Emerson Fisher 2625NS Instruction Manual - Page 8
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2625, 2625SST, and 2625NS Volume Booster
September 2022
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.
Maintenance
WARNING
Always wear protective clothing, gloves, and eyewear when performing any maintenance procedures to avoid personal
injury.
Maintenance requires taking the volume booster out of service periodically. To avoid personal injury or equipment
damage, disconnect or bypass any pressure lines to the booster, and vent any pressure locked in the unit before you begin
maintenance.
Check with your process or safety engineer for any additional measures that must be taken to protect against process
media.
Diaphragm Assembly Replacement
Key numbers refer to figure 4.
1. Remove the six cap screws (key 15) from the perimeter of the spring case assembly (key 3), and lift off the
assembly, taking care you do not lose the input spring (key 8) or the spring seat (key 9).
2. Remove the upper diaphragm (key 6), diaphragm spacer (key 2), diaphragm assembly (key 5), (which includes the
lower diaphragm), and the O‐rings (key 14). Inspect these parts for damage and replace if necessary.
3. Replace the O‐rings (key 14) after coating with lubricant (key 21). Then replace the diaphragm assembly (key 5),
diaphragm spacer (key 2), and the upper diaphragm (key 6).
Note
To ensure proper operation of the bypass restriction, make certain that the holes in the diaphragm and the bypass restriction are in
line with the holes in the diaphragm spacer (key 2).
4. Install the spring case assembly (key 3) on the upper diaphragm (key 6). Make sure the spring seat (key 9) and the
upper spring (key 8) are installed in the spring case assembly (key 3). Press on the bottom of the spring seat with
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Instruction Manual
D100348X012