Product - BE Boiler Start-up Valve

​Once-through boilers require a minimum evaporator flow to cool the boiler tubes during start-up (minimum evaporator flow for spiral wound evaporators is approximately 30%). A recirculation system recirculates water out of the water separator back into the feedwater tank or to the economiser/evaporator to ensure the minimum evaporator flow. Different layouts of the recirculation system exist, recirculation of the water from the separator back to the feed water tank and water recirculation from the separator back to the economiser inlet with a recirculation pump. In addition to the above operating modes the start-u​​p valves can be used during boiler-filling and evaporator (air) purging.This operating mode typically requires high flow at low differential pressure.​​​​​

Key features

Trim design
  • Seat room purging: The trim is designed with a control edge upstream of the seat which shuts off the flow path for potentially damaging particles before the plug reaches the seat.
  • Vena contracta separate from seat: In normal control mode the smallest flow area of the trim is downstream of the seat, keeping potential erosion away from the seat.
  • Controlled gradual flow diversion: In the critical high velocity area, special care is taken to achieve a gradually controlled flow diversion preventing erosive water steam mixture hitting trim surfaces with high velocity.
  • Anti-erosion coating on control surface: Proven, hard anti erosion coating to ensure long life time of the trim.
Flashing conditions

Flash​ing water is highly erosive if it hits body or trim parts with high velocity. This must be avoided by design or the parts which are hit must be erosion resistant.

An angle over-the-plug configuration with its straight outlet for the flashing steam is therefore the most favourable configuration. A rapid increase of flow diameter at the point where the medium expands, avoids erosion downstream of the valve.
In the Z-shaped valve body, an outlet cage is needed to protect the body. It is recommended to have a straight pipe run downstream of the valve because the flashing water will also erode pipe bends.


Boiler start-up valves often experience debris, because the water separator is typically the debris collector of the boiler. On the other hand the valve has to be absolutely tight for long operating periods. If the seat is only slightly damaged by debris which has been clamped between seat and plug, then continuous leakage of flashing water will quickly erode the seat further and increase the seat leakage. This will lead to severe damage of the valve. Therefore the trim design should prevent particles being trapped between seat and plug when the valve is closing.


  • Specifically designed as a separator drain valve for supercritical boilers.
  • For operation with flashing water (saturated condition at the inlet).
  • Quick change trim for easy maintenance.
  • Seat area purging reduces particle damage.​
  • ​Angle and Z-shaped body design available.
  • For easy inspection and maintenance, none of the internals are welded or bolted to the body or bonnet.
  • Block tight according to MSS-SP61 or EN 12266-1 Class B.​​

​​Product specification

Design code
EN 12516-2, others upon request
Body style​
Angle type; Flow-to-close
Z-type, Flow-to-close
Fluid data range
Inlet: 320bar / 450°C; Outlet: 60bar / 300°C
Pipe connection
Butt-welding according to customer requirement
Other connection types upon request
Unbalanced, quick change trim
Double-acting hydraulic actuator
Seat/stem tightness
EN 12266-1 Cl. B or MSS-SP61or ANSI/FCI 70.2 Cl. V
Replaceable stem/plug, seat, inlet cage, outlet cage (Z-type design)
Bolted bonnet
Transition pieces for large pipe diameters and material compatibility
Standard actuator vertical up, others upon request​

​Typical materials​

General information

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Product - BE Boiler Start-up Valve