Diesel & silicon sealent?

[ted655]

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? :confused:

[Gypsie]

Check out this product called Fuel Master FAC 240 http://www.fixtech.com.au/index.php?process=views/catalogueItemB.php&itemId=3139&categoryId=571 might be what you are looking for.
Cheers
Gypsie

[FAST FRED]

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

[murdomack]

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/webcatalogs/EN/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

[ted655]

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. :mad:
, 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. :D
THANKS,

[marshmat]

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/DesignStandards/oring/oring_chemical.cfm?SM=none&SC=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?

[ted655]

:) Thanks. Just the type of info that reveals the basic nature of a material. I'm amazed that so many are NOT compatible.

[murdomack]

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

[Landlubber]

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!

[ted655]

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:D
I am fully prepared to pay when it's reasonable, but enough is enough.

[marshmat]

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!
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.

[murdomack]

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

[Landlubber]

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?

[murdomack]

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

[ted655]

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. :D

[murdomack]

Ted,

I'm almost certain that you have the same filter as I have on my own boat. It was originally a Duplex set, but when I re-engined three years ago I split them up and placed one bowl on either side of the engine space so that I could slide my body through easier (it gets more difficult as I get older, :D).
Thinking back, I am sure it's a UNF thread and the fittings were union couplings similar to JIC. I'll be down there in the next few days and see exactly what I have.
When you say that the 1/2" NPT tightens with 3 threads left that's what leads me to think that the bowl is 7/8"-14 UNF. The OD of 1/2" pipe is 0.84" which is actually smaller than 7/8" (0.875"), and the max finished thread dimension is 0.832" for NPT because of the flat crest. The female 7/8" UNF small diameter is quoted as between 0.814" and 0.798" so you could be starting to tighten up about this point but your thread will never be seated properly in the flanks.
You could get a special oversize thread (to about 0.9" Max diameter) made as mentioned earlier, but unless you can get it made as a favour then you would be better getting the proper fitting as it will be cheaper and correct.

If you have or can borrow a vernier caliper and measure the inner thread dia. of the thread in the bowl and if it is about 0.80" up to 0.81", then you can almost be certain that it is 7/8" UNF. Thread gauges will confirm the pitch and if it is 14 then all you need is an adapter fitting from male 7/8" UNF to 1/2" NPT or whatever your valve is. Try hydraulic hose suppliers for these threads as they are more likely to have them.

I just got this link of fittings, what worries me is that the Racor 500FG max port size quoted is 3/4" UNF and there is no way you can put a 1/2" NPT up to its last threads in that. You need to get that vernier and get the true inside diameter. :D

http://www.ftginc.com/distribution/Racor%20Fittings%20Applications.pdf

My fittings are the sae straight and elbow types. How I adapt from that to pipe threads I will need to check as I can't remember right now but you can see that you can get connectors direct to NPT.
I am begining to think that you might not be using a 1/2" NPT for your trial fit. Send me the lesser diameter of your filter thread and I should be able to work it all out,


Murdo

[ted655]

:o . So sorry, reamy words as you have read them, I mis-spoke, The 1/2" NPT does not tighten up UNTIL it is complerely in and the last 3 threads of the taperfinaly have enough diameter to START holding..
If I try a 1/2" straight thread fitting, it "almost" slips freely into the hole. The tips of the threads barley touch the tips of the bowl thread. Un fact, uf I rock it side to side, I can pass the fitting completely through, ubto the bowl, no twisting needed..
Did I miss the 500 listed in your link? I saw it jump from 400 to 600.:confused:

[murdomack]

Hi Again,

Directly below the table you mention is all dedicated to the 500FG. This is the road and plant model, the marine might be different, hopefully not. Try and get a measurement of the diameter as requested. You can give me an accurate outer diameter of the thread that just rocks through, it might give a pointer to what the bowl thread is. Fractional or millimeters will do for now if you don't have a vernier or a micrometer to hand

Murdo

[murdomack]

Ted

You mention the factory spigot a few posts back, so if you still have this then you have the thread and just need to ID it using the Swagelok website as a reference. Then you can order a connector to suit your valve.
You could also take this spigot and your valve to a large diesel specialist or a large hydraulic hose and fittings supplier and see if they can get you the fitting that you need.
It could be a time versus money decision

Murdo

[ted655]

Murdomack, perhaps you can help with another problem.
The inner (swwing) bolt holding my alternator was badly rusted. I finally got it out. I want to clean up the threads. The head of the bolt has 3 hash marks "BUFO, UNF, 88 on the head.
.
My M12-1.5 die "seems the closest, but something is a tad off maybe? I could have "pulled" the threads as I struggled to remove the bolt. Is a UNF a metric? This is a Volvo AQD40A. metric right? Bolt isn't that important but I sure can't mess the block threads up.

[murdomack]

Hi Ted,

From what you describe about the markings on the head, The three hash marks and the 88 (look again, I think it will be 8.8) suggest that the bolt was manufactured in Europe/Asia, but has been threaded UNF, which is an American thread, Imperial not Metric. This would not be uncommon as UNF is used on a lot of engine threads worldwide. Conversely, my new US-built Westerbeke engine has a lot of Metric on it. It all depends on the donor engine that is marinised.
8.8 is to do with the bolts steel strength. I think the American structural grade A5 is superior if my memory serves me right.
The way I ID a bolt thread if I don't have my thread gauges handy is very simple, although I have had to have a few goes with some, my eyes are not as sharp as they were.
Measure the thread diameter as accurately as possible then, using a rule or a measuring tape that has inches and millimeters find the thread pitch.

If the thread is long enough try and place the zero and the 1" mark on the crests of two threads and if you can do that, count the number of threads between them. With a tape you would use two markings away from the end of the tape as the hook would stop you lining it up properly. You have to be certain that the markings are spot on the crests.

If the thread is too short, try and place the 1/2" markings on two crests or on a crest and a root where the thread is an odd number. For example if the thread pitch was 13 you would be counting 6-1/2 threads in the 1/2" space. Sometimes you can match on the 1/4" marks and mutiply by 4 for the pitch.

If you cannot get the marks to line up with the inch markings, then you have to suspect that it is metric. Try and line up groups of threads with the millimeters on your measure, if the pitch was 1.5 then you would have 2 threads at 3mm, if it was 1.25 you would have 4 threads at 5mm and so on.
It's a bit crude compared to using thread gauges, but with care it will get you the answer.

Compare your results to the tables attached,

http://www.portlandbolt.com/technicalinformation/thread-pitch.html
This one gives UNC, UNF and UNS. You are only interested in the collumns that say "Nominal size and Threads per Inch". The three sizes that I suspect could be your bolt are 7/16, 1/2" or 9/16" UNF. Note that 7/16" and 1/2" are the same pitch, so you will have to double check your diameter.

http://www.engineeringtoolbox.com/metric-threads-d_777.html
These tables are of the metric sizes, note that there are course and fine pitches.

It's a bit long winded but I hope you can follow it OK

Murdo

[ted655]

:D Will do, (rather my son will), I've tired eys myself.

[Landlubber]

Murdo,

No you must be right about the fule label instead if fine as I believed it to be, if the threads are the same pitch, that is the end of the discussion really eh, as fine does mean finer pitched threads, thanks for your reply.
I will reset my brain.

[murdomack]

:o . So sorry, reamy words as you have read them, I mis-spoke, The 1/2" NPT does not tighten up UNTIL it is complerely in and the last 3 threads of the taperfinaly have enough diameter to START holding..
If I try a 1/2" straight thread fitting, it "almost" slips freely into the hole. The tips of the threads barley touch the tips of the bowl thread. Un fact, uf I rock it side to side, I can pass the fitting completely through, ubto the bowl, no twisting needed..
Did I miss the 500 listed in your link? I saw it jump from 400 to 600.:confused:

Ted

I am begining to think that you are using a 1/4" NPT thread and assuming it is a 1/2" NPT. When you mention a 1/2" straight thread do you mean that the thread diameter is 1/2". If so, I would guess that your bowl thread is 9/16" UNF which is a size that Racor quote. It has the same pitch as 1/4" NPT,18 tpi, and would alow a 1/2" diameter to wiggle through.

The nearest metric is M14-1.5, but I have only seen M16 mentioned by Racor. They could have used M14 in the past, so you will need to be carefull.

When we say 1/2" NPT we are talking about a pipe thread where the 1/2" is the nominal bore of the pipe. It's thread diameter is almost 7/8".

If I am right in my assumptions then you need a male 9/16" UNF to 1/4" FNPT adapter, 9040-6-4 in the Racor file I sent you earlier. You will also need a 1/4" NPT nipple from that to your valve.

Just in case I am not right, why don't you obtain a 9/16" UNF bolt and try and screw that into your filter before you commit to buying fittings.

An online chandlers here in the UK sells the metric versions of these adapters for about $6 each so I think they should be even less in the USA.

Murdo

[TollyWally]

The mystery of similar but not exact matches. This is just in time, as I am fitting out an aluminum diesel day tank for my new stove installation. This was a factory purpose built diesel tank. It has a standard 1 1/2 fill neck at the top, and what I thought were standard 1/2 pipe thread at top and bottom for vent and outflow.

I have a double handful of misc. brass and bronze fittings and valves in the archives that I have tentatively dry fit into various assemblies trying to figure out a clean installation.

I am barely literate in pipe thread trivia. I knew about pipe threads and machine threads and of course have some grasp of fine and course. I was completely unaware of a specific thread for fuel. I was work on the tank installation today but I think I will wait for a little more enlightenment and do some fiberglassing instead. The weather suits anyhow.

On a related note, I had a hell of a time with the old bronze pipe cap that was used as a filler cap in the past. It was always a bit "sticky" in the past. Even though I put a bit of antisieze on it, it had been a year or so since I last opened it. ( with a new stove I decided to move the old tank to facilitate a few other engine room issues.)

Since this is my boat and any maintence and repair in the future will be done by me I always design new installations for ease of service. What is the hot ticket for choosing and preparing (magic goop, tape etc.) the fittings that screw into the Aluminum tank?

Thanks, I appreciate being able to tap into the wellspring of accumulated wisdom assembled here.

[murdomack]

The earlier discussion about threads for fuel does not mean that ordinary well made threads, with a suitable sealant will not do for diesel. The NPTF or the dryseal thread as it is known is used more in process plants, where pressures are higher, and leaks could develop through the tiny gaps in the threads. A lot of sealants will not withstand the combined effect of the hydocarbons and the pressure. Leaking hydrocarbons will explode, therefor the special thread. Diesel is very tame in relation to these liquids and gases, but you will see NPTF in the manufacturers specs for diesel equipment quite often.
In case you are confused by my mention of FNPT in my last post, this simply means female npt.
Running diesel from a daytank to a heater or an engine will not be subject to any great pressure, indeed it will be in suction at times in the case of the engine so as long as the threads are matched properly, Teflon tape should be fine. Check for leaks after the engine has been running for a while, the vibration will set them off if they are there. If the leak doesn't take up with tightening then you will need to either change the fittings or try using a sealing paste that is good for diesel.
I am not sure that aluminum and brass/bronze are compatible metals. Aluminum is closer to steel in the tables. You could buy aluminum pipe fittings (www.mcmaster.com) to come off your tank threads then convert to tubing or use what you have. If the tank is much bigger than the bronze fittings and normally dry it should be OK. Was your bronze cap on an aluminum tank as well, maybe that's why it was siezing after a while.

[murdomack]

Ted


Just in case I am not right, why don't you obtain a 9/16" UNF bolt and try and screw that into your filter before you commit to buying fittings.

Murdo

Ted

Reading the spec for a 500 FG, the thread on the T-bolt that tightens the filter is threaded 9/16" UNF. See if this fits the inlet and outlet port threads

Murdo

[TollyWally]

Thanks for the info, I'll use teflon as per normal and maybe swap in a stainless or nylon nipple to start my manifold etc.

[seastalkercat]

Be cautious using it before any kind of pump as it finds its way into and can ruin pumps. It is best to use it only upstream of the secondary filter.

[ted655]

;) Thanks. Actually it is up streame of both the primary (2 micron), and secondary, (10 micron), filters.
It's been there awhile now. No problems yet, it seems to be doing the job. I have a "test" glob that is immersed in a tube of diesel. I check it reguarly also.

[murdomack]

Hi Ted, Seastalkercat,

Teflon tape was a great invention but like all things it has it's downside. I mentioned earlier that good threads are more important than the sealant and the problem mentioned here is partly caused by people habitually rolling on too many layers of tape than what is needed.
When I was an apprentice, I can only remember the important bits its so long ago, we were told that two layers was more than enough.
I was recently working on an engine with a young Marine Engineer who had been told by his uncle, a Chartered Engineer, that he should apply seven layers. I explained to him that all the extra tape was preventing the threads from seating together and some of the tape would find its way inside the fitting with the diesel. I have seen him since and he says that he is following my advice with good results.
In the Petro-Chemical industry the tape is not allowed on some systems for similar reasons to that mentioned by Seastalker and also where there are finely calibrated instruments and valves

[marshmat]

Generally speaking, I consider the primary seal to be the job of the properly matched threads, with the one or two wraps of Teflon tape being there only to seal the tiny gaps that might or might not be left by the inevitable variations in thread machining tolerances. Excess sealing tape only gums things up later.

[Ben Machine]

Murdomack, could you advise a supplier of NPT fittings in the UK.
Cheers

[murdomack]

Murdomack, could you advise a supplier of NPT fittings in the UK.
Cheers

Hi Ben

I am away on holiday at the moment. I will send some names on Monday night. There are quite a lot in fact.

Murdo

[Ben Machine]

Thanks Murdo

[murdomack]

Hi Ben

Two boating online cataloques, www.aquafax.co.uk and www.asap-supplies.com have some npt versions of their fittings, phone and ask as they do not always have them in the online cataloques.
Try www.hydrasun.com, they are a hydraulic supplier but carry a lot of quality pipe fittings.

Try a search for "npt pipe suppliers" on a UK site (say www.virginmedia.com) that alows a UK only search. You will get a lot of leads from this, I've added two here,
www.nero.co.uk
www.waverleybrownall.co.uk

If you are still struggling why not order from the US, www.mcmaster.com have a great onlne cataloque and will send worldwide. I have used them many times. If the order is small it probably won't attract the Customs taxes, but the prices are good even if you have to pay the extra.

Murdo

[Ben Machine]

Murdo
Thanks for the information I think I have found what I neeed at Hydrasun.
Cheers
BM