Selection of Displacer or Float Level Switch Connection

[From:来自网络] [Author:admin] [Date:12-06-05] [Hit:]

Selection of Displacer or Float Level Switch Connection

The displacer or float level switch has several possible connections i.e. side-bottom, side-side, and direct mounted or internal type. The connections at top of chamber or cage are rarely used and not available in the market (due to switch enclosure put at top of chamber or cage).  So which one we shall use?

First of all, the level switch (without continues measurement or transmitter) usually serve an individual alarm services. Some of them serve a multi alarm service like HL & LL at the same time. But for this last application, it appears only in several applications. The most used are the individual alarm.

Because the level switch only serves an individual alarm, it doesn’t need to cover all range of the liquid level. For example, the level switch LS-XXXA serves a HHLL (High High Liquid Level) at the closed drain vessel. This level switch doesn’t need to cover also the LLL (Low Liquid Level) alarm since it will be useless. With this situation, the level switch will only need some short external cage or chamber. Long chamber or long cage isn’t needed and will make it costly.

Based on this configuration, the default of the level switch connection is preferred to be side-bottom connection. With the side-bottom connection, the length of chamber or cage will be minimized so that the cost will be decrease, of course without loosing the accuracy of switch actuation. Side-side connection normally will have longer chamber due to two weld involve in the side of chamber. Also, usually there is a specific project requirement to have minimal distance of switch actuation point with the process connection. The type of connection such as NPT or flanged will be as per specific project specification. If there is no any specific requirement regarding this connection, the NPT connection will be the default connection (due to low cost consideration).

The internal type or direct mounted level switch usually is used on the atmospheric vessel or sump application where maintenance of instrument can be done with isolate the vessel without shutdown other part of plant. This is common practice due to the connection between the level switch and the vessel is connected directly without isolation valve installed. When the configuration like this isn’t possible (isolate the vessel without shutdown all plant), then the direct mounted level switch shall not be used.

 

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