[PSUBS-MAILIST] Fw: O2 cleaning

Tue Jan 14 08:23:24 EST 2020

PTFE is fine to use. There are some liquid / paste thread sealants out there which may not be O2 compatible. Sometimes, the liquids have the advantage of being less likely to introduce fouling particles / debris into the system than a tape sealant, but this is largely dependent on technique. If you're careful to avoid wrapping over the end of the fitting with tape, and don't do too many wraps, you'll be fine. Keep in mind that the primary purpose of a PTFE sealant is actually to act as a lubricant, in order to allow greater engagement of the interfering tapered threads at lesser torque. Gap filling the spiral leak path is secondary. There may also be liquid sealants which are okay for oxygen use, but you need to check.

On a slight tangent, particulate filters are always a good idea upstream of any critical components, and certainly where you don't have easily actuated manual shutdowns/ overrides. Where I employ certain electronic regulators in gas pressure control systems, I make a point of filtering at 40 microns maximum, and finer is better, though more maintenance intensive. There's nothing more frustrating than breaking down a failed regulator to discover that it failed because it was fouled by a bit of sand, or a bit of PTFE tape.

Sean

-------- Original Message --------
On Jan. 14, 2020, 05:07, James Frankland via Personal_Submersibles wrote:

> Hi Sean
> You said here.
> "Finally, if you're assembling any tapered thread connections (NPT), use a PTFE or other thread sealant suitable for oxygen systems".
>
> You got me slightly worried now.  I used ptfe tape on two BSPT joints I have on my O2 system.  I was careful to keep the ptfe tape only on the tread, but still.  It was just ordinary ptfe tape.  They are downstream of an outside mounted O2 clean regulator set to relieve at 14bar max, so its only low pressure in the pipe.
>
> Do you think i need to re seal them with something else?
>
> Thanks
> James
>
> On Tue, 14 Jan 2020 at 02:50, Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
>> Barring the presence of obvious open sources of ignition, fires in oxygen systems can also occur as a result of localized heating due to adiabatic compression, and to flow phase transitions (I.e. laminar to turbulent). If you, for example, have a dead headed volume downstream of a 1/4" ball valve at zero gauge pressure, and high pressure oxygen upstream, and you open that valve suddenly, the compression of the gas within the downstream volume will generate a lot of heat, which can conceivably cause the spontaneous ignition of any fuels present. Such fuels can include not only residual hydrocarbons from insufficiently cleaned systems, but also the system fittings themselves. Often machined fittings can have thin-walled features (e.g. intersections of drilled holes in elbow fittings), and these locations are at risk of localized heating to the point at which the metal itself begins to burn, which can be catastrophic in the presence of high pressure pure oxygen. Using needle valves allows you much finer control over the rate of pressurization - the idea being that by avoiding fast pressurization rates, the heat from adiabatic compression has time to dissipate from the system plumbing, and the ultimate maximum temperature of the compressing volume is kept lower, reducing the risk of a spontaneous fire.
>>
>> Sean
>>
>> -------- Original Message --------
>> On Jan. 13, 2020, 19:25, Ian Juby via Personal_Submersibles < personal_submersibles at psubs.org> wrote:
>>
>>> Hey Sean,
>>> I'm new to the group, but you said in your reply "You also want to avoid the use of any fast acting valves in oxygen systems. Use needle valves where possible."
>>> Why do you suggest avoiding fast acting valves?
>>> Tanks eh!
>>> Ian
>>>
>>> On Mon, Jan 13, 2020 at 9:07 PM Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>>
>>>> If you don't already own a copy, pick up a copy of the Oxygen Hacker's Companion, by Vance Harlow:
>>>>
>>>> http://www.airspeedpress.com/newoxyhacker.html
>>>>
>>>> That said, plain carbon steel is a less ideal material for O2 use than is brass or stainless. You also want to avoid the use of any fast acting valves in oxygen systems. Use needle valves where possible.
>>>>
>>>> To clean parts for O2 use, just avoid the use of solvents and use a hydrocarbon free cleaner. My preference is Orange TKO, but there are many others. Simple Green also seems to be popular. Use as directed, and check both your cleaning brushes and the rinse water with a UV light to ensure that it is coming away clean. Just repeat the cleaning / rinse until it does. To dry, small parts and fittings can dry in ambient air, but tubing, hoses, and more complicated parts with dead spaces will have to be blown dry. This must be done with hydrocarbon-free air (I.e. nitrox quality) or e.g. pure nitrogen, to avoid recontaminating the parts.
>>>>
>>>> You want to replace any soft parts in your oxygen system with oxygen compatible materials where necessary (I.e. Viton O-rings and oxygen compatible valve seats), and then use O2 compatible lubricants exclusively. The gold standard for this is CHRISTO-LUBE MCG 111.
>>>>
>>>> Finally, if you're assembling any tapered thread connections (NPT), use a PTFE or other thread sealant suitable for oxygen systems.
>>>>
>>>> Sean
>>>>
>>>> -------- Original Message --------
>>>> On Jan. 13, 2020, 15:53, hank pronk < hanker_20032000 at yahoo.ca> wrote:
>>>>
>>>> Hi Sean,
>>>> I am installing the O2 paediatric regulator in E3000 now.  I have a tower valve that accepts the regulator, and the valve screws directly into the hull penetrator.  The hull penetrator is a steel nipple.  How do you recommend I clean the nipple and fittings?  I have an O2 braided ss hose to the tank.  The hose is actually from my O2 cascading set up.
>>>> Hank
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>>>
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