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O-ring sealing problem
2

O-ring sealing problem

O-ring sealing problem

(OP)
Hi every body
I want to seal an electrode which is installed into a hole with an viton material O-ring. The o-ring size is 3mm as inner diameter and 1.5mm as thickness. The operation pressure is 30bar and the maximum temperature will be 120 degree centigrade. the o-ring is 0.6mm compressed after installation. Other dimensions have been mentioned in the attached link.
After assembling this setup it is noticed that there is a leakage even in lower pressures (10 bar) in the place of sealing o-ring.
I would like to help me and tell me where is the mistake and how should I change the design to overcome this problem.
Moreover is there a standard maximum pressure range which small o-rings can seal?

RE: O-ring sealing problem

The surface finish of the counterbore face may be a spiral. A cirular finish would be better. How is the counterbore created?
That seems to be a high compression, also.

Ted

RE: O-ring sealing problem

(OP)
Hi Ted
The groove is made by lathe and I have not measured its surface roughness but it is very smooth visually and the other contacting surface has been grinded and smoothly polished with the surface roughness Ra=0.5
By the way according to the O-ring makers handbook the compression is a little higher than the standard but does is affect the sealing immediately after assembling? I mean the set up have been tested by the pressurized air right after assembling and there is not any effects of temperature or other circumstances over time.
my other question is that is there any standard which tells us that there is a maximum pressure the o-rings with small cross sections can seal? I want to know if I can achieve better sealing by increasing the cross section of the o-ring?

RE: O-ring sealing problem

Which side is pressurized? Does the o-ring fit to the ID or OD of the groove in its free state?
O-rings fail primarily by extrusion though a clearance, not by pressure compression.

Ted

RE: O-ring sealing problem

(OP)
the fluid pressure is from the right side (according to the drawing).
the o-ring fits to the outside diameter of the groove in its free state.

RE: O-ring sealing problem

So are you saying the seal leaks after passing the initial test? What processes occur after the initial test?

Ted

RE: O-ring sealing problem

(OP)
not actually, the seal leaks during the initial test and can not pass the test.
after the test there is a liquid with maximum pressure 30 bar and maximum temperature 120 Degree centigrade in the right side of the drawing.

RE: O-ring sealing problem

Hi vahabsolgi

How are you applying the sealing force? Also have you done a tolerance check to ensure the ‘o’ring always protrudes by 0.6mm beyond recess it locates in, I have this feeling that tolerance build up between the two mating parts might be preventing the correct ‘o’ ring compression.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

RE: O-ring sealing problem

(OP)
Hi
Yes I have Checked the tolerances and there is nothing wrong there. the sealing force is applying directly to the back of metal part.
I think the cause might be because there is a maximum pressure limit for any o-ring size which in my case the test pressure is higher than that. does every body have any idea about that? I did not find anything about it in the literature.

RE: O-ring sealing problem

What are you using to apply the sealing force? And how much force are you applying? What fluid are you sealing? Does the o-ring appear damaged after the test? What are the gland dimensions? I 'd make sure you're not exceeding 90% gland fill. O-ring manufacturers generally do not provide a maximum pressure for a particular o-ring, as that will vary with the application, there's a lot of variables that would go into that. They do have technical support that is pretty good about offering guidance/advice in my experience. That said 10 bar relatively is not much, especially with 40% squeeze.

RE: O-ring sealing problem

(OP)
A plate in contact with the back side of the Electrode (the metal part) is applying the sealing force by tightening 4 bolts.
The o-ring does not damage after the test.
the gland dimensions: Inner Diameter: 2mm, Outer Diameter: 6mm, Depth: 0.9mm
the o-ring dimensions: Inner Diameter: 3mm, Outer Diameter: 6mm, Thickness: 1.5mm
so the gland fill is: %98 which is higher than 90 percent

RE: O-ring sealing problem

Hi vahabsolgi

Can you show a sketch of how the four bolts are arranged around the electrode? Also do you have a bolt tightening sequence? What method are you using to ensure consistent bolt tightening?

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

RE: O-ring sealing problem

Not sure if it's causing your leaking issue but 98% nominal gland fill is an issue. Typically you'd shoot for around 75% gland fill nominally, taking into account manufacturing tolerances so that you do not ever exceed 90%.

RE: O-ring sealing problem

(OP)
Dear Ifw618, the information was helpful.
Another question, does big compression (40% which is more than the standard) affect the sealing?

RE: O-ring sealing problem

I still come back to the lay of the sutface finishes creating a path across the oring sealing faces. Any finishing process done by traversing across a face creates a texture that crosses the sealing faces.
What is the durometer hardness of the oring?

Ted

RE: O-ring sealing problem

(OP)
Hi Desertfox
The bolts arrangement has been enclosed. As you see, actually we have two electrodes which are being pushed toward each other by two solid plates.
Meanwhile the bolts are passing trough the holes in one of the solid plates and end of them are been fastened to four nuts on the other plate in addition the bolts are been tightened in a Criss-Cross sequence.

RE: O-ring sealing problem

Hi again

Is the leaking occurring at one side of the device for example:- it leaks on the side where the bolt heads are?
Also from the tolerance build up what is the maximum and minimum compression of the ‘O’ring.
Hoe Are you controlling the tension on each bolt during tightening? I can see a possibility of some of the compressive bolt load distorting the plate and not contributing to ‘O’ ring compression particularly as the ‘o’rings are directly opposite each other.
It would be better if the compression of the ‘o’ring was independent of each other on each side.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

RE: O-ring sealing problem

(OP)
Dear hydtools
The O-Ring durometer hardness is ShoreA=70.
what will be the results if I use an o-ring with lower harness? can it help? I mean that is there any general rule about choosing the o-ring hardness?

RE: O-ring sealing problem

(OP)
Dear desertfox
It is not Clear that which one of the o-rings leaks during the test! it can be either of them. There is not a huge tolerance buildup here. It ranges from +0.05mm to -0.05mm in the o-ring compression.
The bolts are being tightened in a Criss-Cross sequence and the plate material is very rigid (CK 75 spring steel) so there is not a noticeable distortion in the plate after assembling.

RE: O-ring sealing problem

Hi

How do you know when the bolt is tightened enough, I agree with the criss cross pattern of fastening

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

RE: O-ring sealing problem

It appears that the electrode retaining structure may be very flexible in the area of the electrodes. Is there outward displacement when the electrodes are at pressure allowing the electrodes to move allowing the orings to leak?

Ted

RE: O-ring sealing problem

Hi vahabsolgi

Can you change the sealing arrangement so that the ‘o’ ring seals on the radial parts of the electrode and internal bore of the vessel see sketch. Sealing as shown means the bolts don’t need to compress the seal, the bolts merely stop the parts falling out. It might mean though you need a bigger size ‘o’ring to do this.

{img https://res.cloudinary.com/engineering-com/image/u...]

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

RE: O-ring sealing problem

(OP)
Deasert fox
the bolts are been fastened very tightly by hand.
there is not enough room to change the o-ring arrangmnet to seal radially.

RE: O-ring sealing problem

(OP)
hydtools
if there was any displacement it will be very small and there is no way to measure it but I think this is not our issue because the plates are very solid

RE: O-ring sealing problem

Hi vahabsolgi

I suspect that you cannot tighten the bolts hard enough, those seals will take a lot of force, also even though you cant see any plate deformation it might still be happening and you are losing compression load. try googling the load to compress an 'o'ring and you will see what I mean, what size of bolts are you using and can we have some dimensions of the bolt centres, the more info youcan give in a single post the more we might help

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

RE: O-ring sealing problem

Material hardness is generally chosen to be soft enough to compress and hard enough to prevent extrusion. In this case with little chance for extrusion, a softer oring will work. It will be easier to compress and conform to irregularities.

Ted

RE: O-ring sealing problem

(OP)
Hi All
I was Checking the Sealing system practically and I realized that the problem is not from the electrode. The leakage come from the other part of the assembly.
Please take a look at the attached drawing. I let the pressurized air flow into the tube and the checked every point of the system by soap bubbles. It came out that the leakage occurs mostly right after the pass in which the "flange B Sealant" and "O-ring (b)" are supposed to seal there.
some of the dimensions and sealing properties have been mentioned in the drawing.
the questions is that why the o-rings and the flange Sealant (b) can not seal the system.
meanwhile the pressure I ran the test was 15 bar and also the flatness of the seal contacting surfaces is visually excellent.

RE: O-ring sealing problem

Hi vahabsolgi

It looks to me at flange B You are pressing the o’ring and flange seal against each other, can you either blow the drawing up in that area or confirm my thoughts thanks.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

RE: O-ring sealing problem

Which seal is leaking? Face seal or diametral oring.

Ted

RE: O-ring sealing problem

(OP)
Hi Hydtools
I do not have any Idea. I can only check both seals together. the leakage can be from either of them!

RE: O-ring sealing problem

Let us assume the oring seal does not leak.

Create a circular textured face for the flat gasket to seal against instead of a smooth face. Do this to create hills and valleys in a circular pattern across the flat faces. Test.

Ted

RE: O-ring sealing problem

(OP)
Ted
About your previous question both face seal and diametral one are leaking because the pressure pass through the flange seal and then through the o-ring where the bubbles are visible there so no one of the seals are doing well! Why is that for!?
Anyway great suggestion, I will create a circular textured face for the flat gasket and let you know the results. but was wondering if there is any rule or general principle which I should consider in design such gaskets.

RE: O-ring sealing problem

If the gasket seal arrangement works, the oring seals would be redundant.

Ted

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