Positive Displacement Blower

Positive displacement blowers, commonly referred to as PD blowers or rotary lobe blowers, are one of the two main types of vacuum producers used on hydrovac trucks. They work by using two or three meshing lobes that rotate inside a housing, trapping air on the inlet side and pushing it to the outlet side. This mechanical displacement of air creates the vacuum that powers the excavation.

The key advantage of PD blowers is their ability to maintain consistent vacuum levels even as the hose becomes partially restricted or the dig depth increases. This makes them ideal for deep dig applications and remote dig scenarios where friction loss in long hose runs would significantly reduce the performance of a centrifugal blower. PD blowers can typically achieve 15 to 27 inches of mercury vacuum.

PD blowers are generally heavier, more expensive, and noisier than centrifugal blowers. They also require more maintenance, including regular oil changes, belt inspections, and lobe clearance checks. Despite these drawbacks, PD blowers are preferred by many hydrovac operators for their reliable, consistent performance across a wide range of operating conditions.