Explosion Isolation Flap

An Explosion Isolation Flap (EIF) is also called a no return valve. It is a passive isolation device used to prevent a deflagration from propagating back upstream in ductwork in the event of a dust collector explosion.

It is installed on the ductwork upstream of a dust collector. The manufacturer will have installation requirements specifying the minimum and maximum distance from the dust collector inlet to locate the unit.  If the duct is protected by Spark Detection and Extinguishing System, the system components should be installed upstream of the EIF location.

An EIF contains a flap held open by the normal process airflow. Should a pressure wave from an explosion in the collector propagate through the ductwork in the reverse direction of the normal airflow, it will force the flap down to prevent the flame front from passing further upstream.

EIFs are to be used in applications where the dust collector is properly vented.  The Kst value of the material being conveyed must be considered in selecting the appropriate model.

NFPA 69 provides important information concerning the requirements which EIFs (or Flow-Actuated Flap Valves) must meet in able to meet recognized industry standards. Among these requirements are third party certification and a latching mechanism which will initiate an automatic shutdown of the protected area.

When purchasing an EIF it is important to consider the amount of static pressure loss that you will incur in the airstream after installation.  The amount of drag on the air flow may vary considerably among available units.