How to Choose and Adjust Laboratory Exhaust Arms

Step 1: Selection Guide – How to Pick the Right Exhaust Arm?

1. Material Selection – Core Factor: Chemical Resistance

The material determines durability and suitability. This is the primary selection criterion.

2. Key Specifications – Performance Guarantee

After choosing the material, check these mandatory parameters:

• Face velocity (capture velocity) : ≥ 0.35 m/s (at the hood opening). This is the most critical indicator. Below this, harmful substances cannot be effectively removed.

• System airflow rate : Typical design range per unit: 150–350 m³/h; commonly 200–300 m³/h. For duct design, maintain main duct velocity at 6–8 m/s.

• Duct diameter : Common sizes: 75 mm and 110 mm – must match the system.

• Reach radius : Choose based on workstation layout; common reach around 1.6 metres.

Step 2: Practical Guide – How to Adjust Airflow?

1. Routine operation – Use the manual damper on the hood

Most exhaust arms have a manual adjustment valve at the hood opening. By rotating or sliding it, you directly open/close the baffle to quickly change airflow.

2. System optimisation – Adjust duct valves

If the arm is connected to a central system and one valve controls multiple units, or if total airflow is too high/low, a trained technician should adjust the main or branch duct dampers to balance the system.

3. Professional testing – Verify minimum face velocity

For safety, airflow must be validated. Use a hot-wire anemometer (never a vane anemometer). With the hood fully open, measure the air velocity at the centre of the hood opening. It must be ≥ 0.35 m/s.

Step 3: Design & Installation – Foundation for Long-Term Performance

• Positioning : Place the hood as close to the contaminant source as possible – recommended distance 15–30 cm (for welding applications, ≤25 cm). The vertical distance from mounting point to ceiling is typically between 1710 mm and 2440 mm.

• Basic procedure : Secure the bracket with expansion bolts → connect ducting and lock joints → adjust joints and hood position, tighten knobs → test airflow. Ceiling and wall mounting have slight differences – follow the product manual.

Operation and Maintenance Tips

• Good practices : Turn on the fan before starting experiments, delay shutdown after finishing; after repositioning the arm, tighten the knobs; avoid forceful pulling.

• Regular maintenance : Check joints for looseness monthly; clean inside and outside every six months (avoid damaging parts); replace filters (e.g., activated carbon) as specified by the manufacturer.

• Safety warnings : NEVER use the exhaust arm for high-concentration, flammable/explosive, or highly toxic gases. Regularly check activated carbon or other filters – replace immediately when spent.