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hringm (Mechanical) (OP)
6 May 10 10:48
Does anyone know where to find good information on stopping leaks at bolts? Especially information on what washers or gaskets would be good to use? The information I've found on my own hasn't been helpful.

My project is that I have a stainless steel chamber that sometimes contains oil. The pressure doesn't really ever go above 1 bar. On one end of the chamber there are bolts that connect it to the rupture disk and shock absorber and other piping. The leaks occur around these bolts at this end.

Currently, the bolts have silicon applied to them before being screwed in. Some ideas that have been suggested are to use a copper or brass washer, or a nitrile gasket or washer. Using an o-ring was another idea but it was apparently tested and wasn't successful. I don't have any information from the tests, there apparently weren't any reports made.

If anyone knows where I can find information on preventing leaks at bolts, I'd appreciate it.
btrueblood (Mechanical)
6 May 10 14:18
Do the bolt holes penetrate to the inside of the chamber?  I.e. is the leak path through the bolt threads?

If so, have you tried using thread sealant and/or thread locking compounds?  Loctite, e.g.
hringm (Mechanical) (OP)
6 May 10 14:34
The bolt holes do go to the inside of the chamber. The arrangement is that there is a chamber with a flange on one end. The bolts go through the bolt holes in the flange, with the bolt heads on the side of the flange that's inside the chamber. I'm new at the job, and haven't seen one of the devices assembled and haven't seen a leak personally, but as far as I can tell it seems the leak is through the bolt threads.

They do currently use silicone sealant, and it doesn't seem to work. I'm not sure what silicone they use, if another one of them would be better. Is Loctite better than regular silicone sealant?
btrueblood (Mechanical)
6 May 10 16:33
Um, well, Loctite will seal bolt threads, but it sounds like the leak path is (starting from inside the chamber) - under/around bolt heads, up the side of the bolt, and out under the nut on the outside of the flange, or thru the gap between threads and nuts, correct?

In this case, you need to seal under the bolt head, or between the bolt and the bolt hole.  The bolt head could be sealed with a sealing washer, or a seal screw (o-ring in a groove under the bolt head).  Google either term, or search either term at McMaster.com
flexibox (Mechanical)
8 May 10 18:25
Not knowing the wall thickness of the housing, I would drill and ream about 10mm then use a shoulder bolt and machine an Oring groove 2mm below the head. Ensure you include a small shamfer as a lead for the Oring.   Fit an Oring in the groove proble will be solved.

trust this helps.
iainuts (Mechanical)
9 May 10 14:43
Try a sealing washer:
http://www.mcmaster.com/#sealing-washers/=70m7t1

McMaster Carr shows 3 different types.  
- One has an O-ring bonded to the ID.  This would work under the head of the bolt as long as the hole isn't larger than the O-ring.
- There's a triangular shaped middle which is supposed to seal threads, so this would go on the nut end.  The straight edge of the triangle seals fluids that work around the threads in a spiral direction.
- The bonded washer has a rubber backing on a steel washer.  The steel is shaped like a belleville washer so when it crushes down, the ID displaces inward, grabing onto the shaft of the bolt.  Use this under the head of your bolt.  I don't like this one because they tend to loosen over time and you can't put as much torque on them.

You can always try a solid rubber or plastic washer under the head of the bolt, but the problem with that is you can't torque the bolt too much, so they can't be used where you need a decent amount of torque.

One other option is to thread the part you are putting the bolt through and then add silicone to the thread.  That way, it gets into the very small clearance of the thread and has a much better chance to seal.  You still put the nut on the other end to hold whatever it is on, the threaded through hole only serves to provide a very small clearance so that silicone has a chance to hold back the pressure.
hringm (Mechanical) (OP)
10 May 10 9:56
Thanks for the advice everyone. I will look into all of that, especially the sealing screw and sealing washers.
sreid (Electrical)
11 May 10 22:08
Possibly Hex-Seal.

http://www.apmhexseal.com/

 

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