Purging issues with diaphragm seals
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I wonder if anyone has encountered this situation: in the level measurement of towers, diaphragm sealing is used to take pressure readings. On the side with higher pressure, the pressure tap is purged using flushing oil, while on the side with lower pressure, gas is used for purging since the normal operating condition there is a gaseous phase. Since the differential pressure values used for level measurement are generally quite small, the purging gas generated by two systems will inevitably introduce significant errors in the measurements of the entire system. I would like to ask everyone what the advantages of purging in this way are, and what considerations underlie it.
I’m wondering if the entire system needs to be purged? If it is a system purge, this transmitter must be isolated. If only the transmitter is purged, I don’t think this method of purging is appropriate; it isn’t very effective. If something sticks to the diaphragm, can it be blown off? Increasing the pressure to achieve purification will surely have an impact on the transmitter. I suggest isolating the transmitter first, removing it for cleaning – preferably by immersing it in a solvent that won’t corrode the diaphragm – and then washing it with water and allowing it to air dry.
When using a dual-flange differential pressure transmitter to measure liquid level, it is generally not necessary to use flushing oil; if flushing oil is used, it should be applied to both the positive and negative pressure chambers. Before applying the flushing oil, the transmitter must be disconnected to prevent damage to its diaphragm. There is no such design where one side is flushed with flushing oil while the other side is purged with fuel gas – this approach is not very reasonable. If the liquid level rises and the negative pressure chamber fills with viscous, easily condensing substances, using fuel gas will not be very effective. It is better to apply flushing oil to both pressure chambers.
I think the method of continuously applying flushing oil to both the positive and negative sides is a viable approach, as it essentially applies the same pressure to both sides. The main purpose of continuous flushing is to prevent clogging.