Direct-contact heaters of feed water are especially popular as low-pressure heaters (LPH). These devices are successfully used in Russia during a long time both for conventional and nuclear power plants. Moreover, abilities of such devices to operate as deaerators led to the development deaeratorless schemes. One of most important conditions of reliable operating of such LPH is the prevention of damage of steam turbines, because of back flow of wet steam to the turbine. In this paper processes of boiling up are considered in direct contact LPH-2 which occur during stopping of turbine and its specific features concerned with dependence of sonic speed two-phase flow on vapor and liquid volumetric portions during flow enter in compensating tubes. Computer analysis showed, that the rate of generation of steam in the superheated water depends on the pressure exceptionally strong.
Zone of churn flow regime, which is formed in the upper part of the condensate tank appears very sensitive instrument of flow rate control. As it is shown in such a situation, the system becomes self-governing and will not miss a steam consumption, which leads to the entrance some part of churn regime zone to pressure equalizing tubes. The calculations show that the safety can be ensure even in the conditions when backpressure valve absent. Such the conclusion is confirmed by the experience on operation direct contact LPH in Russian power plants.