Piston pump and seal ring

A single-stoke pump comprising:

• a working cylinder having a working fluid inlet, a working fluid outlet, and a throat;
• a pump cylinder having an inlet end and an outlet end, wherein the inlet end is attached to the throat;
• a reservoir fluidly connected to the pump cylinder and configured to store a pumped fluid and to provide the pumped fluid to the pump cylinder;
• an outlet valve connected to the outlet end of the pump cylinder;
• and
• a piston disposed within the working fluid cylinder and extending into the pump cylinder through the throat, wherein the piston comprises:
• a piston head disposed within the working fluid cylinder;
• a pump rod extending from the piston head through the throat and into the pump cylinder;
• a retaining device connected to a distal end of the pump rod;
• and
• a seal ring extending about the pump rod and disposed within the pump cylinder, wherein the seal rod comprises:
• a body extending between a first end and a second end;
• and
• a bore extending through the body between the first end and the second end;
• wherein the pump cylinder defines a pump chamber extending between the seal ring and the outlet valve, wherein a volume of the pump chamber decreases as the piston proceeds through a forward stroke and increases as the piston proceeds through a return stroke;
• and
• wherein the seal ring is configured to be movable between a first position in which the seal ring sealingly engages the pump rod during the forward stroke to prevent fluid within pump cylinder from flowing around seal ring during the forward stroke, and a second position in which the seal ring is disengaged from the pump rod during the return stroke such that a refill flow path is opened through the bore to allow the pumped fluid from the reservoir to flow into the pump chamber.