Penis pumps work to pull more blood into the penis than would normally be present during engorgement resulting from sexual arousal. The result is a slightly larger, firmer penis that is more sensitive to contact. This enlargement is not long-lived, and there is no evidence that a man can permanently enlarge his penis by repeated use of a pump.
However, you can maintain the enlargement and sensitivity longer by fastening a erection ring around the base of the penis after the pump has been used and the maximum amount of blood has been pulled into the penis. The erection ring will slow the blood flowing out of the penis, so the enlargement can remain longer. To prevent damage to the blood vessels, we do not recommend that you wear a erection ring longer than 30 minutes in this circumstance.
This method also works for a penis with a less-firm erections due to medications or the effects of aging. Again, we recommend only wearing the erection ring for a maximum of 30 minutes, to avoid any damage.
There are stories of penises who have permanently damaged their penises from over-pumping, stretching out the skin and ligaments. As with anything, moderation is the best way to experiment with a penis pump.