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301/303/305/306/307 Flowmeters and Controllers Instruction Manual
Mechanical Connections
2.4.1.
Gas Quality (Filtering)
Impurities or foreign debris in the gas lines can have negative effects on device performance. The
smallest of the internal passageways in the HFM-300/HFC-302 Series is the diameter of the sensor tube,
which can be 0.026" (0.66 mm), 0.017" (0.43mm), or 0.014" (0.36mm), so the instrument requires
adequate filtering of the gas supply to prevent blockage or clogging of the tube.
2.4.2.
Mounting
There are two mounting holes (#8-32 thread) in the bottom of the transducer that can be used to secure
it to a mounting bracket, if desired (HFM-306 has 4 mounting holes of ¼-28 size).
As explained in section 2.6.3 (High Pressure Operation), pressure can significantly affect readings and
accuracy. When mounting a flow instrument in anything other than a horizontal attitude, consideration
must be given to the fact that the heater coil can now set up a circulating flow through the sensor tube,
thereby throwing the zero off. This condition worsens with denser gases or with higher pressures.
Always check and match the direction of gas flow through the instrument and the arrow marked on the
flow instrument label. Whenever possible, install the instrument horizontally.
Always re-zero the instrument with zero flow, at its normal operating temperature and purged with its
intended gas at its normal operating pressure.
NOTICE: The flow instrument should be installed in a clean and careful manner. Take care not to
drop the product and avoid impacts to prevent damage.
WARNING: Make sure the work area is safe (de-pressurized) before installing a flow instrument.
Make sure emergency shutoff or pressure release valves are available for safe working
conditions. Do not exceed 500 psig unless the flowmeter is specifically rated for higher
pressures
2.4.3.
Plumbing
The pressure regulator and the plumbing upstream must be of sufficient size to minimize changes in the
upstream pressure. When switching from full flow to zero flow, the inlet pressure of instrument should
rise to no more that 30% above the inlet pressure at full flow. In general, high-capacity regulators and
large internal diameter plumbing help make the system more stable. The pressure drop between the
regulator and the instrument due to line resistance should be minimized.
See the fitting options in the specifications section (1.2). Note the O-rings for the end cap are Viton
(optional Kalrez, Neoprene or Buna-N). It is suggested that all connections be leak-checked after
installation. This can be done by pressurizing the instrument (do not exceed pressure rating of the
instrument) and applying a diluted soap solution to the flow connections (bubbles would indicate leaks).
EAR99 Technology Subject to Restrictions Contained on the Cover Page
Page 12 of 32
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