Since penis pumping is a medically-recognized technique for treating ED, they have published guidelines for their use at"
External Penile Rigidity Devices Special Controls Guidance
You will note that the talk about 17 inches of mercury (usually written as
17" Hg ) as a maximum safe vacuum. I've been pumping for about 30 years and have always targeted about 15" Hg as my maximum. I've never had so much as a single broken capillary (which would cause a "spot" bruise or purple spot a fraction of an inch in diameter). But, if you exceed this limit, the likelihood of vascular injury becomes much greater. Pumpers too often fall into thinking that if a little is good, more is better and want to accelerate long-term gains. I can tell you from experience that it only increases danger - it takes months to see noticeable permanent changes and years to gain inches. But, with dedication to a routine and lots of patience, it does work. That being said, I sure wish I had my current size when I was 20 and had a body to match!