Balanced pressure seal for high pressure pumps

A pressure balancing system for a pump having a hydraulic fluid sump, the pressure balancing system comprising:

• a bore in fluid communication with an oil chamber;
• a plunger;
• a plunger chamber with a seal between the plunger and the plunger chamber;
• a fluid passage from the plunger chamber to the bore;
• a pressure balancing valve in fluid communication with the bore, the valve comprising:
• an outlet port including an outlet check valve;
• an inlet port including an inlet check valve;
• a spool sliding in the bore to cover and uncover the inlet port and the outlet port;
• a fluid displacement device having a pumping side, and an oil side;
• and
• a spring intermediate the spool and the fluid displacement device and applying a biasing force to the fluid displacement device, wherein the spring is configured to exert a force of about 5 psi when the fluid displacement device is at a center position.

A method of operating a plunger pump, the plunger pump including:

• a diaphragm having a first side and an opposite second side, the first side comprising a hydraulic fluid side;
• a plunger reciprocating in a cylinder the plunger comprising a first portion with a first diameter, and a second portion with a second diameter smaller than the first diameter, the second portion being closer to a free end of the plunger;
• a seal sealing against the second portion of the plunger;
• a hydraulic fluid chamber between the seal and the first portion of the plunger;
• an unrestricted first fluid path between the hydraulic fluid chamber and the first side of the diaphragm;
• a second fluid path between the second side of the diaphragm and pumped fluid;
• a radial clearance between the cylinder and the first portion of the plunger configured to allow hydraulic fluid to escape past the first portion of the plunger during a pressure stroke of the pump;
• the method comprising:
• allowing hydraulic fluid to escape past the radial clearance;
• supplying an amount of hydraulic fluid to replace the escaped hydraulic fluid;
• wherein during a suction stroke, the pumped fluid drops in pressure from retraction of the plunger, allowing the diaphragm to freely float to drop pressure in the hydraulic fluid chamber to balance pressure across the seal;
• and
• wherein during the pressure stroke, the pumped fluid increases in pressure from extension of the plunger, pressing the diaphragm to increase the pressure in the hydraulic fluid chamber to balance pressure across the seal.