How to Size a Spark Trap

How to Size a Spark Trap

You’ve got a ductwork system with 18-inch pipes and need to install a spark trap to extinguish sparks from the grinding, welding, and cutting done in your shop. So you get an 18-inch spark trap, right? Wrong.

Why is the Spark Trap’s Size Important?

Improperly sized spark traps can result in significant pressure loss issues, causing the system to lose suction at its pickup points. A correctly sized spark trap will keep the velocity of the air flowing through the trap between about 3,000 feet per minute and 3,500 feet per minute, so the pressure loss of the spark trap itself is only about 0.8 inches of water column.

Properly Sizing a Spark Trap

The two essential pieces of information you need to know to size your spark trap are:

  • Air velocity of the system
  • Trunk size of the ductwork

For example purposes, we’ll imagine we’re designing a ductwork system for a metal shop. The shop’s airflow velocity is 4,500 cubic feet per minute, and the ductwork is 18 inches in diameter.

  1. Calculate CFM Down to 3,000 and 3,500

Using a CFM table we can find the pipe diameter we need to get the CFM between 3,000 and 3,500.

We should pick the 22-inch diameter because:

  • It gets us the closest to the actual amount of air we'd be drawing through the 18-inch pipes (7,960)
  • It gives you a little bit more capacity in case anything happens in the future

For this system, we will need a spark trap with a 22-inch inlet diameter for our application.

  1. Get the Dimensions of Your Spark Trap

Then refer to the spark trap spec sheet, also available on our website, to find the spark trap’s maximum diameter and length.

The US Duct spark trap with a 22-inch inlet has an overall length of 85 inches and a maximum diameter of 40 inches.

 It's as simple as that! Have questions? Contact us