Level switches come in built-in and external types; how are they distinguished?
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Level switches come in built-in and external types; how are they distinguished? Some petrochemical requirements specify that the built-in flanges should be of at least DN80 size ； The external flanges are DN50 or DN25. Is there any special reason for this?
First, you need to understand what internal and external types mean; I’ve heard of them for the first time as well. In my opinion, an internal type refers to a level gauge that is placed inside the device, usually installed at the top, while an external type involves a separate measuring cylinder, so it requires less space.
Level switches of the fork-type and internal floating ball-type are generally installed internally, that is, the sensing device is inserted into the container; a larger opening is required to fit it in； Those such as external-mounted types with pressure diaphragms are external; similar to pressure transmitters, they only require one outlet pipe, which does not need to be very thick.
The built-in pressure is generally less than 300 pounds, and there are no valves to shut off for maintenance. If the above conditions are met, an internal installation can be considered. The density of hydrocarbons is less than that of water, even below 0.6; since the volume of a floating ball is inversely proportional to its density, 4 inches is a reasonable value. The external cylinder can be made as large as 3 inches or 4 inches, while the connection flanges can be smaller. Many external ones are tubular floats. For low-pressure tank areas, an external installation can be considered; if it’s to be installed inside the facility, an external setup is preferred.
You mean that as long as it’s not inside the tank, it’s external
So are the tuning fork or gyroscopic level gauge built-in?
That’s how I understand it; the built-in system doesn’t allow the device to be removed, while the external one can be taken apart by closing the valve, making it possible to repair or replace it