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  #1  
Old 01-07-2008, 09:20 AM
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ted655 ted655 is offline
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Diesel & silicon sealent?

Anyone have any experience using a silicon adhesive/sealant around diesel?
Not fresh exposure, but resistance to fully cured.
I've got some damaged threads that drip. I don't want to epoxy the fitting permanently, I want to remove it in the future. I can let the parts fully cure for a few days..
Silicon VS diesel?
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  #2  
Old 01-07-2008, 07:44 PM
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Check out this product called Fuel Master FAC 240 http://www.fixtech.com.au/index.php?...categoryId=571 might be what you are looking for.
Cheers
Gypsie
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  #3  
Old 01-08-2008, 06:28 AM
FAST FRED FAST FRED is offline
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Location: Conn in summers , Ortona FL in winter , with big dock & room for O'nite stop .
GO for the historic cure.

Get some string that plumbers used 50 years ago and wrap the threads.
Then use whatever sealant you ordinarily would chose to as the seal.

Non hardening Permatex , works fine.

Will come apart when desired with less hassle than using "form a gasket" silicone to glue it in place.

FF
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Old 01-08-2008, 07:23 AM
murdomack murdomack is offline
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The main cause of leaking threads is usually more to do with the threads than with the sealant. There are so many types of threads out there that even people who have spent all their lives at the game still get problems matching fittings. Diesel and most fuels need good joints which is why there is a special taper thread in the American system called NPTF where the F stands for fuel. Other fittings can be encountered where the threads are parallel and need a metal grommet either at the face or shoulder.

The string (hemp) and compound solution, from Fast Fred, will work but is not a serviceable solution unless you carry some in your spares box along with a stiff wire brush.

Is it possible to repair your damaged threads? Could you use a tap or die-nut to make them good again? I am attaching an excellent web link which you may not need but is the best guide to threads I have seen so far.

http://www.swagelok.com/downloads/we...N/MS-13-77.pdf

Co-incidentally, I am going to try and seal a leaking inspection hatch that I installed in the top of my stainless tank. I used the hatch as a template and drilled and tapped the tank which, being quite thin and with the hole already cut, another mistake, bellied in causing leaks when the tank is full and I am in sailing mode. I will try a silicon sealant first as it is the easiest solution and keep myfingers crossed.

Murdo
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  #5  
Old 01-08-2008, 08:36 PM
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These are "proprietary threads", bigger than 1/2" & smaller than 3/4". A special cut so no other fitting could be used. What would be a $8.00 shut off valve, "They" want $40.00 for their specific one. Positively BULL S..T!, it's just a water drain valve. I'm sorry, I'm tired of this marine industry "sticking" it to me when there is no good reason.
, A simple .45 cent PVC 1/2" bushing will enable me to use a "regular" valve. The string is a good idea. A 1/2" NPT will tighten at the last 3 threads. I'm going for it! When I try to research the resistance of clear, high grade silicone adhesive/sealant, I get SO many conflicting reports. I was hoping someone had used it around diesel.
Guess I'll be the one to know, later, & help the next guy.
THANKS,
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Old 01-08-2008, 09:39 PM
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Strictly speaking, one should always use properly matched threads on any kind of fuel fitting....
But if it's a bloody proprietary part, then replacing both parts of the fitting with something a little more conventional gains appeal.
Here's a little article from efunda regarding the compatibility of various gasket / O-ring materials with diesel oil. http://www.efunda.com/DesignStandard...C=Diesel%20Oil
It would appear that silicone and diesel do not get along all that well. (Note that whatever the grade or intended use, silicone sealants all share a similar fundamental chemistry and thus share similar chemical vulnerabilities.) Butyl sealants are also out. Teflon and other fluorocarbons, though, appear quite compatible- thus, a few wraps of the standard Teflon tape might help?
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Old 01-08-2008, 10:06 PM
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Thanks. Just the type of info that reveals the basic nature of a material. I'm amazed that so many are NOT compatible.
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  #8  
Old 01-09-2008, 06:06 AM
murdomack murdomack is offline
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I was once in this same situation with makers oddball threads. I decided to fabricate an exhaust elbow and use the engine company's cooling water injection nozzle. When it arrived I was amazed to find that it had a thread that I had never seen in my life, and I have seen thousands as pipework is my trade. I found that the thread was a 7/8" BSP thread and despite my trade contacts I could not find anyone that sold or made them. In the interim I made a temporary nozzle arrangement which worked fine while I tried to solve my problem.
Someone from the boat trade that I spoke with told me of a training school nearby who were always glad to take on small turning jobs as training excercises. I went to see them and two days later I had a new coupling that I could weld into the elbow. They did not want any money so I left the price of a few drinks, as you do.
If you know of anywhere like this that could make you a reducing nipple or bushing it may be your solution. If you can measure the thread and find that the pitch is the same as NPT, then an adjustable pipe threader with the 1/2"-3/4" dies installed can be adjusted to the fitting size. A heavy wall 3/4" X 1/2" reducing nipple could be turned down like this by a friendly plumber, I'm sure you must know one. Check that the thread is not parallel, though, as it could be NPS or ISO. The pitch is the same as NPT but the ISO/BSPP thread is a different profile (Whitworth).
I would try and identify the thread and use the correct fitting as a diesel spillage is not something that can be got rid of easily.
Google 5/8" BSP and compare that with what you've got. Even proprietary threads are usually based on some standard.

Murdo
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  #9  
Old 01-09-2008, 07:41 AM
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Landlubber Landlubber is offline
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Stagg Jointing Paste will do the trick, it is used in the petrochemical industry for both steam and petroleum products. It is a red paste, available in a tube (recommended) or a can. I have used it for 40 years and NEVER had a failure, not bad eh!
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Old 01-09-2008, 09:21 AM
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Oz has some great products. Not always "readily "available here.
This is a Racor fuel bowl. Polycarbinate I think, I'm not sure if it would re-tap.
.
I'm on a campaign I guess,, I am sick of being screwed. I knew long ago that the marine environment causes higher material costs, out of necessity. I know boats are expensive, My father taught that "you get what you pay for",
BUT... I'm not stupid. I know when that's not true. Some of these greedy bastards are just TOO obvious.
Try buying a Racor element packaged in a WIX box, it's $4.00 cheaper than if it is in a Racor box.Same element. OR, 10# hyd. steering oil, $17.00 a quart from Teleflex, OR $16.00 a gallon from anywhere else. The list is endless, there ought to be a sticky
I am fully prepared to pay when it's reasonable, but enough is enough.
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  #11  
Old 01-09-2008, 06:08 PM
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marshmat marshmat is offline
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Quote:
I am fully prepared to pay when it's reasonable, but enough is enough.
Can't argue with that.
Some things marine do need to be built better. Others are the same as what they sell you for your car, backhoe, whatever at twice the price. The trick, I suppose, is to be able to tell these two possibilities apart without breaking too much boat in the process!
Quote:
This is a Racor fuel bowl. Polycarbinate I think, I'm not sure if it would re-tap.
Polycarbonate is not fun to work with. Unless you're ready to pay to replace the whole thing, I doubt attempting to re-tap polycarbonate will go anywhere good.
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  #12  
Old 01-10-2008, 06:49 AM
murdomack murdomack is offline
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Racor threads are normally 3/4"-16 UNF or 7/8"-14 UNF. There is an option for metric offered, which from your description, could only be M22 X 1.5 if yours was metric. They offer NPT fom 3/4" NPT upwards so that does not fit in with what you describe.
I am quite sure that you have the UNF, probably the 7/8" from what you describe, but it should be easy to determine. If you go back to the Swagelok link that I sent you, from page 24 onwards describes UNF fittings.
You will notice that no sealant is required as this is a mechanical thread as opposed to a sealing thread as in NPT. An O-ring or a fibre or metal gasket is employed to make the seal.
If your thread is only lightly damaged you may be able to clean it out with a tap, it's function is not to seal, only to pull the facing joints together.
If it is indeed a 7/8" UNF you have another option in that it is the same pitch and profile as NPT but is parallel instead of tapered. Screwing a taper into a parallel is done regularly in the BSP system and works fine, especially if you use Stag paste (or similar) and hemp. You would need to make an oversized threaded fitting as I descrbed earlier unless it tightened on the threads. You may be lucky and get away with it. I would still try and get the correct fitting to screw in before I go down this route,

Murdo
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  #13  
Old 01-10-2008, 06:52 AM
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Landlubber Landlubber is offline
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murdomack,

Your comment that NPTF, the F is for fuel. My understanding is it is for Fine, as in Fine thread as opposed to course thread for instance.

Am I wrong all these years?
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  #14  
Old 01-10-2008, 08:43 AM
murdomack murdomack is offline
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Hi landlubber,

You may be right or wrong, definitions vary from source to source. There probably is a true definition written down in stone, but I am going on what I have read over the years and selected my own choice.
When talking about threads fine, to me, means a finer pitch. NPTF is the same pitch as NPT but is machined so that no leaking route exists through the crests and roots which rely on sealant in ordinary NPT. NPTF should require no sealant but some will be added to prevent galling, especially on stainless steel fittings. It is called a dryseal joint. Fuels are always hard to seal with ordinary threads and will be potential hazards because of their explosive tendencies.
Attached is a reference to Fuel from one website, but I would rather call it "National Pipe Taper Fuel".

Other thread systems include Acme thread form, BSP (British standard pipe thread which exists in a taper and non taper variant; used for other purposes as well) and BSC (British Standard Cycle) a 26tpi thread form, CEI (Cycle Engineers Institute, used on bicycles in Britain and possibly elsewhere), British Standard Brass a fixed pitch 26tpi thread, NPT (National Pipe Thread) and NPTF (National Pipe Thread Fuel),

I could show references to Fine as well, so it is one of those things that people decide for themselves.

Murdo
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  #15  
Old 01-10-2008, 09:26 AM
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Definitely not 7/8 , & pretty sure 3/4 is also too big. I know 3/4 NPT is too big. I'm not sure , it "could" be metric, but this is a US installation, 1984 500FG (old style).
I tried straight threads & tapered threads of both 1/2 & 3/4. Much like Goldylocks, one was too small, the other too big. The 1/2 NPT "will" tighten at the last 3 threads, hence the query about silicone sealents. I thought of a fiber washer but had no straight shoulder on the fitting.
I suppose I'm being anal about this but damn, wouldn't it be nice to have something that could be field repaired. The pisser is, the factory spigot is sorry & weak to begin with! I don't WANT to put a new one back in.
I show great loyalty to brands that are reasonably prised, do an honest simple job & are easily, quickly repaired. WHOOPS, back to the real world of engineered obsolescence.
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