Introduction to gas valves currently used in China gas industry - part one

Posted: 03/09/2020 02:03:39   Hits: 14
1. Oil-sealed plug valve
 
In the 1980s, China's gas was mainly made of artificial coal, and there were more impurities and "gas glue" in artificial coal. The traditional single disc sluice valve used in the past is more and more unable to adapt to the needs of gas working conditions. This type of valve generally has the problem of being closed without enough tightness and stem sticking. And, the oil-sealed plug valve for gas pipeline solves the problem of being closed without enough tightness and stem sticking. Its main technical features: it has a hard sealing structure, so that it has a scraping effect; the sealing surface is not in contact with gas impurities, there is no valve stem in the cavity, there is no problem of valve stem sticking: sealing grease and O-ring are pecially developed in resistance to gas medium erosion, improving the performance of the plug valve.
 
However, oil-sealed plug valves also have their weaknesses.
First, it does not have the same diameter as the pipeline, which is about 75% of the pipeline circulation area, which increases the flow resistance and eddy current, and a scraper cannot pass through the pipeline;
Second, it is necessary to add grease before opening and closing the valve, which brings inconvenience to the user;
Third, the nominal diameter is generally less than DN300, for DN400 is difficult to manufacture, and DN600 or above is too heavy to be welcomed by users;


Introduction to gas valves currently used in China?gas industry

2. Parallel double discs gate valves for gas
 
With the development of the gas industry and the establishment of gas plants, gas-specific valves with large or even especially large nominal diameters are required. The parallel double-gate gate valve for gas is used to solve the problems that occur in artificial gas, and the maximum diameter is up to 1600mm.

First, the parallel double gate valve can scrape off the "gas glue" on the sealing surface during the opening and closing process, solving the big problem that the gas impurities adhere to the sealing surface and affect the valve sealing;
Second, equipped with a valve stem cover, so that the valve stem is not eroded by "gas glue";
Third, the lower part of the valve has side covers of the drain hole, which can clean the garbage falling at the bottom of the valve cavity;
Fourth, the full-path design has a small flow resistance and a scraper can pass through it;
Fifth, the valve body adopts the specially designed "mouse cage frame stiffener" to reduce the overall weight of the valve and enhance the strength and rigidity of the casing;
Sixth, the housing of RZ series gas gate valve is made of gray cast iron, and the price is low;
Seven, the series of gate valves are equipped with fully enclosed opening and closing indicators, so that the operator has a clear understanding of the state of the valve.
 
3. Butterfly valve
 
Compared with the above-mentioned valves, the butterfly valve is light in weight, large in diameter and low in price. Some gas companies used butterfly valves in the early 1980s. After ten years of use, it is generally considered that the effect is not good.

First, the sealing width of the butterfly valve is too narrow, which may cause the valve flap to be over- or under-position during the closing process, which affects the sealing;
Second, the valve flap is in the middle of the valve cavity, the flow resistance is large, and the cleaner cannot pass through it;
Third, because the part of the seal is made of rubber or PTFE, it is easy to damage or fall off during gas scouring, and the service life is short. Practice has proved that butterfly valves should not be used on gas pipelines except for special locations.
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