Discussion on π-type liquid seal design (please advise)
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It is said that a π-shaped liquid seal can be used to maintain the liquid level in the storage tank, with the highest point of the π-shaped tube being at the same level as the liquid level in the tank. However, the drainage outlet is usually located at a low position; could a siphon effect occur during drainage, thereby drawing all the liquid out of the tank? I’ve seen that valves are installed at the highest point in many cases; if the medium is toxic or cannot be allowed to be in contact with air, then such valves remain closed and fail to serve the purpose of preventing back-siphoning. Some systems are equipped with balance pipes that connect the gas space inside the storage tank to the highest point of the π-shaped tube. While this helps to prevent siphoning, if the amount of liquid discharged is small and the π-shaped tube behind that highest point is not filled with liquid, then the gas in the storage tank will be in contact with the system downstream. The purpose of installing a liquid seal is precisely to prevent gas from entering the downstream system along with the liquid; so doesn’t the use of balance pipes undermine this function? Is there anyone skilled who can give some advice? Thank you
“Some systems are equipped with balance pipes that connect the gas space inside the storage tank to the highest point of the π-shaped tube. While this helps to prevent siphoning, if the amount of liquid discharged is small and the π-shaped tube behind that highest point is not filled with liquid, then the gas in the storage tank will be in contact with the system downstream. The purpose of installing a liquid seal is precisely to prevent gas from entering the downstream system along with the liquid; so doesn’t the use of balance pipes undermine this function? ” Reply: Connecting the pipeline to downstream equipment involves using a stub pipe
In that case, it involves using the insertion tube of the downstream device to create a liquid seal. Since there is already a liquid seal downstream, isn’t the π-shaped liquid seal here less necessary?
It also serves to maintain the liquid level in the upstream equipment
Thank you very much for your explanation, but I still have some questions. If the upstream device is a liquid seal tank, then it is necessary to maintain the liquid level in that device; however, if the upstream device is something like a tower top condenser or a hydrogen chloride falling film absorber, there is no need to maintain a liquid level. The purpose of the π-shaped liquid seal is to prevent the gas phase from upstream from entering the storage tank downstream. But according to what you said earlier, the problem of gas leakage can be resolved by installing bottom pipes in the downstream devices, in which case the π-shaped liquid seal becomes unnecessary. But in fact, all the designs seen have π-shaped or U-shaped liquid seal tubes
Sometimes it is for liquid phase sampling or to install a flow meter
I have also been researching this issue recently, and my thoughts and questions are the same as those of the original poster. Has the original poster managed to solve their problem?