Instruction Manual
D103317X012
VBL Volume Booster
May 2017
7
Principle of Operation
Refer to figures 3, 4, and 5.
Because of the restriction, large input signal changes register on the booster input diaphragm sooner than in the
actuator. A large, sudden change in the input signal causes a pressure differential to exist between the input signal and
the output of the booster. When this occurs, the diaphragms move to open either the supply port or the exhaust port,
whichever action is required to reduce the pressure differential. The port remains open until the difference between
the booster input and output pressures returns to within the deadband limits of the booster. With the bypass
restriction adjusted for stable operation, signals having small magnitude and rate changes pass through the bypass
restriction and into the actuator without initiating booster operation. Both the supply and exhaust ports remain
closed, preventing unnecessary air consumption and possible saturation of positioner relays.
Figure 4. Typical Installations with Piston Actuator
ACTUATOR
VBL
VOLUME BOOSTER
PIPE NIPPLE
POSITIONER
SUPPLY
BOTTOM CYL
TOP CYL
67D, 67DR OR
95H REGULATOR
SIGNAL
E1212
