1. The upper part of the extraction valve is provided with swing-type check valve controlled by oil pressure, which oil circuit is connected with control circuit of the main steam valve. When the oil pressure is available, the piston moves up to open the extraction valve; when the security system acts and the main steam valve closes, the extraction valve will close too.
2. The butterfly valve of the extraction valve is disconnected with the revolving shaft controlled by piston, when the exhaust pressure of the exhaust valve is higher than the pressure of steam admission side, the butterfly valve will automatically close under the function of steam pressure.
3. When the butterfly valve is in OFF position, it is shown by the travel switch connected with the electric circuit, in addition the oil circuit connected with the check valve is provided with two-position three-way solenoid valve, which can be powered on to close the check valve.
4. The extraction pipe is provided with pipe over-pressure protection device composed of one set lever-type pulse valve and one safety valve.