Pressure in the penis

After reading in another thread about how a pressure of 1500mm Hg (29psi)can rupture the tunica, I started wondering what sort of pressure different PE techniques can generate.

Clamping seems the technique that can produce the highest internal pressure. Since human blood pressure produced by the heart is only around 120mm Hg (2.3 psi) to get a good erection the penis is filled with blood and then “sealed”. Now since blood is a virtually incompressible liquid any applied force constricting the penis will result in an increase in the internal pressure in the penis. Using the PC muscles to kegel in more blood is also good for raising the pressure.

When manual clamping with just the thumb and forefinger grip at the base of the penis how much pressure build up can be generated? I know that if I use the remaining four fingers to squeeze in a whole hand grip I would never squeeze at maximum strength because I intuitively know the pressure is too high.

I would be interested to know how much internal pressure the human grip can develop by sqeezing a flexible, phallus sized, fluid filled object. The experiment should be easy to conduct for anyone with a pressure gauge and a flexy tube. It would also be interesting to see what pressure a cable clamp generates. Anyone fancy carrying out the experiment - if not I guess I’ll have to find a pressure gauge and try it myself.

HuWa! Good one mbuc! I am definitely interested.

Come ‘on, somebody break out your pressure gauges!

I’ve just blown the dust an old stress analysis text book and found something that might interest the PE community.

Basically it’s this - pressure inside a thin walled tube creates an axial stress and a circumferential stress on the wall of the tube and (here’s the interesting bit) at any given pressure the circumferential stress is twice the axial stress.

No wonder pumping, clamping and Uli are better at gaining girth rather than length!

Don’t forget jelqing too, mbuc. When you think about it, jelqing is basically just forming a weaker and movable clamp compared to a standard clamp (which is intended to be strong and immovable), so it would also make sense that jelqing is primarily a girth-gaining technique.

How so? The pressure is the same in all directions, so how does the stress differ? Are our dicks the same as the thin walled tubes described in your book?

Flip is using a brake-fluid pump, and pumps until the vacuum no longer increases.
This results in the occasional (blood) hickey.

Does anyone know what is the approximate vacuum that these pumps can create (it is a plastic one) ?

Flip never has pain during pumping, only mild discomfort.
So it seems that the pump will not reach 1500 mm Hg,
or that Flip has a tunica made of steel.

Flip thinks the last is true, in view of his extremely slow gains…

Hobby, the thin wall I would say was the tunica holding together the internal penile structure. During an erection (or when artificially creating pressure) the tunica behaves like a thin walled tube containing the pressure.

The proof and derivation of the axial and circumferential stress are made in general terms for any thin walled cylinder under internal pressure.

When a thin walled tube is subject to an internal pressure, p, then the axial stress at a point on the tube can be calculated as being pr/2t where r is the tube radius and t is the thickness of the tube wall.

Similarly at the same point the circumferential stress can be calculated as being pr/t.

In other words, although it may seem counter intuitive, at any given pressure, the tube wall is twice as highly stressed in the circumferential direction as in the axial.

Why would the thickness of the tube wall have anything to do with the stress applied?

I’m also noticing that pr/2t is in units of pressure. Shouldn’t stress be in units of force?

http://dvsun3.g kss.de/Themen/W … EngMech2004.pdf

This problem is discussed at page 55. I’m still reading.

Pressure of a fluid is not exerted equally in all directions, force is. Pressure is dependent on the amount of force and the amount af area in which the force is applied. In your penis, there is more circumferential area than axial. Therefore more circumferential pressure.

Tritium,

Mechanics isn’t my area, but I think that’s backwards. Pressure is the same in all directions, but force depends on the area over which the pressure is acting. Say you have a pressurized container that has a hole in it of area A. If the hole is plugged, the force exerted on the plug is P*A. The units work out.

If you double the area, the force becomes P*2A.

The pressure inside the tube exerts an equal force on every square inch of surface area of the tube. But that’s not the issue. THe issue is what axial stress and circumferential stress those forces cause. That has to do with the geometry of tube. So, I’m starting to see how this is possible.

Good find, Mbuc.

MM, your link in post#9 contains exactly what I’m talking about on page 51 sect. 8.4 . It even states that the axial stress is half the circumferential for any given pressure and gives the same formulae for calculating them.

Edit: Stress and pressure are both measured in the same units, force per area

I highly doubt anyone can gather up 29 psi. with a clamp, I would think there would be warning bells going off when someone even flirted with the possibility of blowing out the tunica. I have 100% faith that with common sense and the ability to listen to what your body is telling you, it is next to impossible to suffer such a injury without ignoring the alarm system.

AH

The total axial force on a thin walled tube which causes the axial stress on the wall of the tube is simply the cross sectional area of the tube times the pressure.

Imagine an erect penis. The blood pressure alone is causing the elongation and circumferential expansion of the penis. Once the penis is engorged to its erect state the tough fibres of the tunica resist any further expansion.

For a penis of diameter 1.5” with an internal blood pressure of 2.3psi (120mm Hg mercury) then the axial force on the tunica (assuming it takes all the pressure) is 3.14x0.75x0.75x2.3 which equals roughly 4lb. This force must be great enough to fully extend the penis to its erect length.

From experience of hanging in a flaccid condition I can confirm that 4lb is ample to axially stress the penis to the point where the tough fibres of the tunica resist any further easy elongation!