Manual Penis Pump Negative Pressure/suction helps to relax the smooth muscle cells, which allows for sponge swells After the sponge expands, arterial blood flows in to speed up the sponge hyperemia and increases the hardness of your penis The more the sponge is inflated, the more solid your penis will be and the more it will grow Air pressure will increase your cavernous body, with low vacuum pressure in the cylinder, your cavernous body will be exercised in physical safe way Universal design fits all