Brooks Instrument BM50 - Manual (Page 27)

3-3
Section 3 Operation
BM Oval Series
Installation and Operation Manual
X-PD-BM-Ovals-eng
Part Number: 541B031AAG
January, 2009
3-5 Operating Precautions
Periodic inspections should be made during flowmeter operation. The
following points should be checked and the flowmeter shut down if any
discrepancy is found.
1. When changing flowrates
In applications where the flowrate varies or where shut-off valve opening
and closure takes place in batch operation, avoid rapid changes in
flowrate across the meter. Operating the meter at flowrates in excess of
the maximum allowable flowrate will nullify the guaranteed accuracy,
reduce the meter life and may result in faulty conditions, such as
seizure of bearings or rotor-to-measuring chamber contact.
2. Where the temperature of metered fluid changes
Avoid rapid temperature changes in the meter. Temperature changes of
the fluid in the meter should be held within 3°C, 37°F per minute.
Extra care should be used particularly when making a flow
measurement in batch operation without the provision of heat tracing
of the piping where the fluid temperature differs from atmospheric
temperature.
NOTE: If rapid temperature changes are anticipated, heat trace the piping assembly as
well as the meter.
3. Liquids of low steam pressure
Liquids with low viscosity and low steam pressure are prone to vaporize
and their temperature and pressure should, therefore, be strictly
controlled. During operation, the temperature of bearings in the meter is
usually higher than that of the metered fluid. Vapors around the
bearings can be causes of faulty conditions, including generation of
unusual noise and bearing seizure.
4. Corrosive liquids
When you make a measurement of highly corrosive liquids, appropriate
materials should be used for tanks and piping assembly.
Heterogeneous materials originally contained in the metered fluid or
corrosive substances liquated out from tanks and pipes of inappropriate
materials may lock the rotors in the measuring chamber and lead to
costly downtime.
3-6 Precautions at Operation Shutdown
1. Valves should be closed progressively.
Rapid valve closure could, under certain piping conditions, cause a
sharp pressure rise by water hammer, or hydraulic shock, resulting in
damage to the meter.
2. Precautions against pressure buildup on closure.
Complete closure of valves upstream and downstream of the meter
produces a totally enclosed space between the valves. A pressure
buildup relative to a rise in atmospheric temperature could lead to
damage to the meter.