Section 2 Installation
Special considerations for high pressure installations:
The SLA-Series mass flow devices are capable of operation in high pressure
applications. To ensure proper operation the user must be aware of the pres-
sure conditions specified for the device. Inlet and outlet pressure conditions
can be found on the device label and calibration sheet. The device was sized
and tuned to operate at the specified pressure conditions. If the differential
pressure during start up exceeds the specified differential pressure, hydraulic
forces may keep the valve from opening and/or controlling properly. In these
applications it is important to bring the pressure up in a controlled manner.
One method to assure successful startups is set a 100% setpoint command
or valve override open command and then gently ramp the pressure up to
operating (specified) conditions. This will allow you to bring your process pres
-
sure up to normal operating conditions where the SLA mass flow controller will
function as specified.
Another method is to utilize a bypass valve to allow pressure around the de-
vice while ramping up the back pressure to normal operating conditions.
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 pres-
sure 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 sus
-
ceptible to damage by pressure spikes or surges. For this reason, it is recom-
mended that process line startups are handled with care.
The bellows spring is offered in two levels. A low force for low differential pres-
sures (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 pres-
sures and/or pressure differentials that the SLAMf53 is exposed to may be dif-
ferent from the final process conditions. For higher pressure applications, and
especially those with the low force bellows, it is important to bring the pres-
sure 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 de-
vice 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
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