Instruction Manual
D100348X012
2625 and 2625NS Volume Booster
January 2015
7
WARNING
If a flammable or hazardous gas is to be used as the supply pressure medium, personal injury, property damage or
equipment damage could result from fire or explosion of accumulated gas or from contact with hazardous gas. The volume
booster has no provision for piping away the vented exhaust gas. Therefore, do not use flammable or otherwise hazardous
gas as a supply medium unless the unit is in a well‐ventilated area and all ignition sources have been removed.
Exhaust Ports
Exhaust to the atmosphere is through exhaust ports in the side of the unit. Keep the exhaust ports free of any
obstructions or foreign materials that might clog them.
Operating Information
The only operating requirement of the volume booster is the adjustment of the bypass restriction for stable actuator
performance. Although systems with different characteristics may require different adjusting techniques, the
following adjustment procedure is recommended when using the actuator for throttling control.
Note
When sizing the booster, select the lowest C
g
that will meet the stroking speed specifications. Oversizing the booster in a closed
loop may lead to stability problems, thus requiring the bypass to be opened so far that the booster will never operate.
Prior to operation, turn the bypass restriction adjusting screw (figure 3) four or five turns counterclockwise from the
fully closed position. With the actuator in operation, slowly turn the restriction clockwise until the booster operates in
response to large changes in the input signal, yet allows small changes to move the actuator without initiating booster
operation.
If the actuator is to be used for on‐off control, the restriction should be closed (turned fully clockwise).
Principle of Operation
Refer to figures 2 and 3.
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.
