Control Valves for Power Generation

Control valves in power generation range from the critical turbine bypass valve (handling sudden full-load rejection at Class 2500) to feedwater control, attemperator spray control, and extraction steam throttling. Vajra Industrial Solutions supplies high-pressure globe and cage-guided control valves in alloy steel for steam service, including noise-attenuating multi-stage trim for high-pressure-drop steam bypass applications and fast-acting actuators for turbine protection.

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What control valves does the Power Generation industry use?

Key Applications - Control Valves in Power Generation

Turbine Bypass Valve (HP/LP Bypass)

Fast-acting control valves for HP turbine bypass (boiler outlet to reheater) and LP turbine bypass (reheater outlet to condenser). Must open fully within 2 seconds on turbine trip. High-pressure-drop steam service - multi-stage pressure-reducing trim with downstream desuperheating spray. Alloy steel (WC9/P91) for HP bypass at Class 900–2500.

DN100–DN300, Class 900–2500, WC9 / P91, multi-stage trim, <2 sec opening, ASME B16.34

Boiler Feedwater Control Valve (BFP Recirculation)

High-pressure control valves for boiler feedwater flow control at economiser inlet and BFP minimum flow recirculation. Class 900–1500 for high-pressure feedwater at up to 350 bar. Anti-cavitation trim for BFP recirculation (large pressure drop from high-pressure feedwater to deaerator). WC6 for temperatures above 250°C feedwater.

DN25–DN150, Class 900–1500, WCB / WC6, anti-cavitation trim, ASME B16.34, IBR

Attemperator Spray Control Valve

Control valves for superheater and reheater attemperator spray water injection - regulating steam temperature by injecting high-pressure feedwater as spray. Must provide extremely precise control (small Cv, high rangeability) and survive large differential pressure and thermal shock from cold water into hot steam piping. Stainless steel (F316) or WC6 body.

DN15–DN50, Class 900–2500, WC6 / F316, high-rangeability trim, ASME B16.34, IBR

Extraction Steam and Auxiliary Steam Control

Control valves for turbine extraction steam pressure regulation to feedwater heaters, deaerators, and process steam headers. Throttle duty with varying pressure differential as turbine load changes. Cage-guided globe valve with equal-percentage characteristic for stable control across load range. WC6 at higher extractions; WCB for LP extraction steam.

DN50–DN200, Class 150–600, WCB / WC6, cage-guided, equal-% trim, ASME B16.34

Required Certifications

ASME B16.34 - Pressure-Temperature Ratings (all steam control valves)ASME B31.1 - Power Piping installation standardIBR Schedule IV - Indian Boiler Regulations (steam service in India)ANSI/ISA-75 - Control valve sizing standardEN 10204 3.1 / 3.2 MTCs - Material traceabilitySIL (IEC 61511) - Turbine bypass and emergency steam controlATEX / IECEx - Actuators in hazardous areas

Recommended Materials

A216 WCB - LP steam and condensate control, feedwater below 250°C

A217 WC6 (1.25Cr-0.5Mo) - HP feedwater and steam above 250°C to 540°C

A217 WC9 (2.25Cr-1Mo) - HP/IP turbine bypass, supercritical steam to 595°C

A217 C12A / P91 - ultra-supercritical HP bypass to 650°C

A182 F316 (SS 316) - attemperator spray, condensate and corrosion-risk feedwater

Inconel 718 trim - high-temperature, erosive steam service

Selection Factors

Pressure drop: High ΔP steam bypass - multi-stage trim mandatory to avoid noise (>120 dB), erosion, and vibration

Speed: Turbine bypass requires <2 second stroke - pneumatic piston actuator with volume booster, not spring-and-diaphragm

Anti-cavitation: BFP recirculation - large ΔP across liquid water requires anti-cavitation trim (FL factor must prevent cavitation)

IBR: All control valves on IBR-classified steam piping in India require IBR registration

Rangeability: Attemperator spray requires rangeability >100:1 - use characterised trim or separate small/large parallel valves

Positioner: HART/FF positioner with valve diagnostic capability for critical turbine bypass and feedwater valves

Technical FAQs

Why does a turbine bypass valve need to open in under 2 seconds?

During a full-load turbine trip (sudden disconnection from grid), the boiler continues generating full steam flow for several seconds before the burner management system reduces firing. This steam must be rapidly diverted around the turbine - through the HP and LP bypass valves into the reheater and condenser respectively - to prevent boiler pressure exceeding the safety valve set point and to protect the turbine from over-speed on re-start. Fast opening (1–2 seconds) is essential: if the bypass valve is slow, boiler pressure rises rapidly and safety valves lift, causing a major upset. Pneumatic piston actuators with volume boosters are used to achieve this speed.

What causes noise in high-pressure steam control valves and how is it reduced?

Noise in steam control valves is generated by high-velocity jet mixing as steam passes through the throttling restriction - acoustic energy is radiated through the valve body and piping. At high pressure ratios (P1/P2 > 2), steam reaches sonic velocity (choked flow) and noise can exceed 120 dB, causing hearing damage, piping vibration, and valve fatigue. Noise reduction strategies: (1) multi-stage trim - reduce pressure in steps, keeping each stage below choked flow; (2) downstream inline silencer/diffuser; (3) increase pipe wall thickness (acoustic lagging). Multi-stage trim is the most effective and is standard for turbine bypass and high-pressure reducing valves.