Vintage Double Hose

(In an effort to keep the "NEW PHOENIX OWNERS" thread on it's intended course, I am moving this discussion here, even though it probably is nearly concluded. It is here for the benefit of anyone who has been following the discussion.)

duckbill wrote:...the higher the legs of the horseshoe where they contact the fingers of the diaphragm plate, the more the friction between those two surfaces during operation.

"...the more the friction ..." is not true, but my intended meaning is, as explained below.

luis wrote:When I analyze the geometry, I can’t see how you came up with such a conclusion. Do you care to explain?

duckbill wrote:So, it should be apparent that the more vertical a lever is, the more the lateral movement for any given vertical motion applied to the tip of the lever arm (like a horseshoe). The least lateral movement occurs when the lever is horizontal.

Friction in this case occurs whenever the tips of the horseshoe must slide across the tabs of the diaphragm.

luis wrote:As you can see the magnitude of the friction force is not affected by the distance traveled.

Luis, I see my error and why you called me on it. In trying to keep terms simple in my original comment, I used the term "friction" in a generic sense.

You are correct to say that "the magnitude of the friction force is not affected by the distance traveled."

I understand that the coefficient of friction (related to the materials and surface conditions) and the force (related to the pressure acting upon the diaphragm and the resultant lateral force under discussion) are not affected by the distance traveled (lateral sliding movement in this case).

However, what does change with the distance traveled is the work involved. As you know, work is the product of force and distance traveled (effective displacement). So, for a fixed coefficient of friction and force, more work is involved the more distance the surfaces travel against eachother. It is this work that should be reduced or eliminated, if possible, to help enhance regulator performance.

Reducing the work in this case can be achieved by:
a) Reducing the angles involved to as near parallel as possible i.e. the horseshoe as near parallel to the diaphragm as practically possible (no "bending" up).
b) Reducing the coefficient of friction by polishing the surfaces where they slide past eachother.

That is what I was trying to get across, hopefully in more accurate terms this time.

I love brain teasers, engineering, and analytical problem solving (when I have time), but I have no formal engineering training. I apologize that the terms I use are not always technically correct by definition. At least I know what I'm trying to say

Duckbill

I appreciate your interest on the mechanics and physics involved in diving and in particular the functionality of the demand regulator (since I share the same interest). For the benefit of everyone involve, we need to be very careful at what we present as being fact versus opinions. I make mistakes as anyone else, but I always try to distinguish what I know as facts versus my opinion. On the other hand, I am sure that I am also not always clear.

Some examples:

Facts:

• "the magnitude of the friction force is not affected by the distance traveled."
• “work is the product of force and distance traveled”

The above examples are generic factual statements.


This statement:
“It is this work that should be reduced or eliminated, if possible, to help enhance regulator performance.”
I believe this is just your opinion, since there are no numbers or magnitudes indicating the importance of this effect. Now IMO I think this is a minor effect and I hope to provide some reasonable numbers and calculations in the next few days or weeks.

Lets not confuse the work described above with the “work of breathing” (WOB) used now a days to describe regulator performance. Most of the “work” during WOB testing occurs when the demand valve is already open (and not necessarily moving). The WOB is the product of pressure/ vacuum multiplied by the flow rate (equivalent to force multiplied by distance).

Part of the empirical reason I have to believe that the effects of sliding friction has been blow out of proportion is my experience with the Poseidon Cyklon regulator. The Cyklon has a compound linkage were a couple of joints rotate, but no lever slides against the diaphragm. It performs well, but it is not the magical answer.

In any case my main point is that some of my statements above are just my opinion.
I am not saying that the effect of friction can be ignore, but the magnitude of its importance needs some numbers (or literature research) to back it up. With some numbers I may prove that my opinion was right or wrong. After all, at this point it is just my educated guess.

Until I have more time to do some more calculations and explore this further, there is no point in me debating this further.
BTW: I have done a little bit of analysis (not enough yet), but the more time consuming is going to be putting it in a presentable form.



The main purpose of this post is to remind us all (very much including myself) that we need to be very careful about distinguishing what we think it is the true or our opinion, from what we know to be facts (and can back up if need be). I am sure you will agree that confusing facts with our opinions would be a big disservice to everyone.

Heck… if we mix our opinions with facts and present them as fact, we might as well be posting over at ScaryBoard (I mean ScubaBoard)

I would like to add that I do appreciate your opinion as well as the opinion of must of the other members of these boards (including VDH, VSS, and even many of the members in ScaryBoard ). It is just that I think that some times I feel that we need to make it clear that it is our opinion.

I believe this to be particularly the case when it involves science, technology, and related engineering subjects; since an assertive statement from some of us can be easily interpret as an undisputed fact. This in turn can be very misleading and perhaps in some extremes dangerous.

To add a bit of my thoughts on this subject. I haven't closely studied it but it seems that because of the rounded shape of both the tabs on the diaphragm and the ends of the horseshoe in the AquaMaster that the motion between them is more of a rolling motion than sliding. This design may have been done to correct what I see as a problem in the earlier DA horseshoe which had two square edges where it contacted the diaphragm. I have had some improvement in the old DA Navy Approved by rounding the two square edges.

Luis,

I'm sorry you consider this a "debate". I thought I had brought the differences to agreement when I acknowledged and corrected my faulty wording regarding "...the more the friction..."


Just for fun, here are my responses to the new points which you have made:

luis wrote:This statement:
“It is this work that should be reduced or eliminated, if possible, to help enhance regulator performance.”
I believe this is just your opinion, since there are no numbers or magnitudes indicating the importance of this effect.

Keep in mind that opinions in and of themselves do not make a statement false just because a person doesn't have equations or quantities to prove their statement. Unqualified or unquantified opinions can often be "known" (by loose definition) to be true based on common sense and past observations.

For example:
I don't need an equation to "know" that an object which is heavier than air will fall when dropped from a rooftop (assuming no wind, blah, blah..).
I don't need an equation to "know" that I can help to improve my car's gas mileage if I remove the drive belt to my air conditioner compressor and/or lubricate dry wheel bearings.
I don't need to have specific quantities to "know" that in a+b=c, ab=c, a/b=c, "c" will always increase in value when the value of "a" is increased and "b" remains unchanged.
I don't need an equation or numbers to "know" that a regulator will move more freely if less friction must be overcome during it's work cycle.

luis wrote: ...since there are no numbers or magnitudes indicating the importance of this effect......Now IMO I think this is a minor effect...

That is what I have been saying all along (words denoting opinion in bold type):

duckbill wrote:Does it really make a difference, when it comes to regulators and performance? Probably not, UNLESS:...

duckbill wrote:I would guess that making sure the diaphragm tab ends and the horseshoe fingers are polished as smooth as possible would be more important than worrying about the angle of the horseshoe.

duckbill wrote:The angle of the horseshoe will just add lateral movement to the ears as it is raised further from horizontal, but I don't think that at the angles we're talking about that it amounts to much at all.

luis wrote:Part of the empirical reason I have to believe that the effects of sliding friction has been blow out of proportion...

Not by me. (See my quotes above)

luis wrote:Lets not confuse the work described above with the “work of breathing” (WOB) used now a days to describe regulator performance.

I agree. Performance of the regulator is one thing, like quantity of air available at depth, etc.

However, to clarify, isn't WOB directly related to overcoming any resistance of the working parts within the regulator?
And, isn't a reduction of anything hindering movement of these parts beneficial to WOB?
And, while performance and WOB are separate issues, couldn't a change in the mechanics of a regulator affect both?

luis wrote:... and I hope to provide some reasonable numbers and calculations in the next few days or weeks.

That would be great. I, for one, am looking forward to learning from it.