Slow Opening O2 valve

[cathal]

I should also add that the opening action of the Nautec O2 valve is practically binary in type. Either it immediately opens or closes. You need a fine gradual opening action for use with O2, like a needle valve, and the AP are so much better in this regard.

 

[Akimbo]

You need a fine gradual opening action for use with O2, like a needle valve, and the AP are so much better in this regard.

True in theory but solenoid and demand valves are exceptions. They are considered acceptable when they discharge to ambient pressure and are not HP, thus much lower velocity.

This subject came up during my saturation training in the US Navy. Engineers in Washington DC did a bunch of calculations that OK'd it. This was in the early 1970s so everyone was very concerned after the Apollo and NEDU fires. The O2 solenoid was mounted at the control console and discharged into about 50' of tubing with a venturi diffuser at the end inside the chambers.

Oxygen feeding the BIBS (Built-In Breathing System) demand valves was a similar situation but the differential pressure was even lower than the metabolic Oxygen makeup system.

Rotating spindle valves with needle seats (needle valves in the US) are highly recommended for HP Oxygen valves that discharge into long tubing runs where rapid equalization can occur. It is all about contaminants being heated to combustion temperature by aerodynamic resistance — analogues to high speed objects entering the earth's atmosphere from space.

 

[mr_v]

Oxygen fire safety. The objective is to minimize high velocity gas flows that can pick up particles, typically metallic particles, and accelerate them to speeds that heat them cherry red. Secondarily, it is to minimize heat buildup due to rapid compression.

High pressure Oxygen's unique properties can cause materials that are normally incombustible to oxidize at very high rates, which is what a fire or explosion is.

Yep, we are all about safety here. But.. would you not be able to achieve the same thing by opening your valve slowly? I guess, what I am really asking is: are the slow opening valves THAT much better?

 

[cathal]

But.. would you not be able to achieve the same thing by opening your valve slowly?

Not really, some manufacturers use thread types that do not allow for a gradual release of O2 into the HP line. You need a fine the thread type, so that the seat iincremently unseals.

 

[Akimbo]

But.. would you not be able to achieve the same thing by opening your valve slowly? I guess, what I am really asking is: are the slow opening valves THAT much better?

Fair question. Oxygen fire safety is a continuum rather than binary OK/explosion. Measuring and controlling all the variables is difficult so the recommendations and practices tend toward the safest in order to make up for some of the unknown or unforeseeable variables.

Obviously the vast vast majority of time using a fast operating valve is fine as demonstrated by the millions of times it is done without an explosion or fire. The Oxygen charging system at the UDT/SEAL base in Coronado operated fine for years with 1/4" ball valves — until it blew up in the early 1970s.

Valves are measured by the Flow coefficient or C_v. Most rotating spindle valves used in Scuba diving have flat seats:

I couldn't find a C_v chart for this valve but flat seat valves' flow looks something like this:

Needle valve seats are more like this:

Needle valve seat C_v curves are much flatter, meaning the percentage of the valve's flow is more proportional to the number of turns of the spindle.

 

[mr_v]

Fair question. Oxygen fire safety is a continuum rather than binary OK/explosion. Measuring and controlling all the variables is difficult so the recommendations and practices tend toward the safest in order to make up for some of the unknown or unforeseeable variables.

Obviously the vast vast majority of time using a fast operating valve is fine as demonstrated by the millions of times it is done without an explosion or fire. The Oxygen charging system at the UDT/SEAL base in Coronado operated fine for years with 1/4" ball valves — until it blew up in the early 1970s.

Valves are measured by the Flow coefficient or C_v. Most rotating spindle valves used in Scuba diving have flat seats:

View attachment 733857


I couldn't find a C_v chart for this valve but flat seat valves' flow looks something like this:

View attachment 733860​

Needle valve seats are more like this:

View attachment 733859

Needle valve seat C_v curves are much flatter, meaning the percentage of the valve's flow is more proportional to the number of turns of the spindle.

Thank you so much for this info. Now, this totally makes sense.

 

[Akimbo]

Just to close the circle on the needle valve discussion, some are designed to to have super linear C_v curves such as those with veneer micrometer handles.

Very flat C_v curves are also useful in computer controlled applications for blending to reduce "hunting" by the controller. They can also be useful in manual and semi-closed rebreather applications using continuous flow.

 

[Brad_Horn]

Valid to the topic as it provides clarity for why suddenly a couple of rebreather manufacturers started offering progressive opening Oxygen valves A technical diving-related burns case: treatment in a remote location