Piston rod rotation features in a spray fluid pump

A piston rod elongate along a reciprocation axis and configured to reciprocate along and rotate on the reciprocation axis, the piston rod comprising:

• a first end, a main body, and a second end located at an opposite end of the main body from the first end, the main body including an elongated cylindrical surface;
• a piston coupling including a head and a neck disposed at the first end;
• an interior piston chamber formed in the second end and open in a first direction along the reciprocation axis and closed in a second direction along the reciprocation axis;
• one or more channels formed on an exterior of the piston rod;
• and
• one or more side bores extending through the piston rod and fluidly connecting the interior piston chamber with the one or more channels respectively, wherein each of the one or more side bores is associated with a respective channel of the one or more channels and each of the one or more side bores is angled offset relative to the reciprocation axis to direct the flow of paint along a vector to impart a moment on the piston rod to induce rotation of the piston rod;
• wherein each channel of the one or more channels extends at least partially axially and is open along a length of the channel;
• wherein each of the one or more channels is angled offset with respect to the reciprocation axis;
• and
• wherein the flow of paint ejected from each of the one or more channels imparts a rotational moment on the piston rod during pumping to induce the rotation of the piston rod.