Question Valve Question

[Endler's]

I like Thermo better than XS Scuba for two reasons:
(1) Easier to open slowly, because it takes more turns to open.
(2) Larger gap between knob and neck fits my finger while toting. XS Scuba's gap is too narrow and "pinchy".

 

[rjack321]

I like Thermo better than XS Scuba for two reasons:
(1) Easier to open slowly, because it takes more turns to open.
(2) Larger gap between knob and neck fits my finger while toting. XS Scuba's gap is too narrow and "pinchy".

I am the exact opposite lol

The machining on the Thermos is top notch. But I dont like the chrome plating very much and I find it corrodes easily. The crush washers I really dislike and their stock knobs are too long

The DGX valves' chrome seems to survive less than perfect rinsing. The Orings keep water out of the bonnet nut threads. The orings are vastly cheaper and I find this leads me to just pop off the bonnet nut and replace the stem orings more often

 

[SlugLife]

Can valves which come with a crush-washer, be used with an o-ring instead?

 

[rjack321]

Can valves which come with a crush-washer, be used with an o-ring instead?

No absolutely not. They have their own unique sealing surfaces. Which are under full tank pressure when you open the valve.

 

[Tanks A Lot]

Which are under full tank pressure when you open the valve.

Certain Z-Valves have the packing nut under pressure regardless of the cylinder being turned on or not.

Packing nuts that get sealed with a copper gasket will have the threads going all the way to the outer part of the valve. There is no room/groove for an O-Ring

Packing nuts that get sealed with an O-Ring will have a groove cut into the end of the valve where the packing nut will sit. The packing nut will not reach the lower ledge where the seat threads start, so no copper gasket could be placed and crushed there.

Can you be more specific on what the other important areas are that you mentioned?

I would pick my valve according to these things:

1. Is the valve and the spare parts readily available in your region? A valve is no good if you can't service it after a while because you are missing parts.
2. Am I using it on a heavy cylinder and therefore may want a valve that is easy to grip and carry? Or does it sit on a small cylinder which is easy to carry anyway.
3. Do I want a convertible DIN/Yoke, or do I have only Yoke regulators anyway, then I may as well go for a yoke only valve and safe an O-Ring.
4. Do I have a 232bar cylinder or a 300bar cylinder?

Valves from the known manufacturers all have their pro's and cons and only you can really know how that valve is going to be used. As long as you don't go for something sketchy from Alibaba you can't really go wrong.

DiveGearExpress seems to sell normal Thermo valves. XS-Scuba has slightly changed the Thermo valve, with a different packing nut and a bigger handwheel. It comes down to personal preference if you'd like that big handwheel.
I'm not familar with DiveRites valves, but the rather old schematics that I have from them makes me believe that they are not manufactured by Thermo. It looks like BtS could be the manufacturer, but I may very well be wrong on that.

 

[SlugLife]

I was considering doing local VIPs, since I just got the training. I guess I might need a few of these on hand.

Copper Crush Gasket - Made in the USA

john@northeastscubasupply.com

northeastscubasupply.com

I would pick my valve according to these things:

I'm a big fan of the "modular" valves, because they provide a good "handle," and are also great for sidemount. You could also theoretically convert them to doubles or a k-valve if you really wanted to.

I believe the majority of DIN valves should accept an insert, and have a dimple at the back, which lets them be used as yoke-valves, and those inserts are cheap. There are a couple exceptions, like some older Genesis valves I have. IMO, there's almost zero reason to have a yoke valve, even if you have yoke-regulators.

 

[rjack321]

Certain Z-Valves have the packing nut under pressure regardless of the cylinder being turned on or not.

I have no idea what you mean by a "z valve".

The stem packing and the bonnet nut seal are under pressure when the valve is turned on. In theory these will stay under pressure when you turn the valve off but in practice that tiny space eventually returns to ambient as you grip the knob/stem

 

[Tanks A Lot]

Z-Valves are valves that look a little like a Z with a bit of imagination. I admit that they probably resemble the number 7 more than the letter Z. Notable manufacturers include Cressi, Aqualung, Lavo and so on.

In theory these will stay under pressure when you turn the valve off but in practice that tiny space eventually returns to ambient as you grip the knob/stem

This is not quite right, the air bleeds past the threads of the seat, not the thrust washer. If that were the case, certain Z-Valves would empty slowly over time.

The stem packing and the bonnet nut seal are under pressure when the valve is turned on

While true for most valves, certain Z-Valves have the packing nut pressured at all times. This has the big advantage of allowing for a butter smooth operating. The downside is that parts like the spindle cannot be changed unless the cylinder is depressurized.

A cutaway of a ScubaPro K-Valve shows that the seat seals the packing nut and spindle from cylinder pressure when in the closed position. This is a classic downstream valve. Parts can easily be changed, except the seat itself of course, while the cylinder is under pressure.

A cutaway of a Lavo Z-Valve shows a classic upstream valve. The packing nut and spindle are constantly exposed to cylinder pressure, regardless of the valve being opened or not. Seat threads do not stop air, it will leak around them. Parts can't be changed while the cylinder is pressurized.

IMO, there's almost zero reason to have a yoke valve, even if you have yoke-regulators.

The big advantage of a yoke only valve is that they are very tolerant to impacts on the head. A convertible valve is prone to collapse in the G5/8" thread area when a hit occurs. This almost always renders the valve unserviceable, bending the thread back into shape is almost always impossible. Personally I neither would go for a Yoke only valve, but that is because I like the freedom to choose what I want.
As I said before, everyone's use case is different, there is no best valve for every situation. A person that only uses yoke regulators and has no intention of ever changing to DIN, has no reason to not use a sturdier Yoke only valve.

 

[OMyMyOHellYes]

Me, personally, I prefer the copper crush washer. But I try to limit the ever increasing fleet of tanks to Thermo valves on big bottles and Blue Steel on ponies. And they use common parts (until you get to the DIN converter donuts). I have a few bastard XS valves that snuck in more because I inherited them on tanks I bought and so I ordered a few of the orings for them... Would have preferred to stay with the plain Thermo units. But all their cost me was just a rebuild kit. Other XS parts are in common with the Thermo/BS valves. Oh, and I threw away the red light-green light Fornicator knobs in favor of just plain black rubber (the Forincator knobs are too big and bulky to comfortably carry bottles with.)

 

[OMyMyOHellYes]

Can valves which come with a crush-washer, be used with an o-ring instead?

Not really. I tried asking if I could use crush washers on the XS valves. The bonnet nut is a different size and the cast valve stem arm is configured a little differently.

a bag of crush washers is not that much more expensive than the orings in a materiality sense.