O-Ring failures

From pressurised water systems, which ‘inspired’ this little post, engines, the air weapons and firearms I use for pest control, the humble ‘O’ ring  is everywhere.
Yet when it fails it’s usually a symptom of a bigger fault i.e. mechanical wear, chemical attack, or poor low temperature control.

A lot of folk call them rubber ‘O’ rings yet you seldom find one in pure rubber.
A few “common” materials are listed

  • Nitrile (Buna-N)
    General Purpose, good resistance to tears and abrasive treatment.
    May react to brake, nitro, and hydraulic fluids.
    Clue is if it evaporates easily, nitrile may not like it.
  • Ethylene Propylene Rubber (EPR)
    Mainly found in hydraulic pumps and where steam, water, silicone oils, brake fluids and alcohols are used. They don’t handle mechanical stress well and wears out easily or is easily torn.
  • Fluorocarbon (Viton)
    Mr. versatile and found a lot in vehicles as it wears well.
    Yet it doesn’t do well with light fluids like ethers.
  • Neoprene
    Found mainly in AC, refrigeration units, and works with petroleum products.
    Can cause skin irritation, may contain lead so not good for potable water work.
  • Polyurethane
    Top dog as far as wear and tear is concerned but lacks when you need a combination of high temperature and good compression performance.
    Having said that you’ll find it in hydraulic fittings, cylinders and valves, pneumatic tools, and firearms.
  • Silicone
    Now this works at all temperatures yet it’s the weakest when looking at wear and tears.
    So don’t fit these where they are exposed to daily “abrasion” i.e. on pressure washer hose seals. They just don’t last!
  • PTFE.
    Tough, high temperature working, material but hard to fit as they are so stiff.
    Good corrosion and abrasion resistance, non-permeability, chemical inertness and low absorption. But having said that, it’s best used for static work i.e. not on sockets or plugs.

So what are the common ‘O’ ring killers?

  • Cold. Tends to make them brittle and less flexible.
  • Heat. sustained temperatures over 100 ºC or 212 ºF can degrade them.
  • Wear. In connectors the main failure is muck that abrades them and poor insertion by the operator, aka you being heavy-handed! So heavy use connectors need a good eyeball before and after use. Just blowing off the fluff and wiping them on a rag is just not good enough to ensure a long life.
    (A few profiles of ‘O’ rings)
    The contact area of the ring isn’t that great so if a metal fitting starts to wear, the possibility of leakage by excess strain on the connector is a real possibility. Most everyone instantly changes the ‘O’ ring.
    Few actually look at the physical connector.
  • Chemicals. A funny one this as ‘O’ ring composition is picked what it is being used for.
    Then along comes the end-user. As always the weak link.
    The fitting is getting a bit tight?
    On goes the WD40 or other ‘easing fluid’ or even grease. Only the formula for them may not suit the material. It can chemically alter its properties i.e. turn brittle, sticky, or even porous.
    A cautionary note, grease and high pressure air can ignite grease aka BOOM!
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4 Responses to O-Ring failures

  1. shtfprepper says:

    Saving this one for future reference. Thanks, kind sir.

  2. shtfprepper says:

    Reblogged this on SHTF Prepper and commented:
    A good one to keep for future reference.

  3. Rifleman III says:

    When I need any hydraulic or pneumatic packing, the local hydraulic shop is my source. I bring the packing, or as best describe the application, and usually they have just the right stuff. Look for shops that service sanitation (trash) lorries, or dump lorries. Packings, also require servicing periodically. I learned that while obtaining (a long gone) federal aircraft mechanic license (airframe and powerplant). I recall one of the U.S. Columbia space shuttles blew to hell, for a $3.00 (USD) packing that was substituted for a 70 cent packing.

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