The extraction check valve is used for the steam extraction of the turbine and the exhaust pipe of the high-pressure cylinder to prevent the steam or condensate from flowing back into the turbine and play a protective role. The principle is that when the valve is opened, it is energized through the cylinder solenoid valve, the cylinder enters the steam, the compressed air presses the spring, releases the limit of the check valve, pushes the check valve plate through the flowing medium to open the check valve, the medium flow is large, the valve core opening is large, the flow is small, and the valve core opening is small; when the valve is required to be closed, the signal is sent to the solenoid valve, and the solenoid valve loses power and quickly exhausts the air in the cylinder. At this time, in addition to the self weight closing force of the door panel itself, plus the auxiliary closing force of the air cylinder, to achieve the purpose of quick closing.
structure of extraction check valve
1. Extraction check valve without heavy hammer:
The so-called internal balance refers to the internal balance of the valve cors self weight. The valve core is supported by the shaft and rotates freely around the shaft. The valve core is not directly connected with the shaft. The action of the shaft is directly connected with the side working cylinder piston. When the valve seen from the outside is opened in place, it is actually the valve's allowable full open signal. The actual opening of the valve inside cannot be confirmed.
2. Extraction check valve with heavy hammer:
Due to the heavy weight of the gradually larger diameter valve core, the steam extraction check valve with a heavy hammer is used to balance the self weight of some valve cores (about half of the weight of the valve core). The valve core with the heavy hammer extraction check valve is directly connected with the rotating shaft. The actual internal opening can be seen from the angle change of the external rotating arm. If the internal is not fully open, the external display is not fully open. The valve is a free swing, gravity closed check valve. When the inlet pressure is slightly higher than the outlet pressure, the valve core will open. When the inlet pressure is slightly lower than the outlet pressure or there is backflow, the valve core will close.
Limit switch of extraction check valve
The limit switch is located in the side working cylinder 3. The function of the cylinder outside the extraction check valve
Function of outer cylinder of extraction check valve
The extraction check valve is usually equipped with an external side cylinder. When it needs to be opened, the action of the solenoid valve uses the compressed air introduced from the lower part to make the piston rod rise and rotate the shaft pin, so as to increase the opening range of the upper part of the valve core arm section, so as to allow the valve core to operate freely. In case of air loss, the valve core shall be provided with a closing force. Before the flow in the pipe is reversed, the valve core shall be close to the valve seat to avoid the severe scour of the pipe support system caused by water hammer.
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Resin sand casting, etc.
Manual test characteristics of extraction check valve
All the pipes between the air inlet and exhaust ports of the cylinder are equipped with three-way valve for manual test. When the manual test valve acts, air enters the upper part of the cylinder, so as to balance the pressure on both sides of the piston, make the cylinder spring move down the piston and lever arm, so as to turn the shaft and valve core towards the closing direction. This action will not completely close the valve under normal fluid, but only provides an inspection.is the way to verify whether the valve and cylinder work normally.
Operation and status of valve
When the extraction check valve without heavy hammer needs to be opened, the check valve sends the opening command, the solenoid valve is charged, the air inlet of the cylinder presses the spring, so that the piston drives the rotating shaft to rotate and open, at this time, the rotating shaft rotates, the valve core does not move, the valve opening position seen from the outside is actually the valve's full open signal, which is to open and release the extraction check valve, and confirm the extraction check valve is in the open position on the spot. The actual opening inside the valve cannot be confirmed. Only when the inlet pressure of the check valve is greater than the outlet pressure can the check valve be opened. At this time, pay attention to the water level of the high-pressure heater, and the stage by stage self flow may cause the high internal pressure extraction check valve of the next stage to fail to open normally
When the extraction check valve without heavy hammer is closed, the solenoid valve is de energized to close the intake air, the cylinder releases the compressed air, the spring forces the piston rod to descend and rotate the shaft, pulls the piston rod back and rotates to the closed position, drives the valve core arm to insert the shaft pin of the shaft, pushes the valve core to provide a positive auxiliary closing force towards the valve seat to close the valve, and the actual closing of the check valve is that the inlet pressure is less than the outlet pressure. The pressure and valve core will be closed automatically. At this time, confirm that the piston rod is fully closed when it is closed locally;
When the steam extraction check valve with heavy hammer needs to be opened, the check valve sends the opening instruction, the solenoid valve is charged, the air inlet of the cylinder presses the spring, so that the piston moves upward and releases, the valve core will run freely, the valve will open by the heavy hammer and the medium flow, the medium force is large, the valve core opening is large, the medium force is small, the valve core opening is small, the actual internal opening is from the angle of the outer swivel arm. The change can be seen that if the interior is not fully open, the appearance display is not fully open. Confirm the release and opening of piston rod and the actual opening position of check valve locally;
When the steam extraction check valve with heavy hammer is closed, the signal is sent to the solenoid valve. When the solenoid valve loses power, the air in the cylinder will be quickly discharged, and the spring forces the piston rod to move downward. At this time, in addition to the self weight closing force of the valve core itself, plus the auxiliary closing force of the cylinder, the purpose of fast closing is achieved. Confirm the actual closing position locally, and close the piston rod downward;
When the high discharge check valve needs to be opened, the check valve sends the opening command, the solenoid valve is electrified, the air inlet of the cylinder presses the spring to make the piston move upward and release, the valve core will be released to run freely, the valve will be opened by the hammer and the medium, the medium force is large, the opening of the valve core is large, the medium force is small, the opening of the valve core is small, and the actual opening of the internal can be seen from the angle change of the external swivel arm. If the internal is not fully open, the appearance display is not fully open; if the high-pressure exhaust check valve switch signal cannot be confirmed at this time, check whether the high-pressure bypass is closed, and then the high-pressure exhaust pressure rises gradually, and the high-pressure exhaust temperature drops to judge whether the high-pressure exhaust check valve is open;
Check the startup and normal operation of the unit to confirm that the exhaust check valve and the release rod of the cylinder outside the high exhaust check valve are all open, otherwise, the exhaust check valve will not be fully opened, causing the exhaust check valve throttling loss (as shown in the figure) for a long time, the release rod will not be fully opened and released, the check valve will not be free, and will be limited to open, causing the check valve throttling.