392 valve observation

392 valve observation

Joined: June 7th, 2010, 12:14 am

June 9th, 2012, 4:49 am #1

While taking down the 392PA, I observed an interesting air flow pattern associated with the valve and o-ring seals.

The reason for the take down was some modifications I had in mind.

http://www.network54.com/Forum/275684/m ... r+progress

On the prior disassembly but a few days prior, I had coated the exterior of the valve body during assembly with generous quantities of petroleum jelly. Reasoning that such methods would aid assembly without o-ring seal damage, and any incompressible material in that area would aid in efficient transfer of the charge air to the pell.

I will say that on this day's disassembly I was surprised but not confounded by the pattern of petrolatum that showed.

The migration of material was decidedly towards the front most seal. Yes, towards the pump "head space". And so, cycled back through the inlet check valve and the pop-open valve it's self! Showing at last on the poppet and the transfer port. Full circle! I confess, a mess of petroleum jelly on all surfaces of the valve, inside and out. Corrosion control!

It is easy enough to visualize the pressure changes through pump up and discharge cycles. The hi pressure air effecting an even greater seal on the rear most valve o-ring. All the while a more "balanced" pressure differential was defeating the self energizing sealing at the front. Thus the migration.

Has this anything to do with enjoying air guns? Perhaps not.

Cheers

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Joined: December 14th, 2010, 5:08 am

June 9th, 2012, 5:47 am #2

i typically do the same thing to the valve to make it slide in easier. i hardly lube the pump cup and its always puzzled me why it was like that.. then i added an oring around the outlet hole and polished the interior of my tube so i wouldnt have to oil it so much, but never paid enough attention before to make any connection. but then, i hardly lube at all since polishing...


""Has this anything to do with enjoying air guns? Perhaps not."" OF COURSE IT DOES! taking things apart and using copious amounts of oil on anything makes a man feel good lol
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Joined: June 25th, 2002, 1:34 pm

June 9th, 2012, 12:58 pm #3

While taking down the 392PA, I observed an interesting air flow pattern associated with the valve and o-ring seals.

The reason for the take down was some modifications I had in mind.

http://www.network54.com/Forum/275684/m ... r+progress

On the prior disassembly but a few days prior, I had coated the exterior of the valve body during assembly with generous quantities of petroleum jelly. Reasoning that such methods would aid assembly without o-ring seal damage, and any incompressible material in that area would aid in efficient transfer of the charge air to the pell.

I will say that on this day's disassembly I was surprised but not confounded by the pattern of petrolatum that showed.

The migration of material was decidedly towards the front most seal. Yes, towards the pump "head space". And so, cycled back through the inlet check valve and the pop-open valve it's self! Showing at last on the poppet and the transfer port. Full circle! I confess, a mess of petroleum jelly on all surfaces of the valve, inside and out. Corrosion control!

It is easy enough to visualize the pressure changes through pump up and discharge cycles. The hi pressure air effecting an even greater seal on the rear most valve o-ring. All the while a more "balanced" pressure differential was defeating the self energizing sealing at the front. Thus the migration.

Has this anything to do with enjoying air guns? Perhaps not.

Cheers
the valve is pushed in, I think that grease is then pushed into the valve by the piston, if air can't pass the o-ring grease should not be able to either?
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Joined: November 28th, 2002, 6:26 pm

June 9th, 2012, 2:37 pm #4

While taking down the 392PA, I observed an interesting air flow pattern associated with the valve and o-ring seals.

The reason for the take down was some modifications I had in mind.

http://www.network54.com/Forum/275684/m ... r+progress

On the prior disassembly but a few days prior, I had coated the exterior of the valve body during assembly with generous quantities of petroleum jelly. Reasoning that such methods would aid assembly without o-ring seal damage, and any incompressible material in that area would aid in efficient transfer of the charge air to the pell.

I will say that on this day's disassembly I was surprised but not confounded by the pattern of petrolatum that showed.

The migration of material was decidedly towards the front most seal. Yes, towards the pump "head space". And so, cycled back through the inlet check valve and the pop-open valve it's self! Showing at last on the poppet and the transfer port. Full circle! I confess, a mess of petroleum jelly on all surfaces of the valve, inside and out. Corrosion control!

It is easy enough to visualize the pressure changes through pump up and discharge cycles. The hi pressure air effecting an even greater seal on the rear most valve o-ring. All the while a more "balanced" pressure differential was defeating the self energizing sealing at the front. Thus the migration.

Has this anything to do with enjoying air guns? Perhaps not.

Cheers
The O-ring in the front of the Benji valve, for example, is subjected to reversals of pressure as the pump piston moves between the intake and compression phases of the stroke, which probably pushes and pulls the ring from one side of its groove to the other.

So maybe it shouldn't be too surprising if it "squeegees" lubricant along for the ride.

Steve
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Joined: June 7th, 2010, 12:14 am

June 9th, 2012, 3:19 pm #5

During a cycle, the front o-ring first held full pump pressure trying to move the valve body (and it's o-ring) back towards the butt. Then, with the firing cycle, the transfer port area is fully pressurized trying to blow that o-ring out the front and into the pump chamber. That's just about as far as an o-ring should ever move in service, and it's small wonder that a bit of "pumping" is not associated with the action.

Does anyone have any crafty methods for sealing the retention stud to pump tube interface?

cheers
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Joined: May 22nd, 2007, 3:28 pm

June 11th, 2012, 3:41 pm #6

Just a hurried response, possibly with more later, but petroleum jelly/Vaseline may be a very poor choice of lubricants. It's not suitable for high-speed metal to metal or metal to rubber lubrication at all. It's not intended to withstand temperature variations while retaining its lubrication ability. It's not necessarily compatible with various o-ring materials and may break down some matrials. It has no real 'cling' properties making it suitable, instead it migrates just as described above.

In other worlds of things mechanical petroleum jelly is a major no-no, as in hydraulics, pneumatics or pneu-draulic machinery assembly. It's never to be used in an automatic transmission assembly because it can attack o-rings, clog up pumps and valves, same with lots of pneumatic or pneu-draulic equipment. It changes state and may harden in combination with other substances, or in heat/cold cycling, or break down entirely. Adding other chemicals or lubricants can form strange combinations that do more harm than good. It offers very poor wear protection while also lacking in lubricity.

Best to use lubricants specifically designed for the stresses, environment and materials present in a cherished airgun's mechanism. Silicone, moly, specialized synthetics etc. can be much better choices.
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Joined: June 7th, 2010, 12:14 am

June 11th, 2012, 9:14 pm #7

Some of the information you have shared is not complete.

Petroleum jelly is one lubricant that does completely dissolve in the presence of other petroleum oils. A perfect example is the assembly of an automotive "slush box". Grease has it's binders (often Soap base) that can stop up orifice and passage ways. Petroleum jelly has none!

And as to o-ring life , unless the o-rings are meant for hydraulic brake service, most "industrial" o-rings are completely compatible with oils, greases and Vaseline!

As to it's use as lubricant? If you read the post, you will find that the petroleum jelly was used as an assembly aid to a static positioning of the valve assembly. There it serves to lubricate the o-rings to limit tearing while sliding the unit into position, and also as a barrier to corrosion.

Having been a stead fast user of petroleum jelly for many years in many applications, I have found the material to be very useful. I will not hesitate to continue it's use for any hydraulic or pneumatic assembly I may have need. But as a hi performance lubricant for metal to metal , I would use something better.

Perhaps the stories you have heard that decry the use of petrolium jelly have been authored by those who use too much of everything, or use materials poorly suited to the application.

And most significantly, these extractions from Wikipedia!

* It was recommended by Porsche in the owners manual of their cars as a preservative for light alloy anodized Fuchs wheels to protect them against corrosion from road salts and brake dust. Every three months (after regular cleaning) the wheels should be coated with petroleum jelly.[6]

* It was also recommended by Porsche in maintenance training documentation for lubrication (after cleaning) of "Weatherstrips on Doors, Hood, Tailgate, Sun Roof". The publication states "before applying a new coat of lubricant" "Only acid-free lubricants may be used, for example: glycerine, Vaseline, tire mounting paste, etc. These lubricants should be rubbed in, and excessive lubricant wiped off with a soft cloth."[7]


Ideas differ...Isn't it a wonderful world;)

For some applications, You just cant' beat Sil-Glyde! But that stuff does not play well with petroleum products.
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Joined: November 28th, 2002, 6:26 pm

June 12th, 2012, 12:06 am #8

Because, in their haste,
They used library paste,
Instead of petroleum jelly.

Steve
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Joined: May 22nd, 2007, 3:28 pm

June 12th, 2012, 5:41 am #9

My only reason for posting was to save folks from possible grief. It's certainly a matter of opinion and personal preference on use of petroleum jelly. As a former owner I seriously admire Porsche engineering but please note, their advisory addresses alloy wheel and body weatherstrip maintenance, not o-rings.

I won't trot out my resume here but I spent a lifetime with a huge variety of equipment that depended on o-rings. If an o-ring is made of or contains any petroleum-based compound then petroleum jelly may cause that o-ring to break down, actually melting it. It may take a while to realize it happened. When an airgun is shot whatever is used for assembly lubricant will be distributed throughout the gun eventually. Several but not all plastics are damaged by petroleum jelly so if the 'wrong ones' are anywhere in the gun that may cause problems over time.

A particular mfgr. of a product may suggest using petroleum jelly on their o-rings, because they know what their o-rings are formulated from and have done their research. That's not to say then that all o-rings can tolerate petroleum jelly. Other o-ring formulations may not be compatible with it and might require a specialized lubricant, maybe silicone based. However silicone based lubricants will attack silicone o-rings. Some info at the link:

http://www.parker.com/portal/site/PARKE ... nextfmt=EN

http://www.theoringstore.com/index.php? ... s_id=11310


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Joined: June 7th, 2010, 12:14 am

June 12th, 2012, 9:36 pm #10

Compatible with petroleum products?

At least I would.

And if o-rings swell and fail? dry out and fail? get cut on installation? well they do that anyway
Catastrophic or dangerous failure in a pump up is highly unlikely, at least due to seal failure.

They are replaced at a few cents cost while doing something pleasant on a dark winter's evening.

Corrosion is more likely a significant long term trouble. Do we need to paint these thing?

If one could readily determine the materials used by the manufacturer, that would be great. More often, they don't even know.

More and more, I use UTTO (Universal Tractor transmission oil) for just about every casual lubrication application. It's in several of my shop oil cans, the lathe head stocks run in it, the tractors both use it everywhere but the engine. All my cars use it in the power steering, Audi's at that. It's clear and clean, It has great additives for anti-wear and lubricity, foaming control, corrosion inhibitors etc. and doesn't smell bad. Available at any auto supply store, and it's not expensive.

Just don't put it in the brake reservoir, and it's not grease!
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