Mechanical barrier fluid pressure regulation for subsea systems

A subsea fluid processing system, comprising:

• a rotatable machine configured for subsea deployment where a process fluid is processed, the rotatable machine including one or more mechanical seals to separate a barrier fluid and the process fluid;
• a barrier fluid supply source configured to be located at a surface location;
• and
• a mechanical barrier fluid pressure regulation system configured to maintain a pressure differential between the barrier fluid and the process fluid between a predetermined upper limit and a predetermined lower limit, the pressure regulation system comprising:
• a valve mechanism configured to provide the barrier fluid to the rotatable machine when the pressure differential reaches the predetermined lower limit and to dump the barrier fluid when the pressure differential reaches the predetermined upper limit, wherein the valve mechanism comprises:
• a pressure balanced supply valve with a valve housing;
• a pilot piston mechanically coupled to the supply valve and slidably positioned within a pilot chamber within the valve housing to separate a process fluid side of the pilot chamber from a barrier fluid side of the pilot chamber;
• and
• a return seal disposed in the pilot chamber that isolates a pressure in a discharge chamber of the valve housing to delay the supply valve actuation when a pressure of the barrier fluid increases rapidly and to generate hysteresis in the opening and closing of the valve mechanism;
• wherein the discharge chamber and the barrier fluid side of the pilot chamber are in fluid communication with each other and a discharge nozzle is positioned within the discharge chamber such that the barrier fluid flowing through the discharge chamber passes through the discharge nozzle to generate the hysteresis.