For the purpose of control and overpressure protection in pipeline systems of power industry and pressure vessels, indirect-action valves consisting of a main valve and a pilot valve are often used. Such devices are characterized by smaller reliability due to complication of their structure depending on operability of these two valves. A pilot valve controlling the whole safety system is the weakest element of the system. It is especially typical of machines operated in severe conditions, since life of sensing elements quickly decreases during work with high-temperature and polluted media. The authors considered the ways for improving reliability of pressure control systems operated in severe conditions by redundancy of the sensing element of the valve with a system equipped with a metal bellows. The authors analyzed reliability of initial systems and redundant systems at various operating temperatures.