Here is an official video explaining how to use the HydroXtreme model.
HOW THE HYDROPUMP WORKS
The Hydropump functions by creating a vacuum seal against the pubic area of the user, enclosing the flaccid penis.
When the pump is pushed downwards against the body, the bellows compress and water is ejected from the end of the pump via the open valve.
When released the bellows expand and the valve closes, creating a partial vacuum inside the pump. This causes the penis to expand and fill with blood, creating an erection.
Re pumping increases the vacuum, and so increases the size of the erection.
The user controls the valve by rotating the valve cap clockwise to lock the valve and anticlockwise to unlock the valve.
When the valve is locked the internal vacuum cannot be released. This position is used when pumping or using the handball pump. When unlocked the valve cap can be pressed inwards against the spring. This opens the valve and allows air or water back into the body of the pump, thereby partially or fully releasing the vacuum.
The vacuum in Bathmate Hydropumps is created by the elastic recoil strength of the bellows gaiter pump, so the user cannot exceed the safe partial vacuum levels allowed under European and USA medical regulations.
OPERATING THE VALVE
The black pip on the top of the valve is moved by pressing inwards and moving to the right or left, where it should “click” into position closing the valve. The closed position should only be used whilst filling the Hydropump with water in the shower. At all other times the black pip should be in the central (open) position. Failing to ensure that the black pip is in the central position will prevent the Hydropump from operating correctly.