Brooks Instrument Mfi Series - Manual (Page 23)

2-5
Brooks ® Mf Series
Section 2 Installation Installation and Operation Manual
X-TMF-Mfi-Mfx-eng
Part Number: 541B074AAG
August, 2009
pressures and/or pressure differentials that the Mf53 is exposed to may
be different from the final process conditions. For higher pressure
applications, and especially those with the low force bellows, it is
important to bring the pressure up in a controlled manner in order to
prevent a possible pressure spike to the bellows spring and main valve
diaphragm. A pressure spike could deform the bellows, damage the
diaphragm or blow out the bellows O-ring seal. This typically results in a
failure to shutoff (leakby at zero setpoint).
One method to assure successful startups is to set a 100% setpoint
command or valve override open command and then gently ramp the
pressure up to operating conditions. This will allow you to bring your
process pressures up to normal operating conditions and the Mf53 will
then function as specified.
Another method is to utilize a bypass valve to allow pressure around the
device while ramping up pressure to proper operating conditions.
The main point is to not instantly open a ball valve and allow a high
upstream pressure or high back pressure surge into the Mf53 main valve.
Proper process line venting is also important. If operating at pressures
greater than 50 psig, be sure to perform a controlled pressure release
from inlet and back pressure simultaneously in order to prevent bellows
damage from excessive back pressure.
Following careful startup and venting procedures will contribute to a long
problem free life of your Mf53 controller.
Stable Operating Conditions:
As stated above, the Mf53 model utilizes a pressure operated main valve.
Valve performance is dependant on stable system pressures. Oscillating
or unstable upstream or downstream pressures are likely to cause the
device flow control to become unstable. For the best performance, it is
important to create a stable pressure environment by utilizing quality inlet
and back pressure regulators. In many cases, the addition of a back
pressure regulator will isolate the Mf53 from the unstable downstream
pressures inherent in many process designs.
For more information, please contact the Brooks Technical Service group.