There are two kinds of LNG ultra-low temperature butterfly valves according to the classification of top-mounted structure, one is positively mounted, and the other is side top-mounted (also known as the structure of the maintenance bin).
(1)Top-mounted butterfly valve
As shown in the figure below, the positive top-mounted butterfly valve valve flap adopts the top-mounted structure, when the valve needs maintenance, the whole butterfly plate, valve stem and sealing ring on the butterfly plate can be taken out from the upper part of the valve body, so as to carry out the maintenance and replacement of the valve inner parts, valve stem, butterfly plate, sealing ring and bearing. Regardless of the size of the valve calibre, online maintenance can be achieved on the outside of the valve, and its maintainability is very high.
In addition, as can be seen from the figure below, there is only one connection between the top-mounted butterfly valve and the valve body and bonnet, so there is only one potential leakage channel for this type of butterfly valve.
(2)Side top mounted butterfly valve
As shown in the figure below, the side top mounted butterfly valve butterfly plate adopts the side mounting method to lengthen one end of the valve body, and the side of the lengthened valve body is equipped with an access port: when the valve needs to be repaired and replaced with internal parts, it needs to be operated from within the access port. This structure can not be directly extracted from the butterfly plate and other internal parts, when it is necessary to repair or replace the internal parts, it is necessary for the operator to explore or enter the access chamber for maintenance, and its maintainability is not high.
In addition, as can be seen from the figure below, there are two connections for the side top-mounted butterfly valve, one between the valve body and the valve cover, and one between the access chamber port and the cover of the access chamber, so there are two potential leakage paths for the valve of this structure.
