Bronkhorst Mass Flow - Manual (Page 10)

BRONKHORST HIGH-TECH B.V.
P1
pilot valve pressure
compensating
valve
P2
flow control valve
1.5.3 Pilot operated valve
For high flow rates the pilot operated valve has been designed. A
solenoid driven control valve controls the pressure difference
across a piston, which lifts the main plunger.
1.5.4 Bellows valve
This valve type is a direct driven, low power, solenoid operated control valve. A special design, incorporating
a metal bellows allows for a relatively large orifice opening to be controlled. The design is suited for low
pressure or vacuum applications.
Bronkhorst High-Tech strongly advises to mount the bellow valves in an upright position
1.6 Sensors and laminar flow devices
Flow devices are used to determine the total flow rate of a gas flow meter or controller.
Mind that liquid flow sensors and pressure sensors do not require a flow device.
Depending on the application the flow sensors have different removable capillaries, requiring a different
laminar flow device.
Furthermore for flow rates higher than 1250 l
n
/min the main laminar flow device is used in combination with a
capillary / flow device arrangement in order to compensate for the non ideal transfer function of the main
flow device.
In general 3 types of capillary tubes are available:
- Small bore (C-type)
The following notes apply to this type of sensor:
- These sensors have a pressure drop of approx. 35 mbar
- The laminar flow device consists of a stack of discs with precision etched flow channels.
Each flow channel represents approx. 10 ml
n
/min airflow at 35 mbar delta-P.
- In general instruments with these sensors may be mounted horizontal, as well as in a vertical
position, at low operating pressures. At high pressures (>10 bar) the instruments should be
mounted in a horizontal position.
- Large bore (D-type)
To this type of sensor the following remarks apply:
- These sensors are preferably used for reactive gases and at low pressure applications.
- The pressure drop is less than 0.5 mbar.
- The laminar flow device forms together with the main channel an annular channel. The dimensions
of this annular channel determine the flow capacity of the instrument.
- The instrument must always be mounted in a horizontal position.
- Medium bore (E-type)
This sensor is used in the “EL-FLOW series” and is used for increasing the flowrange of the “low deltaP
series”. The same remarks as the D-type apply to this sensor, only:
-The pressure drop is approx. 2.5 mbar .
page 10 9.17.001