In control valves and safety valves – the way of closing the passage is the same – it consists of a valve head and a seat, in which the working surface of the plug is pressed against the working surface of the valve seat. In plug valves, the tightness between the steel plug and the steel seat of the control valve depends on the clamping force. In plug valves, the pressure is usually applied by tightening the stem, which deforms the contact surface of the plug and the valve seat. The pressure of the plug to the seat equals to 10 × pn (pn – nominal pressure in the valve), ensuring an appropriate level of tightness. The paper presents the results of tests of safety valves, in which the leakage in the valve was measured depending on the pressure value of 0.1 × pn to the value of the opening pressure. Valves with different roughness values of the working surfaces of the plug and valve seat were tested. The tests were carried out for these valves and valves after 1000 cycles of opening and closing the passage. The roughness parameters were determined, the achievement of which during surface treatment will allow for obtaining a higher level of tightness.