Brooks Instrument SLAMf Series - Manual (Page 28)

2-4
Section 2 - Installation
Installation and Operation Manual
X-TMF-SLAMf-MFC-eng
Part Number: 541B032AAG
April, 2013
Brooks ® Digital MFC's and MFM's
Special considerations to be taken when installing the SLAMf53 MFC:
The Model SLAMf53 has a valve design that is different from standard low
flow Brooks TMFC’s. The SLAMf53 consists of a dual stage, pilot
operated valve. The pilot valve (located on top of the MFC) controls a
differential pressure across the main valve which, in turn controls the flow
through the device. The main valve is a pressure operated valve that
utilizes a bellows spring and diaphragm to control flow. This bellows and
diaphragm assembly can be susceptible to damage by pressure spikes or
surges. For this reason, it is recommended that process line startups are
handled with care.
The bellows spring is offered in two levels. A low force for low differential
pressures (delta P < 30 psig), and a high force (delta P >30 and <300 psig).
The selection of the bellows spring is mainly determined by the differential
pressure as specified on the customer order. This should reflect your
actual process conditions. The low force bellows consists of a softer
bellows spring which is required to allow flow control at lower differential
pressures.
During startup conditions, when a process line is being pressurized, the
pressures and/or pressure differentials that the SLAMf53 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 SLAMf53
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 SLAMf53 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 SLAMf53 controller.
Stable Operating Conditions:
As stated above, the SLAMf53 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 SLAMf53 from the
unstable downstream pressures inherent in many process designs.