Altitude Valves

Altitude valves automatically control water tank filling and emptying by responding to tank water level changes through a pilot system. The valve opens when tank levels drop below a preset point and closes when the desired level is reached, maintaining consistent water supply without manual intervention. These valves typically maintain tank levels within ±6 inches of setpoint across flow ranges from 50 GPM to 5,000 GPM in municipal applications. The primary trade-off is their dependency on adequate upstream pressure differential (minimum 10-15 psi) to function properly, which can limit their effectiveness during peak demand periods or when upstream pressures fluctuate.

• Elevated Storage Tank Fill/Drain Control: Altitude valves automatically maintain water levels in elevated tanks between 85-95% capacity during peak demand periods. Installed on tank inlet lines (8-24 inch diameter), they open when system pressure drops below tank static head and close when predetermined high level is reached. Selected for reliable unattended operation and protection against tank overflow.

• Reservoir Level Management: Used on raw water intake lines (12-48 inch) to maintain optimal reservoir levels for treatment plants. Valve opens when reservoir drops to minimum operating level, closes at maximum safe level. Critical for plants with limited raw water storage capacity.

• Pump Station Surge Protection: Installed downstream of high-service pumps (6-36 inch lines) to prevent water hammer during pump cycling. Opens gradually during pump startup, closes slowly on shutdown. Essential for protecting distribution piping in systems with significant elevation changes.

• Distribution System Pressure Control: Controls flow to pressure zones in hilly terrain, maintaining consistent service pressure while preventing overflows in elevated areas.

Daily Operations: Operators verify proper valve position through SCADA indication or local position indicators. Check pilot system pressure gauges and float chamber operation. Monitor tank levels to confirm valve opens/closes at correct set points. No routine adjustments needed during normal operation - altitude valves are designed for automatic unattended service.

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Maintenance: Annual inspection includes cleaning debris from pilot system strainers, checking control tubing for leaks, and verifying float chamber operation. Valve internals require service every 3-5 years including diaphragm replacement and seat inspection. Standard PPE sufficient for most tasks. Confined space entry may be required for tank-mounted components. Millwright or instrumentation technician skills needed for pilot system work.

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Troubleshooting: Common failures include plugged pilot system orifices causing erratic operation, torn diaphragms resulting in valve hunting, and frozen control lines in winter. Warning signs include tanks overflowing, valves failing to open during low-pressure conditions, or excessive cycling. Typical service life 15-20 years for valve body, 5-10 years for pilot components with proper maintenance.

• Main Valve Body: Cast iron or ductile iron construction, flanged connections. Sizes 4-48 inches for municipal applications. Full-port design minimizes head loss. Selection based on line pressure (150-250 psi typical) and flow requirements.

• Pilot Control System: Diaphragm-actuated mechanism responds to downstream pressure changes. Stainless steel components resist corrosion. Adjustable set points typically 10-150 psi range. Critical for accurate level control.

• Float Chamber/Level Sensor: Remote float assembly connects to tank or reservoir via small-bore tubing. Bronze or stainless steel construction. Provides hydraulic signal to pilot system reflecting actual water level.

• Control Tubing Network: 1/4 to 1/2 inch copper or stainless steel tubing connects components. Must be properly sloped and protected from freezing. Includes shutoff valves for maintenance isolation.

• Needle Valve Assemblies: Throttling valves control opening/closing speed, preventing water hammer. Typically 1/8 to 1/4 inch brass construction with fine adjustment capability.

• Flow Velocity: 3-8 fps through valve body for 6"-36" sizes; oversized valves (>10 fps) cause excessive pressure drop and seat wear

• Pressure Rating: 150-300 PSI working pressure typical; high-zone applications may require 400 PSI rating with ANSI Class 300 flanges

• Cv Sizing: Select for 80-90% of maximum flow at 3-5 PSI pressure drop; undersizing causes hunting and instability

• Tank Elevation Differential: Minimum 10-15 feet between inlet and overflow elevation for proper modulation; insufficient head causes erratic operation

• Response Time: 30-120 seconds full stroke typical for municipal applications; faster response (15-30 sec) needed for surge-prone systems

• Accuracy: ±6 inches water level control under steady conditions; ±12 inches acceptable during high flow periods

• Pilot System Pressure: 15-25 PSI minimum differential required for reliable pilot operation; low-pressure mains (<30 PSI) may require external pilot supply

• Temperature Range: -10°F to 140°F for buried installations; extreme climate locations require insulated pilot systems

• Flow Coefficient: 0.7-0.9 of equivalent gate valve for properly sized installations; significant reduction indicates undersizing

• What maximum flow rate and pressure drop are acceptable? Altitude valves sized for <5 PSI drop at peak flow prevent cavitation and extend service life. Excessive pressure drop (>10 PSI) indicates undersizing and leads to premature failure. Engineers need peak hour demand projections and system curves.

• Should the valve fail open or closed during power/pilot failure? Fail-open prevents tank overflow but may drain elevated storage during emergencies. Fail-closed protects against drainage but risks overflow damage. Decision requires evaluation of downstream consequences, emergency protocols, and redundant controls.

• What level control accuracy is required for the specific application? Standard municipal applications tolerate ±6-12 inch level variation. Critical applications (fire storage, treatment plant clearwells) may require ±3 inch accuracy with electronic level controls. Tighter control increases costs 40-60% and requires more maintenance.

• Is surge protection required for the installation? Fast-closing altitude valves in long pipelines can generate dangerous pressure surges exceeding pipe ratings. Systems with >1000 feet of pipeline typically require surge anticipation or slow-closing modifications, adding 25-35% to valve costs.

• Division 40 - Process Integration

• Section 40 05 23 - Control Valves

• Primary specification location for altitude valves in water treatment applications. Alternative: Section 33 11 00 (Water Utility Distribution Piping) for distribution system installations.

• Material/Equipment Verification:

• Verify bronze/stainless internals for chlorinated water compatibility
• Confirm AWWA C540 compliance for municipal applications
• Check pilot system materials and pressure ratings

• Installation Requirements:

• Minimum 5D upstream, 3D downstream straight pipe
• Bypass valve and isolation valves required
• Access platform for maintenance (valves >12")

• Field Challenges:

• Pilot tubing protection during backfill
• Proper tank level sensing line installation
• Coordination with SCADA integration

• Coordination Issues:

• 12-16 week lead times for larger valves
• Early coordination with tank manufacturer for sensing connections

• Cla-Val: Model 25 Series altitude valves, widely used in 4"-24" municipal applications. Strong municipal reference base across North America.

• Bermad: Model 720 Series, popular for 6"-36" installations with excellent municipal track record.

• OCV Control Valves: Model 108 Series, competitive pricing for smaller municipalities, 2"-16" range.

• APCO: Model AV-06 Series, reliable performer in harsh climates, 4"-48" available.

• Pump Controls with Check Valves: Lower cost ($3K vs $8K for 12" valve) but requires reliable power and more complex controls. Preferred for smaller systems with existing pump automation.

• Float-Operated Valves: Mechanical operation, no pilot system. Cost-effective for remote locations but less precise control.

• Electronic Level Controls: Modern SCADA-integrated systems offer remote monitoring but higher complexity. Preferred for large systems requiring precise level management and data logging capabilities.

Establish direct relationships with manufacturer technical support—they provide invaluable troubleshooting assistance during commissioning. Specify factory pre-testing for valves >16" to avoid field adjustment delays. Consider standardizing on one manufacturer across your system for parts inventory efficiency. Request pilot system schematic drawings early; many installation issues stem from improper pilot connections rather than main valve problems.