Brooks Instrument BM02 - Manual (Page 17)

3-1
Installation and Operation Manual
X-PD-BM01-02-eng
Part Number: 541B042AHG
March, 2008
Operation
Brooks ® Models BM01 and BM02
3-1 General
The flowmeter has been completely assembled, checked and calibrated at
the factory. Therefore, no adjustments are required for installation.
3-2 Flowmeter Principle of Operation (See Figure 3-1)
The Oval Flowmeter accurately measures liquid flow by using a slight
pressure differential to rotate a pair of oval gears. The meshed gears seal
the inlet from the outlet flow, developing the pressure differential. When in
the position as shown in Figure 3-1A, Gear A receives torque from the
pressure difference, the torque upon Gear B cancel one another, and Gear
A drives Gear B as depicted in Figure 3-1B. When Gear A rotates to the
position as shown in Figure 3-1C, it loses torque, but Gear B obtains
torque and drives Gear A. This alternate driving action provides a smooth
rotation of almost constant torque without dead spots. Figures 3-1D, 3-1E,
3-1F, 3-1G, 3-1H, and 3-1J illustrate this principle through a complete cycle
bringing Gear A back to its original position as shown in Figure 3-1A.
During rotor rotation, the rotors trap precise quantities of liquid in the
crescent shaped gaps or measuring chambers. Total quantity of flow for
one complete cycle of the rotors is four times that of the crescent shaped
gap. Rate of flow is proportional to the rotation speed of the rotors.
Because the amount of slippage between the rotors and the measurement
chamber wall is minimal, the flowmeter is essentially unaffected by
changes in viscosity and lubricity of the liquid.
3-1D 3-1F 3-1E
3-1A 3-1C 3-1B
A
B
B
B
A
A
A
B
B
A
A
B
A
B
A
B
1 2 3
4 5 6
7
8 9
A
B
FLOW
FLOW
3-1G 3-1J 3-1H
Figure 3-1 Principle of Operation