A rotary positive blower, sometimes called a Positive Displacement, or PD blower, is a machine that "pushes" a relatively constant volume of the gas handled at the inlet through to the discharge. It doesn't internally compress the gas, so it isn't considered a compressor. The amount of gas the machine handles is fixed by the configuration of the casing and rotating parts.
Flow through a PD machine is relatively constant, regardless of pressure changes. This is different from a centrifugal compressor, which maintains a relatively constant pressure while the flow varies.
The Roots™RAM™-DPJ Whispair™ rotary blower has an exclusive discharge jet plenum design that allows cool, pressurized system air to flow into the cylinder. This unique design permits operation at high pressure levels with a single stage unit. The RAM high pressure roots displacement blower is designed for continuous operation at discharge pressures up to 30 psig. It has no valves, vanes or Teflon rings. Clean, dry discharge air or gas provides usable heat for your process.
Available accessories for Roots (PD) blowers, gas blowers, and exhausters include driver, relieve valves, inlet and discharge silencers, inlet filters, check valves, extended base, V-belt drive or flexible coupling and drive guards.
Here's how it works...
As the dual, figure-8 shaped impellers rotate, a fixed quantity of gas (or air) at the inlet is trapped between the impeller and the casing parts. With each revolution, four of these "pockets" of gas are trapped, then forced out the discharge against whatever pressure exists in the system.
When each of these pockets is expelled, a pulse is generated, which imposes a certain shock load on the blower and the downstream system. A ROOTS improvement on the basic PD design is the Whispair® Blower. It lets the gas in the pocket pressurize slowly to discharge conditions via the internal "jets." This significantly reduces pulsations and shock load on the equipment.