Telescoping Valves

Telescoping valves are specialized control valves designed for deep reservoir or tank applications where water levels fluctuate significantly, commonly used in municipal clearwells, finished water storage, and wet wells. The valve features an extending stem mechanism that maintains proper sealing depth regardless of water level variations, typically accommodating 15-40 feet of level change while maintaining consistent flow control. These valves can handle flows from 0.5 to 25 MGD depending on size and configuration. The primary trade-off is higher maintenance requirements due to the complex telescoping mechanism and potential for stem binding in debris-laden environments.

• Outfall Discharge Control: Telescoping valves control final effluent discharge to receiving waters, connecting downstream of chlorine contact basins via 12"-48" ductile iron piping. Selected for precise flow modulation and ability to maintain backpressure against varying downstream water levels.
• Pump Station Discharge: Installed on raw water intake and wastewater lift station discharge lines (8"-36" diameter), connecting between pump headers and force mains. Chosen for throttling capability during pump startup/shutdown sequences and flow balancing between parallel pumps.
• Process Flow Splitting: Used in treatment trains requiring proportional flow distribution, particularly between parallel clarifiers or filter banks. Connects via flanged steel piping (6"-24" typical) with upstream flow measurement.
• Backwash Control: Controls filter backwash flow rates in gravity filtration systems, installed between wash water pumps and filter underdrain systems. Provides precise flow control during backwash sequences while withstanding high differential pressures up to 150 psi.

Daily Operations: Operators monitor valve position via SCADA displays, verifying alignment between commanded and actual positions within ±2% accuracy. Flow rate adjustments made through control system interfaces, with manual override capability during emergencies. Position feedback alarms alert operators to actuator malfunctions or stem binding conditions.

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Maintenance: Quarterly packing adjustments and actuator lubrication required. Annual disassembly for plug and seat inspection, typically requiring 4-hour maintenance windows with confined space entry procedures. Operators need basic mechanical skills and standard PPE including hard hats, safety glasses, and cut-resistant gloves. Actuator rebuilds every 5-7 years require specialized technician support.

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Troubleshooting: Common failures include packing leakage (visible weepage), actuator hunting (continuous small movements), and flow coefficient drift indicating seat wear. Cavitation damage appears as pitting on plug surfaces, typically after 8-12 years in high-differential applications. Warning signs include increased operating torque, position feedback.

• Valve Body & Seat Ring: Cast iron or ductile iron construction with bronze or stainless steel seat rings. Body sizes range 4"-48" for municipal applications. Material selection based on water chemistry.
• Telescoping Plug Assembly: Multi-stage cylindrical plug with precision-machined flow passages. Typically 316 stainless steel construction with hard chrome plating. Plug geometry determines flow characteristics.
• Actuator System: Electric or pneumatic actuators sized for 150-300 lb-ft torque requirements. Electric actuators preferred for remote locations lacking instrument air. Position feedback via potentiometers or encoders.
• Stem & Packing: 17-4 PH stainless steel stems with EPDM or Viton packing systems. Packing design accommodates frequent positioning cycles typical in automated control applications.
• Bonnet & Yoke: Cast iron construction with corrosion-resistant coatings. Removable bonnet design enables in-situ maintenance without valve removal from pipeline.

• Flow Control Range: 0.1-50 MGD typical municipal range, with turndown ratios of 10:1 to 100:1 depending on valve design. Critical parameter is minimum controllable flow - typically 1-2% of maximum rated flow for quality installations.
• Pressure Requirements: Operating pressures 10-150 psi typical, with pressure drop across valve ranging 5-25 psi at design flow. Higher pressure drops improve control accuracy but increase pumping costs.
• Control Accuracy: ±2-5% of setpoint for quality installations under steady-state conditions. Hysteresis should not exceed 3% of full scale. Response time typically 30-120 seconds for full stroke.
• Sizing Parameters: Cv values range from 5-5000 for municipal applications. Size based on 70-80% valve opening at maximum design flow to maintain control authority. Consider 25% safety factor for future capacity.
• Physical Constraints: Valve stroke lengths 6"-48" typical. Minimum straight pipe requirements: 5D upstream, 2D downstream. Operating temperature range 32-140°F for potable water applications.
• Actuator Requirements: Electric actuators 120-480V, pneumatic systems require 80-100 psi instrument air. Fail-safe positioning critical - specify fail-open or fail-closed based on process safety requirements.

• What is the required control range and minimum flow accuracy? Municipal plants need 20:1 turndown minimum for effective low-flow control during night/weekend conditions. If minimum flow drops below 5% of maximum, consider parallel valve arrangement or variable speed drives instead.
• Should the valve fail open or closed during power/air loss? Critical safety decision requiring process hazard analysis. Raw water intake valves typically fail closed to prevent contamination. Effluent discharge valves may fail open to prevent backup.
• What level of remote monitoring and control integration is required? Basic 4-20mA positioning vs. smart valve positioners with HART/Modbus communication affects initial cost by 30-50% but enables predictive maintenance.
• What are the site-specific installation constraints? Valve vault dimensions, crane access, and underground utilities dictate valve orientation and actuator mounting. Horizontal vs. vertical installation affects cost by 15-25%.

• Primary: Division 40 22 13 - Flow Control Valves
• Secondary: Division 40 05 23 - General-Duty Valves for Water Utilities
• Flow control applications with actuators fall under 40 22 13. Basic manual telescoping valves without automation use 40 05 23.

• Material/Equipment Verification: Verify NSF-61 certification for potable water contact, Confirm AWWA C508 compliance for municipal specifications, Check actuator sizing against available air pressure (80-120 PSI typical)
• Installation Requirements: Minimum 10D upstream, 5D downstream straight pipe runs, Concrete thrust blocks required at direction changes, Access requirements for actuator maintenance (typically 4-6 feet clearance)
• Field Challenges: Actuator freeze protection in northern climates, Air supply reliability and backup considerations
• Coordination Issues: SCADA integration requirements with control systems, Lead times typically 12-16 weeks for municipal-grade units

• Cla-Val - Model 90-01 telescoping valve, widely used in 8"-48" municipal applications
• DeZURIK - PWK Series telescoping valves, popular for 12"-60" water transmission mains
• Val-Matic - Model 207 telescoping valve, common in smaller municipal systems 6"-24"
• APCO - Model 700 telescoping valve, established in western US municipal markets
• All maintain active municipal references and provide field service support for installations.

• Butterfly Valves with Actuators - 30-40% lower cost, suitable for on/off service but limited throttling capability. Preferred for simple isolation applications.
• Globe Control Valves - Superior throttling characteristics, 50-70% higher cost. Better choice for precise flow control in treatment processes.
• Pressure Reducing Valves - Pilot-operated alternatives for pressure control applications, similar cost but different control characteristics. Preferred when constant downstream pressure is primary requirement rather than flow control.

Establish relationships with manufacturer field service early - most offer commissioning support that prevents costly startup issues. Specify redundant position indication (mechanical and electronic) as single-point failures are common. Consider factory pre-testing for critical applications over 24" diameter. Negotiate spare parts packages during initial procurement when pricing leverage is highest. Many municipalities save 15-20% on lifecycle costs by standardizing on single manufacturer across multiple projects, gaining volume pricing and simplified maintenance training.