Pumping Physics

Hi all

I’m perplexed as to why when pumping, the cylinder is drawn in to the body harder the stronger the vacuum.

I understand the basic principle as to decreasing atmospheric pressure in the cylinder allows your member to expand further, but why is the cylinder drawn in to you groin when pumping, even when the base has been sealed?

Any enlightenment would be great. Thanks.

The cylinder has a fixed piston (the end or cap) and a moving piston. (your shaft) When you pull air out of the cylinder, the two pistons try to move closer together. Since only the shaft end can move, the tube is pulled down against your groin.

Stretch a condom over the end of your cylinder and begin to pump it up. What happens? The condom expands inside the cylinder forming a condom balloon. That is because the air pressure inside the cylinder is lower than the air pressure outside the cylinder.

That’s what happens when you pump, but your cock and body act the same as the condom, trying to fill the inside of the cylinder due to the pressure differential.

As a career machinist, I laughed at this fantastic reply; well said AndyJ!

To the OP… Another way to look at this is thru the concept of “equal, but opposite reactions”.

For every action, there is an equal, but opposite RE-action.

If I deadlift a 405# barbell, I have also applied 405# to my feet (in addition to my existing body weight).

If you put your penis in the cylinder and apply vacuum pressure, you are pulling on the end of your penis, and depending on the size of the cylinder, with respect to your girth, you are also pulling on the sides of the cylinder.

For the sake of brevity, let’s temporarily ignore the forces on the side of your penis and the cylinder and just focus on the pulling of your glans toward the end of the cylinder… As vacuum is applied, your glans is being pulled toward the end of the cylinder; we could call this the “action”. The RE-action is the movement of the cylinder in the opposite direction. This is also felt by you, as that opposite direction is occupied by your pelvic area.

I hope that is useful.

-Horseman1978-

Thank you all for the responses. I’m always impressed by the collective knowledge on this forum. The piston analogy is very simple.

My confusion was that vacuum is not a pulling force, its nothing. However I’m wasn’t taking into account the positive force the body has ,to cope with earths atmospheric pressure.

Not to sound like a contrarian, but vacuum can most assuredly be a “pulling force”.

Air pressure, be it positive (air compressor) or negative (vacuum pump), is simply a generalized “force”; the type of force generated, is dependent on the design of the system USING that force.

Another way to say it is this; whether that force is positive or negative is not immediately relevant; it’s just “force”. The means of DIRECTING that force determines what I may do with it.

For example, if I hook up a double acting cylinder to operate on compressed air, it will extend and retract on cue as I apply positive air pressure to the appropriate ports. Not surprisingly, I can operate that same cylinder by VACUUM, assuming I attach the vacuum source to the appropriate ports.

The difference will be in the net amount of force I can apply, bit that’s a different discussion altogether.

The real point is to simply say that positive or negative air pressure is not a “pushing” or “pulling” force, but simply a “force” in general.

As an example: The vents, a/c and 4x4 hub engagement system on my old Jeep are all operated by vacuum cylinders. They are all required to create a pulling force.

Cheers,

-Horseman1978-

The vacuum pump is creating suction.

From Freedictionary.com:
Suction- 2. A force that causes a fluid or solid to be drawn into an interior space or to adhere to a surface because of the difference between the external and internal pressures.

It just works.

What?

Pumping, it just works.

Nah, it was the fixed point part that tripped you up. The piston analogy described that really well.

To understand it, change the perspective. In reality, he cylinder is not being pushed against your groin. Rather, by decreasing the internal pressure of the cylinder, you are being sucked in. Since you dont fit inside the tube, only the surrounding area of the penis is sucked in.

Picture breaking a window on an airplane at 38,000 feet of altitude. What happen? The window sucks everything out, including people, because the pressure outside is way lower than the pressurized cabin.

A more radical scenario, space. If you got out the hatch on a space suit into empty space and suddenly you open your helmet, you die instantly due to 2 things: low pressure and freezing temperatures. Basically as soon as you open the helmet your eyes, ears and every single orifice in your body explodes instantly and a second later you are frozen like a rock. But the point is, pressure. In space is so low that all your internal blood boils and explodes violently out of any way it can find in your body in a fraction of a second.

Instant death from zero vacuum in space only happens in Hollywood. NASA testing indicates you could survive zero vacuum for a couple of minutes.

Survival in Space Unprotected Is Possible—Briefly - Scientific American