Grit is a term used to describe various small solid particles that accumulate in the Influent stream entering a wastewater treatment plant. Grit is composed of small stones, sand, road cinders, gravel and similar materials. It is normally removed during the first stage of treatment and it is very abrasive.
Due to the small particle size of grit, it can easily work its way past valve packing into seals and seats, and behind balls and plugs. It scores sealing surfaces of metal valves, creating leak paths. Most seating arrangements cannot close upon entrapped grit, again allowing a leak path.
Red Valve Control Pinch Valves are found in thousands of de-grit chambers because they do not suffer these common problems with typical ball or plug valves. Rather than using an expensive metal alloy for abrasion resistance, Red Valve Control Pinch Valves have resilient rubber sleeves to absorb the impact of grit particles and bounce back to shape. The sleeve is full-ported, just like a piece of pipe, and is the only wetted part of the valve. This eliminates all packing and seals entirely. The flexible, yet rugged, rubber surface of the sleeve allows it to seal tightly around entrapped debris.