O'ring size chart versus hole size

nnam

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Can someone please help answer these questions? Thanks.

Is there a chart for a optimal oring size for a given drill hole to provide the highest PSI without permanent deform the oring?

If a chart is not available, is there a formula, such as percent compression of o-ring height, or compression of the cross sectional dimension?
 

RJSakowski

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A quick on line search for o ring design will turn up design guides from multiple manufacturers.
 

nnam

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A drilled hole typically does not leave a very good surface finish. And is not a good enough finish for an O ring seal.
I probably will try to polish it a bit with sand paper and add silicone gasket maker to it and pressure test it.
 

RJSakowski

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There is a significant difference between static and dynamic seals. Static seals are far more tolerant of poor surface finish. Elastomeric materials are incompressible. It is fairly easy to calculate the volume of the glands that seat the O ring and comparing it to the O ring volume. If the O ring volume exceeds the gland volume, the O ring will will be extruded through the clearance gaps potentially causing failure. Adding RTV to the gland will decrease the remaining gland volume. If RTV is used, it should be sparingly.
 

NortonDommi

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nnam
What is the application? O-ring's are wonderful things but they do have limitations. Yes there are are charts etc but without data for application no real answers can be given.
 

nnam

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I hope I don't bore you with this, but here it goes. This is for a vehicle oil re-routing (external filter, etc.). I tig welded aluminum without issue, but this housing, I couldn't do it without leak, even after I preheat the aluminum and heat again with propane torch. It wasn't working, yet I had no problem with other aluminum welding at all. The pressure is expected to be much lower than 50 PSI, but I would test it for 80 PSI or even 100 PSI.

So after the failed tig weld attempt, I tried to use brazing. I used low temperature 730 degree rods (harbor freight, and elsewhere), and it melted easily. But it still leaked. I have brazed HVAC without problem with silver solder (using micron gauge to check for leak and also pressure check with nitrogen).

The braze rods above doesn't flow into gap. It's just the way it is. Even clean up shiny and using acetone to clean it up more. That's not good. I tried to test it somewhere else, with flux and it worked. But when I did it with the real thing, somehow with the flux, it didn't melt the rod, but the oil housing melted, even I moved my hand all the time to keep the heat evenly. Really frustrated. So I decided to change the design a little, and decided to use gasket maker to seal it. So think of it as an aluminum cylinder and I put a round aluminum disc inside and brazed it up, and it leaks around the perimeter. So on the other side (the outside), I cut another piece of aluminum, brazed in/out oil ports to it and bolt it down on top of the bottom round one I brazed in before. I also put gasket maker around the perimeter to seal it up and tested with pressure air and soap bubble. The RTV would not have much direct contact with oil.

The perimeter no longer leaks. But to my great surprise, the upper piece (where the hoses are connected) has some leaks, which never happen before (I did this before, but that older piece wasn't round, wasn't meant to seal the perimeter). This time, I cut it round to seal around the perimeter. So I was very disappointed. I knew I can fix that with brazing, but this brazing method doesn't flow into the gap, and only very thin material keeps the bung attached to the metal hoses (round aluminum disc has 2 holes, each brazed with aluminum tubing then to a bung for connecting to hydraulic hose). So vibration may break it or cause leak again. I decided to use flux on it, and filler metal flown into gaps good. But it caused some distortion and just plain ugly, and I wasn't happy at all. Somehow the flux cause the rod to melt at a very high temperature.

I decided that I am going to change the upper piece to be steel/stainless steel and all connectors to be stainless, because I did welded it with it before and no leak whatsover, not like aluminum, easy like walk in a park.

But I decided to change the gasket maker to use gasket instead because I wanted to be able to take it out just in case there is a leak in the future. If I put a large glob of RTV in there, I may not be able to pry it up again.

On the drilling part, I used a drill on the lathe. The cut is much more beautiful than using the drill press, no smoke and just nice. But I can definitely see it's not super smooth.
 
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nnam

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On the drilling part, I used a drill on the lathe. The cut is much more beautiful than using the drill press, no smoke and just nice. But I can definitely see it's not super smooth.
The perimeter wasn't cut with the lathe. I mounted it on my horizontal mill and cut the inside to make it round. But after some dirty brazing clean up with a rotary tool, it's very ugly. So I will have to use RTV on it, just hopefully less when I put in an oring along with that. With less RTV, I hope I can pry it open again if I need to do that.
 

RJSakowski

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Without the advantage of actually seeing what you are trying to do, is it possible to just drill and tap for a pipe fitting? I have used RTV to seal joints before but they have had strong mechanical joints. RTV doesn't like large gaps. It will flow under pressure.
 

nnam

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I will post some pictures later when I get back home.
 

RJSakowski

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The perimeter wasn't cut with the lathe. I mounted it on my horizontal mill and cut the inside to make it round. But after some dirty brazing clean up with a rotary tool, it's very ugly. So I will have to use RTV on it, just hopefully less when I put in an oring along with that. With less RTV, I hope I can pry it open again if I need to do that.
I should add that RTV doesn't go well with oil. It softens and swells. Some formulations are better than others. I recently used one called Gear Oil Gasket Maker by Permatex for rebuilding a tractor transmission. No data on how it is holding up as yet though.
 

nnam

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20190814_190637.jpg
This is my first attempt using this "top" adapter to bold down into the oil housing. It has no leak.
It looks ugly because I tried to remove it, one bung is not shown, already removed.

However, there is a leak around the circular perimeter (not shown above). So I made a rounded base below to seal with silicone gasket maker:

20190814_190708.jpg

The two metal tubes protrude pass the bottom, and I put two orings on it. Around the base, I put gasket maker (below it). This is then bolted onto
a similar circular metal piece with 5 holes tapped (not through, it's 1/2" thick).

Also, it looked ugly just because I tried to remove it. There was no leak between the tubes and the base. It leaked at the bungs and the tubes.
 
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nnam

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20190814_190809.jpg
Here's the aluminum housing. You can see the left and right was morphed due to brazing with flux heat.
The middle piece is a steel piece I cut and put in it to show what it would look like. Below that metal piece is
an aluminum piece of same size, already brazed into the housing (where there is a leak around the perimeter due to bad brazing).

I plan to weld two stainless tubes into those two holes. Protrude onto the other side a little with orings around them. I also will drill 5 holes to bolt it down.
Around that black steel piece, I will cut around the perimeter to slide a large oring into it.
I will have to use gasket maker to help sealing it.
 
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NortonDommi

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Please correct me if I have this wrong. Are you wanting to remotely mount an oil filter? I have done this usually because the stock location is a P.I.T.A. and occasionally to route to a bypass auxiliary filter such as a toilet paper can.
If coming off the original filter mount a simple disk of Aluminium about 1 1/2 - 2",(40-50 mm),thick is all that is needed. Have a good look at the mounting face of an oil filter and mimic it. Drill and tap,(bore a hole and cut a thread to match the screwed in hollow stud in the block), a center hole. Cut a rebate between the center boss that the mounting stud is in and the outer perimeter,(a recessed area that mimics the area on the face of an oil filter that is the oil inlet, the area with holes spaced around the center),and rebate a groove for an O-ring outside of that where the OEM oil filter has one.
That takes care of the interface with the engine block.
On the fresh face facing the world now you need to tap an oil return in the center and an oil outlet that taps into the recessed area between the center stud and the outer O-ring. Use off the shelf fittings from a hydraulic supply shop,(hose doctor),run hoses to where ever you want to mount your filter. Remoter filter mounts are off the shelf items from filter manufacturers/retailers. If you have problems finding one and don't want to make one any good ships chandlers will have them in stock.
Have a look at the chart below. If you have access to a lathe this is a very easy job and needs no welding.
There is an old engineering adage K.I.S.S. - Keep It Simple Stupid and don't try and re-invent the wheel.
Using off the shelf parts wherever possible is something to keep in mind at all times. I hope this helps.
Sorry the chart is too big to upload but here is a link to where you can find the information you need:
A verynear and a set of thread gauges,(Imperial and metrickery), are all you need to get started.
.
 

nnam

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Yes, this is a remote filter adapter for connecting hoses. I already have everything up and running. But I redesign this because currently there are some issues I don't like and not wanting to get into here.

Here is a picture of what the above filter housing bolt into:
s-l400.jpg

You can see it is a bit complicated.

Here is tue picture of oem oil filter housing bolted on top of it. This housing also has a fuel filter housing attached to it:

images.jpeg

The small one is fuel filter. I cut out most of the larger one, leave an inch at the bottom and welded a round aluminum piece with two holes welded tubes and bungs and the story continued above ...
 

nnam

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If I just saw off the fuel filter housing, and made the remote adapter from scratch (thick aluminum piece as you said), it would have been much cheaper and done. But doing this, I keep the fuel filter, and thought it wouldn't cause issue.

Well, I will see. I may go your route, or go with all steel or stainless. But for now, I think I am far enough that I will try to finish it this way.
 

nnam

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I should add that RTV doesn't go well with oil. It softens and swells. Some formulations are better than others. I recently used one called Gear Oil Gasket Maker by Permatex for rebuilding a tractor transmission. No data on how it is holding up as yet though.
I used Permatex grey rtv. It looks like the Permatex ultra black rtv can handle oil and high temp
 

nnam

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I found this article very helpful. One of the oring I plan happens to have the same cross section as of the diagram:


It looks like higher squeeze, the longer it lasts in term of keeping the elastic force. However, it may suffer pinching issue.
I am still a bit confused by this, if 25% squeeze, then it only lasts for 300 hours, which is 12.5 days. That's very low.
 

RJSakowski

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I found this article very helpful. One of the oring I plan happens to have the same cross section as of the diagram:


It looks like higher squeeze, the longer it lasts in term of keeping the elastic force. However, it may suffer pinching issue.
I am still a bit confused by this, if 25% squeeze, then it only lasts for 300 hours, which is 12.5 days. That's very low.
O ring seals obviously are good for much longer times. O rings are used in plumbing valves, in hydraulic cylinders being examples. Seal life will depend on multiple factors. Material and operating temperature being two big ones. The chart you are looking at is for 257ºF
I believe you will find the Apple Rubber design guide to be more informative. https://www.applerubber.com/src/pdf/seal-design-guide.pdf
 
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