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Glossary

Positive Displacement (PD) Blower

What is Positive Displacement (PD) Blower?

A positive displacement (PD) blower is a high-vacuum air pump used on vacuum and hydrovac trucks that produces strong lift for deep digging and long hose runs, moving air by trapping and displacing fixed volumes.

A positive displacement blower generates vacuum by trapping air in cavities between rotating lobes and forcing it out, delivering high vacuum lift (measured in inches of mercury) even through long or vertical hoses. This makes PD blowers well suited to deep potholing, remote spoil removal, and heavy material.

PD blowers contrast with fan blowers, which move more air (higher CFM) at lower lift and excel at shallow, high-volume work. Choosing between them depends on dig depth, hose length, and material. Vac4Rent listings note blower type and CFM; submit a free request to match the right blower to your job.

Guides that cover Positive Displacement (PD) Blower

Related terms

CFM (Cubic Feet per Minute)Vacuum TruckHydrovac TruckDig Tube / Wand

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Positive Displacement (PD) Blower: common questions

What is Positive Displacement (PD) Blower?+

A positive displacement (PD) blower is a high-vacuum air pump used on vacuum and hydrovac trucks that produces strong lift for deep digging and long hose runs, moving air by trapping and displacing fixed volumes.

How does a PD blower compare with a liquid ring vacuum pump?+

Both can create strong vacuum, but they suit different work. A PD blower moves air and relies on separators and filters to keep debris and water out of it. A liquid ring pump seals with a ring of liquid inside the pump, which lets it tolerate moisture and run continuously at deep vacuum. Liquid ring units are common in demanding industrial cleaning, while PD blowers are widely used on hydrovac and vacuum trucks.

How is a PD blower protected from debris and water?+

PD blowers are sensitive to solids and liquids entering them, so trucks use protective stages between the debris body and the blower. These commonly include cyclone separators, filter housings, and a float or shutoff device that closes the air path if the tank overfills. Operators should check filters and shutoffs as part of daily inspection. When renting, ask how the protection system works and what the operator is expected to maintain.

Are PD blowers loud enough to matter on residential or night jobs?+

They can be. PD blowers produce significant noise, and most trucks use silencers to reduce it. On jobs near homes, hospitals, or schools, or during night work, local noise ordinances may limit operating hours or sound levels. Crews should also wear hearing protection as required by their employer's safety program. If noise is a concern, ask the rental company about the unit's silencing setup and check local rules before scheduling.