A blast gate is simple hardware with an outsized effect on a system: sized and placed well, it balances airflow; sized poorly, it starves branches or lets material settle and plug the run.
Match the diameter to the branch
The first rule is the simplest: the gate should match the diameter of the branch it serves. An undersized gate becomes a restriction that robs the branch of airflow and drives up static pressure; an oversized one drops velocity below the point where dust stays airborne.
Hold the transport velocity
In dust-collection and particulate exhaust, the branch must maintain enough velocity to keep material entrained. Fall below it and solids drop out, accumulate, and eventually block the duct.
| MATERIAL | TARGET VELOCITY |
|---|---|
| Vapors / light fumes | 1,500–2,000 fpm |
| Fine, dry dust | 3,000–3,500 fpm |
| Average industrial dust | 3,500–4,500 fpm |
| Heavy or moist material | 4,500+ fpm |
Choose the gate type
- Manual gates suit branches that are opened or isolated infrequently, or set once during balancing.
- Pneumatic gates suit branches cycled often or automated with the collector, so the fan only pulls where it’s needed.
- Saddle-mount gates add or isolate a branch on an existing main without cutting a full tee — ideal for retrofits and tight tie-ins.
Placement affects balance.
Leave a few diameters of straight duct upstream and downstream of the gate. Crowding it against elbows or tees creates turbulence that undermines both flow and measurement.
Balance the whole system
Blast gates balance a network only when every branch is sized around a common transport-velocity target. Set each gate so its branch pulls its design share, then verify total static pressure against the fan curve — the same discipline used when sizing fume-hood exhaust duct.
- Size each branch for its required CFM at the target velocity.
- Match gate diameter to each branch.
- Set and lock the gates during balancing, then re-measure.
