Abstract: The invention relates to a method of maintaining the pressure difference in a heat treatment plant such as, for example, a pasteurizer for liquid foods. In a temporary production disruption, the insufficiently treated product is caused to recycle by a return stroke. The pressure difference is maintained in that the already heat-treated product is enclosed in a conduit on the downstream side (14) of the plant, and that the space for the product in the conduit is restricted. The space for the product is restricted either in that a food gas is led into the conduit, or alternatively that the product conduit (29) is provided with an expansive portion (27). The expansive portion (27) consists of a pipe length (28) with an inner elastic wall (30) which expands by means of a gas or a liquid.

Abstract: An arrangement for measuring the content of crystals in a mixture of liquid and crystals comprises a pipe line (2) and a pump (5), by which a constant flow of the mixture is pumped through the pipe line (2). In this, a unit (6), preferably an electrical resistance wire, is arranged to transmit a constant amount of heat to the flow. There are also temperature sensors (7, 8) before and after the unit (6), arranged to transmit impulses representing the temperature difference to a unit (11), which with the aid of information about the velocity of the flow, the added amount of heat, the specific heat of the liquid and the melting heat of the crystals, calculates the content of crystals in the mixture. The content may be shown on a screen or a corresponding signal may be transmitted to a controlling unit, which influences the formation of crystals in the liquid.