Check Valve

Check valves are used on all machines to prevent material from flowing over the screw as it is moving forward during injection.


The most common check valve used is the slip ring check valve. When the slider moves to the right, it seats itself against the screw and blocks the melted plastics from flowing back over the screw. During injection, if the screw drifts forward through the melt cushion, the check valve is not functioning properly.

Material tends to collect and degrade in the check valve, causing a poor seal-off. The check valve specifically designed for PVC does not block the back flow of material as well as the slip ring check valve. However, due to its high viscosity, PVC does not tend to flow back over the screw during injection.