Blast Gate

A blast gate is a simple thing: a body that sits in a dust line with a flat plate you slide across it, closing that branch off or opening it up. Shops run one at every drop -- one per machine -- so the collector's suction goes where the work is instead of being shared out across every idle port in the building.

Why it matters more than it looks

A dust collector or shop vac moves a fixed amount of air. Split that between five open branches and every one of them gets a fifth of it, which in practice means none of them collects properly. Close four gates and the fifth gets the lot. That's the whole idea: gates are how a permanent duct run behaves like a hose you plugged straight into the tool.

The other job: keeping something open

There's a second use that only turns up once you own a cyclone separator and a plastic drum. Block the inlet of a running vac -- a clogged hose, a sanding pad flat against the work, a gate you closed on the only open branch -- and the motor keeps pulling against a sealed container. The pressure inside drops, the atmosphere outside doesn't, and a thin-walled bucket or drum can collapse.

Leaving one gate open somewhere in the line gives the vac air it can always reach, so it never gets to squeeze the container flat. A relief valve on the drum lid does the same job automatically, and a rigid steel drum sidesteps it, but an open gate costs nothing.

Choosing and fitting them

• Size to your duct, not to the fashion. 4" is the common shop size; shop vac hoses are usually much smaller, and gates in those sizes are harder to find. An adapter with a branch you can open and close does the same job.
• Self-cleaning gates have an open bottom, so dust doesn't pack into the track and stop the plate closing. The cheapest gates don't, and they jam eventually.
• Metal or plastic matters less than where it sits: a gate you can't reach without walking round the machine is a gate you stop using.