed the hose and fittings, and heated the hose with a hot air gun. The PVC hose barb fittings have 7 barbs. For the life of me, I could not get the hose past the fifth barb. I have 5 barbs engaged by the hose, and 2 barbs showing.

Is this sufficient? If not, what's the deal? It has been suggested that the lube/heat technique works really well; what could I be doing wrong?

 

[Peggie Hall HeadMistress]

If you'll search for "gray PVC fittings" in the Head Mistress forum

You'll find out why you can't get a 1.5" hose onto 'em. The cure: replace any 1.5" gray PVC fittings with marelon or even nylon...which you can get from any decent marine store.

 

[Roper]

Thanks, I read that post about the gray fittings before I started the project. I'm using white schedule. 40 PVC from Lowe's, are these the same as the gray? I'm using short lengths of PVC to turn corners too acute for hose alone. The fittings I'm using to mate with the hose are female sleeves on one end and 1-1/2" hose barb on the other. The fittings are glued to the short pipe runs.

 

[Peggie Hall HeadMistress]

Measure the diameter of the barbed end

I suspect you'll find that BOTH ends of a female-barbed pvc fitting are 1.5" ID (inner diameter), when what you need is 1.5" OD (outer diameter) on the female end and a 1.5" ID (inner diameter) on the barb end. And I don't think you're gonna find that at Lowes.

So I think you're gonna have to bite the bullet and pay "marine" prices to get the right size hose-pipe adaptors. Go to the Dometic/SeaLand site http://www.sealandtechnology.com/productpages.asp?pid=66 The PVC adapter 307341425 is what you need. Scroll to the bottom of the page to see the drawings of all the fittings.

I also think you should be using radius fittings (street ells) instead of gluing a bunch of short pieces of pvc together.

 

[Peggie Hall HeadMistress]

Oops...I got it backwards! What you REALLY need is...

I suspect you'll find that BOTH ends of a female-barbed pvc fitting are 1.5" ID (inner diameter), when what you need is 1.5" ID (inner diameter) on the female end and a 1.5" OD Outer diameter) on the barb end.

What I should have said:

I suspect you'll find that both ends of your female - barb fitting are 1.5 Inner Diameter--giving you an OD of 1 5/8" on the barbed end--when what you need is a fitting that has 1.5" OUTER diameter on the barb!

It's Monday...and it's gonna be Monday alllll day...

 

[Alan]

No offense but I still contend that rigid PVC everything is the way to go. No hoses or barbs to deal with, no smells to deal with. Once its installed it done for good. And to top it all off it's the cheapest and easiest way out.

Peggie, I just don't see a down side of rigid PVC, can you enlighten me?

 

[Peggie Hall HeadMistress]

Hardpipe is only recommended for long straight runs

Which are scarce on most boats under 50'. When there are lots of bends, there have to be lots of unions...and every glued union is a potential leak. Plus, when done correctly, all pipe connections to anything rigid--toilet, tank thru-hull, pump etc--should be "soft coupled" with enough hose to provide shock aborption...a bunch more glued connections. You haven't done that, but you'd find out why you should have if you ever go far enough offshore to be tossed around in heavy seas for days or even hours.

If hard pipe were the right way to do it, don't you think that boat builders--who'll do ANYthing they think they can get away with if it'll save 'em a buck-- would use it? You've gotten away with it...but I can't recommend it.

 

[woodster]

the down side to riged pvc will rear its ugly head when you have to repair the system because of a break in it ....i like the fact that pvc does not leak orders .....and i think the only saveing in the long run would be when you only buy 3 or 4 ft of the high priced hose as opposed to 30 or so ft ....but with hoses if there is flex (and i am sure their is) in the boat you more than likely will not break something ...


regards

woody

 

[Alan]

Peggie, I couldn't agree with you more about manufacturers trying to save a buck everywhere. With flex in mind I did a few tests of assembled pipe parts. I twisted and bent them far more than any small flex they might see onboard. The ability of 'rigid' PVC to flex is nothing short of astounding. I also installed support straps wherever they were needed. As for the glued connections, once they are assembled these connections are there forever. Assuming you glue them correctly, which isn't difficult, it's virtually impossible to make them leak. I also installed a clean-out plug near the tank, just in case of a clog. PVC plumbing is used in millions of houses and RV's without any ill affects. I guess I'm gonna play guinea pig and wait to see what unforeseen bugs there are in my system. To this point I am very pleased with the way it has all worked out. I have increased the holding tank capacity by 2 1/2 times and there is absolutely no 'head' odor anywhere onboard since my upgrade.

 

[Head Master18695]

PVC pipe

The PVC pipe itself can flex quite substantially without problem, but when it does crack where do most of the cracks occur? Right at the glued connections. Why? PVC cement is a solvent, and when it sets up, yes, the joint is permanent. However, the area that was exposed to the solvent cement has been weakened somewhat and is no longer as strong as the actual pipe itself or the fitting. That's why when it does crack, it's usually right at the joint where the pipe enters the fitting.

Peggie is correct about putting in something more flexible every so often (every 6 or 8 feet), to relieve the stress on the pipes and fittings from vibration while the boat is running - even if it's just the black rubber Fernco couplings.

 

[Alan]

Head Master, I greatly appreciate your input and explanation. I have no argument with the fact that there is a minimal amount of flexing existing in a moving boat (likewise on RV's). But this minimal amount of flex is nothing near the breaking force needed for cemented PVC. In fact the pipe I have installed in my boat is under almost no flexing stress whatsoever. All pipe lengths more than 2' in length are supported by rubber coated straps.
Having said that, I will gladly be the test bed for PVC plumbing onboard. All the while I use it I will never have to worry about the noxious odor of the head and its associated parts. If in the future a connection fails I will gladly report it to the forum but my thought is this is a highly unlikely possibility.

 

[Peggie Hall HeadMistress]

Alan...the bottom line is...

It's YOUR boat....and, as long as it doesn't violate any USCG regs, what you choose to do on your own boat is entirely up to you.

Have a safe and odor free 4th...remembering what it celebrates.

 

[Alan]

If memory serves, it's still the country's birthday?? We'll be out on the bay celebrating and at about 2100hrs there will be a magnificent fireworks show that the owner of Cablevision/MSG will be putting on in front of his bay front home. Roughly 1000 boats show up each year for his display.

Happy Fourth to all!