Valve stem seals

[Smache]

Recently, one of my tank valves started leaking out of the valve stem whenever the tank was turned on. I fixed the problem with a full valve service, but I still want to make sure I understand the role of each part of the valve for next time. Does this all sound right?

The cavity inside the bonnet nut (5) is pressurized to tank pressure whenever the valve is open. Therefore, there needs to be a seal between the bonnet nut and valve stem (9) to prevent gas from escaping in the hole in the bonnet nut. This seal is made of two parts: the teflon packing washer (7) and valve stem o-ring (8). The teflon packing washer seals against the circular knife edge on the inside of the bonnet nut, and the valve stem o-ring creates a seal between the teflon packing washer and valve stem.

If the teflon packing washer was missing, the valve might not leak at first, but the valve stem o-ring would quickly get chewed up when the valve stem was turned. If the valve stem o-ring was missing, the valve would leak because the valve stem does not have a knife edge like the bonnet nut.

 

[Still Kicking]

"The teflon packing washer seals against the circular knife edge on the inside of the bonnet nut"

This part sounds off. The teflon washer doesn't seal anything; it protects the stem washer from wear (as you said previously).

The bonnet nut is sealed either with a copper crush washer (Thermo) or in XS Scuba's improved design an O-ring (see part #6 above).

 

[tbone1004]

"The teflon packing washer seals against the circular knife edge on the inside of the bonnet nut"

This part sounds off. The teflon washer doesn't seal anything; it protects the stem washer from wear (as you said previously).

The bonnet nut is sealed either with a copper crush washer (Thermo) or in XS Scuba's improved design an O-ring (see part #6 above).

this with the followup that you can do all of the repairs to that side of the valve with the tank pressurized, so that can be considered a field repair. No need to drain the tank before servicing

 

[Smache]

"The teflon packing washer seals against the circular knife edge on the inside of the bonnet nut"

This part sounds off. The teflon washer doesn't seal anything; it protects the stem washer from wear (as you said previously).

The inside of the packing nut does have a ring that leaves a circular groove in the teflon washer. Does that ring serve a purpose?

 

[rjack321]

The inside of the packing nut does have a ring that leaves a circular groove in the teflon washer. Does that ring serve a purpose?

Yes the pressure of the gas seals the teflon washer against the bonnet nut. That raised ring enhances the seal to the bonnet nut. The oring seals between the teflon washer and the stem. In the process the teflon limits the wear on the Oring.

"The teflon packing washer seals against the circular knife edge on the inside of the bonnet nut"

This part sounds off. The teflon washer doesn't seal anything; it protects the stem washer from wear (as you said previously).

The bonnet nut is sealed either with a copper crush washer (Thermo) or in XS Scuba's improved design an O-ring (see part #6 above).

The cone shape of the stem base forces the oring inwards under pressure to seal around the stem. The gas pressurizes the space around the outside portion of the oring and then around the teflon. The raised groove inside the bonnet nut against the teflon is a sealing surface too.

 

[Still Kicking]

Yes the pressure of the gas seals the teflon washer against the bonnet nut. That raised ring enhances the seal to the bonnet nut. The oring seals between the teflon washer and the stem. In the process the teflon limits the wear on the Oring.

The cone shape of the stem base forces the oring inwards under pressure to seal around the stem. The gas pressurizes the space around the outside portion of the oring and then around the teflon. The raised groove inside the bonnet nut against the teflon is a sealing surface too.

True. The handwheel spring also exerts tension on the stem, keeping the oring, washer and nut snug, and hopefully airtight.

 

[johndiver999]

this with the followup that you can do all of the repairs to that side of the valve with the tank pressurized, so that can be considered a field repair. No need to drain the tank before servicing

You would take out part 5 and replace oring 6 under pressure?

 

[Smache]

You would take out part 5 and replace oring 6 under pressure?

Yup! Parts 1-9 can all be removed while the tank is pressurized. The valve seat (10) is what keeps air in the tank.

 

[johndiver999]

Ok but if that seat gets bumped/turned, then you got a jet propelled piece of metal between your legs. I’m cheap but I can afford an air fill, I’m not pulling that piece off when it is pressurized.

 

[happy-diver]

And how on earth would that occur, is that like if she doesn't drown she's a witch, and if she drowns bad luck

and what about the flat stem base, only sealed with PTFE Teflon washers, No Oring and boy are those smooth


AND THEY ARE NOT CRUSH WASHERS, AS THERE IS NO REQUIREMENT TO CRUSH ANYTHING, FOR SEALING