A pressure regulator for an x-ray apparatus includes a piston housing having a recess formed therein and a piston seated in the recess. The piston is free to reciprocate, and define a variable volume chamber, within the recess. A circumferential groove is formed in an exterior surface of the piston, and a seal is seated in the circumferential groove. A manifold in the piston housing places the chamber in fluid communication with an exterior of the piston housing.