Question O-Rings Vs Quad Rings for Piston Seal on MK10 Clone

[JP_SCUBA]

Hey there ... My question is fairly straight forward and that is, Why doesn't anyone use a Quad type O-ring for a piston seal? Has anyone here ever tried one? and if so then how did it function in comparison to a std. O-ring. I would think it would be an improvement in dependability as the Quad ring has actually 4 sealing surfaces instead of only two. I'm not talking about just a square piece of Buna rubber like a some of the Hydraulic/Pneumatic cylinder piston seal rings. (please see attached picture). This type of seal actually allows the fluid medium to get between the o-ring groove wall and seal and provide additional force to assist the quad ring in sealing. I'm going to be experimenting with an old MK10 clone regulator and see what results. Any input on this would be appreciated. The ring in the picture is not the size I'm replacing. I just used one a lot larger for a visual. The size I'm trying is a -017 for the piston on the MK10 clone..... Thanks in advance

 

[lexvil]

I look forward to your findings.

 

[JP_SCUBA]

I look forward to your findings.

Hey Lexvil .... thanks for responding. Have you ever seen/heard of this being accomplished? I've been in the Fluid Power Industry for most of my career and substituting a Quad ring for an O-ring is done quite frequently for a better seal.

 

[Fibonacci]

Hmm... yes also be interested in hearing how you go!

Generally known as X Rings in AU.

Quad Rings / Xrings - Sealing Australia

About quad rings aka x rings. Why use quad rings?

sealingaustralia.com.au

Not sure if in SCUBA piston reg applications you would want sea water or debris trapped in the valley of the X being held against the cylinder wall vs hydraulic fluid which would act as a lubricant and prolong the seal life.
This seems to be an eventual failure mode of piston regs with a standard o-ring even if well rinsed.
If you filled the recess in the X with silicone grease to avoid water retention, wouldn't it then just act like a standard o-ring?

Some OEMs use a PTFE split backing ring in conjunction with a standard o-ring to prevent extrusion under high pressure.
Maybe @rsingler can comment?

 

[Kupu]

When thinking where to improve upon standard o-rings for MK10, the high pressure piston shaft oring (-010 size) is what comes to my mind. A reduction in friction and high stability in dynamic applications is good. But can a single quad ring handle 3000+ psi?

A quad ring may work for the -017 piston oring at IP, but does that one need improvement?
Perhaps quad rings cost more and I have never heard of any issue that would need a "better" oring in that position.

Just my off the top of head thoughts, the idea is interesting. Look forward to hearing more.

 

[lexvil]

Hey Lexvil .... thanks for responding. Have you ever seen/heard of this being accomplished? I've been in the Fluid Power Industry for most of my career and substituting a Quad ring for an O-ring is done quite frequently for a better seal.

I have a feeling I’ve seen them used in a scuba regulator, perhaps it was in the Drager. I also feel the shaft seal may be a better application but you have to start somewhere. In the 70’s we were changing quad rings over to some with a extra wiper in the middle which gave it a third wiper, this was on hydraulic accumulators on subs, I don’t know how those worked long term but they were a #itc@ to install.

 

[JP_SCUBA]

Hmm... yes also be interested in hearing how you go!

Generally known as X Rings in AU.

Quad Rings / Xrings - Sealing Australia

About quad rings aka x rings. Why use quad rings?

sealingaustralia.com.au

Not sure if in SCUBA piston reg applications you would want sea water or debris trapped in the valley of the X being held against the cylinder wall vs hydraulic fluid which would act as a lubricant and prolong the seal life.
This seems to be an eventual failure mode of piston regs with a standard o-ring even if well rinsed.
If you filled the recess in the X with silicone grease to avoid water retention, wouldn't it then just act like a standard o-ring?

Some OEMs use a PTFE split backing ring in conjunction with a standard o-ring to prevent extrusion under high pressure.
Maybe @rsingler can comment?

Hey Fibonacci ... Thanks for responding... Agreed, for the most part, however, I think that when the IP gas pressure is applied it pressurizes the area between the side of the seal groove and the quad ring resulting in an action similar to a lip seal. This would push the I.D. and O.D. seal lobes tighter against the piston and the bore. Since the opposing force on the piston is primarily spring applied that would leave the seaward side lobe acting as a wiper. Any ambient water pressure could also enter the area between that side of the seal groove and the seal and increase the wiping efficiency. If all of these events transpire correctly then it seems less likely that contamination would enter the area between the two sealing lobes. Thoughts?

 

[JP_SCUBA]

I have a feeling I’ve seen them used in a scuba regulator, perhaps it was in the Drager. I also feel the shaft seal may be a better application but you have to start somewhere. In the 70’s we were changing quad rings over to some with a extra wiper in the middle which gave it a third wiper, this was on hydraulic accumulators on subs, I don’t know how those worked long term but they were a #itc@ to install.

Lexvil,
I completed the assembly of one regulator and its currently on one of my tanks and holding 2850 psi. I had a leak at my HP gauge hose and had to change it. The gauge indicated zero so I removed it. I noticed that even with the gauge port open, the IP remained solid at 135 psi. Installed replacement HP gauge and everything is holding fine. We'll check it again tomorrow am. If all is well then I'll see how it breathes and If that checks then it's into the pool we go.

 

[JP_SCUBA]

When thinking where to improve upon standard o-rings for MK10, the high pressure piston shaft oring (-010 size) is what comes to my mind. A reduction in friction and high stability in dynamic applications is good. But can a single quad ring handle 3000+ psi?

A quad ring may work for the -017 piston oring at IP, but does that one need improvement?
Perhaps quad rings cost more and I have never heard of any issue that would need a "better" oring in that position.

Just my off the top of head thoughts, the idea is interesting. Look forward to hearing more.

When thinking where to improve upon standard o-rings for MK10, the high pressure piston shaft oring (-010 size) is what comes to my mind. A reduction in friction and high stability in dynamic applications is good. But can a single quad ring handle 3000+ psi?

A quad ring may work for the -017 piston oring at IP, but does that one need improvement?
Perhaps quad rings cost more and I have never heard of any issue that would need a "better" oring in that position.

Just my off the top of head thoughts, the idea is interesting. Look forward to hearing more.

Hey Kupu, Thanks for responding..
I agree with you on the 010. I'm contemplating changing that one to a quad as well. How this whole thought process started was I ran out of -017 o-rings but had a quantity of 017 quad rings so I started thinking, why not? So I thought I'd inquire on Scubaboard and see how crazy you guys thought I was. I have more 017 o-rings coming so if failure occurs, I'll be able to return to square one. My completed regulator is currently mounted to one of my tanks and holding 2850 psi with a solid 135 IP. We'll check it again tomorrow in the am and report....

 

[rsingler]

This would push the I.D. and O.D. seal lobes tighter against the piston and the bore. Since the opposing force on the piston is primarily spring applied that would leave the seaward side lobe acting as a wiper. Any ambient water pressure could also enter the area between that side of the seal groove and the seal and increase the wiping efficiency.

I think the idea is great. I think it would certainly work on the piston head, and the notion of using it for the HP seal is even more appealing.
Buuuuut... the phrase that I bolded, as @Fibonacci has suggested, is problematic.
I think that water is bound to enter the compartment between each pair of lobes that seal. The part is assembled at 1atm, gets pressurized to IP or tank pressure (depending upon which o-ring we're talking about), and flexes two lobes. When depressurized, it seems inevitable that sea water droplets will travel under the lip of the "wiper lobes" and get trapped in the space, free to work their corrosion during storage.

I think it's fascinating however, to consider filling that groove with lubricant, where it would serve as a reservoir to maintain supple travel - one of the big problems for the HP o-ring. As tempting as that prospect is however, the lube will eventually disappear, due to lobe flex. And I suspect that it will be replaced by seawater.

I think it would be reasonable to sacrifice an old Mk5 or Mk10 to answer the question. Stick one on the piston head and dive it several times without a reservoir of lube in the gap. Blow it out and let it dry. Open up the cap a few days later and see if there's moisture trapped between the two lobes facing the cap. If so, you can imagine what will happen to the land in the piston cap, or worse, to the critical seal along the piston shaft during months of storage in a two year service interval.

Still, great inventiveness and a good solution!