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Sealing an "O" Ring

06/13/2011 6:06 PM

I have an "O" ring on a water filter system, right at the top where the cap and dial go.

Its on older filter and I just can not stop a drip, drip, drip after installing a new "O" ring. NO cracks in the cap or threading.

I tried Plumbers putty and the white gel like sealant that you use on threaded pipe. That slowed it so i know I am on the right track. I now need some help.

Does anyone have any experience with sealing one of these drippy "O" rings.

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#1

Re: Sealing an "O" Ring

06/13/2011 6:18 PM

Make sure the surfaces where the o-ring sits (both the cap and the body) are very clean and smooth. Check the o-ring for any nicks/cuts. Don't use putty. Use plumber's o-ring lubricant. If it continues to leak, you might try a different o-ring with a slightly larger cross-section.

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#3
In reply to #1

Re: Sealing an "O" Ring

06/13/2011 7:53 PM

I used the "O" ring lube and it did nothing. The pvc sealant was the only thing that slowed down the dripping.

I can not see and knicks or cracks and the leaking is almost all on one side.....very small drip, but drip none the less.

The "O" ring is exactly the same size as the one that wsa there before ( in diameter).

It is 6" diameter.

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#33
In reply to #3

Re: Sealing an "O" Ring

06/15/2011 3:56 PM

You want the same diameter but slightly thicker.....

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#34
In reply to #33

Re: Sealing an "O" Ring

06/15/2011 10:31 PM

Andy,

I have that thing so super coated in teflon tape, silicon and whatever else would harden up....I doubt I can find the O ring.

The tank fittings , top and bottom look worn. I suspect the lugs are worn out and being that is is molded plastic, the whole top section should be replaced.

Thank you for the input though.

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#18
In reply to #1

Re: Sealing an "O" Ring

06/15/2011 1:07 AM

Some good ideas so far. Pantaz gave a good basic answer. I should point out that finding a slightly larger o-ring basically means finding a ring of the same standard size (that "AS" number which defines the groove diameter) but a slightly greater width within the .139 +/-.004 tolerance. Best chance of that is to find a 258 o-ring from a different manufacturer. Take your micrometer with you.

For everybody's benefit the mechanical design engineer's "bible" on o-rings has always been the Parker O-ring Handbook.

http://www.parker.com/literature/ORD%205700%20Parker_O-Ring_Handbook.pdf

It's 292 pages to print out. Go to section 4 "Static O-ring Sealing". Scroll down to page 82 in the PDF file.

On page 85 there is a good tabulated drawing "Design Chart 4-1" on gland design for o-rings followed by some pages of actual dimensions in o-ring size number order. By the way, the Parker numbers have the" AS" number preceded by a "2-". For all intents and purposes these are the "standard" US o-ring sizes for mechanical design, aerospace and milspec variants notwithstanding. Parker also has some special sizes with "5-" prefixes. Most engineers stay away from designing them into products or systems. There are also "3-" Parker sizes for tube fittings.

Scroll to page 252 of the PDF and find section 10 that gives a lot of info on o-ring failures. I don't see anything there that specifically addresses netmaker's problem; but it's good info to know about.

So I'll throw out what I think---

We still don't know whether this o-ring setup is a face seal or a gland seal (like the view in Chart 4-1). Likely the latter. The important issue for o-ring performance is that the gland depth dimension be in the range of .111 to .113 or pretty close to that. Since there is a locating pin that sets the position of the top there is only size for the groove. What I would do is "clay" the groove at 6 or 8 places in the same manner that we trial assemble a race engine during the initial build process by placing little "pea size" lumps of modeling clay on the piston heads, installing and torquing the cylinder head and then hand turning it. Following which the head is pulled and the clay thickness is "miked" to see if the piston is getting too close to the cylinder head or valves.

Next I'd consider the possibility that when installing the top friction against the o-ring is distorting it so it cannot seal uniformly. Also consider the possibility that the O-ring is twisted on itself then installed. This is a common problem with the thin large diameter o-rings like this one.

And of course lubricate the o-ring just the way Parker says to. Just a thin film that changes the shine of the o-ring surface. No lumps of grease. For drinking water use Vaseline if you are finicky about plain old lubricating grease.

Lastly note the way an o-ring works to seal pressure. Unlike a simple flat gasket that is squeezed into one position the o-ring gets pushed by pressure against it and moves slightly in the groove to seal on two or three surfaces against which it deforms slightly to make a good seal. If the groove and o-ring are not perfect then it may take some measurable pressure beyond a fraction of an inch of water to make the seal. So there can be a slight leak until some pressure builds in front of the o-ring to make it take that tiny movement and deformation.

Hope some of this helps. ………… Ed Weldon

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#2

Re: Sealing an "O" Ring

06/13/2011 6:56 PM

Pics would help

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#4
In reply to #2

Re: Sealing an "O" Ring

06/13/2011 8:03 PM

I have the whole thing screwed up tight right now and allowing this little drip to contnue. I would like to hold off taking the top back off until I am ready with another plan.

The ring just sits snug around the out peremeter in a little groove.

The top section with the turn dial handle assembly locks down on top of that, lines up wityh a small hole and a pin drops in to make sure the thing doesn't move when you manually move the lever to go from filter to backwash .

The ring is about 1/8" thick x 6" diameter.

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#5
In reply to #4

Re: Sealing an "O" Ring

06/13/2011 8:17 PM

I'm wondering if you're over tightening it. If you had a fresh ring you could try it at a loose fit and progressively tighten it until the seal was formed.

I assume you've checked and threads are clean and not cracked. You can also turn the ring on itself and make sure it is crack free. You should be able to get a seal if the ring is the correct size and you're using the proper lube. I'd leave the plumbers putty on the shelf.

good luck

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#6
In reply to #4

Re: Sealing an "O" Ring

06/13/2011 9:21 PM

O rings are mostly all standardized. It sounds like yours is an AS568-258. It's nominal dimensions are 5.985" dia. and 0.139" thick.

There is a tolerance to the diameter. If your groove is not well contained, the particular o ring may be a little too big or too small. If it's too small, stretch it out a little and fix it in place before it reverts to it's original size. If it's too big, cut out a small piece, and refasten it with rubber cement.

They also come in different materials and durometers.

Check McMaster-Carr, at WWW/mcmaster.com for a selection.

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#7
In reply to #6

Re: Sealing an "O" Ring

06/13/2011 9:28 PM

"O rings are mostly all standardized."

There are a few people in the aerospace business that might argue that point with you.

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#8

Re: Sealing an "O" Ring

06/13/2011 9:40 PM

I have lots of equipment with O rings. They almost always set in a machined groove. Once the ring is in place and the second piece is brought up to the ring, the seal is crushed just a little to ensure no leaks. I have to think that if all you say is correct, you might have some distortion between the two hard parts. What stops the tightening process? Is there a place where the two hard parts touch to stop the tightening? You might need to take off a few thousandths to crush a little better. Most rings used for water are made from buna N. The ring will swell in the presence of water, but only a small amount, so it may stop in a day or two. I would not recommend trying to go thicker, as the groove cut for the ring will just cut the ring if a thicker one is used. What you might try if you can not get any other tip to work, is to chase down a very thin ring with a 6 inch dia. and put it in the groove first, and then install the correct ring on top of it. It works almost like a shim for the ring. I you give us the dimensions of the existing ring, I will try to get you some numbers for rings in different variations from Grainger, or MSC. Good luck.

Forget the sealing compounds. That is for pipe thread, and flanges only.

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#9

Re: Sealing an "O" Ring

06/13/2011 9:57 PM

Tonight I noticed the filter is leaking with the putty . I dismantled it and wiped off the putty off. I then put a good layer of O ring sealant and lube over the ring and reinstalled.

I have re-plumbed somewhat and noticed that there is NOT a full load of water coming in as yet. I need to adjust so that there is more water meeting the fliter.

Tonight I will let the water level increase higher so that when I start the filter, there is no cavetation .

I do remember this happening years back and when I installed the new O ring, it actually stopped laking in a day or so.

Other wise I will look into taking off a touch of the plastic locking mechanism ( lugs) and letting the top section turn a little more. However, there is a hole in the top section that alligns with the filter section so a pin can drop in and keep the top from turning.

The entire top section when seated only turns about 2-3 inches before locking. there are no threads just some lugs.

I'll take pics tomorrow afternoon in the day light.

Thank you all so far.

Bon Soir

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#10

Re: Sealing an "O" Ring

06/14/2011 6:05 AM

I'd guess the O ring isn't being compressed, lapping down the appropriate face may solve the probleb by allowing the parts to screw down a bit further.However such a solution requires a good understanding of the mechanical arrangement and a steady hand with a flat bolck and fine abrasive paper.
I have done similar repairs on washing machine solenoid vlaves where the plastic has moved with time.
Alternatively cut another ring from rubber sheet to use as a replacement or aditional ring (same terms and conditions apply)
Del

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#11

Re: Sealing an "O" Ring

06/14/2011 6:47 AM

Has it sealed OK in the past, but now started leaking, or has it never been right?

What is design pressure? Is the actual pressure below this?

Codey

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#13
In reply to #11

Re: Sealing an "O" Ring

06/14/2011 7:18 AM

It did leak a few years back . I used a rubber mallet and knocked the top section just a bit and it closed up.

Now I see the old "O" ring was broken so I replaced it with a new one. It leaked last night no matter I did.

I am wondering if the entire top is just a tiny bit out of position??? It just will not stop leaking water.

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#14
In reply to #13

Re: Sealing an "O" Ring

06/14/2011 7:46 AM

Difficult to judge without seeing it, but it looks like you can only tighten it a certain amount (till the pin aligns with the hole, and perhaps a mechanical stop) and if it's old and worn maybe it needs more. In that case possibly a thicker O-ring would cure it.

And the pressures?

Cheers........Codey

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#24
In reply to #13

Re: Sealing an "O" Ring

06/15/2011 8:26 AM

I find it odd that the old one was "broken".

If it is only exposed to water, then consider installing a softer o-ring (I would try this before trying a larger x-section o-ring).

If the o-ring is getting hard, then sounds like either a temperature or chemical compatibility issue. If this is the case, you will need to find a different material for your o-ring.

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#12

Re: Sealing an "O" Ring

06/14/2011 6:59 AM

please cheack hair crack , in the area where the leak come from

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#15

Re: Sealing an "O" Ring

06/14/2011 10:55 PM

I am not sure if you are referring to cartridge filters or something somewhat larger. If it is a cartridge filter where you install a filter in the housing and then seal the top with an o-ring I would suggest you recheck for small hairline fractures. These fractures are hard to see but once the filter is back on line pressure the leaking begins. I sold many thousand of these cartridges and almost always when the leaking occurred it was a small hairline fracture that was very difficult to notice.

If it is a larger filter housing with threaded connections and an o-ring sealant also check for hairline fractures on the filter housing or head. If the threads are leaking and not picked up by the o-ring, try some hemp rope strands wrapped around the threads before you install it back together. The hemp will swell once it gets wet and help create a seal. It may also work on the cartridge type. Failing to detect a fracture does not mean you don't have one and takes careful examination.

Purchasing a new cartridge or filter housing is relatively cheap and not worth the aggravation of a leak.

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#16

Re: Sealing an "O" Ring

06/14/2011 11:01 PM

From your description/picture, I get the impression that this is a typical sand filter like what is used for swimming pools. When you removed the backflush valve it is possible that you caused the pipe that the runs from the center of the valve to the bottom of the filter to shift upward. This is common. The valve usually has another seal where the pipe enters, and this drags the pipe up through the filter medium when you remove the valve. When you reassemble it, the pipe is now too long and prevents the valve from seating properly, and you are not getting proper compression on the o-ring.

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#17
In reply to #16

Re: Sealing an "O" Ring

06/14/2011 11:56 PM

Another thought - If these pats are plastic, have any of them distorted slightly?

That, also could cause your problem after they have been disturbed .....

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#19

Re: Sealing an "O" Ring

06/15/2011 1:08 AM

Is the o ring a replacement from the manufacture or a generic from a local supply house. In the past, I have found that generics can have a molding flash around the inside and outside. Under high magnification, the flashing can be seen. Sealing on the face surfaces isn't a problem but if you require a side seal, it's hit or miss. Seek out a mainstream brand like Parker or specify a mil spec o ring, which is buffed so there is no flashing left. First contact the manufacture. They've probably heard it before.

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#20

Re: Sealing an "O" Ring

06/15/2011 1:30 AM

It's possible that tiny bits of rubber have stuck to the mating surfaces or the surfaces have small imperfections, especially if attempts to improve sealing were done with anything abrasive. There are o rings that are referred to as "square" or "four lobed". This type will change the location of, and double the sealing surfaces. I've seen them used effectively in steering rack assemblies.

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#21
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Re: Sealing an "O" Ring

06/15/2011 3:52 AM

To add to this good response, such O-rings are also described as "quad" rings, having an X-shaped cross-section with rounded corners.

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#36
In reply to #20

Re: Sealing an "O" Ring

06/19/2011 7:41 PM

These "quad rings" use the same numbering system as National O rings do, just preceded by a 4.

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#22

Re: Sealing an "O" Ring

06/15/2011 7:05 AM

Here is a trick that works with old as well as new o-rings:

Use Teflon tape to wrap the o-ring totally with several layers of tape.Then install normally. 99% of the time this works if its caused by a small tolerance deviation of the o-ring.

I have used this method successfully on sliding o-rings in a cylinder, simply put the Teflon tape in the groove UNDER the o-ring.Works as good a a new o-ring.

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#26
In reply to #22

Re: Sealing an "O" Ring

06/15/2011 9:11 AM

Thank you.

I tried that and it seemed to work....still had a small leak.

So I coated the entire groove, tape and O ring with some of that clear sealant , not sure of the brand.The leak is still there but now down to a trickle.

nm

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#27
In reply to #22

Re: Sealing an "O" Ring

06/15/2011 9:15 AM

If the tank is old it may have 'grown' a bit from the constant pressure and now the two grooves for the O-ring in the opening at the top and in the lid don't line up anymore.

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#23

Re: Sealing an "O" Ring

06/15/2011 8:13 AM

I seen you post and thought, our Mechanical Seal Basics and Seal Selection Procedure Training Software download should cover this. As your problem is so common. But to my surprise, after reviewing the huge table of contents, I didn't see "O" ring anywhere. ha ha

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#25

Re: Sealing an "O" Ring

06/15/2011 9:02 AM

i'd try using a small layer of good Silicone RTV in the O-ring groove, install the o-ring, and add another thin layer of Silicone RTV, and then attacehd the top.

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#28

Re: Sealing an "O" Ring

06/15/2011 11:21 AM

Try cutting out small pieces from a aluminium pop can and inserting them on top of the lugs as you are tightening the top down. That would put a little bit of extra pressure on the O-ring.

You might also try a good quality clear silicone in the grooves first, then lay the O-ring in the silicone and then tighten down the top. I would wait an hour or so to let the silicone set up alittle first before turning on the water.

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#29
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Re: Sealing an "O" Ring

06/15/2011 2:54 PM

Try to find a food grade silicone. It will work but getting it back off will be interesting.

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#35
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Re: Sealing an "O" Ring

06/19/2011 2:49 PM

3-M 5200 will seal anything as long as you don't ever want it to come apart again.

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#30

Re: Sealing an "O" Ring

06/15/2011 3:38 PM

Thank you all.

The filter is old and the plastic lugs are worn too.

The grooves did leak on one side.

The teflon tape and silicon on top, then the O ring seemed to cut the leak down to a very , very small livable water loss.

I am reasonably sure that the two joining halves are worn and possibly warped.

A new filter is probably on the wish list sometimes this year or early next.

All ideas were tried and I am happy to say that a combination of them have fixed my problem as well as it needs fixing.

Thank you all.

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#31
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Re: Sealing an "O" Ring

06/15/2011 3:41 PM

Thanks for the update, usually once someone gets an answer they just take off and are never heard from again.

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#32

Re: Sealing an "O" Ring

06/15/2011 3:52 PM

Moma always told us that a good ol' suthern boy always said , "Thank You".

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