Issues regarding the flange of single-flange differential pressure transmitters
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This post was last edited by A Entropy on 2022-7-27 at 14:29. Previously, double flanges were used because it required a tight seal; this time, it’s essentially an open-type water tank with an overflow port, so I thought single flanges would suffice. After filling out the instrument specification sheet, I wanted to find out what size flange should be used – whether it would be the same as those used with double flanges – so I checked the relevant standards. As shown in the figure below, the information in the standards left me a bit confused. My understanding was that a single flange could be installed at the bottom of the water tank, meaning just one flange opening would be enough. So why does the standard mention an upper flange as well? What is the purpose of this upper flange?
If the top of the storage tank is sealed, an upper flange is installed to allow pressure to be released from the tank top; if it is open, then the other inspection port can be left open to the atmosphere. Whether it is a double-flange or single-flange type, there are high and low pressure sides labeled L and H; in the case of a single-flange pressure transmitter, the H side is connected to the bottom of the water tank, while the L side is connected to the atmosphere.
It’s a reserved port, to be used depending on the circumstances. Some storage tanks are too tall, so they are designed with a single flange, allowing piping to be connected from the top, thereby avoiding situations where the capillary tube is either too long or not long enough.
Thank you; I think I understand a bit now. It seems I had a misunderstanding before – I thought that a single-flange design meant it could only be used to measure containers that were open and connected to the atmosphere. But that’s not the case; it simply eliminates one flange, and it can still be used to measure sealed containers, with just a different design for the pressure tapping point. You can understand it that way.
Thank you. In other words, a single-flange type can also be used to measure sealed containers; the difference between it and a double-flange type is merely that the pressure tapping point on the upper side has a different design. You can understand it that way.
That’s the principle, provided that the maximum liquid level does not reach the upper pressure tapping; otherwise, some substances may block the pipes.
I have the feeling that this specification refers to differential pressure type gauges; it’s not the same as pressure-based level measurement. Is there another specification called static pressure level gauges?
Double-flange differential pressure should be used for sealed containers. This upper flange is not very useful; it’s only for blocking air
Using a single-flange gauge to measure a sealed container will not give accurate results
Pressure tap. The above applies to air; it’s not necessary if the pressure is taken from a sealed system.