Extraction check valves are used to prevent the back flow of the working medium in extraction pipeline at steam turbines. Each extraction check valve is designed exactly for the specified extraction parameters according to the customers requirements.

The applicability of the given type of extraction check valve is up to +450 °C and pressure class PN 100 (Class 600). This type of valve can also be used for water or non-aggressive gases, for example natural gas, after adjusting the balance.

Unique construction

The extraction check valve is designed as a check valve with double eccentricity. The disc with conical sealing surface is swinging on a shaft which is carried in plain bearings. In the CLOSED position, the sealing surface of the disc is in contact with the valve body seat. The shaft also bears a counterweight to balance the mass of the disc. The balancing guarantees minimum pressure losses not exceeding 1%.

This counterweight is situated, off the valve body bore, in a separated pressure-closed box. Standardly, valves up to DN 300 are manufactured from a machined forged semi-finished product, and from DN 350 the construction is welded from formed semi-finished products.

The extraction check valve can be equipped with an actuator which guarantees the quick acting function of the valve. The torque accelerates closing and holds the plate in a closed position (reduces unwanted knocking). The actuator can be placed both on the right and left side in the direction of the flow.

Alternatively, can be the check valve equipped with linear actuator placed vertically which close the disc of the check valve from above. The type of actuator is specified by customer, and it can be pneumatic or hydraulic actuator.

On the other side of the valve is placed lever for function control or mechanical position indicator or even with electric position sensor. Both the actuator and the lever are carried on a separate shaft so that their passive resistances do not affect the valve function.

The extraction check valves C09.6 may be supplied with designs for either horizontal or vertical piping. The valve shall be positioned between the connecting ends of the piping in the direction in which the flow of the fluid from the turbine opens the disc. The main shaft of the valve (axis of disc rotation) must be in horizontal position.

Maintenance-free

The extraction check valve is designed as maintenance-free valve. After a certain time, depending on the operating conditions, it is only necessary to replace the graphite seals. The sealing surfaces of the main closing part are designed for the total service life of the valve, at least 25 years.

Very important thing for the correct operation of the valve is the cleanliness and non-aggressiveness of the medium without abrasive or sticky particles, which could cause clogging of the sealing surfaces and increase the peeling torque of the closing part.

Advantages

Extraction check valves are TOP products of ARMATURY Group. And that is due to its advantages, which makes them unique according to the customer’s requirements. Advantages of this type of valve are:

• possibility of installation into both vertical and horizontal pipings
• unique design for the specified extraction parameters
• guaranteed tightness class
• low pressure loss
• low passive resistances
• no axial forces
• no castings are used
• maintenance-free valves with long service life
• design variability

For more information:

Patrik Sniehotta, Designer