Angle-style turbine bypass and process steam letdown valve — up to 500 mm seat diameter, ANSI 4500, 620 °C
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Download the BVT-TB steam conditioning valve brochure (PDF, document B-001)
For installation, disassembly and maintenance procedures, refer to product manual M-004 BVT-TB and to the general instructions for BVT valves and desuperheaters in M-001, which cover lifting, storage, installation, commissioning and safety.
How the BVT-TB works
The BVT-TB is designed to reduce the temperature and pressure of steam to match downstream requirements. Pressure is controlled using a proven trim technology in which a series of perforations in the valve cage are progressively revealed as the plug moves. Steam then passes to the outlet through a series of pressure reduction stages. These stages are selected specifically for the operating conditions on a case-by-case basis in order to reduce noise, and the pressure reduction pipes also create a flow profile that improves atomization of the spray water.
The valve plug design is optimized for low actuating forces. This balanced design allows smaller actuators to be used, and makes pneumatic actuation viable on valve sizes that would otherwise demand hydraulic actuation.
Control of temperature takes place in the outlet, where a number of spring-loaded spray water atomizing nozzles are installed perpendicular to the steam flow. The selection, placement and design of these nozzles are chosen to match the desuperheating requirements of the system, and to reduce the risk of free water being injected into the downstream piping. The nozzles are spring loaded to avoid thermal cracks in the outlet pipe and can be replaced quickly and easily.
Applications
Turbine bypass to condenser
A turbine bypass system consists of both pressure reduction and steam desuperheating. Turbine bypass valves are installed in parallel with the turbine's pressure stages and provide a secondary conduit for the superheated steam. The valves may be used for controlling downstream pressure and temperature during normal turbine operation or during a turbine trip. In a typical three-stage arrangement (HP, IP and LP) connected to an HRSG, an HP steam conditioning valve is connected in parallel with the high pressure stage and fed from a spray water control valve, while a second steam conditioning valve feeds a downstream dump tube that dumps steam to the condenser.
Bypass to process
Two BVT-TB valves can be installed in parallel with a turbine together with two BVT-DLP multi-nozzle desuperheaters. Steam is desuperheated by both the valves and the desuperheaters before being output to process, with spray water controlled by external spray water control valves.
Typical markets
- Combined cycle power plants
- Combined heat and power (CHP) plants
- Concentrated solar power (CSP) plants
- Process steam plants requiring conditioned steam export
Specifications
| Valve style | Angle-style, forged body |
|---|---|
| Valve sizes | Up to 500 mm seat diameter |
| Pressure class | Up to ANSI 4500 (higher rating on request) |
| Design temperature | 620 °C as standard (650 °C on request) |
| Leakage class | ANSI Class III, IV, V; MSS SP-61 |
| Rangeability | Up to 25:1 for the complete valve |
| Regulatory requirements | ASME, EN, PED, IBR, CRN. Manufactured under ISO 9001 and ISO 14001. |
| Materials | Forged material adapted to connecting pipe material |
| Bonnet | Pressure seal bonnet |
| Actuation | Pneumatic, hydraulic or electrical |
| Connections | Fully customizable inlet and outlet connections |
Options
- Quick change type seat — reduces maintenance downtime
- Erosion resistant trim with long cage — reduces wear on trim internals caused by wet steam or particles by moving the critical pressure drop
- Expanded outlet — improves secondary atomization through increased steam velocity over the nozzles, improves tertiary atomization and increases rangeability
- Live load gland seal packings
Key features
- Fully customizable inlet and outlet connections.
- Complies with ASME, EN and PED.
- Forged valve body with uniform thickness, and trim design optimized to withstand thermal cycling.
- High shut-off class (to ANSI Class V).
- Great rangeability, up to 25:1 for the complete valve.
- Pressure reduction stages and spray nozzle arrangements optimized for the actual operating conditions and for reduced noise. The pressure reduction pipes also create a flow profile that improves atomization.
- Balanced plug design requires smaller actuating forces, allowing smaller and pneumatic actuators.
- Pressure seal bonnet for simpler and quicker maintenance — no special tools necessary.
- Compatible with pneumatic, hydraulic and electrical actuation.
- Easily exchangeable seat available as an option for further reduced maintenance downtime.
- Optimized packing design.
- Long cage design reduces wear on trim internals caused by wet steam or particles.
- Spring-loaded nozzles designed to avoid thermal cracks in the outlet pipe; quickly and easily replaced.
Actuation options
Pneumatic actuation
BVT valves can be equipped with pneumatic piston actuators. The cylinders are chosen to overcome the forces created by the steam flow, and the accessories are chosen to handle the required stroke speeds and functionality.
| Cylinder types | Double acting or single acting; spring open or spring close; top mounted or side mounted hand wheel |
|---|---|
| Air supply | 4 – 10 bar |
| Standard accessories | Air filter regulator |
| Optional accessories | 3-way valves (quick open/close), limit switches (open/close position), position transmitters, air locks, boosters |
Electro-hydraulic actuation
As an alternative to pneumatic actuation, BVT can supply the BVT-TB with electro-hydraulic actuators. These are powered and controlled by the BVT Hydraulic Control Panel (HCP) and Hydraulic Power Generator (HPG). Pump control in the HPG is handled by default by the Intelligent Power Manager (IPM), which monitors oil level, temperature and pressures and warns the DCS of any issues. Positioning is handled by default by the Intelligent Actuator Control (IAC), which can control two modulating and two on/off actuators. Commissioning tools and hydraulic pipes, fittings and hoses are also available.
Installation, commissioning and maintenance
The following summarises requirements from BVT product manual M-004 and general instructions M-001. These are general guidelines — any individual installation may require special considerations, and if the stated pipe distances cannot be achieved, contact BVT Sweden AB for an installation-specific calculation.
Important: all BVT steam valves are designed for dry steam. Wet steam, condensate and magnetite damage valves, and such damage is not covered by warranty. Drains and vent valves must take care of pipe prewarming.
Minimum pipe distances
Non-uniform upstream flow patterns create rotational forces that strain valve parts, and injected water droplets need time and distance to fully evaporate. Where multiple criteria apply, the highest value must be used.
| Distance | Condition | Must exceed |
|---|---|---|
| Straight pipe upstream of inlet | Single upstream bend, Ø < 200 mm | 1 metre |
| Straight pipe upstream of inlet | Single upstream bend, Ø 200–400 mm | 5 × Ø |
| Straight pipe upstream of inlet | Single upstream bend, Ø > 400 mm | 3 × Ø |
| Straight pipe upstream of inlet | Multiple upstream bends, Ø < 200 mm | 3 metres |
| Straight pipe upstream of inlet | Multiple upstream bends, Ø 200–400 mm | 15 × Ø |
| Straight pipe upstream of inlet | Multiple upstream bends, Ø > 400 mm | 9 × Ø |
| Straight pipe downstream of water injection (L2) | BVT-TB, mechanical atomization — bypass to process, to cold reheat or to district heating | 0.1 s × V, maximum 8 × Ø |
| Water injection to downstream temperature sensor (L3) | Water-to-steam ratio r < 15% | 0.2 s × V, maximum 12 metres |
| Water injection to downstream temperature sensor (L3) | Water-to-steam ratio 15% ≤ r < 18% | (0.2 + (r − 15%) / 0.3) s × V, maximum 12 metres |
| Water injection to downstream temperature sensor (L3) | Water-to-steam ratio r ≥ 18% | 0.3 s × V, maximum 12 metres |
Avoid multiple bends upstream of the valve, as these cause rotational steam flow. If unavoidable, allow a minimum of 6 metres of straight pipe after the last bend. The orientation of the nearest upstream flow divider also matters: a divider running parallel to the valve plug is preferred, while one installed perpendicular to the plug produces a flow pattern that can impose rotational forces on the plug.
Drainage
Water entering a steam conditioning valve can damage internal parts and disturb downstream temperature measurement, so drains are required both upstream and downstream of the valve. Maximum condensate normally occurs during cold startup and must be considered at the design stage when sizing the drainage system. As an estimate, a water mass of typically 7–14% of the upstream piping weight needs to be removed through the condensate system during startup.
An undersized upstream drainage system that cannot handle condensate from pipe warming during a cold start is the most common cause of valve damage. The drain valve should remain open during startup and any other condition producing condensate, and must stay open until the steam is above saturation + 20 °C. A temperature sensor should always confirm that upstream steam is dry before the valve is opened.
Temperature sensor placement
The downstream temperature sensor must be positioned where it measures the temperature actually being controlled. If it is installed too close to the spray water injection point it may be struck by unevaporated droplets, producing a false low reading and unstable temperature control. No branches, isolation valves or other obstructions may be placed in the steam line between the spray water injection point and the temperature sensor. A higher degree of superheat or a higher water temperature shortens the required distance; lower values lengthen it. BVT can supply a protective shield that encases the sensor, installed with its hole facing downstream.
BVT also recommends installing a temperature sensor and a pressure sensor upstream of the steam conditioning valve, both to confirm dry steam before the valve opens and to support feed-forward outlet temperature control.
Insulation
Any valve intended for hot service must be insulated. Thermal insulation should be applied to all exterior surfaces of the valve body and bonnet, and should help keep the body adequately warm while the valve is closed. Proper insulation minimises heat loss, maintains thermal stability, reduces the risk of condensation and water hammer, and improves personnel safety.
- Insulate the valve body, inlet and outlet piping, and adjacent flanges.
- Do not insulate actuators, positioners or other temperature-sensitive electrical equipment — the actuator and its accessories must be protected from excessive heat.
- Do not cover the yokes or add material that makes removing valve internals difficult.
- Ensure the insulation does not interfere with plug or stem movement.
- Keep nozzle cover plates accessible and uncovered.
- The insulation must not trap condensate around the valve body.
Insulation also provides noise attenuation. A −10 dBA arrangement uses 1 mm cladding steel plate over 300 mm mineral wool at 200 kg/m³ density. A −15 dBA arrangement adds a heavy self-adhesive noise damping layer (approx. 7 kg/m²) and a 50 mm mineral wool layer between two cladding plates.
Body material temperature limits
| Carbon steel (internals Tenifer surface hardened) | 480 °C |
|---|---|
| Low alloy steel | 580 °C |
| 13CrMo4-5 / ASTM Gr.12 | 580 °C |
| 11CrMo9-10 / ASTM Gr.22 | 580 °C |
| X10CrMoVNb9-1 / ASTM Gr.91 | 580 °C |
| Low alloy steel (internals Cobalt hard faced) | 650 °C |
Before welding into the pipeline
- Verify that the installation direction is correct, and that any arrow on the valve body points in the same direction as the flow in the pipe system.
- Align the pipe ends properly so the valve is not subjected to unnecessary strain.
- Remove the valve trim and spray nozzles before welding the valve into the pipeline.
- Remove any commissioning tools (hydrotest, blowout, etc.) before welding.
- Welding and any necessary heat treatment are the contractor's responsibility and must be performed in compliance with applicable standards by qualified personnel.
Commissioning and steam blowing
Debris generated during installation or major repair can damage valve trim and sealing surfaces, clog spray nozzles and cause improper valve operation. Steam blowing removes loose particles from the pipework, but the procedure itself can severely damage trim parts, so protective equipment such as a blow out tool, blow through tool, dummy nozzles or sacrificial trims must be installed first. BVT must be informed of the planned steam blowing method in advance and can supply the required tools.
| Steam temperature | 50 – 100 °C above saturation point |
|---|---|
| Steam velocity | More than 50% of maximum steam velocity, and at least 70 m/s |
| Max. temperature for BVT steam blowing tools | 425 °C as standard |
If the steam velocity is too low, particles may not be carried along and can fall back into the pipework where they are difficult to detect.
Upstream stop valve
An undersized steam stop valve creates a high pressure drop as it constricts the flow, which in turn gives the steam control valve a non-linear characteristic. Undersized stop valves with a reduced bore upstream of a steam control valve are known to cause noise and vibration due to high vena contracta velocities and non-uniform velocity distribution. An angle-style stop valve can be welded directly to the inlet connection of the BVT-TB as a single unit, but BVT must be informed in advance if such an arrangement is planned.
Maintenance notes
- Confirm that the pressure vessel is depressurized and sufficiently cooled down before starting any work, and wear protective gloves, clothing and eye-wear.
- Before maintenance on a valve in an operational facility, a double block-and-bleed configuration must be installed upstream. Each component in the block-and-bleed system must be individually proven for the highest expected pressure.
- Ensure the packing gland is firmly tightened before pressurizing the valve. Never remove the gland nut or flange while the valve is pressurized.
- Ensure drain and vent valves are open and discharging.
- The pressure seal must be replaced after every disassembly.
- Stem packing rings must be replaced after every disassembly.
- The valve and yoke must never be lifted using the actuator or eye bolts installed on the actuator.
- If live load is used, note the compressed height of the belle-ville washer sets before removing the gland yoke nuts.
- No alteration should be made to any valve without the involvement of BVT service engineers.
Frequently asked questions
What is a steam conditioning valve?
A steam conditioning valve reduces both the pressure and the temperature of superheated steam in a single device. Pressure is reduced by throttling the steam through a staged trim, and temperature is reduced by injecting atomized spray water downstream of the throttling point. The BVT-TB performs both functions inside one forged angle-style body.
What is the BVT-TB used for?
The BVT-TB is used for turbine bypass and process steam letdown. In a turbine bypass system it is installed in parallel with a turbine pressure stage and provides a secondary conduit for superheated steam, controlling downstream pressure and temperature during normal turbine operation and during a turbine trip. It is also used to condition steam that is exported to a process.
How does the BVT-TB reduce pressure without generating excessive noise?
The plug progressively uncovers a series of perforations in the valve cage, and the steam then passes to the outlet through several pressure reduction stages. The number and configuration of these stages is selected case by case for the actual operating conditions, which limits the pressure drop taken across any single stage and therefore limits aerodynamic noise.
What rangeability can the BVT-TB achieve?
Up to 25:1 for the complete valve. The optional expanded outlet design increases rangeability further by raising steam velocity across the spray nozzles, which improves both secondary and tertiary atomization of the spray water.
What is the difference between an angle-style and a globe-style steam conditioning valve?
An angle-style body, such as the BVT-TB, turns the flow through 90 degrees and gives a straight outlet section in which the spray water nozzles and pressure reduction stages can be arranged. A globe-style body, such as the BVT-TBG, keeps inlet and outlet in line. Angle-style bodies are generally preferred where a long, unobstructed desuperheating section is required downstream of the throttling point.
Why does the BVT-TB use a balanced plug design?
A balanced plug requires lower actuating forces. This allows a smaller actuator to be used and makes pneumatic actuation practical on valve sizes that would otherwise require hydraulic actuation, reducing both cost and installed footprint.
How is free water downstream of the valve avoided?
Temperature control takes place in the valve outlet using spring-loaded atomizing nozzles mounted perpendicular to the steam flow. The number, placement and design of the nozzles are selected to match the desuperheating duty of the system, so that spray water is fully atomized and evaporated rather than being injected as free water into the downstream piping.
What maintenance does the BVT-TB require?
The pressure seal bonnet allows the trim to be accessed without special tools. The pressure seal and the stem packing rings must be replaced after every disassembly. Spring-loaded spray nozzles are replaceable individually, and the optional quick change type seat further reduces maintenance downtime.
Does the valve trim need to be removed before welding the valve into the pipeline?
Yes. The valve trim and the spray nozzles must be removed before the valve is welded into the pipeline, and any commissioning tools such as hydrotest or blowout tools must also be removed first. The pipe ends must be properly aligned so the valve is not subjected to unnecessary strain, and the installation direction must be verified.
Which actuation options are available for the BVT-TB?
Pneumatic, hydraulic or electrical. Pneumatic piston actuators run on a 4 to 10 bar air supply and are available as double acting or single acting, spring open or spring close. Electro-hydraulic actuation is supported by the BVT Hydraulic Control Panel and Hydraulic Power Generator, with Intelligent Actuator Control positioning and Intelligent Power Manager pump control.
How much straight pipe is required upstream of a BVT-TB steam conditioning valve?
With a single upstream bend, allow at least 1 metre for pipe diameters below 200 mm, 5 pipe diameters for 200 to 400 mm, and 3 pipe diameters above 400 mm. With multiple upstream bends, allow at least 3 metres below 200 mm, 15 pipe diameters for 200 to 400 mm, and 9 pipe diameters above 400 mm. Where several criteria apply, use the highest value.
How far downstream should the temperature sensor be installed from a BVT-TB?
The distance from the water injection point to the downstream temperature sensor depends on the ratio of water to steam. For a ratio below 15 percent allow 0.2 seconds multiplied by steam velocity, up to a maximum of 12 metres. For a ratio of 18 percent or above allow 0.3 seconds multiplied by steam velocity, again up to 12 metres. No branches or obstructions may lie between the injection point and the sensor.
Why does a steam conditioning valve need drains upstream and downstream?
Free water entering the valve damages internal parts and disturbs downstream temperature measurement. Maximum condensate occurs during cold startup, when typically 7 to 14 percent of the upstream piping weight in water must be removed through the condensate system. An undersized upstream drainage system is the most common cause of valve damage. The drain valve must remain open until the steam is above saturation plus 20 °C.
Does a BVT-TB steam conditioning valve need to be insulated?
Yes. Any valve intended for hot service must be insulated across all exterior surfaces of the body and bonnet, which minimises heat loss, maintains thermal stability and reduces condensation and water hammer risk. Actuators, positioners and other temperature-sensitive electrical equipment must not be insulated, yokes must not be covered, and the insulation must not trap condensate around the valve body or block nozzle cover plates.
What steam conditions are required for steam blowing before commissioning?
Steam used for flushing should be 50 to 100 °C above the saturation point, at a velocity exceeding 50 percent of maximum steam velocity and at least 70 m/s. Protective equipment such as a blow out tool, blow through tool, dummy nozzles or sacrificial trims must be installed first, since steam blowing can severely damage valve trim. BVT steam blowing tools are rated to 425 °C as standard.
Can wet steam be used with a BVT-TB?
No. All BVT steam valves are designed for dry steam. Wet steam, condensate and magnetite damage valves, and this damage is not covered by warranty. Drains and vent valves must handle pipe prewarming, and a temperature sensor should confirm that upstream steam is dry before the valve is opened.
Related BVT products
- BVT-TBG — globe-style steam conditioning valve
- BVT-DLP — multi-nozzle desuperheater, often installed downstream of a BVT-TB in bypass-to-process arrangements
- BVT-Z / BVT-ZP — seat and quick exchange seat designs
- Spray water control valves — trims selected to prevent cavitation and flashing, with quick exchange trims (PT, HSC and HEST types)
About BVT Sweden
BVT Sweden AB was started with the ambition of becoming world leading in critical applications in process steam and thermal power plant turbine bypass. Based in Säffle, Sweden, BVT Sweden employs experts with over 30 years of experience in turbine bypass, steam conditioning, temperature control, design and manufacturing processes. BVT designs turbine bypass valves and selects actuation to fit each customer's requirements. Products are optimized on a per-order basis, and include steam conditioning valves, pressure reduction valves, stop valves, desuperheaters and spray water control valves.
Contact BVT Sweden for application-specific sizing and selection.
Manufacturer: BVT Sweden AB, Industrigatan 1-3, 661 32 Säffle, Sweden (Factory Support Office) · Körkarlsvägen 8, SE-653 46 Karlstad, Sweden (Sales Office).
Source documents: datasheet B-001 BVT-TB, product manual M-004 BVT-TB, general instructions M-001. Last reviewed: 2026-09-25.