Fisherr 2625 and 2625NS Volume Boosters
A Fisher 2625 or 2625NS volume booster is used in
conjunction with a positioner on a throttling control
valve to increase stroking speed. The 2625NS is a
nuclear‐service version and uses elastomeric
components that better withstand high temperature
and radiation environments.
The booster incorporates fixed deadband, soft seat
construction, and an integral bypass restriction to
eliminate positioner saturation problems that can
occur with volume boosters that do not have these
features. Adjustment of the integral bypass restriction
is necessary for system stability. This adjustment does
not affect the deadband of the volume booster, but
does permit the control valve to respond to small input
signal changes without sacrificing steady‐state
accuracy. It also allows the booster to deliver
high‐volume output for fast stroking when large, rapid
input signal changes occur.
The volume booster is used to improve stroking speed.
If precision valve control is required, the use of a
positioner is recommended. If the volume booster is to
be used only with an actuator, for on‐off control, the
integral bypass restriction on the booster must be
closed (turned fully clockwise).
Connectors and piping can be installed with either
2625 or 2625NS volume booster for diagnostic
The 2625 is certified for use in Safety Instrumented
System (SIS) applications. Certification is by exida
Consulting LLC, a global provider of functional safety
and control system security. SIS certification is
identified on the product by the EXIDA logo on the
n Fast Response—Booster delivers the volume needed
for rapid actuator stroking when large input
changes suddenly occur.
n Adjustable Response—Integral bypass restriction
tunes the booster response so that smooth actuator
motion follows the slow signal changes.
n Efficient Operation—Soft seats provide tight shutoff
to reduce unnecessary air consumption and
eliminate saturation of positioner relays.
n Maintains Accuracy—Booster permits high actuator
stroking speeds upon demand without degrading
the positioner steady‐state accuracy.
n SIL 3 Capable - Certified for use in Safety
Instrumented System (SIS) applications.
2625 Volume Booster