Abstract: Methods and apparatus for efficiently compensating for pressure changes in a active vibration isolation system are disclosed. According to one aspect of the present system, system that reduces the vibrations experienced by a mass includes a chamber that supports the mass, a control device, a valve mechanism, and a bypass mechanism. The control device monitors a pressure level within the chamber. The valve mechanism includes a first flow path that is in fluid communication with the chamber. The valve mechanism also alters a capacity of the first flow path in response to a control signal generated by the controller. Finally, the bypass mechanism defines a second flow path that enables fluid to flows through the second flow path into the chamber. The second flow path is parallel to the first flow path to enable parallel fluid flow to occur.