Mounting tanks upside down

[TRUETEXAN]

Hey Pipedope,
How in the hell do you get into an 18" pipe?? I am very interested in what you and all commercial divers do, my next door neighbor is an underwater welding specialist and he works on the offshore drilling rigs but only for a couple months out of each year, and the stories he tells sometimes are very interesting. I was wondering if there are any web sites on the type of diving that you do, and did ou have to go to one of the commercial dive training agencies to get trained for what you do?

 

[Divesherpa]

Roak,
You've got quite a drive to these warm water holes I fill my day in. How's the lakes this time of year? See any good trout recently.
Ha ha

Anyone who spends time in Cow is alright in my book, unless that's your handprint,


Cheers

 

[roakey]

Originally posted by Laurence Stein DDS
Whew! You beat the c--p out of me. I will admit to being bad at math at 6 in the morning if you can admit you can't read. I am NOT an instructor. Put downs kinda p--s everyone off don't they!

Your initial post had an incorrect statement. I corrected it and made several points, the most significant of which is that you had it backwards (with the 1st stage lower in the water column the IP would be higher and therefore make breathing easier).

Your next post continued to posit the same theory, completely ignoring the fact that I had pointed out that it was backwards, which can only mean one of three things:

You didn’t read what I said.
You didn’t understand what I said.
You completely ignored what I said.

So the first time I pointed you in the right direction. When that failed I lined the path with flashing neon signs.

If someone disagrees with you, read what they said. There’s always the remote possibility that they’re right.

Roak

 

[roakey]

Now for your third post...

Originally posted by Laurence Stein DDS
I contacted a really great scuba shop locally. First, the position of the first and second stages DOES affect breathing. Both the repair staff and an instructor said the same thing. Maybe you want to chew them out too. Next, inches of water used to measure cracking pressure and calculate the work of breathing is still a measurement of pressure...as in pounds per square inch. It can be converted to pounds per square inch This is NOT apples and oranges. It is simply a convention used for this type of measurement. Keep your "noise" for your electrical, radio and stereo measurements.

Ok, I’ll have to assume that you’re simply ignoring what I'm saying because I said “forget what the shop told you” and you went and asked a shop. Hang out in the technical forum and/or subscribe to some technical lists and you’ll quickly find that the number of “really great scuba shops” starts to asymptotically approach zero. It’s not zero, but it’s darn close. One of the major problems in the scuba industry is that it preys on naive customers. For the few customers that become well informed, many shops no longer look so great. I’ve heard horribly incorrect statements from staff and instructors. Make no mistake about it, they’re some good ones, too, but being a staff or instructor does not mean that their word is taken without question.

Chew them out? No. If they made an incorrect statement on this board, I’d point out why it was incorrect (I don’t argue from authority, I give reasons). If they stated it again I’d use a bigger hammer.

Now, onto your post. First problem is that you confused the issue by saying, “the position of the first and second stage DOES effect breathing.” Of course the position of the 2nd effects breathing, I’m only addressing the specific point where you stated that slight changes in depth of the 1st stage would be reflected in breathing effort. This, and only this is what I’m addressing, so keep in mind that my topic is very, very narrow.

Of course inches of water and PSI are apples and apples. However, comparing cracking pressure to the IP is like saying that applying 1 pound of force to a hydraulic jack handle creates 1 pound of lift on the lifting side. You can’t compare the jack handle pressure to the lifting pressure because there’s a whole hydraulic/mechanical system between the two. THAT’S why I say it’s apples and oranges to compare cracking pressure to the IP.

So, since the flashing neon signs didn’t work in my second post, let’s go through it step by step.

The 1st stage reduces the gas in the cylinder to about 130 PSI over ambient pressure. This is the intermediate pressure or “IP.” The 2nd stage reduces the 130 PSI IP to ambient pressure. To keep the valve closed, you have a spring inside the 2nd stage that’s exerting 130 PSI back against that IP. So you’ve got 130 PSI of gas pushing on the valve face via the orifice and you have a 130 PSI spring pushing back keeping it closed. In a perfect world any amount of force applied to the valve would open it in this situation. Now let’s put the 1st stage three feet (1.5 PSI) ABOVE (not below as you were arguing) the diver and see what happens. The IP drops to 128.5 PSI but the downstream valve’s spring is still pressing back with 130 PSI of force. So at first blush that’s a 1.5/130=1% increase in work of breathing, not 10% as you initially stated (as well as claiming that the % would change with depth, which it won’t, since the IP is a fixed pressure above ambient).

But wait. There’s a lever or fulcrum associated with the arm that goes from the 2nd stage diaphragm to the valve. In very simple regulators it simply tips the valve to open it. There’s a lot of travel of the diaphragm and very little of the valve itself, resulting in a large mechanical advantage. An off the cuff guess would be a 10 to 1 advantage. So that 1% has now shrunk to 1/10 of 1%.

In other words, noise.

This is why, as I stated, we can leave the 1st stage topside while we’re working in the Aquarium exhibits without a problem. The fact that pipedope can go down 75’ with this setup came as a shock to me. I knew the system was somewhat insensitive to variations in IP, but I had no idea it could tolerate THAT much of a delta (IP about 30PSI too low!)

So pipedope’s datapoint gives me an idea for an experiment you might want to try. Drain a cylinder to 100 PSI and put a regulator and try breathing off of it. This will make the IP 30 PSI too low, just like pipedope at 75’ and you can see first hand how having a delta of 75’(!) between the 1st and 2nd would effect your work of breathing.

Originally posted by Laurence Stein DDS
However, there must be a logical reason why the majority of dive set ups are valve up.

I didn't see you, roakey, coming up with any logical reasons.

You’re absolutely correct, because that wasn’t the issue I was addressing.

Now for an aside.

Are you interested in testing your shop? It truly may be a great one, but this could help you find out. Here are a couple questions. If the questions are answered correctly it won’t prove that they’re a great shop, but if answered wrong will tell you that they’re not so great. I believe in the medical world you would state that this is a test that can produce “false negatives.” Just ask them these questions and don’t let them research them. They really are quite simple and a really great shop will know them.

Ask to speak with their PSI trained cylinder inspector.
Ask how long ago they were trained.
Tell them you have a five year old Pressed Steel cylinder that needs a hydro. Ask how do you go about keeping the plus rating to get the 10% overfill you’ve been getting since it was new.

That’s it. Tell us what happens.

Roak

 

[neil]

"Dammit, Jim!! I'm a DOCTOR, not a fluid dynamics expert!!"

Larry "Bones" Stein, DDS

(name used completely without his permission, but he's a mensch and will approve, no doubt)
Neil

 

[roakey]

Originally posted by Divesherpa
Anyone who spends time in Cow is alright in my book, unless that's your handprint

Heck no! Not my handprint! My greatest amount of stress in a cave is over making sure I don't touch ANYTHING. In Akumal we were in some very tight passages (for back mount, belly-and-tank-rubbing-at-the-same-time stuff) and despite the area around the line already being pretty beat up, every time I touched the cave I'd curse myself.

Roak

 

[devjr]

The aquamaster two hose reg was fitted with a 1/4" oxygen nut for attachment of hooka hose. This was fed by a regulated supply from the service. I doubt that setup could be used confortably below 30 feet unless the supply pressure was stepped up. The famous Teddy Tucker of Bermuda used a rig like that to salvage treasure. Mostly, he seemed to work at depths of around 20 feet. It seems to me that today's hooka diver would want to use an adjustable second stage, tune it for lower effective supply pressure (free flow) and use the control knob to regulate breathing effort.

PS to "roakey": The force exerted by the diaphragm is related to its size. Force multiplication is proportional to the square of the radius.

 

[roakey]

Originally posted by devjr
PS to "roakey": The force exerted by the diaphragm is related to its size. Force multiplication is proportional to the square of the radius.

Right, I completely agree. I assume that this statement is in response to my reference to a mechanical advantage.

The mechanical advantage I'm referring to however is not the force exerted upon the lever by the diaphragm, but the mechanical advantage of the lever on the valve.

Roak

 

[Laurence Stein DDS]

Roaky,

You know, you have a real anger management problem. Don’t ever become an instructor. You are NOT instructor material. You lack tact, patience, intuition, respect and manners. You certainly did not teach me anything. However, you made yourself look like a giant jackass.

I would be very careful about who should be contacting the Regulators. They might pull you because you’re mean and you give this forum a black eye. Now everyone is laughing at YOU, you putz.

Unlike your response, devjr and Uncle Pug were gentlemen. I learned something from them. I learned that all that stupid junk about noise really had nothing to do with the way a regulator breathes. I presume you didn’t know either or else you would have tactfully taught me what I needed to know. I also learned a great deal about you as well as all those who read your tirades and insults.

I used to know people like you when I was in grade school. They were called bullies. I think it would serve everyone’s best interests if you would stay off the forum for a while.

Get some help soon.

Sorry Neil, I can only be a mensch so long.

Larry Stein

 

[Uncle Pug]

Originally posted by Laurence Stein DDS
Roaky,
Get some help soon.

Ohhh...Larry....
Cut him some slack....
Roaky is one of the good guys....
He's just kinda crusty right now cuz he's all dried up...

You see for a guy of his caliber diving in an 8' deep tank just doesn't give him the soakin' that he really needs.

I think we ought to take up a collection and send him to Florida for a few cave dives... or ship him up here to the PNW and I'll take him through Deception Pass for good old churnin'.