Low pressure sealing technique
Low pressure sealing technique
(OP)
I'm having a bit of a problem sealing at low pressure, 5 to 10 psi difference from atmosphere(could be above or below). It's a static face seal.
I'm currently using two O-rings in two separate grooves, both with 17% compression ratio(0.103" CS o-ring in 0.085 deep groove). The other mating face is teflon coated 1/8" aluminum plate. There is little control over the surface finish of that, and may be the source of the leak. However, I've also tested the setup with 1/8" stainless steel plate with good surface finish and it will still leak at a very low pressure, sometimes even at 1 or 2 psi.
Should I use gaskets instead because of the low pressure? What are some of the steps I can take?
Thanks!
I'm currently using two O-rings in two separate grooves, both with 17% compression ratio(0.103" CS o-ring in 0.085 deep groove). The other mating face is teflon coated 1/8" aluminum plate. There is little control over the surface finish of that, and may be the source of the leak. However, I've also tested the setup with 1/8" stainless steel plate with good surface finish and it will still leak at a very low pressure, sometimes even at 1 or 2 psi.
Should I use gaskets instead because of the low pressure? What are some of the steps I can take?
Thanks!





RE: Low pressure sealing technique
I would not use a gasket because the clamping forces required to achieve a seal are much higher than for an Oring.
Looks like your groove depth is wrong and not sure what your width is but check against attached and you should be fine. surface finish is important.
trust this helps
RE: Low pressure sealing technique
The groove depth is 0.085" and width is 0.125". The o-ring I'm using is 0.103" in diameter, which should yield 17.4% compression (0.103"-0.085")/(0.103")=17.4%
The other mating surface is 1/8" aluminum plate or 1/8" stainless steel plate
RE: Low pressure sealing technique
How do you tight the plate? Are to sure the plate stays flat when it is compressed against the o-ring?
RE: Low pressure sealing technique
the plate is tightened to the sealing ring with o-ring grooves by 20 evenly spaced #6-32 flat head screws.
RE: Low pressure sealing technique
I am not even sure that 20 #6-32 screws can create enough force to compress this large O-ring. You need to calculate the needed force to compress the O-ring 17% of its wire thickness. In addition you probably need a much thicker plate than 1/8" that will not deflect under the compression force on the O-ring. You may continue to use the 1/8" plate if you can add a thick ring above it to keep it flat.
RE: Low pressure sealing technique
RE: Low pressure sealing technique
Thanks israelkk! I was afraid that may be the cause. A quick and simple FEA with SolidWorks Simulation Express shows that the deflection between the screws is 0.00106" with the aluminum plate, which isn't much compare to the 0.018" of compression, is it(there should still be 16% compression)? The problem is that even stainless steel plate results in leaks as well, where deflection between screw is reduced to 0.00039".
RE: Low pressure sealing technique
A thicker plate would do some good, over that large surface even a relatively low pressure is a large force.
SP
RE: Low pressure sealing technique
thanks for all the suggestions thus far!
RE: Low pressure sealing technique
We do low pressure seals all the time, some leaking parts are a result of as little as a hair across the seal surface.
Could there be loose contaminats disrupting the seal?
Maybe the o-ring is cut, damaged from installation maybe? These cuts can be almost impossible to detect. Try a new one.
Is the surface finish in the groove acceptable?
You could try a quad seal, that might work better for you.
Hope something in here helps...
SP
RE: Low pressure sealing technique
How important is surface finish? Is 16 rms really necessary for air seal as suggested by Parker handbook? The groove is machined and then anodized so the finish on that is easily worse than suggested by the handbook, however, it is still smooth to the eyes.
Will surface finish from powder coating or equivalent surface treatment be not acceptable for use of o-ring seal?
RE: Low pressure sealing technique
You also don't say how good the sealing has to be. There is no such thing as zero leak. What is your requirement?
RE: Low pressure sealing technique