Silicone valve

[crthomps]

I was wondering if anyone had any ideas as to how/why a valve of ours would operate as it is: it is a dime-sized silicone valve with a dacron mesh sandwiched in the middle. To me, everything looks symmetrical. When this valve is inserted one way, it works perfectly, but when it’s inserted with the wrong face down, it doesn’t work properly.

I’ve had a few ideas, such as the mesh not in the directly in the center, so it favors one side over the other. Another idea was that the two halves have different hardness/density. I tested them to find their durometers were the same. Does anyone have any ideas?

 

[patprimmer]

I think you hit it with the polyester reinforcing fabric not being on centre, but it could be more relaxation shrinkage on one face of the fabric if the silicone is cured anywhere near the polyester heat setting or annealing temperature. That is if both sides have slightly different temperatures during curing.

Regards

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[MikeHalloran]

It's common for knitted _wire_ mesh to behave asymmetrically in bending, i.e. to be easy to curl in only one direction, and stiff in every other direction. I'd expect similar behavior from any knitted mesh, because the knit is not really symmetrical about its central plane.

I'd expect a _woven_ mesh to behave a little more symmetrically.

There seem to be two solutions to the problem; change the reinforcement so it behaves symmetrically, or key the valve so it can only be assembled one way.



Mike Halloran
Pembroke Pines, FL, USA

 

[Dtuck]

Two questions come to mind. 1) If you cut the seal, is the fabric directly in the center? 2) Are you sealing against an orifice? Thicker sections of elastomer compress more over nozzles causing a beter seal but a later release duiring regulation.

 

[crthomps]

1. Yes, the fabric is directly in the center (no evidence of concavity)

2. Yes, we are sealing against an orifice. Since both sides are the same thickness, I am a little confused as to why it might favor one side over the other.

 

[Dtuck]

If the die cut material was calandered on two passes as many are, the penetration into the fabric may have come from one side and thus cause a different physical behavior one side to the other as you are using it. Usually a higher durometer elastomer will be run both sides at once.