A purge valve is an integral component of a vacuum material conveying system that not only provides an on/off flow of material into a conveying line, but also a way to purge that conveying line with air at the end of every material loading cycle.  Air purging is vital to prevent contamination and quality problems: purging clears the line before another material is conveyed through the same conveying line.

A basic purge valve is typically connected to a material distribution box. There, it allows material to flow into the conveying system and follows it with air to purge material remaining in the line.  The material infeed and flow are regulated by the adjustable tubes within the distribution box.

How Purge Valves Work. One part of the purge valve controls material flow.  When a vacuum conveying system cycles on to answer a demand for material, the purge valve is not energized, so its material valve is open to allow resin to flow from the source to the destination.  After sufficient material has been released, the material valve closes and an air-purge port is opened, allowing the valve and conveying line to draw in a flood of air. This flood of air purges the valve and conveying line through to the destination receiver, removing remaining material that could otherwise contaminate or discolor the next material that flows through. When this purge is complete, the vacuum conveying cycle ends.

Note that the air-purge port of a purge valve can be connected either to ambient air (drawn through a filter on the air inlet) or to a flow of dry air.  Dry air flow is recommended when moving dried materials from a resin dryer or storage hopper to equipment for processing. Purge valves can be retrofitted to existing conveying systems that need an air purging capability.

Adjustable purge valves are a variation on purge valve design that offer additional capabilities.