Fabio Fioravanti There's no good or bad solution in principle. Your bullet proof approach consists in validating your solution through worst case scenario testing. What you say the o-ring is placed for in the design, shows it is a design output to address a specific design input, so you should demonstrate it works as part of your v&v process. So for example, select an aerosol generator with particles similar to those you want to protect your appliance from, design a test protocol to pollute your environment with such aerosol, and use a particle counter or other quality testing technique to detect any significant leakage through the o-ring. Consider running your test in different conditions, if possible, including worn out o-rings, moving parts still and operational, etc. gather your data, and check that your initial acceptance criteria (e.g. maximum particle count or similar criteria ) are met.

Steve Kent One basic example is a Thorpe type medical gas flowmeter. The spindle which connects to the control knob and controls flow (and therefore rotates) will have at least one o-ring.

John, in my experience, the discussion starts with your hazard analysis. In this case a FMECA. If the failure of the o-ring results in significant risk than all of the "analysis" to justify why an o-ring works is simply a set up for the testing/validation that demonstrates that the o-ring will do what you intend and for what service interval. If the risk is low, most o-ring manufacturers have standard design data that you can point to show that the design is appropriate with low risk if it does fail. Hope that helps.

John, pulmonary ventilators and anesthesia machines are filled with O-rings. There are many between blocks, valves, pneumatic connectors ...

It's not a question of whether an o-ring is used in other industry examples. Neither is it a question of the engineering/physical principles of an o-ring. It is a question of proving that this particular o-ring and seat design; coupled with dimension, material and quality variability; will do the job intended to within the safety margins required, across the range of challenges it will see in use. Risk assessment, theoretical modelling, specific physical testing may all be needed to qualify your choice of this solution.

Arthroscopic Shavers would be an example.

How about a syringe?

Dr. Robert Zakoff I am in unfamiliar territory. It seems to me that a rotating shaft with a O-ring needs a compression factor to ensure the seal.

Jonathan Wacks You need a new RA consultant. You perform Risk Analyses and Design Validation.

Like every device there's limitations to form/functional design & types of materials used. O-Rings do fail however, OEM specs & Device service management usually will keep these aspects in check & replace as recommended/required.

Health Tech Solution Ltd 'o' rings are used in medical gases. For example on a bullnose fitting for a regulator on a medical gas cylinder.

You need to conduct dFMEA, verfiy and validate your device, provide mitigation strategy for any failure mode related to the O ring. If the risk is low or high but can be mitigated (for example, the device can detect a leak due to insufficient sealing by the o-ring and prompt the usr the test is invalid amd result should not be used, then it is a non issue). The focus is not about whether you can you a o-ring or not.

Most have this right. Your first task is to do the risk analysis . If the risk is serious or critical, you will have to provide mitigation. Then you will have to find the correct standard - probably 60601 - and have it tested at an independent lab to insure the design meets criteria.

Allan O'Brien John, my background is in high vacuum equipment used in the semiconductor industry but I thought I'd offer some input. Elastomer o-rings used on rotating shafts are fairly commonplace. We measure their leak integrity by helium leakchecking (if a small helium atom can't penetrate the seal, then neither will any other atmospheric gases). Material selection is important (viton, silicone, etc) in terms of temperature and chemical resistant properties. The duro number of the seal is also important. If you find that a static standard seal isn't fit for purpose in your application, there are many solutions. The first being a quad seal, which has an increased surface area. If this isn't sufficient, you can employ a differential key pumped seal where two O-rings are used and low vacuum is pumped between these seals. A more expensive option and which requires a bit of redesign, is a ferro fluidic seal. I'm not sure about the suitability of these in the medical equipment sector given that they contain magnets and ferrous liquid but they are very reliable and used extensively in our industry. Hope this info is useful to you. Good luck.

Agree to all above ESP validation! Remember, anyone 35 or older may still associate "O-ring failure" with the official root cause of The solid rocket booster / Challenger explosion. This sounds like more of an ignorant / emotional objection. Secondary Redundant O-rings make people feel better even if unnecessary but still worth considering if possible. Validate it in all applicable conditions and those beyond the real world application (sorry to cite this example again but in the case of challenger the shuttle was outside during lower than normal temperatures which was a big part of the investigation) so perhaps validating with a large positive minus standard deviation of both temp and humidity would make people "feel" better since this is more emotion than anything.

Used in the waste management systems, used in surgery

Nigel Heales CEng MIMechE Oxygen Valves - Shut off mechanism uses a threaded spindle. Use of O-rings are used on the spindle to provide a seal to prevent leakage. Could you also refer to published standards that reference checking O-rings in the testing? Demonstration of test results meeting or exceeding published standards for the device, including intended lifetime confidence testing should also provide factual and non-opinionated evidence. Of course the key is specifying the correct o-ring for the intended application, designing the grooves etc correctly for the application and having supplier control in what you receive. Not sure if this helps ..... good luck.

Phill Brown As above, but also consider the life experience if the part if exposed to repeated heat (autoclave) or chemical action (drug, cleaner). If the failure of the I-ring would mistreat the patient or cause damage to the device such that further misstatements are possible then it is a legitimate question

O ring is the rubber type o, it Mainly set in between the joints and contact to prevent the leackege and also be save from corrosion because of rubber natural quality

Christopher Smith Have the design validated and risk analysis done to comply with standards. It seems that the product by your questions is to do with medical air. Oxygen seals are another ball game, as it is very dangerous and when I worked with it in Aviation it was taken very seriously. My medical experience with it however has shown me that the industry does not understand nor take it anywhere as serious. The standards, either EU or US, are pretty relaxed, such as automotive for example. You shouldn't have too much trouble validating it. The auditor is right to ask questions, even if they do not understand the engineering. You cannot learn if you do not ask.

Mark Proulx, CQA, cSSBB John Magill much like when you were in school, sometimes the easiest answer is starting asking "What does the teacher want?" I think a good idea would be to find out what your RA consultant is looking for as far a confidence: are they looking for reassurance, are they looking for capability/reliability numbers, are they looking for complete functional characterizations, etc.? If they are questioning the design decision to use an 0-ring, trust that there is a reason. Look for a way to prove what you know to be true through characterization, dFMECA, Hazards Analysis, stress testing, etc.

I have worked with many analizers that use o-rings, and I can say you compresion factor is very important to obtein a good seal, I know an electrolyte analizer device that use them, for pipette aspirator that moves up to down through the hole where o rings are placed.

Possibly an FEA in the minimum tolerance condition will help assure them that the O-ring will work. It's definitely overkill, but may be helpful.

This is the kind of readings that all the professional associated to LinkedIn desire to read, by the way consult to Dow Corning elastomers group

Rob Packard I used to design, operate and repair bioreactors. These reactors are used for cell culture and fermentation. The bioreactors have an agitator shaft that is sealed form the outside world by a mechanical seal and an o-ring. Some designs use double o-rings, but a single o-ring is preferred, because contamination will become stuck between the o-rings. The design of these reactors uses steam between the o-ring and the mechanical seal to prevent leakage. For all other ports of a bioreactor, o-rings are the only type of seal typically used. The more expensive mechanical seals are limited for use with turning shafts.

Used at the back of anesthesia machines to secure the e-cylinders for oxygen. Often times with torque /high pressure, you can secure tanks without o -rings but circuit will show leaks or runs out oxygen sooner than expected.

Im my history I have a few stories about o-rings and sealing challenges I could share, but here is my most curent and prime example of a moving seal challenge.
http://www.artel-usa.com/products-and-services/vms-volume-measurement-system/
The system use 8 pistons stroking ~15mm to pressurize air into a microtiter plate to measure the volume in a well.
The established accuracy for the system is ±5uL (it actually does better than that).
The tested life for the 8-piston o-ring seals is 1,000,000 strokes before replacement.
I would argue that the stroking piston issue is a tougher design goal than a rotary application.
The KEY to o-ring sealing is the design of the mating surfaces.
Get your dimensions correct and they perform as designed.

I have used o-rings in several designs. Mating surfaces are one key, but you better be sure of you o-ring material, and what chemicals they can come in contact with both in use and during cleaning.

Allan O'Brien If you can then match these parameters with the application - chemicals exposed to the o-ring, temperature of the rotating shaft under normal conditions, you may go some way to demonstrate it's suitability but not necessarily it's reliability.

Allan O'Brien John, my background is in the semiconductor industry where elastomer O-rings are used extensively in high vacuum systems where 1ppm of air ingress is considered unacceptable.

The standard method of quantitatively validating the leak integrity of any chambers with O-rings is a helium leak check. If helium can't pass through the seal, it's unlikely air at atmospheric pressure will. If you have this data for the units in questions, both for new units and periodic, then I'd share that data with the individual.

If you don't have this data, you can either gather the data by leak checking it (let me know if you need more info on how to approach this) or you can indirectly prove it's suitability by providing the datasheet for the elastomer used.

There are several parameters that will be provided for a given o-ring namely; material (which defines compatibility with chemicals, operating temp, hardness), duro number and of course dimensions.

Environment and materials are key to understanding how the seal may wear over time. Cycle testing is important as well for determining the shelf life and/or when the o-ring should be replaced. Rubber o-rings, and really rubber in general has material issues due to a very focused (almost single sourced) material supply. Research the rubber material source meticulously to make sure it's truly traceable. You'll be surprised to see this material is tough to trace the true raw material origin.

Well, there are leak testers and provision to replace worn O-rings....

John Hogan John: Your comment about gravity is excellent!! The use of elastomeric o-rings has been longer than than the Medical device market has existed. The key element is inspection, chemical resistance(external to and internal to atmosphere) and the proper choice of material compression set. All elastomers exhibit some set under compression and this should be addressed in the design of the closure. As William has noted, the surfaces have a critical effect and must be thought out for longest life of the o-ring. Excessive 'squashing' [overtightening and subsequent distortion] will result in premature failure by compression set. Additionally, the use of coatings, e.g. oil(s), solvents, etc. can cause failure by 'solvating' the base polymer and 'cracking' the ring. The use of a proper material in a(n) rotating paddle system has been used by bench chemists in reactors, large paddle systems in polymer manufacturing and huge in bulk latex maceration systems. (See Part 2 following)

John Hogan John: Part 2
These have been pressurized up to 30-40 Atm. with no leakage and, properly chosen, have lasted years. The key is inspection, proper compression, good surfaces and maintainence between cycles. Suggest you also reach out to some of the polymer manufacturing folks for assistance as to the life-cycle of their paddle/stirring systems within the reactors. Good luck attempting to convince the legal beagles that gravity works every day!!!! Sabra Best, CQE CQAJohn

ive worked on a big range of medical equipment and o rings are used to create a seal on static or linear movement components but not when a seal is required on a rotating shaft. different types of mechanical seals will seal rotating shafts.

Some Rotating piston pumps use O-Rings. (the ones we sell do not)
There are also O Rings in some brands of Aerosol MDI Cans which help to ensure that the crimp to the can is tight - these do not however rotate.

Use of O rings in rotating piston pumps ( or not) explains it all: you need them for handling higher viscosities of liquids than so called sealless pumps ( metal to metal contact) = higher pressures across the seal. However you need to check material compatibility and consider preventative maintenance- regular replacement. Avoid in cases requiring sterilisation.
Hope this helps