Well that was a heck of a read… a lot of great ideas were thrown in the mix, even if the majority of this thread wandered off the titular subject. A number of concepts sound brilliant, but I noticed a few conclusions based on misconceptions and faulty logic.
I’m not going to appeal to my education or knowledge; if anyone has a grasp of mathematics and physics, my take should make some sense. My numbers may not be perfectly accurate, but the argument is relative. I just want to show how pressure works. To be honest, pudendum’s conclusions were fairly close, but the take away probably should have been "proper jelqs are better than either clamping or pumping", which may be somewhat ironic.
PRESSURE
The first thing that needs to be cleared up is how little difference there is between the two mechanisms (and please catch me if I overlook something here). The tunica is a membrane which is always subject to pressures… on both sides. The atmosphere is about 30 inHg. Human blood pressure is 120/80; in inches that’s 4.7/3.15 inHg. That means (in a healthy human at rest) there is always around 33-35 inHg on the inside of the penis and 30 inHg on the outside. This is just enough to maintain a flaccid hang of what is a fairly sturdy but flexible organ.
Now, when pumping, there’s no "pulling" involved, the only thing that changes is that air pressure drops from baseline atmospheric (29.9 inHg). I think the most common pumping amount I’ve heard is ~3 inHg, so if we were pumping flaccid at this level, it would look like this:
33-35 inHg >|< 27 inHg
If we introduce an erection, the internal pressure will increase as well, creating a greater differential pressure. I couldn’t find an absolute answer for this, but according to this thread - Erectile Pressure - an erection is about 6 inHg. Since the erection is mainly isolated (the CC no longer has a pulse) we have this:
36 inHg >|< 27 inHg
Now we kegel! According to the Lavoisier study quoted earlier, from "Journal of Urology 136 (1986)", the kegel was measured to increase pressure between 4-22.6 inHg. Therefore, suppose our incredible athlete can produce this:
58 inHg >|< 27 inHg
If we replace the pump with a clamp, there are only two changes. The easy one is external pressure, which is neutral again (atmospheric pressure). The "hard" one is the function of the clamp as a fulcrum, which I don’t have the math for, but from experience we know is quite significant. In this case:
58+? inHg >|< 30 inHg
Again, the numbers are not critical. The point I want to drive home is whether you clamp or pump, you are simply tipping the balance of pressure, which exerts directional force on the tunica. It’s irrelevant whether you are "pulling" or "pushing" the compliance of the tunica only effects how much it expands (and thins and tightens etc.), not how much force it is subject to. pudendum also made mention of the pressure dropping inside the CC because of this volume increase, but this is also irrelevant. The pressure created inside is limited by the strength of your ICS muscle, which is the same whether your girth is 4" or 7".
FLUID - Though it’s been mentioned and I think most will say it’s a lesser issue, it bears summary. I believe that fluid is inevitable and variable depending on your methods. Some people get more with pumping and some more with clamping. I get it at the base near the clamp, but I think it’s because I’m always edging and accidentally pushing it downward! Others probably get a lot less clamping because the clamp isolates the penis from the body more so than the pump… with the pump it just leaks in from more directions. The bottom line is both clamping and pumping produce a pressure differential from the circulatory system to the extra-cellular spaces, so both can produce edema.
COMPLIANCE
The second misconception that must be addressed is the notion of working on the tunica while it is compliant, i.e. "pumping with a semi" etc. I think pudendum hit on something critical here, but he seemed to have misinterpreted it.
The penis has fibers that run lengthwise and fibers that run circumferentially. Sure, they are coiled up when flaccid, but to gain erect length and girth, they must stretch or grow longer, there is no other mechanism unless somehow your elastic fibers are so strong you never actually have 100% erection (which would technically be a genetic defect if it is even possible). Whether lengthwise or girthwise, we must apply tension to those fibers. Just like stretching a spring with a given amount of force- the spring extends and compliance drops until a balance is achieved or the spring breaks (please god no). Now pudendum’s conclusion that we must aim to over-stretch our girth without stretching lengthwise is probably very good insight, but this cannot be achieved in a cylinder unless there is something mashing down our glans (like the dishrag analogy… the pump is that other guy pulling the mesh lengthwise), forcing all expansion in a radial direction. Therefore I’m not sure I see the benefit of pumping semi… the tunica can still be pumped to an over-extended dimension (like the spring), but the only difference is the internal pressure will be lower, since you are trying to create a pressure differential with the entire circulatory system rather than a closed tunica (not to mention kegelpower…).
I think our biggest takeaway should be that jelqing is still technically a better mechanism for growth, and clamping and pumping are only more effective because most of us have weak hands. When we jelq, and draw that wave of pressure is along the tunica, we are not only stretching those fibers in both axes, but possibly "de-tangling" or "limbering them up" in a way. This may not sound very scientific, but I suspect it is what’s going on in there. Also, I would suggest that jelqs stimulate growth much like the ellipse action under a clamp… only the force is applied from base to glans.
In other words, my take is the majority of the thread went off-topic to reinforce the usefulness of jelqing skill, and the difference between clamping and pumping is small. Do whichever is easier or effective for you. Personally, after a year of clamping I’m going to shift back to jelqing… as much as I have the strength for.