The technique of an estimation of tightness of hydraulic props of mechanical supports which is reduced to the decision of two basic problems is offered: definition of a gap between the piston and the cylinder in a place of a seal and revealing of character of deformation of a seal in this gap under the influence of pressure of a working liquid. The character of seal operation and determination of gaps are established by means of the finite element method as a result of solving the model of joint interaction of seal, cylinder, piston, rod, gland bush and working fluid taking into account material properties and real working conditions of the hydraulic prop.
