Industrial Valve Selection Guide: Types, Materials, and Applications
Selecting the wrong valve for an industrial exhaust or chemical ductwork system causes leaks within 6 to 12 months, fugitive emissions that violate OSHA exposure limits, and emergency replacements that cost 3 to 5 times the correct valve’s installed price. An industrial valve selection guide for corrosive exhaust service must account for the valve type, body and seat material, end connection, pressure class, and actuator type — and each choice depends on the chemical composition, temperature, and pressure of the exhaust stream. This guide covers valve classification and standards, valve types for exhaust and ductwork, material selection for corrosive service, valve sizing and actuator selection, VAV and CAV damper design, installation and maintenance, and an industry application guide with quick-reference selection tables.
Key Takeaways
- Butterfly valves are the standard for exhaust ductwork above 6 inches — they are compact, lightweight, and cost 1/3 to 1/2 the price of flanged ball valves in the same diameter. Wafer-style butterfly valves cost $200-600 for a 12-inch PP valve. Lug-style valves allow downstream maintenance without system shutdown.
- Valve material must match the most aggressive chemical at the maximum temperature — PVC is limited to 60°C, PP to 80°C, and FRP to 110°C. HF attacks glass and metal (PP required). Chromic acid attacks PP (PVC or FRP required). Solvent-laden exhaust requires PTFE-lined alloy valves because solvents attack plastic body materials.
- VAV dampers are the only valve type designed for continuous flow modulation in exhaust systems — standard isolation valves cannot regulate flow without excessive wear. VAV dampers maintain setpoint within ±5 percent across the full flow range. PTFE-coated 316L SS blades are standard for laboratory exhaust. The damper must close to less than 1 percent leakage at 4 in. W.G.
- Check valves for low-pressure exhaust ductwork require cracking pressures below 10 in. W.G. — standard industrial check valves rated at 1-2 psi never open in a 5-20 in. W.G. system. Lightweight disc materials and low-friction bearings are required. The valve must be installed 5 pipe diameters downstream of any flow disturbance.
- Quarterly inspection is required for valves in wet acid gas service — the torque measurement compared to the installation baseline is the most reliable indicator of valve condition. A torque increase above 25 percent indicates seal or seat degradation. Carbon steel bolts in corrosive exhaust fail within 3-6 months — all flange bolts must be 304 or 316 stainless steel.
Valve Classification and Standards
Industrial valves are classified by function — isolation, regulation, or check — and by the motion of the closure member — quarter-turn (90 degrees from open to closed), multi-turn, or axial. Isolation valves (gate, ball, butterfly) are designed for fully open or fully closed service and are not intended for throttling. Regulation valves (globe, VAV damper, control ball) are designed for variable position service and can maintain a set flow or pressure. Check valves (swing, lift, dual-plate) allow flow in one direction only and close automatically when flow reverses. The valve function determines the type selection, which is the first step in the industrial valve selection process.
Standards and pressure classes. Industrial valves are manufactured to ANSI, ASME, ASTM, and ISO standards. The industrial valve selection process starts with understanding these classifications. Class 150 is rated for 285 psi at 38°C and is the standard for most exhaust ductwork applications where the static pressure is typically 5 to 20 in. W.G. (0.2 to 0.7 psi). Class 300 and 600 are used for higher-pressure piping systems. For exhaust ductwork and low-pressure chemical piping, the pressure class is not the limiting factor — the material compatibility and temperature rating are the primary selection criteria. The valve face-to-face dimensions are standardized per ASME B16.10, and the flange dimensions per ASME B16.5 for flanged valves and ASME B16.42 for ductile iron flanges. Refer to ASTM material standards for valve body specifications.
End connection types. The end connection must match the duct or pipe material and must provide a leak-tight seal at the operating pressure. Flanged connections are the most common for exhaust ductwork above 6 inches diameter. The flanges are bolted to matching flanges on the duct or pipe with a gasket between the faces. The flange facing — raised face, flat face, or RTJ (ring-type joint) — determines the gasket type and sealing performance. Wafer and lug connections are used for butterfly valves. The wafer valve is clamped between two pipe flanges with bolts that pass through the valve body. The lug valve has threaded lugs that allow the valve to be installed with bolts on each side, enabling the downstream flange to be removed while the valve remains in place. Threaded connections (NPT) are used for valves below 2 inches in diameter. Socket weld and butt weld connections are used for alloy valves in high-temperature or high-pressure service.
Valve Types for Exhaust and Ductwork
Five valve types cover the majority of industrial exhaust and ductwork applications. An effective industrial valve selection process matches the valve type to the specific function, diameter, and chemical service. The table below provides a side-by-side comparison of the seven most relevant valve types for exhaust system applications.
| Type | Function | Size Range | Max Temp | Pressure Class | Cost Factor | Corrosive Service | Actuation |
|---|---|---|---|---|---|---|---|
| Butterfly (Wafer) | Isolation | 2-48 in | 80-200°C | 150-300 | Low | Excellent (PP/PVC lined) | Manual, Pneumatic, Electric |
| Butterfly (Lug) | Isolation | 2-48 in | 80-200°C | 150-300 | Low-Moderate | Excellent | Manual, Pneumatic, Electric |
| Ball (Full Port) | Isolation | 1/4-12 in | 80-200°C | 150-600 | Moderate | Good (PTFE/FEP lined) | Manual, Pneumatic, Electric |
| Ball (Reduced Port) | Isolation/Regulation | 1/4-12 in | 80-200°C | 150-300 | Moderate | Good | Manual, Electric |
| Check (Swing) | Backflow prevention | 2-24 in | 80-200°C | 150-300 | Low | Good (lined) | Self-acting |
| Check (Dual-Plate) | Backflow prevention | 2-36 in | 80-200°C | 150-300 | Low | Good | Self-acting |
| VAV Damper | Flow regulation | 4-24 in | 60-120°C | Low pressure | Moderate-High | Excellent (PP/FRP) | Electric (0-10V, BACnet) |
Butterfly valves. Butterfly valves are the most common valve type for exhaust ductwork because they are compact, lightweight, and low-cost compared to other valve types for the same diameter. A 12-inch wafer butterfly valve costs $200 to $600 in PP or PVC construction, compared to $800 to $2,000 for a flanged ball valve for corrosive exhaust in the same diameter. The butterfly valve uses a disc that rotates 90 degrees from fully open (parallel to flow) to fully closed (perpendicular to flow). The disc seals against an elastomeric liner or a seat ring. The liner material must be compatible with the exhaust chemistry — EPDM for general acid service, FPM/Viton for aggressive chemical service, and PTFE for solvent-laden exhaust. Butterfly valves in corrosive exhaust service must have a PP, PVC, or FRP body with a lined disc. Standard metal butterfly valves with unprotected discs fail within 3 to 6 months in acid exhaust service due to chemical attack on the disc and seat.
Ball valves. Ball valves provide positive shutoff for liquid and gas service in smaller diameters. The full-port ball valve has a ball with a bore diameter equal to the pipe inside diameter, providing unrestricted flow and minimum pressure drop. The reduced-port ball valve has a smaller bore that creates some pressure drop but costs less. Ball valves in corrosive service must have a PTFE or FEP-lined ball and body. The lining prevents the process fluid from contacting the metal valve body. Lined ball valves are rated for full vacuum service, making them suitable for the negative pressure side of exhaust fans. Ball valves are not typically used above 12 inches diameter because the ball weight and actuation torque become excessive for the valve body structure. For exhaust ductwork above 12 inches, butterfly valves or VAV dampers are the preferred choices.
Check valves. Check valves prevent backflow in ductwork and piping systems. The swing check valve has a hinged disc that opens when forward flow exceeds the cracking pressure — typically 0.5 to 2.0 psi — and closes when flow stops or reverses. The dual-plate check valve has two spring-loaded plates that open at a lower cracking pressure than swing checks and close more quickly, reducing water hammer in liquid service. For exhaust ductwork where the static pressure is 5 to 20 in. W.G., the cracking pressure of the check valve must be lower than the duct static pressure to ensure the valve opens fully at normal flow. A check valve that requires 2.0 psi cracking pressure — equivalent to 55 in. W.G. — will never open in a duct system with 10 in. W.G. static pressure. Check valves for low-pressure exhaust ductwork must be specified with cracking pressures below 10 in. W.G. (0.36 psi), which requires lightweight disc materials and low-friction hinge bearings.
Gate and globe valves. Gate valves are isolation valves that use a sliding gate to open or close the flow path. The gate moves perpendicular to the flow direction. Gate valves are fully open or fully closed — they are not designed for throttling because the partially open gate vibrates and damages the seat surfaces. Gate valves are used in larger diameters (above 12 inches) where a butterfly valve may not provide the required shutoff tightness, or where the process requires a full-bore straight-through flow path with no obstruction. Globe valves are regulation valves that use a disc that moves perpendicular to the seat to control the flow rate. Globe valves create a significant pressure drop — typically 3 to 5 times that of a gate valve at the same flow rate — making them unsuitable for low-pressure exhaust ductwork. Globe valves are used in liquid chemical feed lines for scrubbers and dosing systems, not in exhaust gas ductwork.
Material Selection for Corrosive Service
The valve material must withstand the most aggressive chemical in the exhaust stream. This is the most critical decision in any industrial valve selection for corrosive service. Selecting a PVC valve for an HF service that exceeds 60°C will cause valve failure within weeks. Selecting an FRP valve for a chlorinated solvent exhaust will cause delamination within months. The four standard materials for corrosive-service valves — PVC, PP, FRP, and lined alloy — each have specific temperature limits, chemical resistance profiles, and cost ranges that determine the appropriate application.
PVC valves. PVC is the lowest-cost option for corrosive service valves. PVC resists HCl, H₂SO₄ up to 70 percent, caustic up to 25 percent, and most acid gases at ambient temperature. The maximum continuous operating temperature is 60°C. Above 60°C, PVC softens and loses mechanical strength — at 70°C, the pressure rating drops to 50 percent of the 23°C rating. PVC valves are available in butterfly, ball, and check configurations from 1/2 inch to 14 inches diameter for ball valves and up to 24 inches for butterfly valves. PVC is attacked by aromatic solvents (toluene, xylene), chlorinated solvents (methylene chloride, perchloroethylene), and ketones (acetone, MEK). PVC valve cost is $50 to $400 for a 4-inch butterfly valve, making it the most economical choice for ambient-temperature acid exhaust service.
PP valves. Polypropylene offers better chemical resistance and higher temperature capability than PVC. PP resists HCl, H₂SO₄, caustic, and most organic acids up to 80°C continuous and 100°C peak. PP is attacked by strong oxidizing agents — chlorine dioxide, sodium hypochlorite above 100 ppm, and concentrated nitric acid above 20 percent. PP valves are available in butterfly, ball, and check configurations from 1/2 inch to 24 inches diameter. PP is the standard material for semiconductor exhaust scrubbers and their valve systems. PP valve cost is $80 to $600 for a 4-inch butterfly valve. PP has better impact resistance than PVC at low temperatures, making it suitable for outdoor installations in cold climates.
FRP and dual-laminate valves. FRP valves provide the highest strength-to-weight ratio of any plastic valve material. The FRP laminate consists of a corrosion barrier (inner 2.5 to 5.0 mm of resin-rich surface) and a structural laminate. The corrosion barrier resin is selected for the specific chemical — vinyl ester for acid service, bisphenol A polyester for mild service, and furan resin for solvent service. FRP valves operate at 90 to 110°C depending on the resin system. FRP is attacked by hydrofluoric acid above 10 percent and by strong caustic above 25 percent at elevated temperatures. Dual-laminate valves combine a PP or PVC inner layer with an FRP outer structural layer, providing the chemical resistance of PP with the strength of FRP. FRP and dual-laminate valves are typically custom-fabricated for diameters above 12 inches and cost $500 to $3,000 depending on size and complexity.
Alloy and lined valves. For severe chemical service where plastic valves do not provide adequate temperature or chemical resistance, alloy valves with PTFE or FEP linings are used. The alloy valve body provides mechanical strength, and the plastic lining provides chemical resistance. Lined valves operate at 200°C with PTFE linings and are suitable for solvent-laden exhaust streams that attack plastic valve bodies. The lining thickness is typically 3 to 5 mm for PTFE and 2 to 3 mm for FEP and PFA. Lined valves cost $300 to $2,000 for a 4-inch ball valve — significantly more than plastic valves but less than solid alloy valves. Solid alloy valves (Hastelloy, Monel, titanium) are used where no lining material provides adequate chemical resistance — for example, in bromine or wet chlorine service. Solid alloy valves cost 5 to 10 times the cost of lined valves and are justified only for the most aggressive chemical environments.
Valve Sizing and Actuator Selection
Valve sizing for exhaust ductwork is determined by the flow coefficient, pressure drop, and actuator torque. A proper industrial valve selection integrates all three parameters. Unlike high-pressure process piping where the Cv determines the valve’s capacity at a given pressure drop, exhaust ductwork operates at 5 to 20 in. W.G. (0.2 to 0.7 psi), and the valve’s primary function is isolation or regulation with minimal pressure drop rather than flow control against a high-pressure drop.
Flow coefficient for exhaust valves. The Cv of a fully open valve in exhaust ductwork should be selected so that the valve contributes less than 10 percent of the total system pressure drop. For a duct system with a total static pressure of 10 in. W.G., the valve should contribute less than 1.0 in. W.G. when fully open. The valve Cv is calculated from the gas flow rate and the allowable pressure drop. For air at standard conditions, Cv = Q × √(SG / ΔP) × 0.036, where Q is the flow rate in CFM, SG is the specific gravity of air (1.0), and ΔP is the allowable pressure drop across the valve in psi. A 10,000 CFM duct with 1.0 in. W.G. (0.036 psi) allowable valve pressure drop requires a valve Cv of 10,000 × √(1.0 / 0.036) × 0.036 = 10,000 × 5.27 × 0.036 = 1,900. A 12-inch butterfly valve at 90 degrees open has a Cv of approximately 4,000 to 6,000 and is oversized for this application, meaning the valve contributes well under 1.0 in. W.G. at full open — which is acceptable.
Actuator selection. The actuator provides the torque required to operate the valve against the duct static pressure and the valve stem friction. Three actuator types are used for exhaust ductwork valves. Manual gear operators — a handwheel connected to a gearbox — are standard for butterfly and ball valves above 6 inches diameter. Manual gear operators cost $100 to $500 and are suitable for valves that are operated less than once per shift. Pneumatic actuators — a piston or diaphragm that converts compressed air to rotary motion — provide fast actuation for automated systems. Pneumatic actuators are fail-safe — a spring return closes or opens the valve on loss of air pressure. Pneumatic actuator cost is $300 to $2,000 for a 12-inch butterfly valve. Electric actuators — a motor and gear train that drives the valve stem — provide precise positioning for VAV dampers and control valves. Electric actuators accept 0-10V or 4-20mA control signals and provide position feedback to the control system. The actuator torque must exceed the valve break torque — the torque required to start the valve moving from the closed position — by a safety factor of 1.5 for manual operators and 2.0 for automated actuators. The break torque for a 12-inch PP butterfly valve at 10 psi differential pressure is 300 to 600 in-lb. The actuator must provide 450 to 900 in-lb for manual operation or 600 to 1,200 in-lb for automated operation.
VAV and CAV Damper Design
Variable air volume (VAV) dampers and constant air volume (CAV) dampers are specialized flow control devices for exhaust ventilation systems. Unlike isolation valves that operate fully open or fully closed, VAV dampers modulate the flow rate continuously to maintain a setpoint, and CAV dampers maintain a constant flow rate regardless of upstream pressure changes. VAV dampers are critical components in laboratory fume hood exhaust systems, where the exhaust flow must vary with the hood sash position to maintain face velocity while minimizing energy consumption. CAV dampers are used in general exhaust systems where a fixed flow rate must be maintained from each branch.
VAV damper for laboratory exhaust. A fume hood exhaust VAV damper modulates the exhaust flow from 100 percent of design flow at full sash opening to 30 to 50 percent at closed sash. The damper is controlled by the fume hood controller, which measures the sash position and sends a 0-10V or BACnet control signal to the damper actuator. The damper must maintain the setpoint flow within ±5 percent of the commanded value across the entire flow range. The damper blade must be constructed from 316L stainless steel or PP with a corrosion-resistant coating because laboratory exhaust may contain acid gases from chemical experiments. The damper seals must be PTFE or FEP to prevent leakage when the damper is closed for maintenance. The actuator must provide a position feedback signal to confirm that the damper has reached the commanded position. The response time from command to position is typically 30 to 90 seconds for the full stroke — slower response prevents pressure fluctuations in the duct system that could affect multiple fume hoods.
CAV damper for constant volume systems. CAV dampers maintain a constant flow rate through a duct branch regardless of pressure changes in the main duct. The CAV damper uses a spring-loaded mechanism or an electronic controller that adjusts the damper position to maintain the setpoint flow. Mechanical CAV dampers use a diaphragm that senses the differential pressure across an orifice plate and adjusts the damper position to maintain a constant ΔP, which corresponds to a constant flow rate. Electronic CAV dampers use a flow measuring station and an actuator that adjusts the damper position based on the measured flow rate. Electronic CAV dampers are more accurate (±3 percent of setpoint) than mechanical CAV dampers (±10 percent) but cost 2 to 3 times more. CAV dampers are used in general exhaust systems where multiple branches must each exhaust a fixed flow rate regardless of system pressure fluctuations.
Material and seal selection for dampers. The damper housing and blade material must be compatible with the exhaust gas chemistry. For general laboratory exhaust, 316L stainless steel with a PTFE coating is standard. For acid exhaust from chemical processing, PP or PVC construction is required. The blade seals must prevent leakage at the closed position — a leakage rate of less than 1 percent of the design flow at 4 in. W.G. static pressure is the standard for exhaust dampers. PTFE blade seals provide the best chemical resistance and temperature rating (200°C). EPDM and FPM/Viton seals are lower cost but are limited to 120°C and may be attacked by specific chemicals. The damper frame must include a jamb seal — a compressible gasket on the frame surface that seals against the blade edges — to achieve the low leakage rate. Dampers with jamb seals cost 20 to 40 percent more than dampers without jamb seals but are required for exhaust systems where fugitive emissions cannot be tolerated.
Installation, Testing, and Maintenance
Correct installation and regular maintenance determine whether an industrial valve achieves its design service life. A butterfly valve installed with the disc in the wrong orientation relative to the flow direction will fail within 6 months due to erosion of the disc edge. A check valve installed without consideration of the minimum opening pressure will never open, starving the downstream system of flow. The installation, testing, and maintenance practices described below apply to all valve types used in exhaust ductwork and corrosive service.
Valve positioning in exhaust ductwork. Butterfly valves should be installed with the disc rotating away from the flow direction — the disc should open toward the downstream side. Installing a butterfly valve with the disc opening against the flow direction increases the operating torque by 30 to 50 percent and causes erosion of the disc face at high flow velocities. Ball valves can be installed in any orientation but should be positioned so that the valve stem is vertical to prevent debris accumulation in the stem seal area. Check valves must be installed with the flow direction arrow aligned with the actual flow direction — a check valve installed backwards will block flow completely. Check valves should be installed a minimum of 5 pipe diameters downstream of any flow disturbance — an elbow, a tee, or a pump discharge — to ensure the flow profile is uniform when it reaches the check valve disc.
Corrosion prevention at flanged connections. The flanged connection between the valve and the duct or pipe is the most common leak path in corrosive service. The gasket material must be compatible with the exhaust chemistry — PTFE envelope gaskets for acid and solvent service, EPDM for water and mild acid service, and compressed fiber for general service. The flange bolts must be stainless steel (304 or 316) or alloy, never carbon steel. Carbon steel bolts in corrosive exhaust service corrode within 3 to 6 months, causing the joint to lose bolt tension and leak. The bolt torque must be applied in a crossing pattern to the manufacturer’s specified torque value, typically 30 to 80 ft-lb for 1/2-inch to 3/4-inch bolts. The flanges should be electrically isolated from the ductwork using isolating gaskets and bolt sleeves if the duct and valve materials are dissimilar — for example, a metal actuator mounted on a plastic valve body requires electrical isolation to prevent galvanic corrosion.
Leak testing and inspection frequency. New valve installations must be leak tested at 110 percent of the design pressure before being placed into service. The leak test is performed by plugging the downstream flange, pressurizing the upstream side to the test pressure, and applying a soap solution to the valve stem seal and flange faces. Any bubble formation indicates a leak that must be corrected before the valve is accepted. In-service inspection frequency depends on the service severity. Valves in clean, dry exhaust service at ambient temperature are inspected annually. Valves in wet acid gas service at elevated temperature are inspected quarterly. The inspection includes: visual examination of the valve body for external corrosion, stem seal leakage, and flange joint integrity; operation of the valve through one full cycle (open to close to open) to verify smooth operation; and measurement of the valve torque and comparison to the baseline value recorded at installation. A torque increase of more than 25 percent from the baseline indicates stem seal degradation or disc/seat fouling that requires maintenance. Common valve failure modes in corrosive exhaust service include stem seal leakage from chemical attack on the seal material, disc or ball coating from dried chemicals that prevent the valve from sealing, and flange gasket failure from thermal cycling that relaxes the bolt tension.
Application Guide by Industry
Each industry sector has a typical set of valve requirements. The industrial valve selection process must consider the exhaust composition, temperature, and regulatory framework for each sector. The quick-reference table below summarizes the recommended valve types, materials, and special considerations for each industry. Use this table as a starting point for the industrial valve selection process, and refer to the preceding sections for detailed design parameters and material compatibility data.
| Industry | Primary Service | Recommended Valve | Body Material | Trim/Seat | Special Considerations |
|---|---|---|---|---|---|
| Chemical/Pharma exhaust | Acid gas, solvent VOC, HCl, H₂SO₄ | Butterfly (3-24 in), Ball (<6 in) | PP, PVC, FRP | PTFE, FPM/Viton | Batch variability; actuators need 10:1 turndown |
| Semiconductor fab exhaust | HF, HCl, NH₃, hydride gases | Butterfly (4-24 in) | PP | EPDM, PTFE | HF attacks glass and metal; PP mandatory |
| Metal finishing exhaust | Chrome mist, HCl, HF, H₂SO₄ | Butterfly (6-36 in), VAV damper | PVC, FRP | FPM/Viton | Chromic acid attacks PP; use PVC or FRP |
| Food processing exhaust | Odors, grease, steam, VOCs | Butterfly (4-24 in), Check valve | 304SS, FRP | EPDM, PTFE | Grease accumulation; SS for wash-down areas |
| General industrial exhaust | Dust, fumes, ambient air | Butterfly (6-48 in), VAV damper | Galvanized steel, FRP | EPDM, Neoprene | Lowest-cost option acceptable |
| Laboratory fume hood exhaust | Mixed acids, solvents, VOCs | VAV damper (6-16 in) | 316L SS, PP | PTFE, FPM/Viton | Face velocity control critical; BACnet communication |
The selection guidelines above cover the most common exhaust applications. For each industry, the valve material must match the most aggressive chemical in the exhaust stream at the maximum expected temperature. When the exhaust contains multiple chemical classes — for example, a laboratory exhaust that may contain both HCl and acetone — the valve material must be compatible with both. PP is compatible with HCl but not with acetone at concentrations above 10 percent. PVC is compatible with both HCl and acetone but is limited to 60°C. 316L SS with PTFE lining is compatible with both at any concentration up to 200°C. When in doubt, the most conservative material selection is the safest choice because the cost difference between a PP butterfly valve ($200) and a lined alloy butterfly valve ($800) is small compared to the cost of a valve failure that causes a fugitive emission release.
Industrial Valve Selection FAQ
What is the most common valve type for exhaust ductwork?
The butterfly valve in wafer or lug configuration is the most common valve for exhaust ductwork and the starting point for any industrial butterfly valve for corrosive exhaust selection process for exhaust ductwork and the starting point for any industrial valve selection process. A 12-inch PP butterfly valve costs $200 to $600, compared to $800 to $2,000 for a flanged ball valve for corrosive exhaust in the same diameter.
What valve material is best for acid exhaust service?
PP is the standard material for acid exhaust up to 80°C. PVC is suitable up to 60°C at lower cost. FRP is required for temperatures above 80°C or for large diameters above 24 inches. Lined alloy valves are required for solvent-laden exhaust that attacks plastic materials.
How is a valve selected for VAV exhaust control?
VAV dampers for corrosive exhaust are selected based on the duct diameter, flow range, control signal type (0-10V, 4-20mA, BACnet), and material compatibility. The damper must maintain the setpoint flow within ±5 percent across the full flow range. PTFE-coated 316L SS blades are standard for laboratory exhaust.
What is the difference between wafer and lug butterfly valves?
A wafer butterfly valve is clamped between two pipe flanges and cannot be removed without shutting down the system on both sides. A lug butterfly valve has threaded inserts that allow the downstream flange to be removed while the valve remains in place, enabling downstream maintenance without system shutdown.
How often should valves in corrosive exhaust service be inspected?
Quarterly for wet acid gas service at elevated temperature. Annually for clean, dry exhaust at ambient temperature. The inspection includes visual examination for corrosion, full-cycle operation check, and torque measurement compared to the installation baseline. A torque increase above 25 percent indicates stem seal degradation.
What cracking pressure is needed for check valves in exhaust ductwork in exhaust ductwork?
The cracking pressure must be below 10 in. W.G. (0.36 psi) for low-pressure exhaust ductwork operating at 5 to 20 in. W.G. static pressure. Standard industrial check valves require 1 to 2 psi cracking pressure and will never open in a low-pressure duct system. Lightweight disc materials and low-friction bearings are required.
Conclusion: Select the Right Valve for the Exhaust System
Industrial valve selection for exhaust ductwork and corrosive service requires matching the valve type, body material, seat material, end connection, and actuator type to the specific chemical composition, temperature, pressure, and control requirements of the application. Butterfly valves in PP or PVC are the standard choice for most exhaust ductwork. VAV dampers with PTFE seals are required for laboratory and fume hood exhaust control. The valve materials for corrosive exhaust must be compatible with the most aggressive chemical in the exhaust stream at the maximum expected temperature. For a valve selection review for your exhaust system, contact our applications engineering team at sales@xichengep.com or visit the Air Emissions contact page. For ductwork and exhaust system design, refer to our industrial exhaust system design guide. Per OSHA 29 CFR 1910.94, all exhaust system components must be inspected and maintained to meet design requirements.