How many O-rings would a mechanical engineer use here?

In summary, the discussion revolves around the number of o-rings to use in a mechanical face seal for a part with two cavities for two different fluids with varying liquid dynamic pressures. After considering factors such as chemical compatibility and potential sealing failure, it is determined that two o-rings would work well in this case. Multiple o-rings may be advantageous in preventing leakage from solids contamination, but concerns about mechanical failure are not valid unless the application is very demanding.
  • #1
Roy S Ramirez
24
4
Hello everybody!

Happy 2019! I'm trying to design a mechanical face seal for the part shown below, and I'm struggling with the number of o-rings I'm supposed to use. There are two cavities (rings) for two different fluids. The liquid dynamic pressure for both the internal and external fluids is different but somewhere between 165 and 200 psi. I know I need at least two o-rings between them (as shown in the picture), but for a moment I thought maybe using three o-rings, with two of them located between both cavities would work better :/

How many o-rings would a mechanical engineer use in this case?

upload_2019-1-2_18-6-51.png

Roy S. Ramirez

School of Aeronautics and Astronautics
Purdue University - Class of 2021
Management and French Minor

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  • #2
Roy S Ramirez said:
Hello everybody!

Happy 2019! I'm trying to design a mechanical face seal for the part shown below, and I'm struggling with the number of o-rings I'm supposed to use. There are two cavities (rings) for two different fluids. The liquid dynamic pressure for both the internal and external fluids is different but somewhere between 165 and 200 psi. I know I need at least two o-rings between them (as shown in the picture), but for a moment I thought maybe using three o-rings, with two of them located between both cavities would work better :/

How many o-rings would a mechanical engineer use in this case?
If you have seal ring material perfectly compatible with both fluids, use 2 seal rings. If you have a doubts about chemical compatibility, use 3.
 
  • #3
If you have special concerns about cross-contamination between the two fluids, maybe use 3 o-rings, and vent the space between the 2 that are separating the fluids.
 
  • #4
The grooves to take the seals appear to be the same depths, so the seals will all be the same thickness. The outer groove is about half the width of the inner groove, so there is room for two inner ring seals between the fluids.

O-rings seal by being pushed into a hard corner by differential pressure. For that reason, venting the space between two o-rings cannot be effective, unless they are seated in quite separate grooves.
 
  • #5
Yes, of course, I should have been more clear in my previous post.
 
  • #6
Thank you very much to all of you! The o-rings are most likely going to be Viton which is compatible with both fluids therefore, I guess two grooves would work just fine. My main concern was not some low level of cross-contamination itself, but sealing failure due to both fluids squeezing the o-ring towards the groove's center.
 
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  • #7
Roy S Ramirez said:
Thank you very much to all of you! The o-rings are most likely going to be Viton which is compatible with both fluids therefore, I guess two grooves would work just fine. My main concern was not some low level of cross-contamination itself, but sealing failure due to both fluids squeezing the o-ring towards the groove's center.
From mechanical perspective, double seal rings are advantageous to single rings if you have a solids (i.e. dirt) contaminating your fluid (likely not your case?). Dirt particles in multiple-ring system are less likely to result in leakage, because force exerted by particle lodged between flange and one ring is less effectively transferred to other ring, preserving other ring contact with flange and maintaining the seal.
Concerns about mechanical failure of (less rigid and strong) multiple-ring system similar to one you voiced above are typically not valid, unless you have very demanding application approaching the mechanical limits if the seal.
 
  • #8
trurle said:
From mechanical perspective, double seal rings are advantageous to single rings if you have a solids (i.e. dirt) contaminating your fluid (likely not your case?). Dirt particles in multiple-ring system are less likely to result in leakage, because force exerted by particle lodged between flange and one ring is less effectively transferred to other ring, preserving other ring contact with flange and maintaining the seal.
Concerns about mechanical failure of (less rigid and strong) multiple-ring system similar to one you voiced above are typically not valid, unless you have very demanding application approaching the mechanical limits if the seal.
Thank you very much @trurle
 
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1. How do I determine the number of O-rings needed for a specific project?

The number of O-rings needed for a project depends on several factors such as the size and type of the O-ring, the pressure and temperature requirements, and the design of the mechanical system. It is best to consult with a mechanical engineer who can accurately calculate the number of O-rings needed based on these factors.

2. Is there a standard or recommended number of O-rings to use in a mechanical system?

There is no specific standard or recommended number of O-rings to use in a mechanical system as it varies depending on the specific requirements of the system. However, engineers typically use a safety factor when determining the number of O-rings needed to ensure the system can handle unexpected conditions.

3. Can I use fewer O-rings to save costs?

It is not recommended to use fewer O-rings than what is calculated by a mechanical engineer. O-rings play a critical role in sealing and preventing leaks in a mechanical system, and reducing the number of O-rings can compromise the system's performance and safety.

4. Are there any alternatives to using O-rings in a mechanical system?

There are alternative sealing methods such as gaskets, seals, or adhesives that can be used in place of O-rings. However, O-rings are a popular choice due to their versatility, durability, and cost-effectiveness.

5. Can I reuse O-rings in a mechanical system?

It is generally not recommended to reuse O-rings in a mechanical system. O-rings can become damaged or deformed during use, and reusing them can compromise the system's sealing and performance. It is best to replace O-rings with new ones when necessary.

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