Circulating system for foam reagents - in which layout with control and non-return valves and regulator produces polyurethane foam and prevents steep pressure drops

摘要

A circulation block for mixing heads, and particularly for those with parallel nozzles in equipment for the prodn. of polyurethane foam, has a nozzle with valve needle and seating in which the needle has an annular surface exposed to the pressurised reagent and opened under pressure; a hydraulic control device has a valve in two flowlines, the one being on the closed and the other on the open side of the mixing head; according to the position of this valve either the closed side is subject to the operating pressure or the open side is subjected to opening pressure; the line to the open side is also connected to an annular space in the block which enables the nozzle needle to be closed. This particular flow line has a non-return valve open to the annular space; a regulator is in the line between this valve and the block so that a set pressure is applied to the annular space and held there; another line for pressure release can connect to the line between the regulator valve and non-return valve; when the nozzle needle opens under the pressure of the reagent and when the pressure in the annular space exceeds the set level this pressure release line allows the pressure to drop to the set valve again. ADVANTAGE - The system produces precise operational control. In particular it prevents the occurrence of any excessively steep pressure drop.