Samson 3281 Series 280 Steam Conditioning Valve DN 50-300

SAMSON Type 3281 steam conditioning valve for pressure and temperature reduction

The SAMSON Type 3281 is a steam conditioning valve of Series 280. It is a globe-style final control element that reduces both pressure and temperature of superheated steam to set points given by a pressure controller and a temperature controller. The DIN version covers DN 50 to DN 300 and PN 16 to PN 160 for temperatures up to +500 °C. Seven Star LLC supplies SAMSON valves in Oman and the GCC as an independent supplier in Muscat.

Mechanically the 3281 largely corresponds to a Type 3251 globe valve fitted with a flow divider ST 3. The cooling water is injected through that flow divider, which is what distinguishes a steam conditioning valve from an ordinary steam pressure-reducing valve. The 3281-1 uses a Type 3271 pneumatic actuator (350 to 2800 cm²), and the 3281-7 uses a Type 3277 actuator (350 to 750v2 cm²) for integral positioner attachment.

Type 3281 technical specifications (DIN version)

How the 3281 reduces steam pressure and temperature

The seat, plug with stem and flow divider are installed in the body, and the stem is joined to the actuator stem by clamps and sealed by a spring-loaded V-ring packing. Steam flows through the valve in the direction of the arrow. As it passes the free area between seat and plug, the steam reaches its highest velocity and meets the cooling water at the inner wall of the flow divider, which is fed through the bonnet with a connecting pipe.

The steam and the entrained water are mixed in the narrow wire mesh of the flow divider. Steam velocity falls there, heat is given up over the large surface of the mesh coil, and the water evaporates quickly. The mixture leaves as a fine mist with a high steam content, and evaporation finishes a short distance downstream. Because the steam velocity at the throttling point does not depend on flow rate, atomisation is maintained over the full load range.

Benefits of water injection through the flow divider

• The kinetic energy of the steam is fully used to mix and split up the cooling water.
• Evaporation is fast and independent of steam flow.
• The throttled and cooled steam has a homogeneous condition.
• Thermal shock and erosion are avoided because the water does not touch the valve body.
• Operation is low in vibration and noise.

A separate control valve supplies the cooling water, and a transmitter and controller close the loop on downstream pressure p₂ and temperature t₂, as shown in the datasheet configuration diagrams.

KVS values, sizes and face-to-face lengths for the 3281

Available KVS coefficients are 3.0, 4.8, 7.5, 12, 20, 30, 47, 75, 120, 190, 270, 480 and 750. DN 50 takes KVS 3.0, 4.8 and 7.5, and DN 80 takes KVS 3.0 up to 30. Some larger combinations are available with pressure balancing. The datasheet face-to-face lengths for flanged and welding ends are:

Materials and options for the Type 3281

Body and flanges are cast steel 1.0619 or high-temperature cast steel 1.7357. Seat and plug are 1.4006/1.4008, with Stellite facing or a solid Stellite plug available, guide bushings are 1.4112, the body gasket is a graphite seal on a metal core and the balanced-plug seal is PTFE or graphite. An insulating section (1.0460/1.0619 or 1.7335/1.7357) allows service up to 400 or 500 °C. An ANSI version, NPS 2 to 12 and Class 150 to 900, is covered by a separate datasheet.

Selecting and ordering a 3281 steam conditioning valve

• Inlet steam pressure and temperature, and required outlet pressure and temperature at minimum, normal and maximum load.
• Steam flow cases and cooling-water temperature, pressure and available flow.
• DN, PN, body material, flange or welding ends.
• KVS, characteristic and leakage class; balanced plug if differential pressure is high.
• Actuator 3281-1 or 3281-7, supply pressure, fail-safe direction and accessories.
• Separate cooling-water control valve and controllers, if they are part of the enquiry.

Installation and maintenance of the 3281

Steam lines need drainage upstream so that condensate does not reach the plug, and the downstream pipe must have enough straight length for evaporation to be complete before the first temperature sensor. Place the temperature transmitter where the steam is fully mixed. Warm the valve up slowly during start-up to limit thermal stress, and check packing and flange bolts after the first heat cycle. Inspect the flow divider and plug for wear during turnarounds.

Typical 3281 applications in Oman and the GCC

Steam conditioning valves are used in power stations and combined-cycle plants for turbine bypass and auxiliary steam, in desalination plants for let-down of high-pressure steam into low-pressure heating headers, and in refineries and petrochemical sites where one steam level feeds the next. In these plants, steam quality, heat and fast load changes matter, so correct water injection and a robust high-temperature packing are essential.

Information for your 3281 RFQ

• Process data sheet with steam and cooling-water conditions.
• DN, PN and material requirement.
• Actuator, accessories and control philosophy.
• Tag number and nameplate details when replacing an installed valve.
• Quantity and delivery location in Oman or the GCC.

Documents and quotation

The SAMSON datasheet T 8251 EN for the Type 3281 is attached on this page.

Send the steam conditions and sizes and we will confirm what can be supplied in Oman and the GCC.