Vacuum devices are small pumps attached to a cylinder you fit around your penis. Air is pumped out of the cylinder to create a vacuum, and the lowered pressure increases blood flow into the penis. The blood is trapped by rolling a special rubber ring down to the base of the penis.
More fashionable versions of these rings, made from metal or studded leather, can also be bought from sex shops, if it appeals to you to make the intervention less clinical in this way. The pumps are useful for all types of erection problems (physical, psychological, or a combination of both). Vacuum pumps are generally safe, simple to operate and can be used as often as desired. However, improper use can damage your penis and so they must be used under a doctor's care. While you may need to interrupt foreplay to use them, you can also incorporate use of the pump into erotic play, making it less medical and more natural.