This article discusses the dynamic behavior of a spool plunger with a modernized drive. Modernization of the drive consists in replacing the electromagnet with a stepper motor with the transformation of rotational motion, — with the help of a screw pair, — into a rectilinear one. The contact between the ends of the screw and the plunger is provided by a spring. The value of the preliminary compression of the plunger to the end of the screw is assigned on the basis of guaranteed operation without loss of contact, due to which the plunger practically does not respond to disturbances and is devoid of an oscillatory component during the transient process. The mathematical model includes the influence of fluid friction and hydrodynamic force arising from pressure loss on the distributor 4 MPa. The study of the dynamics of the plunger consists in the accelerated retraction of the screw — which is in force contact with the end face of the spool — and the determination of the limit values of acceleration as a function of the preload force.