A biopsy device includes a needle extending distally from a body. The needle includes a transverse aperture, a first lumen, and a second lumen. A cutter is movable within the first lumen to sever tissue protruding through the transverse aperture. A valve assembly is operable to change the pneumatic state of the second lumen. The valve assembly includes a valve body and a translating member slidably disposed in a bore of the valve body. The valve body includes a first port and a second port. The first port is in fluid communication with the second lumen of the needle. The second port is in fluid communication with atmospheric air. The translating member selectively couples the first port with the second port based on the longitudinal position of the translating member within the bore. The translating member translates relative to the valve body based on the position of the cutter.