Fume Hood Flow Meter Information and Instructions

The following is a guide on how to use fume hood airflow monitors in evaluating the performance of the fume hood.
There are basically two types of airflow monitors used on Campus fume hoods and exhaust ventilation. There are differential pressure gauges and digital monitors with alarms. The pressure gauges are mechanically simple and measure and display negative pressure inside the exhaust duct (above the hood) relative to the room pressure. The digital monitors need electrical power to measure the velocity of the airflow into the hood. The digital monitors are quite sensitive and can be connected to airflow controllers (variable air volume controllers) and have visual or audible alarms when the velocity is low or too high. Because they are more sensitive the digital monitors may need more maintenance or adjustments. Below we list specific information on the one common pressure gauge and five example brands of digital monitors.

Click on the appropriate flow monitor listed below for details and use instructions.


If your fume hood is equipped with a flow monitor not on this list (or has no flow monitor) contact EH&S at 642-3073.
 

Magnehelic and Minihelic


 

magnehelic.gif minihelic.gif

 

Digital display of face velocity No Pressure gauge in "inches of water"
Visual Indicator Yes Needle indicates relative pressure in duct. Target is circle; needle should be in target or above.
Audio or Visual Alarm No Generally no alarm, because need electricity for alarms, Magnehelic has a pointer indicating the relative pressure, and may have a target.

 

Guide to Use

The red pointer indicates the pressure in the exhaust duct for the fume hood. Check to see that the pointer meets or is past the signal flag or target, which indicates sufficient exhaust pressure in the duct and inflow at the face of the fume hood when the sashes are in the proper position. If the gauge does not have a target compare with the reading documented on the hood inspection sticker. If the pressure reading are similar, the face velocity should be similar to the one listed on the inspection sticker, and you can safely work with hazardous materials in the fume hood. If the reading differs significantly from that on the sticker, the hood may not be operating properly. If the arrow is below the target there could be a mechanical problem, and the hood should not be used with hazardous materials; contact the building manager or Facilities Services (formerly PP-CS) to verify if the exhaust system is working properly.

It is recommended to use a visual indicator to verify that the hood airflow is inward. A tissue or Kimwipe taped to the sash or inside the hood provides a qualitative indicator of direction of airflow.

Description

Many fume hoods on campus are equipped with a magnehelic or a minihelic (smaller version). These devices are static pressure gauges that measure the difference in static pressure between the laboratory and the fume hood exhaust duct.

The gauge is a flow rate indicator with a scale that reads in units of pressure (inches of water), rather than velocity. Changes in the magnehelic reading may not be linearly proportional to changes in face velocity; therefore, it should only be used as an indicator of hood performance.

The magnehelic gauge reading at the time of the most recent hood survey is shown on each fume hood evaluation sticker. A big difference from the last reading may suggest that the face velocity may have changed significantly since the last survey. If the user notices a change, or has any other reason to suspect that the hood is not operating properly, contact EH&S or the building manager to resurvey for a repair.

 

AirGard 335 and Air Alert 600


Found in: Hearst Mining Memorial Building, Barker Hall
 

airgard 335 airgard 600

 

Digital display of face velocity Yes Can be switched from qualitative (red/yellow/green) to quantitative (fpm)
Visual Indicator Yes Large color indicator; Bar graph colored zones
Audio Indicator Yes Alarm when velocity too low or too high (red zone)
Alarm points Yes High and Low
Alarm Silencer Yes Test Reset button

Guide to Use

Make sure that the digital display of the face velocity has been turned on. If it is not on, contact your Building Safety Coordinator or Facilities Services (formerly PP-CS) for repair. Keep the air inlet free from obstruction, the inlet is in the middle of the display.

The satisfactory face velocity level is between 100 fpm and 150 fpm. If the monitor is in the red zone, discontinue any use of hazardous chemicals or materials and contact the building manager or Facilities Services (formerly PP-CS) to verify if the exhaust system is working properly.

Pressing the “Test Reset” button may temporarily silence the alarm. The alarm should not be left silenced.

Description

The AirGard 335 continuously monitors fume hood face velocity by measuring the air velocity of clean air from the room passing through the air inlet on the front of the monitor. The monitor then reports this information via audio and visual indicators.

Red (Alarm) — Indicates a high or low airflow alarm.

Yellow (Caution) — Indicates that the airflow is within the caution zone between normal and low alarm.

Green (Good) — Indicates that the airflow is within normal range.

Analog Bar graph Electronic bar graph expands/contracts through colored zones as the flow velocity changes. Colored Bands Red, yellow and green colored bands on LCD glass correspond to alarm, caution, and normal zones.

Digital Display Status indicators and icons reflect the status of monitor features. If digits are enabled, shows airflow velocity measurement either in feet per minute or meters per second.

Test/Reset Button Tests the digital display, LEDs, audible alarm and relay output or, if an alarm is present, silences the audible alarm.

Emergency Purge Button: When configured to operate, activates a relay that can be used to command the fume hood damper to open until pressed again.

 

AirGard 405 and Hamilton SafeAire 54L259


Found in: Barker, VLSB, Koshland, and more
 

airgard405

 

Digital display of face velocity No  
Visual Indicator Yes Red/Green Indicator
Audio Indicator Yes Alarm when velocity too low
Alarm points Yes Only Low
Alarm Silencer Yes Mute button/key

 

Alnor AirGard 405 Hamilton SafeAire 54L259
Green: normal
Red: Alarm
Only low alarm set point
Green: Normal
Red: Alarm
Alarm must be in “on” position for audio
Controlled with key

Guide to Use

These alarms should be used with a magnehelic, to provide both a quantitative and qualitative indicator of the fume hood's performance (refer to magnehelic guide).

These monitors provide a basic visual and audio alarm when the hood's face velocity is insufficient, but do not give quantitative numbers to validate the alarm.

If in alarm, contact the building manager or Facilities Services (formerly PP-CS) to verify if the exhaust system is working properly.

 

TSI Everwatch


Found in: Hildebrand, Latimer, Etcheverry, Birge, Calvin, Stanley

Guide to Use

Before using the hood, always check the digital reading on the monitor to ensure that the hood has sufficient airflow inflow velocity (100 fpm — 150 fpm).

The EverWatch device continuously monitors fume hood face velocity, and displays a digital reading of the measured face velocity. The sensor is mounted in the sidewall of the hood, and should be free from any obstructions.

There are also audible and visual alarms and indicators to alert the user.

Digital display of face velocity Yes Can be turned on
Visual Indicator Yes Small color indicator
Audio Indicator Yes Alarm when velocity too low or too high
Alarm points Yes High and Low
Alarm Silencer Yes Mute button

If the hood is performing normally, the green light will appear over “Normal.” If the face velocity is inadequate, or too great, a red alarm light and audible alarm will turn on. If in alarm, contact the building manager or Facilities Services (formerly PP-CS) to verify if the exhaust system is working properly.

Description

everwatch

Visual Alarm Operation

The red low alarm light is on when a low or inadequate face velocity exists. The red high alarm light is on when a high or excessive face velocity exists.

Audible Alarm

The audible alarm continuously sounds when the face velocity is in an alarm condition. The audible alarm can be temporarily silenced by pressing the MUTE key once, or permanently (not recommended) by pressing the MUTE key twice (yellow light comes on).

TEST Key

The TEST key, when pressed, initiates an instrument self-test. The monitor display, indicator lights, audible alarm, and internal electronics are tested when the TEST key is pressed.

 

TSI Sureflow


Similar to TSI Everwatch monitor, but connected to control that make the fume hood a Variable air volume hood.

Found in: Latimer Hall, Tan Hall
 

Digital display of face velocity Yes Also controls velocity upon movement of sash
Visual Indicator Yes Small color indicator
Audio Indicator Yes Alarm when velocity too low or too high
Alarm points Yes High and Low Flow (typically 80 fpm)
Alarm Silencer Yes Mute button

Guide to Use

Before using the hood, always check the digital reading on the monitor to ensure that the hood has sufficient velocity (100 fpm — 150 fpm). If the monitor's alarm indicates insufficient flow, discontinue any use of hazardous chemicals or materials.

The sensor is mounted in the sidewall of the hood, and should be free from any obstructions. There is a set airflow inflow velocity that the controls try to adjust to, when the sash is lowered the control damper actuator closes down the volume of air exhausted; when the sash is opened then the actuator opens the damper and more volume of air is exhausted.

Close the sash when not working in the hood and the monitor will adjust the velocity to save energy, while providing sufficient exhaust for the hood.

There are also audible and visual alarms and indicators to alert the user. If the hood is performing normally, the green light will appear over “Normal.” If the face velocity is inadequate, or too great, a red alarm light and audible alarm will turn on. If in alarm, contact the building manager or Facilities Services (formerly PP-CS) to verify if the exhaust system is working properly.

Normally there also is room pressurization sensors and controls that feedback to supply ventilation and maintain a constant satisfactory room pressurization.

Description

sureflow

Green light lit — normal operation

Yellow light lit — caution

Red light lit — alarm, air flow is too high or too low, audible alarm will sound, digital display will indicate type of alarm.

Emergency - Opens dampers and puts hood in full exhaust, increasing velocity, the red alarm light will flash and the alarm cannot be silenced. Depress the RESET button to put hood back in normal operation

Mute - depress once to silence alarm, alarm will stay silenced until hood returns to normal operation. If additional problems occur, audible alarm will sound again.

TEST Key

The TEST key initiates an instrument self-test. Pressing the TEST key activates a scrolling sequence on the display that shows the product model number, software version, and all setpoint and alarm values. The unit then performs a self-test that tests the display, indicator lights, audible alarm, and internal electronics to ensure they are operating properly. If a problem with the unit exists, DATA ERROR will be displayed. You should have qualified personnel determine the problem with the unit.

MUTE Key

The MUTE key temporarily silences an audible alarm. Pressing the MUTE key once temporarily silences the audible alarm. The alarm remains silent until the unit returns to control setpoint. Pressing the MUTE key twice, when controller is in alarm, will turn the yellow mute light on and permanently silence the audible alarm.

 

TEL AFA500 & AFA1000


There are just a few of these on campus. The AFA500 is a qualitative monitor that will alarm when the face velocity pressure is not satisfactory. The AFA 1000 also senses the face velocity but is more sensitive and can display quantitatively in FPM. If either monitor is in alarm, contact the building manager or Facilities Services (formerly PP-CS) to verify that the exhaust system is working properly, before working with hazardous materials. You can also try lowering the sash (decreasing sash-opening area) and see if the airflow is more than 100 fpm.

telafa500 telafa1000
TEL AFA 500 TEL AFA 1000