Smear head valve

A smear head causes less stagnation and overpacking than a nonreturn valve. A conventional-type reverse-tapered nozzle with the bore as large as possible without sudden changes in diameter is preferred. Independently controlled, zone-type heaters for heating the nozzle and at least two zones on the cylinder are used. 

An alternative to the check ring valve is a smear head (Fig. 6.33), which is based on the use of a small clearance in the diameter over significant land length. This design restricts the back flow of the melt during... 

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