A vacuum pump and an elastic cock ring ("constricting ring") have been approved to treat ED since at least 2004. There is a document, including a troubleshooting guide, posted at the FDA website:
https://www.fda.gov/media/71326/download
In general, the ring is placed at the base of the penis, then the pump is used to pull blood into the penis ... when the pump is removed, the penis will remain rigid. The FDA guideline is to keep the ring on no longer than 30 minutes to avoid "injury" to the penis.
While I don't have a problem with ED, I sometimes use the same procedure, at relatively high vacuum for 10-15 minutes ... getting super big and hard. After removing the pump cylinder, there is a period of enhanced sensitivity lasting 15-20 minutes ... after that, lack of circulation eventually causes numbness (decreased sensitivity) making orgasm difficult. So, if I want to cum, I do it in the first 15 or 20 minutes ... but if I want to just pleasure my partner with a big cock, I can continue fucking but will likely never cum.
My experience has been that using the pump this way several times a week for many years will result in a permanent size increase.