Valves in Water and Wastewater Applications: An Extensive Guide

Valves are critical components in water and wastewater treatment plants, controlling flow, isolating equipment, preventing backflow, and ensuring safe, efficient operations. This guide provides detailed data on valve types, performance characteristics, installation practices, and lifecycle considerations.

Quick overview: Common valve types

• Gate valves: Isolation of mains and large pipelines; low pressure drop when fully open.
• Butterfly valves: Compact isolation/control for large diameters; economical and lightweight.
• Ball valves: Quick shutoff, tight sealing, smaller lines, chemical feeds.
• Plug valves: Sludge and viscous service; quarter-turn, robust sealing.
• Check valves: Prevent backflow in pump discharges and chemical lines.
• Pressure relief/safety valves: Protect systems from overpressure events.
• Knife gate valves: Slurry and solids handling; sharp gate cuts through debris.
• Control valves (globe, diaphragm, pinch): Precise flow regulation in aeration, chemical dosing, and effluent control.

Valve types and performance data

Gate valves

• Operation: Rising or non-rising stem; wedge gate lowers into seat.
• Size range: DN50–DN2000.
• Pressure rating: PN10–PN25 typical.
• Pros: Low headloss, full bore, robust for isolation.
• Cons: Slow operation, not for throttling, prone to seat wear with solids.
• Best use: Isolation of mains, pump suction/discharge headers.

Butterfly valves

• Operation: Quarter-turn disc rotates in seat.
• Size range: DN50–DN3000.
• Pressure rating: PN6–PN25 typical.
• Pros: Compact, lightweight, economical, good for large diameters.
• Cons: Some pressure drop, sealing depends on elastomer condition.
• Best use: Large diameter isolation, basin inlet/outlet control.

Ball valves

• Operation: Quarter-turn ball with bore rotates in seat.
• Size range: DN15–DN300.
• Pressure rating: PN16–PN40 typical.
• Pros: Tight shutoff, quick operation, chemical compatibility (PVC, PVDF, SS).
• Cons: Not ideal for throttling, seat wear with abrasives.
• Best use: Chemical dosing lines, small bore isolation.

Plug valves

• Operation: Quarter-turn cylindrical/tapered plug rotates in body.
• Size range: DN25–DN600.
• Pressure rating: PN10–PN25 typical.
• Pros: Good for sludge, viscous fluids, tight shutoff.
• Cons: Higher torque, potential wear with abrasives.
• Best use: Sludge lines, digester feeds.

Check valves

• Types: Swing, lift, ball, double-disc, silent check.
• Size range: DN25–DN1200.
• Pressure rating: PN10–PN25 typical.
• Pros: Prevents backflow, protects pumps and chemical systems.
• Cons: Can slam shut; requires correct sizing and damping.
• Best use: Pump discharge, chemical feed lines.

Knife gate valves

• Operation: Sliding gate cuts through solids.
• Size range: DN50–DN1200.
• Pressure rating: PN6–PN10 typical.
• Pros: Handles slurries, solids, fibrous material.
• Cons: Lower pressure rating, not for tight shutoff in clean service.
• Best use: Sludge, grit, screenings handling.

Control valves

• Types: Globe, diaphragm, pinch, eccentric plug.
• Accuracy: ±1–2% of setpoint typical.
• Pros: Precise flow regulation, automated control possible.
• Cons: Higher cost, maintenance of actuators and trim.
• Best use: Aeration air control, chemical dosing, effluent flow regulation.

Comparison snapshot

Selection criteria

• Fluid type: Clean water, sludge, grit, chemicals, air.
• Pressure/flow: Match valve rating to system design.
• Operation: Manual vs. automated (electric, pneumatic actuators).
• Maintenance: Seat/liner replacement, actuator service, accessibility.
• Materials: Cast iron, ductile iron, stainless steel, PVC, elastomers (EPDM, NBR, PTFE).
• Lifecycle cost: Initial capex vs.