Reciprocating cryogenic pumps are employed in several applications where it is necessary to rise the pressure of a cryogenic liquid, such as air gases or LNG (liquid natural gas), up to hundreds of bars. One of many VT-55 high-pressure pumps produced by Vanzetti Engineering suffered a crankshaft failure, this case, although isolated, pushed the company towards the decision to verify the correct design of the crank mechanism, to understand the causes of this breakage and the operative limits of the pump. As starting point, developing a kinematic study, the position, velocity, and acceleration of the piston as a function of the crank angle are obtained.