I go into mine at 100%, watch adult entertainment to keep it going while i pump. When i release pressure I'm always about 75% when i exit, but a couple of kegels and some light jelqs it's back up towards 100% again.
i always come out softer once i remove the pump. i'll stay pumped a bit after but unless you are watching adult entertainment or something to maintain your erection physiologically while pumping once you take it off and the blood flows out you will go soft. the vacuum pressure is just holding the blood in the penis. that is different from a real erection