Alternative to O-rings 2

[Ric1]

I've been tasked with designing a variety of valves for use within a Fuel Metering Unit. Usually we use O-rings for sealing purposes between sleeves and bores.

I'm currenting looking to see if there are any viable alternatives to O-rings, mainly to avoid stepping in the sleeve diameter when a number of seals are required. (Freeze fitting being a non-preferred option).

Typical operating conditions:-

Temp Range: -53 degC to 180degC
Pressure: 800 psi differential

The sleeve will be a hard anodised Al alloy

Does anyone have any suggestions?

 

[mqas]

Ric1,
For the temperatures stated you could use spring energized PTFE lipseals. The main disadvantage of this type of seal is :-

1/it is difficult to fit into a conventional oring groove and a redesign of the major components is necessary.
2/ They are more easily damaged than conventional orings.
3/ more expensive than orings.

The big positive is that they are less likely to be affected by the temperatures and line medium.

Suppliers are Advanced Products and Gulf Coast Seals

 

[tsenthil]

Other than O Rings there are some other alternatives available like followings.

U-Cups:

A u-cup is an o-ring formed into a u-shaped channel. Liquid or air pressure "inflates" the u-cup and affects a seal. The u-cup is ideal for use on linear moving shafts and piston heads, because unlike an o-ring the shape does not try to roll with the movement and create friction. The sides of the u-cup allow the shaft to move virtually unhindered, and seal with a wiping action.If a secondary or even a series of u-cups are used in the design, only the first one is pressurized, so friction is kept to a minimum. Secondary u-cups are used as backup seals in case the first u cup fails

Flat diaphragms:

Flat diaphragms are a flat round disc, usually cut from a sheet material, designed to affect a seal when forced against a valve seat.

Rolling Diaphragms:

This is a diaphragm formed in a convoluted shape. It gets its name because as the stem moves, the diaphragm "rolls" at the convolution. It is frequently used in a manner similar to a u-cup, that is, to seal the gap between a linear moving shaft and the valve body. But unlike the u-cup, the rolling diaphragm is permanently affixed to both the shaft and the valve body. Because it is affixed to the shaft and also "inflates" from fluid pressure, the force of the fluid directly impacts the movement of the shaft. In some cases, such as a relief valve, this force is used to accelerate the movement of the shaft. In a pressure regulator, the force on the rolling diaphragm is what causes the shaft to move, so it is referred to as a "sensing" diaphragm.It is important to eliminate any possibility of water hammer in a piping system where rolling diaphragms are used, as they can be ruptured by the explosive surge.

Sealing Discs:

A disc is referred to as the elastomeric part affixed to the part of the valve stem that affects a seal against the seat. Discs are frequently flat washer-shaped pieces that are assembled into a retainer; they are also frequently a specially-molded shape that is slipped onto the end of the valve stem. Pressure (usually either spring, air, or line pressure) forces the disc firmly against the orifice seat, affecting a seal.

Elastomer Sleeves:

A pinch valve uses a round rubber tube (sleeve) that is "pinched" to affect a seal. It is pinched either mechanically or with air pressure. Sometimes the sleeve may be formed in a special shape, so that the external force will cause it to fold or collapse at specific points.

Hope the abobe is helpful to you

Senthil

 

[EVSP9000]

Have you considered, Metal O rings some of the new designs low load type are very close to the requirements for elastomer o rings

regards

Mike

 

[sealguy]

Sir,

I am afraid that you are stuck with o-rings or maybe x-rings. It is almost impossible to use a spring energized PTFE seal as a plug seal due to installation issues. They are unidirectional seals as well and you will need two seals for every 0-ring that you replace. They also can not pass any ports. U-cups are unidirectional too and also hard to install as a plug seal. You can not use metal seals as radial seals only axial face seals.

If your seals are dynamic you can reduce friction by using a filled PTFE Cap Seal. I have a lot of experience and would be happy to answer any other questions that you may have.

dmmyers@erols.com

 

[scalleke]

EVSP 9000

Who makes metal 'O'-rings.

I would love to test some of those?

Thanks

Scalleke

 

[mrctchlr]

To whown it concerns,

HTMS (High Tech Metal Seals) is a supplier of
metal O-rings and C-rings in materials like Inconell, etc.

http://www.htms.be/products.htm

Regards,
MT

 

[israelkk]

I agree with sealguy. I have an extensive experience of over 25 years in high and ultra high pressure pneumatic valves and systems for aerospace use and we have used O-rings successfully for the range of -54C to 120C. O-rings are quite cheap and the machining of the glands are very common and quite cheap too. There is no way of using metal seals over shaft and inside bore the way you use O-rings. further more the surface machining preparation for metal seal is much more expensive and demand much more attention from the manufacture where helical machining lines are forbiden. All machining lines should be closed circle to avoid leakage and high mechanical pressure should be applyed to the seal.

The reason for the stepping in the sleeve diameter when a number of seals are required is to prevent tearing of the O-rings during installation. All other rubber based seals recomended earlier will suffer from the same problem and even much greater.

 

[howkers]

Metaaaal O-rings:

Wills Rings of Somerset, now part of Shamban seals group.

http://www.busakshamban.us/prod_global.htm?print=1&pid=359

 

[NGiLuzzu]

Please take also a look at:

http://www.plastics.saint-gobain.com/

Hope this helps, 'NGL

 

[bucs2047]

Ric 1,

We recently went through an outage repairing the fuel gas valves for our turbines. I was not directly involed in it however we replaced the standard rubber o-rings to a different compound referred to as 'VAT 80'. Again I was not directly involved in the overhaul but will try to dig in for a little more info.

 

[busakshamban]

The Wills Rings link should be:

Wills Rings C

Wills Rings O

And for Spring Energized PTFE seals Variseal (part of Busak+Shamban) is a world leader:
Variseal

 

[MikeHalloran]

O-rings and derivatives are pretty much it.

Okay, I can think of one more way that might work, depending on the economics of the assembly, and how badly you want to get rid of elastomer seals; a sleeve around the sleeve.

A relatively thick brass sleeve that's a just slightly loose fit around the aluminum sleeve, and a heavy press fit in whatever the housing is. Drop the aluminum sleeve into the brass sleeve, press the brass sleeve and the aluminum sleeve together into the housing, and the brass sleeve shrinks enough to retain the aluminum sleeve. Of course, the stress from the brass squeezing in around it will also shrink the aluminum sleeve, so you have to make your sleeve to spool clearances a little loose before assembly.

Precalculating the clearances and interferences and tolerances sounds like a rather fun problem.



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA