Instructions for use of butterfly valves with fume hoods
I. Selection of Butterfly Valves (For Fume Cupboard Use Only)
1. Type Selection
VAV Butterfly Valve: The preferred choice for laboratory fume cupboards. Equipped with an actuator and air volume feedback, it automatically adjusts airflow according to sash opening to maintain a stable face velocity (normally 0.5 m/s).
Manual Butterfly Valve: Only applicable for constant air volume systems, auxiliary branches or emergency bypasses; not suitable for main exhaust control.
Corrosion‑resistant Butterfly Valve: For applications involving corrosive gases, the valve body and disc shall be made of PP, PVC, 316L stainless steel or coated with fluoroplastic.
2. Key Parameter Matching
Airflow Range: Rated airflow of the butterfly valve shall cover the maximum exhaust volume of the fume cupboard (e.g., 1200–2000 m³/h), with a turndown ratio ≥ 6:1.
Pressure Independence: Pressure‑independent butterfly valves with flow feedback are preferred to avoid face velocity fluctuations caused by main duct pressure variations.
Actuator: Electric actuator (response time < 3 s) with manual emergency operation; explosion‑proof type shall be used in hazardous areas.
Sealing: Soft seal (silicone/fluororubber) with leakage rate < 1%; hard seal for high‑temperature or highly corrosive environments.
II. Installation Specifications
1. Installation Location
Install on the exhaust branch near the fume cupboard (distance ≤ 1.5 m) to minimize airflow disturbance.
Vertical or horizontal installation is permitted; inverted installation is strictly prohibited.
Ensure the arrow on the valve body is consistent with the airflow direction.
Install gaskets for flange connections and tighten bolts evenly to prevent air leakage.
2. Installation Procedure
Clean impurities inside the valve and duct before installation; keep the valve closed.
Align and connect air ducts coaxially and seal flanges to avoid jamming caused by eccentricity.
Fix the actuator and wire it to the fume cupboard controller/control panel.
Install a displacement sensor (for sash position) or face velocity sensor.
Manually test valve opening and closing before power‑on to ensure smooth operation.
III. Control Logic and Interlock (VAV System)
1. Basic Control Modes
Displacement Control (Open Loop):
The displacement sensor detects sash height; the controller calculates airflow and drives the butterfly valve for adjustment.
Velocity Feedback (Closed Loop):
The face velocity sensor monitors in real time and fine‑tunes the butterfly valve to stabilize at 0.5 m/s.
Compound Control:
Fast response via displacement control plus closed‑loop velocity correction, balancing speed and accuracy (response time < 2 s).
2. Intelligent Interlock
Sash fully open → valve fully open with maximum airflow;
Sash closed → valve throttled to the minimum safe airflow (e.g., 30%).
Occupancy Adaptive Control:
0.5 m/s when occupied, 0.3 m/s when unoccupied for energy saving.
Interlock with the laboratory’s main exhaust and air supply systems to maintain negative pressure and pressure balance.
IV. Operation and Adjustment
1. Manual Operation (Emergency)
Cut off power, operate the red emergency handle on the actuator to adjust opening manually.
Lock the position after adjustment to prevent displacement caused by airflow vibration.
2. Automatic Adjustment (Normal Operation)
Set face velocity (0.5 m/s) and upper/lower airflow limits on the controller panel.
The butterfly valve automatically follows sash movement to maintain stable face velocity.
Perform airflow balancing test after initial installation or overhaul; calibrate with an anemometer and fine‑tune valve limits and parameters.
V.Safety Precautions
The butterfly valve must not be fully closed during fume cupboard operation; maintain minimum safe airflow (normally ≥ 300 m³/h).
For toxic, flammable or explosive gases, explosion‑proof and flame‑retardant butterfly valves and actuators must be used.
Conduct regular leakage tests to ensure the exhaust system is tight and protect personnel safety.
Stop the fan and release pressure before maintenance to prevent injury from airflow impact.