That's a really good question, and I was considering starting another thread to address this issue. For me, 5hg is quite low. Even 10 is just a good pump. But then, I've been doing this for decades and most often without a gauge to show exactly how much hg is being applied. That said, I have been using the X40 off and on for several years and I know that by simply using the built in pump, the pressure is not enough to cause problems. But, if you utilize the vac-vin (a wine pump used to pump air out of an unfinished wine bottle to help preserve freshness), then you can achieve very high levels of vacuum. it's not measurable because there is no gauge, but based on what I have experienced with the new Provac cylinder (and this would apply to the regular mityvac cylinders as well as your vacutech cylinder), and with the use of a hand pump with gauge, you can easily achieve pressures exceeding 20hg, which is very high. Is it too high? I don't know. I've done it many times, and other than some fluid retention and light bruising, I've experienced no major injury. Still, caution is key, and everyone's vascular penile structure is different. I would recommend lower levels, at least at the beginning, to see how your dick reacts. Injury is not conducive to gains and will, if anything, set you back. Now that I have the Provac cylinder and my own hand pump with gauge, I may be a little less, shall we say, enthusiastic? I should point out also that relying on a pump for girth gains may be an easy-way-out delusion. In my early years of PE, I used only pumps, because that's all that was available. I was able to achieve great girth increases, but they were always temporary. It helps, for sure, but in my opinion, the manual work ie jelqs, uli's, compression squeezes, clamping (with caution)etc. are the foundation of girth building.
