After the cryogenic valve is closed, there will be some liquid left in the valve cavity. Over time, the remaining liquid in the valve chamber gradually absorbs heat from the atmosphere, returns to normal temperature and re-gasifies. After gasification, the volume of the valve expands sharply, about 600 times, resulting in extremely high pressure and is used in the valve body. This is called abnormal boost.
When abnormal pressure rises, the gate will be pressed on the valve seat, causing the gate to not open. At this time, the high pressure will wash out the middle flange gasket or wash out the packing; it may also cause the valve body, cover deformation, so that the sealing of the valve seat significantly reduced; or even cover rupture, causing serious accidents. In order to prevent abnormal pressure rising, the general cryogenic valve adopts the following measures on the structure:
1 set pressure relief hole, also known as pressure balance hole or exhaust hole, that is, elastic gate or double gate inlet side drilling a small hole, as the valve chamber and inlet side of the pressure balance hole. When the pressure of the valve cavity rises, the gas can be discharged through small holes. This method is relatively simple and has been widely adopted. Use pressure relief hole to prevent abnormal pressure rise, in valve body design, should indicate the flow direction of the arrow; installation, pay attention to the position of the pressure relief hole to ensure that the pressure relief hole to the side of the media inlet, pressure relief hole opening on the gate, more attention. The location of the relief hole is determined by the valve structure, some on the valve body, and some on the gate.
2 set the suction valve on the valve or install the safety valve to discharge the abnormal high pressure. Generally, a safety valve is installed on the bonnet. When the pressure rises to a certain value, the safety valve opens, and the abnormal high pressure is discharged to ensure the safety of the valve body. It can also install an exhaust valve at the lower part of the valve body to exhaust the residual liquid in the valve body cavity to prevent the occurrence of abnormal pressure rise.