Free piston end position limiter

A piston end-position limiter for a free piston machine having a housing with a cylinder and a piston sealingly reciprocatable in the cylinder, the housing enclosing a first space bounded by a first end of the piston, the housing also having a second space bounded by the opposite second end of the piston, the second space containing a working fluid having an average pressure and the first space also containing working fluid having a pressure periodically varying in opposite directions from said average pressure, the limiter comprising:

• (a) a fluid reservoir;
• (b) a first valve connected in communication between the reservoir and the first space, said first valve adapted to open only when the working fluid pressure in the first space varies sufficiently in one direction from the average pressure;
• (c) a second valve connected to the reservoir and connected to the second space for opening to connect the second space to the reservoir in response to the piston reaching a selected end limit of its reciprocation:
• and
• (d) an equalizer for responding to a selected rate of change of reservoir pressure with respect to time, the equalizer comprising a third valve connected for communication between the reservoir and the second space and a valve actuator connected to the third valve and opening the third valve in response to a time rate of reservoir pressure change in excess of said selected rate.