Novel feed water valve design promises trouble-free operation across the flow range

May 15, 2020
TMI Staff & Contributors

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SIP-valve series[/caption]

Schroeder Valves is offering a new type of valve for pressures from 140 to 250 bar: the Schroeder Intermediate Pressure Valve (SIP). This series is ideal in systems with frequent operation in the minimum flow range. It will especially be in use with boiler feed water circuits in gas and steam combined cycle power plants (CCPP) for the protection of centrifugal pumps.

In the past decade, the operating mode of power plants has changed considerably. Historically, process operation was almost exclusively carried out close to the nominal load point of the plants; an area in which the bypass of the minimum flow valve is closed. Today, cases are increasing rapidly with significantly varying load conditions – down to the single-digit percentage range of the nominal load – which then have to be compensated. This applies particularly to combined cycle power plants and is also due to the increasing use of renewable energies.

Cavitation damage[/caption]

Previously, it was difficult to prevent cavitation during regular operation and increasingly difficult when operating just below the minimum flow rate in the critical range. The SIP promises to operate in this range, including in the area of the switch point hysteresis.

The technical innovations that make the valve novel are found in the main direction of the process medium and in the design of the bypass or piston. In the main process direction, the volume flow-controlled cone utilizes a special design. In the bypass, the SIP controls the bypass with a multi-stage piston, which enables a defined multi-stage pressure reduction at all flow rates and ensures cavitation-free operation at all times. The piston of the SIP is actuated directly by the plug via a lever.

The actuating forces are reduced enough by pressure compensation that a supporting pilot system is not required. These innovations provide the unit with optimum protection against wear and cavitation over the entire operating range from 0% to 100% flows. Even if wear does occur over extended time, the design of the bypass ensures full functional operation of the valve.

The design of the SIP does not require a back-pressure regulator in the bypass pipe following the valve. As an added feature, the bypass of the SIP has an integrated non-return function eliminating additional bypass check valve requirements.

The SIP is available in standard nominal diameters from DN80 (3”) to DN250 (10”), and in nominal pressures from PN250 (ASME1500) to PN400 (ASME2500) as per EN 1092 normative. Larger diameters and higher pressures are possible. Also, the SIP is available in the customer’s choice of materials, ranging from carbon steels to super duplex.