Yarway Blow-Off Valves Seatless, Hardseat and Unit Tandem

Overview

A Yarway blow-off valve is a heavy-duty boiler valve from Emerson built for intermittent blow-off service, where dirt, sediment and scale are discharged from the bottom of a boiler and drum level surges are controlled during fast start-ups. Emerson offers three designs: Seatless sliding-plunger valves for pressures to 935 psi (64.5 bar), Hardseat seat-and-disc valves for pressures to 2,455 psi (169 bar), and Unit Tandem valves, which combine a blowing valve and a sealing valve in one forged block for pressures to 3,206 psig (221 barg). Sizes run from NPS 1 to 2½ (DN 25 to 65) with flanged, socketweld or buttweld ends in cast iron or carbon steel.

Seven Star LLC supplies each type of Yarway blow-off valve, along with acid wash trim options and replacement packing, to power stations, desalination plants, refineries and industrial boiler houses in Oman and the GCC. Our Muscat office provides engineering support, from figure number selection to tandem arrangement and handing.

Working Principle

Basic requirements for blow-off valves are set by the ASME Power Boiler Code, Section I, and Yarway valves are designed to ASME Section I, ASME B31.1 and ASME B16.34. Because the code does not allow valves with dams or pockets where sediment can collect, ordinary globe valves cannot be used for this duty. The Seatless Yarway blow-off valve instead uses a hollow Nitralloy plunger that slides through packing rings above and below the ports. When the handwheel raises the plunger, discharge passes through double ports in the lower gland and plunger; on closing, a shoulder on the plunger compresses the packing, and a final hard turn gives drop-tight shutoff. With no seat, there is nothing to score or plug with dirt.

The Hardseat valve works on a seat-and-disc principle with flow entering under the seat. As it opens, a lip on the disc restricts flow until the beveled seating surface is well clear of the seat, which reduces wiredrawing and protects the Stellite sealing faces. Emerson recommends opening these valves rapidly and fully. In tandem service, the valve nearest the boiler is the blowing valve, opened last and closed first, and the valve farthest from the boiler is the sealing valve, opened first and closed last.

Engineering Design of the Yarway blow-off valve Range

Seatless valves (Types 3400 and 3900) are available in angle or straightway patterns, Class 250, 300 and 600, with flanged ends to ASME B16.5. They feature live-loaded packing with heavy compression springs under the yoke nuts, a ball-bearing yoke, dual guide lugs, a long-stroke threaded stem that helps prevent water hammer, and an open yoke that shows plunger position. Body materials are ASTM A126 Class B cast iron for Class 250 and SA216 WCB cast steel for Class 300 and 600, and an acid wash trim with nickel-plated parts is optional.

The Hardseat Yarway blow-off valve (Types 6909-C to 6931-C) comes in angle or straightway patterns, Class 600 and 1500, NPS 1½ to 2½, with socketweld or flanged ends, an F11 disc with Stellite face, a Stellite-faced seat and flexible graphite packing. Each Hardseat Yarway blow-off valve can be manual, fitted with a mounting plate or driven by a Bettis™ XTE3000 electric actuator. Unit Tandem valves use a one-piece ASME SA-105 steel block as a common body for both valves, removing interconnecting welds, bolts and gaskets and saving space; the sealing valve can be handed left or right to suit the boiler layout.

Key Features

Each Yarway blow-off valve design brings practical benefits:

• Design to ASME Section I, ASME B31.1 and ASME B16.34 for boiler systems up to 3,206 psig (221 barg).
• Rugged construction to withstand high pressures, high velocities and precipitated solids.
• Good resistance to cleaning acids, with optional acid wash trim on Seatless valves.
• Seatless design that will not score, plug with dirt or leak, with live-loaded packing.
• Slow-opening Seatless action that will not rapidly drain the boiler drum.
• Hardseat valves with thick Stellite facings on disc and seat for long service life.
• Unit Tandem construction that removes pipe joints and fits confined spaces.
• Manual handwheel or electric actuation on Hardseat and Unit Tandem valves.

Industrial Applications

The Yarway blow-off valve range is used on bottom blowdown and drain connections of water-tube and fire-tube boilers, waste heat boilers and heat recovery steam generators. Typical users in Oman and the GCC include utility power and water plants, refinery and petrochemical steam systems in Sohar and Duqm, fertilizer and LNG utilities in Sur, and process steam boilers in food, textile and manufacturing plants in Rusayl and Salalah. Seatless valves suit lower pressure boilers up to Class 600, while Hardseat and Unit Tandem valves serve high-pressure units.

Seven Star LLC supplies each Yarway blow-off valve model with the related boiler house equipment. Continuous blowdown is handled by the Yarway Hy-Drop throttling valve, and other Emerson steam products on this site include the Yarway AT-18/28, AT-38/48 and TempLow 4300 desuperheater and the Yarway Series 751/761 repairable drip and tracer steam trap. For condensate removal on process equipment see the Spirax Sarco FTS14 ball float steam trap.

Technical Specifications

This summary of the Yarway blow-off valve range is based on the Emerson datasheet VCTDS-00404-EN:

How to Order

For a quotation on any Yarway blow-off valve, send Seven Star LLC the boiler pressure, size, pressure class, end connection, angle or straightway pattern and, for tandem sets, the handing. The Yarway blow-off valve datasheet is available for download on this page. Our Muscat team will confirm availability and lead time and support selection and delivery across Oman and the GCC.