Globe Valves

Globe valves provide precise flow control and tight shutoff in municipal water and wastewater systems by using a movable plug (disc) that seats against a stationary ring seat perpendicular to the flow path. The disc travels linearly through a threaded stem to modulate flow area, creating throttling capability with excellent control characteristics. Typical Cv values range from 0.5 to 2,000 for municipal applications, with control accuracy within ±2% of setpoint. However, globe valves create significant pressure drop (typically 2-15 psi) due to their tortuous flow path, making them unsuitable for applications where head loss is critical.

• Chemical Feed Control - Globe valves regulate sodium hypochlorite, ferric chloride, and polymer feed rates in 2-50 MGD plants. Positioned downstream of chemical pumps with upstream check valves, they provide precise flow throttling from 0.1-15 GPM. Selected for superior throttling characteristics and bubble-tight shutoff compared to ball valves
• Clearwell Drain Lines - Used on 6-24 inch drain lines in finished water storage, globe valves handle infrequent operation requiring reliable sealing. Installed with flanged connections to concrete structures, they're chosen over gate valves for positive shutoff during tank inspections and maintenance
• Sample Line Control - Globe valves control sample flow rates (0.5-2 GPM) throughout treatment processes. Connected to 1-2 inch sample taps with compression fittings, they provide fine flow adjustment essential for accurate laboratory analysis and online analyzer operation

Daily Operations - Operators monitor globe valve position indicators on SCADA systems, particularly for chemical feed control applications. Manual adjustments require 2-3 full handwheel turns from closed to achieve initial flow, then fine-tuning in quarter-turn increments. Flow indication confirms proper valve response during process adjustments.

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Maintenance - Quarterly packing adjustment prevents stem leakage, requiring 14mm wrench and standard safety protocols. Annual internal inspection during plant shutdowns reveals seat wear and disc condition. Maintenance requires confined space entry procedures for vault-mounted valves, with two-person teams and atmospheric monitoring equipment.

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Troubleshooting - Stem binding indicates packing over-tightening or corrosion buildup, typically occurring after 8-12 years in chlorinated water service. Excessive seat leakage shows as flow continuation after full closure, requiring disc/seat replacement. Internal cavitation damage appears as pitted metal surfaces, usually from oversized valve selection or excessive pressure drops exceeding 50 psi.

• Body and Bonnet - Cast iron or ductile iron construction for 4-12 inch municipal sizes, bronze for smaller applications. Bolted bonnet design allows in-line maintenance. Body design creates tortuous flow path enabling precise throttling control
• Disc and Seat - Renewable disc seals against integral or replaceable seat ring. Bronze-on-bronze or stainless steel materials resist wear and corrosion. Disc design (flat, tapered, or needle) determines flow characteristics and pressure drop
• Stem Assembly - Rising or non-rising stem with EPDM O-ring seals. Stainless steel construction prevents corrosion in water service. Threaded connection to disc allows precise positioning for flow control
• Handwheel/Actuator Interface - Manual handwheels for smaller valves, electric or pneumatic actuators for automated control. Square operating nut accommodates standard valve keys for buried service applications

• Flow Velocity: 5-15 fps in valve body; exceeding 20 fps causes erosion and cavitation in municipal systems handling 1-50 MGD flows
• Pressure Drop: Target 5-15 psi across valve at design flow; maximum 25 psi to prevent excessive energy loss. Critical for pump system curves and operational costs
• Cv Coefficient: Size for 70-80% open at design flow. Typical municipal ranges: 2-inch (Cv 25-40), 6-inch (Cv 200-400), 12-inch (Cv 800-1200), 24-inch (Cv 3000-5000)
• Operating Pressure: 125-250 psi working pressure typical for distribution systems; 50-150 psi for plant process applications. Factor 4:1 safety margin minimum
• Temperature Range: 32-180°F for potable water; up to 200°F for heated sludge applications. Material selection critical above 140°F
• Actuator Sizing: Electric actuators 50-2000 ft-lbs torque; pneumatic 100-8000 ft-lbs. Size for 150% of calculated stem torque including packing friction
• Response Time: 15-60 seconds full stroke for process control; 5-15 seconds for emergency shutoff applications
• Rangeability: 20:1 minimum for control applications; 50:1 achievable with characterized trim

• 1. Control vs. Isolation Service? Control applications require characterized trim (equal percentage/linear) and 20:1+ rangeability. Isolation service uses standard trim with tighter shutoff (Class V/VI). Wrong choice results in poor control performance or excessive actuator cycling. Need: process control requirements, frequency of operation
• 2. Actuator Type and Fail-Safe Position? Electric actuators for infrequent operation (<100 cycles/day), pneumatic for frequent control. Fail-open for bypass lines, fail-closed for chemical feeds. Incorrect selection causes safety issues during power/air loss. Need: cycle frequency, safety requirements, utility availability
• 3. Seat Material and Shutoff Class? Soft seats (EPDM/Viton) provide Class VI shutoff but limited to 250°F. Metal seats handle higher temperatures but achieve only Class IV shutoff. Wrong selection causes either leakage issues or premature failure. Need: temperature, shutoff requirements, media compatibility
• 4. Body Material and Pressure Rating? Cast iron adequate for 125-250 psi potable water; ductile iron for higher pressures or burial. Stainless steel required for chlorine dioxide or ozone service. Underrating causes catastrophic failure; overrating wastes budget. Need: system pressure, chemical compatibility, installation environment

• MasterFormat 40 05 19 - General-Duty Valves for Water Utilities
• Secondary: 40 05 13 - Butterfly Valves for Water Utilities (when comparing valve types)
• 40 41 13 - Flow Control Valves (for automated control applications)

• Material/Equipment Verification: Verify body material (ductile iron vs. cast iron) for pressure rating, Confirm seat material compatibility with water chemistry, Check operator type and torque requirements
• Installation Requirements: Allow 18-24" clearance above valve for maintenance access, Install with stem vertical or angled upward to prevent debris accumulation, Provide concrete thrust blocks for larger sizes
• Field Challenges: Heavy weight requires crane access for 12" and larger, Stem packing adjustment needed after initial pressurization
• Coordination Issues: 12-16 week lead times for AWWA-compliant valves

• Pentair Keystone - Figure 912 resilient seated globe valve, widely used for 4-24" municipal applications
• Fisher Controls - ED series for control applications, EZ series for isolation duty
• Mueller Water Products - A-2360 series iron body globes common in distribution systems
• American Flow Control - 2500 series AWWA-compliant globes for waterworks service

• Butterfly valves - 40-60% lower cost, preferred for larger sizes (>12") where tight shutoff isn't critical
• Ball valves - Better for frequent operation, 20% higher initial cost but lower maintenance
• Gate valves - Traditional choice for isolation service, similar cost but higher pressure drop when throttling. Globe valves preferred when precise flow control or tight shutoff is required despite higher cost and pressure loss

Establish relationships with local valve service companies early - they often stock common repair parts and can perform emergency packing adjustments. For budget projects, consider resilient-seated globes instead of metal-seated for non-critical isolation service - typically 30% cost savings. Always specify handwheel removal tools; operators frequently overtighten and damage stems. Request factory pre-testing for valves 16" and larger to avoid field startup delays.