If the medium remained in the cavity after the cryogenic gate valve is closed, the residue will gradually absorb the heat in the air and re-gasify. After the gasification, it will expand violently up to 600 times and generate extremely high pressure on the valve, which is called 'abnormal boost'.

When the unusual occurrence happens, the wedge will be pressed firmly onto the seat and can’t be opened. The high pressure will push the gasket of the flange out or damage the packing. It may also deform the body and bonnet, significantly reducing its sealing performance. What’s worse is that the valve breaks down and causes economic loss.

In order to prevent the misfortune of abnormal pressure increase, we take following measures:

1. Set an orifice, also known as pressure-balancing orifice or exhaust orifice, that is, a small hole drilled on the inlet side of the flexible gate or double gate serves as a pressure-balancing hole in the inner cavity of the valve and the inlet side. When the pressure in the valve cavity increases, the gas can be discharged through the small hole. This method is relatively simple and has been widely adopted. Once an orifice is added to the valve, there should be an arrow dedicating the direction of the flow.

2. Set an outlet pipe on the valve or install a safety valve to discharge abnormal high pressure. Generally, a safety valve is installed on the cover. When the pressure rises to a certain value, the safety valve opens and balances the pressure to ensure the safety of the body.  Or an exhaust valve can also be installed in the lower part of the valve body to drain the residual medium in the cavity, preventing abnormal boost.

Related products: cryogenic ball valve, cryogenic floating ball valve

Installation requirements for cryogenic valves

Due to the special structure of cryogenic valves, the installation of cryogenic valves also has special requirements. Because of the long-neck bonnet of the cryogenic valve, cryogenic gate valves must be installed vertically upward, with the stem direction within a 45-degree angle. And it should also be avoided as much as possible to install the valve on vertical pipelines. Otherwise, the low-temperature medium may fill the extended part of the valve cover, causing the valve packing to fail. In addition, it will transfer the cold to the valve handle, injuring the operator.

For cryogenic ball valves with pressure relief devices, extra attention should be paid to the requirements of the valve pressure relief direction during installation,. The direction of valve pressure relief should be marked on the process flow chart and noted in the pipeline axonometric drawing. If it is necessary to set an orifice but not set it, after the valve is closed, the liquid in the valve path will be heated and vaporized, which can easily burst the valve body. If the pressure relief is installed in the wrong direction, flammable or toxic media may be leaked to the operation and maintenance side.

Cryogenic valve manufacturing

The production of cryogenic valves requires strict manufacturing processes, the participation of special equipment and strict quality control on the component processing. After special low-temperature treatment, the rough-machined parts need to be placed in the cooling medium for several hours (2-6 hours) to release the stress. This can ensure good performance of the material in low temperature conditions, and prevent the valve from leakage caused by deformation due to a change in temperature. The assembly of the valve is also different from that of the ordinary valve. The parts need to be strictly cleaned to remove any oil stains to ensure the perfect performance.