Venting Blowback from Airlocks

Fox Rotary Valve Venting Eductors for Capturing or Eliminating Blowback and Fugitive Dust Emissions from Rotary Airlocks


  • Eliminating Rotary Airlock Leakage and Fugitive Dust Emissions: Returning powder to convey line or to hopper/silo above
  • Capturing Lost Product due to Rotary Valve or Airlock Leaks
  • Reducing Maintenance and Airlock Wear due to Blowback/Airlock Leakage

All Rotary valves and rotary airlocks used in pneumatic conveying produce leakage or blowback, resulting in fugitive dust emissions. This release of both air and product can cause serious operational problems. Among these problems are: reduced conveying throughput; sudden and intermittent airlock failures (shafts, bearings, seal) requiring frequent maintenance; lost product blowing away into floor or into work environment; housekeeping and sanitation problems; explosion hazard.

Fox Rotary Valve Venting Eductors for capturing or eliminating blowback have been used on pneumatic conveying systems for thirty years, retrofitting airlock conveying systems to operate cleaner, with convey higher rates, less airlock maintenance, and no fugitive dust.

There are two types of installations:

Re-Injecting Blowback into the Convey Line with Compressed Air

The simplest and cleanest solution is to use a Fox Venting Eductor to inject the blowback +suspended solids right back in the convey line. This is possible in many cases. However, this retrofit requires that the Fox eductor suck in blowback, leaking out at approx. 0 psig, and compress this gas/solids mix up to convey line pressure. To accomplish this compression requires energy supplied by compressed air at 60 – 90 psig (4 – 6 barg). This solution therefore has a high continuous power cost.

Another concern is the injection of additional air into the convey line, increasing downstream convey velocity. This therefore makes this approach more attractive with larger convey lines.

Fox Rotary Valve Venting Eductor

Re-Injecting Blowback into the Convey Line with Compressed Air

Some airlock and blowback problems occur because the main blower has been oversized by overcautious designers. If at least 30 – 40 SCFM or more can be diverted from the from the convey line, with enough blower output remaining to drive the system, then this can be used to drive the smallest eductors Fox will provide in this mode of operation – a 1-1/2″ RVE eductor discharging through a 1-1/2″ line. (We consider attempting to use a smaller line, such as 1″ (25 mm) as not prudent and too prone to clogging.) Please note that a 1-1/2″ venting eductor may be too small for your application and significantly more motive air may be required. This can only be determined after Fox reviews your specific application.

Fox Rotary Valve Venting Eductor