Attached is a picture of the typical sealing components of a scuba and SCBA valve.
Item 11 in the photo is the piece that actually connects to the high pressure plug (not shown).
I occasionally saw customer tanks that the knob was difficult to turn because item 9, a teflon gasket was starting to extrude along the shaft of item 11 and out the whole in the bonnet nut (item 7).
Typically when that occurred we usually installed a valve rebuild kit which included all gaskets and sometimes item 11. Why does that happen? Good question. Sometimes it’s clearances or maybe someone turns the air on very quickly and air slams item 9 and eventually starts to extrude around the shaft and the gap in the bonnet nut.
Sometimes you can get away with just cleaning the parts and turning the teflon washer over but it’s a crapshoot, better off using a new one.
No lubrication on the teflon washer/s is necessary as teflon is, well you know, teflon. There is sometimes either an O ring or copper crush washer (item 8) that is also a HP seal and normally are not re-used as they have taken a set from assembly torque. That’s why a rebuild kit is usually the best course of action. I have gotten by without a complete rebuild in emergencies but it’s like when you take your car in for a brake job, they replace some parts that are fine but in the long run it’s a good idea (for the auto shop) because if anything goes wrong an unhappy customer comes back and it has to be fixed on the shops dime, not to mention possible safety concerns.
There are multiple sealing methods for that portion of HP valves that use teflon and O rings or just teflon, you’ll know what you have when you get it apart or can confirm with the manufacturer or vendor where it came from.
Note: With some designs it is possible to disassemble the bonnet section of the valve with pressure still in the tank but it is highly discouraged unless you know the exact design of your valve. It is always better to release and verify all air is exhausted.
