Is there any type of sealant that will withstand brake fluid, short of a solid mechanical seal?

I have a couple reservoirs that constantly leak, only subject to static pressure. The seal currently uses copper washers on the fitting but the reservoir tin is pretty thin and very difficult to seal to. I'm looking for some type of sealant that could be put onto the pieces, then made up and after curing, the brake fluid would be introduced

? ? ?

Thanks

Paul

Loctite 569, 592, 243 or 572, and are all avaialbe from McMaster-Carr.

Joe

You might take the cap to your local parts house and see if they have a green "O" ring that may work. Other than that there isn't much that can withstand brake fluid.

The green o-ring is made from Buna-N rubber and its pretty good. O-ring material that performs better than Buna-N with brake and hydraulic fluid are: PTFE, Kalrez, FEP, AFLAS and Fluoro-silicone. You'll want an o-ring in the 70-80 shore A hardness range. Make sure the mating surface is clean and free from radial scratches.



Joe

purity high resistance to chemical attack and more importantly leaching/off gassing. Long ago I learned high purity water will eat the hell out of every grade of stainless steel and about the cutting edge high purity guys that flow all their production gasses and liquids through stuff like Teflon and more commonly Kalrez at exponentially higher cost then Teflon so they can maintain PPB/PPT status in production. The joys of dealing with phosphate esters in (fire resistant oil) that swell typical buna rubber O-rings into donuts but I never in my life had I ever dreamed or thought hardness was any indication of chemical resistance. I can't comprehend how that works....?

I've got books on chemical compatability for gaskets and always the temp range but I doubt they would have Brake Fluid Listed usually it is the raw chemical names.. I'd bet an internet search would come up with seals and maybe even epoxies that could handle it

Re: " You'll want an o-ring in the 70-80 shore A hardness range."

Hardness was not meant to define performance, rather a good compromise between abrogation resistance and the ability to assemble. You can order o-rings that are very soft (shore A 30 and below) to very hard (shore A 90+) which is a separate variable (option) to the material. You could order a Buna-N o-ring that is a shore A hardness of 55, 60,70,75,80 but how do you know which one is 'hard enough'? Without going into the 'gutter' here's .02 worth of an explanation. Too soft of an o-ring, and it can wrinkle, tear and bunch up during installation, especially in a bore seal configuration. Too hard, and the o-ring wont compress during installation, or requires too large of a load, and you can't get the assembly together. Having an o-ring in the 70-80 shore A hardness is a nice 'happy' medium, regardless of the material, for most installations. Also, softer o-rings will seal against slightly less-ideal (rough) surfaces as they will comply against the surface where a harder material wont. Make sense?



Joe

It's hard enough finding proper sized gaskets/O-Rings for specific chemical and temp compatability. You have zillions of sizes/materials/configurations so it turns into Lotto in no time. I imagine my sealing suppliers would go into shock if I not only asked for a Viton Gasket but wanted a specific hardness also.
When I think asbout it I'd presume that the design of the flange area takes into account the application so that simplifies the gasket material by the material itself: In other words if we are running 150# ASME Flanges and the chemical and temp are known and taken into consideration in designing the system the hardness of the gasketing material is rather insignificant because the gasket materials themselves are the key factor. Want a cheap material for flowing ambient temp water then Buna N will be fine where as if your dealing with 160F Nitric Acid but you will not have much variation in the compressability of the few materials that will handle the situation.
Matter of fact I had an experience with a fine mist Jet Water soluable lube application in a beverage container plant where the Maint Guys need to service the filters daily. The water temp was 150F @ 90PSI. They were eating Buna N head/bowl gaskets like candy, we tried viton and a few others and settled on Teflon. Seems like the rubberized gaskets just did not like the routine daily on/off and teflon was like the energizer rabbit going half a year or more. There was no discernable leaking with either product. Normally you would say that the Buna N would be fine esp for such a low stress application and that the softness would be an aid to sealing.

Hi BB,

Your world and my world are a bit different, and I got a chuckle at your 'real world' comment. My world involves rockets, liquid rocket engines and solid rocket motors, from big guys to little tactical rockets. The solids normally use o-rings, and it is very important to get the hardness correct along with material compatibility and temperature range. If you have a tactical rocket motor that must perform between -40F and 150F, material selection as well as hardness are critical to survive the temperature swings of its environment, as well as its environment while in operation. Bore seals are much different and are more sensitive to material hardness especially during assembly, like I stated previously. Luckily Buna-N comes from McMaster Carr at a shore A of 80 .

In your application you're correct, the hardness has little to do due to it being a flange seal. The non-metallic o-ring provides little resistance to the pre-load of the fasteners and flange. Of course if this was a metallic seal like a solid metal o-ring or pressurized hollow o-ring then the calculations get a bit different.

You might try calling Parker-Hannifin and talk with them about material compatibility and various harnesses. Or better yet, have a rep come out and speak with your company, you will be appalled at how much you didn't know and took for granted .

But back to the original question, Paul did I answer it?

Thanks
Joe

Ive spent 25 years in Industrial Filtration and never heard of specifying a hardness of a particular type of seal. The only Cryo customers I've delt with are the maintenance folks at Mayo Clinc and thats for deep freezing and the customers I have that deal with Hot Stuff are in a local steel mill. That stuff all pales next to rockets..



But then you have to agree regular everyday production and aerospace are different levils...One Aw-Shit in production more then likely only means someone needs to grab a mop.....Where as in Aerospace.....
I was surprised getting out of school and going into a big paper mill to see a maintenance guy use channel locks on 1" bolts on a large ASME Code Vessel... Why carry a set of sockets and drive when you can just have a set of Channel Locks
You guys are great!

The oils are esters, and you can't beat them. They are hard but don't get brittle at cyrotemps.

On non ester hydraulics for most things I have done, PTFE has been good. You just have to keep to a fluid change schedule, and the water has to be kept out. Any air-over hydraulic system has to be dried.

On brakelines, a double flare with some removeable loctite has been good enough. Watch it on synthetic brake fluid though. It will eat about anything but Buna-N.

Earls makes crush washers with a rubber of sort in the center. I have used these in place of copper or aluminum crush washers on brake fittings with sucess and no deterioration at this point. Maybe when I take it apart but the sales guys said would be no problem.

Is this a seal issue or actually a mismatch between fittings? I would wonder why you need washer to makw what should be a simple mechanical connection.