Bronkhorst IN-FLOW User Manual download pdf (Page 16)

BRONKHORST HIGH-TECH B.V.

page 16

9.17.022

1.4.3 Maximum pressure drop

For (pilot) solenoid operated control valves with small orifices the maximum allowable pressure drop for

gases is according to the table.

Diameter [mm]

Normally closed

∆p max. [bard]

Normally opened

∆p max. [bard]

0,05

0,07

0,10

0,14

0,20

0,30

0,37

0,50

0,70

1,00

1,30

1,50

1,70

2,00

4,33 x 10

-5

8,48 x 10

-5

1,73 x 10

-4

3,39 x 10

-4

6,93 x 10

-4

1,56 x 10

-3

2,37 x 10

-3

4,33 x 10

-3

8,48 x 10

-3

1,73 x 10

-2

2,93 x 10

-2

3,90 x 10

-2

5,00 x 10

-2

6,63 x 10

-2

3,6

n.a.

For pilot operated valves the maximum pressure drop is limited to 20 bard. If the the pressure drop during

start-up is higher, it is prefered to install a bypass valve. During start-up this valve should be opened. Also the

minimum pressure drop is limited. For exact figures consult factory or proceed according to the technical data

and/or additional instructions given by the sales office or department.

1.5 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, CTA-based 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

/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

/min airflow at 35 mbar delta-P.

- In all instruments with a pressure rating above 100 bar (M-type) the sensor is fitted with metal

seals.

- 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.

- The EL-Flow, EL-press metal seal series are fitted with a metal sealed sensor.

- 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.

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