Why Standard Globe Valves Leak in Continuous Blowdown Service

December 22, 2022 | Blog

Blowdown is an essential process for the continuous production of steam required in most power plant boiler applications. Blowdown is necessary to control water chemistry and eliminate suspended solids and sludge that may have collected at the bottom of the boiler. The removal of solids allows for the generation of higher quality, cleaner steam. Because of the flow rates, pressures and temperatures experienced by valves used in these applications, normal wear occurs and the valve trim (e.g. seats) need to be replaced. Changes in system operating parameters or mistakes in sizing continuous blowdown valves will also result in leakage and require trim or valve replacement.

Why Shouldn’t a Standard Globe Valve be Used?

A standard Y- or T-type globe valve is not the best solution for continuous blowdown in power plants due to various design factors. The seat configuration and disc profile in a standard globe valve are not suitable for continuous blowdown service. Utilizing these valves will result in excessive seat wear (e.g. “wire draw”) due to the high velocity flow across the seat. This prevents the globe valve from sealing properly, resulting in leaks and can eventually cause more severe damage and flow control problems. In a throttling valve, the orifice is sized and the disc profiled to keep fluid velocity across the seat below damaging levels in order to prevent the seat from wearing out. If, and when, wear does occur, the seat can easily be replaced. Additionally, the potential for wire draw is mitigated.

Why Conval Developed the Clampseal® Throttling Valve

Conval, short for Connecticut Valve, developed the Clampseal Valves in 1967 and they are still manufactured in Connecticut today. Conval Clampseal Throttling Valves are purpose made for use in severe service applications requiring both repeatable flow control and dependable shutoff.

What makes the Clampseal Throttling Valves an ideal solution is an innovative design. These valves feature a removable seat/venturi that can be easily replaced or re-sized if conditions change. The Clampseal design provides easy access when service is required and there are no welds to cut and no seal rings or gaskets to replace. It also includes a position indicator, so you always know the valve position.

In a Conval Clampseal Throttling Valve, the disc and seat are properly sized to create an orifice for precise control. The orifice is designed to minimize downstream piping erosion and noise. If actual operating conditions are miscalculated or change, the throttling valve venturi and stem assembly may be resized to match the new condition. The orifice can be resized if needed for longer valve service life. This is especially important as advances in the industry are made.

The dual-orifice concept and the materials used in construction make the throttling valve nearly indestructible, even in the harshest of conditions. The metering nose of the disc remains in the replaceable orifice-seat cartridge and controls destructive high-velocity flows until the valve is open enough that the velocities will not damage the seat surface.

Specifications for World Class Clampseal® Throttling Valves:

  • Classic Clampseal® Design
  • Versatile
  • Low Velocity Across Main Seat
  • Precise Flow Control
  • Pressure-Assisted Seal Bonnet
  • Replaceable Seat/Venturi
  • Repairable & Resizable
  • Precise Control
  • Exceptional Repeatability
  • Ideal for Actuation/Positioning
  • Easy-to-Read Micrometer Position Indicator
  • Integral Gland Wrench for Simple Packing Adjustments
  • Available in Various Tandem Configurations for Blowdown
  • Effective Shutoff
  • Micrometer Dial (New Feature Coming Soon)
  • Standard Sizes: 1’’ to 4’’
  • Pressure Rating: ASME Class 900 through 3045
  • Standard Materials: Carbon Steel SA105, Forged Alloy Steel 182 F22 (Other materials available upon request)

Conval Clampseal® Valve Benefits

Conval Clampseal valves can be easily renewed compared to many other valves on the market. They have a secure, leak-proof bonnet which allows rapid access to valve trim for inspection and maintenance. Conval’s in-line renewable valves do not need to be cut out during inspections or when servicing is required, which allows for shorter downtime and low life-cycle costs.

A complete service, including a reground seat, new packing or stem replacement can often be accomplished in less than an hour. The cost of renewal for a Conval Clampseal valve is significantly less than the cost of valve replacement. The savings related to shorter shutdown times are considerable because the cost of plant shutdown often exceeds the cost of equipment.

Throttling Valve Applications

Throttling valves are increasingly used in many types of steam power plants, like nuclear, coal, and natural gas, including combined cycle heat recovery steam generator (HRSG) plants.

Common applications include:

  • Blowdown
  • Warm-up/bypass
  • Above/below seat drains
  • Severe duty vents/drains
  • Flow control
  • Sampling
  • Attemperation control

Armour Valve & Conval

Conval continuously works to improve the design of all its valves. Conval’s engineering team has been working on the addition of an improved position indicating device for the Conval Clampseal valve to provide even greater precision and consistency, and greater visual aid to workers. Other improvements and additions to the design, including a soon to be released micrometer dial, will be implemented in the future. Armour Valve works with Conval to tailor designs to suit customer-specific requirements.

If you’re looking for a Conval Clampseal Throttling Valve, Armour Valve is the exclusive supplier of Conval solutions in Canada. Visit the Armour Valve website for more information and contact us to discuss your specific needs.

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Marc Soucy, P.Eng

Eastern Region Sales Manager

I am a mechanical engineer with 30 years of plant, sales and service experience. I have been on both sides of the desk and can relate with you when issues arise in the plant. You can trust that I won’t recommend a product unless I know that it will do the job for you.

Marc Soucy, P.Eng

Directeur des ventes de la région de l’est

J’ai un diplôme en génie mécanique avec 30 ans d’expérience dans les usines, les ventes, et le service. J’ai été de chaque côté du bureau et je comprends lorsque des problèmes font surface dans l’usine, l’importance que l’on doit y apporter. Vous pouvez être sûr que je ne recommanderai pas un produit à moins que je sache qu’il convient à votre application.