Roots Blower Discharge Silencers and Pulsation Dampener

Listing ID #4674139

The Roots type blower is a positive displacement lobe pump which operates by pumping, or moving, a fluid, usually air, but in some cases a process gas, using a pair of inter-meshing lobed rotors, which have a profile that looks not unlike the number 8. When operating, the fluid is trapped in the outer pockets surrounding the lobes and is carried, or progressed, from one side of the machine to the other.

The lobe shaped rotors (usually two lobes, but it can be 3 or 4) work in tandem and move the fluid, usually air, from one side of the machine to the other. The lobes do not grab, or scoop the air out of the inlet pipe, but rather as they pass the inlet opening they cause a local low pressure area inside inlet port of the machine into which the fluid will then flow. As the rotors continue to turn the fluid that has entered the machine is trapped by the rotors and progressed from the inlet side to the outlet side. On reaching the outlet side the fluid has no choice but to be pushed out into the discharge pipe.

Each time one of the rotor tips passes either the intake or exhaust port, the passing of that tip causes a pressure pulse to be generated. Therefore in the case of a blower with rotors that have 2 lobes there will be 4 pulses for each complete revolution of the pair of rotors (2 pulses from each rotor for each revolution). This allows for a relatively easy estimation of the principal frequency of pulsation that the machine will generate.

Whilst the frequency of the noise from the passing of the rotor tips at the intake and exhaust ports is well understood, there is a second noise mechanism where the fluid tries to pass back through the machine from the high pressure side to the low pressure side by "slipping" around the rotors at their tips. This is an aerodynamic noise mechanism and is less easy to predict as the noise level changes with the speed of the blower and the gap between not only the rotors, but also between the gap between the rotors and the casing.