O-ring lubrication system

A pressure regulator comprising:

• a cylinder;
• a piston contained in the cylinder;
• first and second O-rings attached to the cylinder and configured to form a seal between the cylinder and an interior wall of the piston;
• a lubrication system comprising:
• a lubrication reservoir between the first and second O-rings defined by an annular groove in an exterior surface of the piston and the interior wall of the cylinder;
• and
• an input port extending through the cylinder to the lubrication reservoir;
• wherein:
• the piston is configured to move along a central axis relative to the cylinder between first and second positions;
• the first and second O-rings are displaced from the input port during movement of the piston between the first and second positions;
• the reservoir includes a maximum gap from the interior wall measured in a plane that is perpendicular to the central axis;
• and
• the maximum gap is greater than about 5% of a maximum diameter of the piston.