A blast gate is a valve used to isolate separate parts of a vacuum extraction system. These valves are usually very simple and typically consist of a sliding or rotating plate which blocks off the vacuum line. They are most commonly encountered in dust extraction systems installed in wood working shops to keep all the vacuum lines to unused machines closed to maximize the vacuum pressure. Blast gates are usually fitted near the machine suction point and are generally hand operated, although automated gates are available which open when the machine is switched on. In large systems with very powerful vacuum pumps, at least one or more of the blast gates are always left open to prevent the vacuum collapsing the hoses.
Dust extraction in carpentry shops and other dusty work environments is an essential part of any health and safety regimen. Most commercial or hobby woodwork shops that have a centralized dust extraction system make use of a vacuum pump which draws dust from the machine source to a safe collection point through a series of hoses. These pumps are often not powerful enough to effectively induce negative pressure in all the extraction points simultaneously. As all machines served by the dust extraction system seldom work at the same time, those not working are usually isolated from the vacuum system by a blast gate. This maximizes the efficiency of the available vacuum at the working machine stations and ensures adequate dust extraction.
Blast gate valves do not have to ensure a perfect hermetic seal and are usually very simple in their design and operation. Most blast gates are of a sliding design, consisting of an appropriately sized in-line hose fitting equipped with a pair of slide grooves to accommodate a flat shut-off gate. To open the blast gate, the machine operator simply lifts the plate to open the hose and allow the vacuum to draw the dust away from the machine. Once the work is complete, the plate is then dropped back down again to close off the hose and isolate the extraction point again.
In more complex systems, the blast gate may be remotely operated and of a rotating circular gate design. These valves use a spring loaded solenoid to open and close the gate to isolate the inlet point. The solenoid will then draw its power from the machine switch; it automatically opens when the machine is started and closes when it is shut off. This system works particularly well in high demand environments and precludes the possibility of blast gates being inadvertently left open. In very large, high power vacuum systems certain relief valves are left open at all times to prevent the vacuum pressure from collapsing the vacuum hoses.