Question re: Overturning tank valve back & Regulator

[battles2a5]

Ha ha, sweet! Thanks, Phil

 

[Luis H]

I think the discrepancy that is being discussed could be because not all valves are created equal. Most valves that I have experience with will basically open fully in ½ a turn, but I have noticed that some valves will take more to open.

Some of this may be different models valves, but IMO it is even possible that with a very deep groove in the valve soft seat it may take more rotation to fully open a valve.

 

[PhilEllis]

I think the discrepancy that is being discussed could be because not all valves are created equal. Most valves that I have experience with will basically open fully in ½ a turn, but I have noticed that some valves will take more to open.

Some of this may be different models valves, but IMO it is even possible that with a very deep groove in the valve soft seat it may take more rotation to fully open a valve.

I agree. MOST valves have exactly the same number of threads per inch (in fact, most on the market today have the exact same seat geometry) and would function about the same. Your comment about the groove in the seat is a good one...an issue I didn't consider. Good discussion.

And Ryan, you are still way fast dude.

Phil Ellis
Discount Scuba Gear at DiveSports.com - Buy Scuba Diving Equipment & Snorkeling Equipment

 

[sytech]

I appreciate all the feedback on my inquiry, but here's another question:

In one of my basic scuba books (I think it was in "The Certified Diver's Handbook" by Dennis Graver) he advocates "rolling" open the tank valve all the way and leaving it there with no 1/2 turn back.

My understanding is that the custom of rolling back the valve a 1/2 turn has to do with reducing wear and tear on the valve seat (or something like that) but if that's the case why should I care whether the dive shop has to replace more valve seats if it could compromise my safety?

Comments amigos?

Thanks,


Sy

I was recently in Cozumel and was made aware of the following.

A diver descended to 40 or 50 feet when his regulator stopped giving him more air other than about 2 gulps.

He then shot to the surface (with no injury) and he told me that he was totally out of breath by that time and his next inhalation would have been salt water. (That's why I carry a Spare Air).

Anyway,when he got back on the boat he realized that he had fully opened the tank valve but apparently "rolled" it back more than a half turn and as he descended his air supply to his regulator was vanishing

Can someone explain the physics or mechanics of what is actually happening inside the tank valve as well as the regulator in such a situation?

Thanks,


Sy

 

[keyshunter]

I appreciate all the feedback on my inquiry, but here's another question:

In one of my basic scuba books (I think it was in "The Certified Diver's Handbook" by Dennis Graver) he advocates "rolling" open the tank valve all the way and leaving it there with no 1/2 turn back.

My understanding is that the custom of rolling back the valve a 1/2 turn has to do with reducing wear and tear on the valve seat (or something like that) but if that's the case why should I care whether the dive shop has to replace more valve seats if it could compromise my safety?

Comments amigos?

Thanks,


Sy

I have heard this "save the seat" comment for many years, as well. With modern materials, I cannot imagine damage to the seat unless one really "beefs" into the turn, and maybe not then. But, I still turn it back out of habit. The only valid use I see for this quarter/half turn back is in boat diving. The divemaster can instantly check that the air is fully on a second before his recreational diver launches into the water.

 

[Noboundaries]

Great thread. As a new diver getting ready to leave for our next trip, this sent me out to the garage to do some quick left/right hand finger roll "feel" checks on a tank to ensure the air is turned on. Left hand facing the tank/BCD like at set up and right hand facing away from the tank, sitting on the floor as if I'm wearing it. It was a good muscle memory/feel check exercise.

 

[PhilEllis]

My understanding is that the custom of rolling back the valve a 1/2 turn has to do with reducing wear and tear on the valve seat (or something like that) but if that's the case why should I care whether the dive shop has to replace more valve seats if it could compromise my safety?

Comments amigos?

Thanks,


Sy

HI Sy. I have heard (and I think read) the same thing about "saving the valve seat". This makes no sense, because once the valve is opened, there is no pressure on the valve seat. It is pulled away from the crown and tweaking it back does nothing.

Phil Ellis
Discount Scuba Gear at DiveSports.com - Buy Scuba Diving Equipment & Snorkeling Equipment

 

[battles2a5]

I've been trying to find a reason why people do this. The only thing I can find is that people did this w/ the older style pillar valves to prevent damage in case the valve was knocked. I've never seen the inards of an older valve, so I'm not sure if this is accurate or not. Maybe one of the old guys...er.. veterans on the board can chime in on this one

I did find the following clip on youtube which is pretty cool for anyone who hasn't seen the insides of their valves.

Anatomy of a valve:

YouTube - Anatomia de una griferia - Scuba tank valve anatomy

 

[Jim Lapenta]

One of the reasons I was given when doing ow was that if the DM checks your air and he cannot turn it back, he may think it's closed and turn it the opposite way and just crack it open. Now it's a simple matter to tell them when I get on the boat to not touch my air. I turn it on when I set up my gear, test it, test it again once I'm in the harness, and again just before I step or roll off. BTW I can reach my valve(s). I will teach students to open it, leave it on, and check it before going in, as well as not let any touch one touch it.

 

[Luis H]

I have heard the same about protecting the valve seat, but I believe what has been meant was protecting the stem seal.

Stem seals are mostly two Teflon thick washers now a day, but in many cases there was also an O-ring instead of one of the washers or in addition in some older valves.

Opening the valve and tightening the stem against the stem seal (full counterclockwise rotation) does put unnecessary wear on the stem seal. I have personally seen plenty of Teflon washers that were getting extruded around the shoulders of the stem.

Unloading the stem seal was probably a bit more important when there was a rubber O-ring, but it is just a good practice to not tighten the stem against the seal. It does put unnecessary wear on it (jut like it is not advisable to over tighten the valve closed, it is unnecessary wear on the seat). The need to actually rotate it a ½” turn or even a ¼” turn is questionable.


Oh Phil
Yes, I have noticed that most modern valves (at least the ones available in the US) seem to have the same seats, but that was not always the case and there are plenty of good vintage valves around.

About the seat indentation, I have serviced valves (that the seat was still sealing) with a very deep groove. I don’t know the thread pitch on the seats, but my guess is that in the case of a heavily grooved seat it could even take a full revolution to fully open the valve