Troubleshooting of orifice plate flow meters
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Let me start by sharing a situation I encountered in these past couple of days as an example: there is flow in the pipe, but the differential pressure transmitter of the orifice flow meter shows a negative pressure of -1.35. When I opened the balance valve, the differential pressure value should have returned to zero, but it didn’t; it remained almost unchanged. I can’t figure out why it doesn’t change. However, even though there was flow, no positive pressure was displayed. I initially assumed that the positive pressure side was blocked, and later found that it was the primary valve on the positive pressure side that was blocked. During this time, I also unscrewed the screw that led to vacuum behind the positive and negative pressure chambers of the differential pressure transmitter (I’m not sure what its technical name is); yet the reading remained almost unchanged after doing that as well. ...Then it was zeroed out again, and after that it was put into use – everything worked fine. In any case, the problem was solved while still having doubts! So I would like to ask for some advice: 1. Regarding the points I don’t understand mentioned above, why is that? Are both the positive and negative pressure sides completely blocked? Then it just so happens that the zero point of this differential pressure transmitter is inaccurate, which causes the reading to remain unchanged even after unscrewing the balance valve and those two set screws at the back What’s going on here? 2. I would like to ask what the reasonable sequence for analyzing and handling this problem should be? The step-by-step approach (I’ve always believed that having a good strategy and analysis process makes it possible to address problems more effectively and quickly) would be useful; it would be good to expand on the sequence for analyzing common faults in orifice plate flow meters. 3. There’s another question I’m a bit embarrassed to ask: there is a small screw behind each of the positive and negative chambers of the differential pressure transmitter – what is its function exactly? Under what circumstances is it necessary to unscrew it? (Because when I was dealing with this issue, I unscrewed it; I think it was a pointless action when trying to resolve that problem, right?) What is its actual function?) 4. It’s already past 1 a.m.; will people be unable to see this post tomorrow? (I’m not very familiar with this HaiChuan Chemicals forum). If that’s the case, I’ll try to ask questions during peak times, so as to avoid posting them when no one is around to see them. How do posts sink? What if no one replies to solve the problem? Should I post again and ask? Seeking advice! I plan to stay here in the long term!
The positive and negative pressure valves are closed, the balance valve is open, and the differential pressure should be zero. Open the drain valve to check whether the positive and negative pressure taps are blocked. The small screw is the exhaust plug.
I would like to ask: When a differential pressure transmitter shows a negative value of -1.35, is this displayed on the transmitter itself or on the monitoring instrument? The reading shown on the transmitter can only be used as a reference; in actual troubleshooting, it is necessary to use a standard ammeter to make a determination. There is a small screw behind each of the positive and negative chambers of the differential pressure transmitter – what is its function exactly? It is used for venting air; if there is condensate present, opening it allows the condensate to be discharged and the air in the pipeline to be removed. It can also be used to determine whether the pipeline is unobstructed. Under what circumstances is it necessary to unscrew it? Before operation or during maintenance.
One more question: if the medium is gas and the instrument gives inaccurate readings, can the plug be used to drain the condensate? Is that how the plug is utilized? When what problems occur in a orifice plate differential pressure flow meter whose medium is liquid, does it become necessary to open the drain plug? A situation like mine above should have nothing to do with whether there’s air condensate or something like that inside, right? ...When dealing with this issue, all I need to do is turn off the positive and negative pressure valves, open the balance valve to check whether the reading returns to zero, and then open the drain valve to see if the positive and negative pressure lines are blocked. That’s it, right? This is the process for handling all faults in orifice plate flow meters, right? What other common faults are there?
So, the common problems with orifice plate flowmeters are dealt with in this way, right? First, the positive and negative pressure valves are closed, then the balance valve is opened to check whether the reading returns to zero; if it doesn’t return to zero, it means the zero point is incorrect Then open the drain valve to check whether the positive and negative pressure blocks are in place; that’s how such instruments work, right? Is that so? ? Maybe I was too superficial in my explanation; in fact, there are many other common problems that require different solutions
With this transmitter, when there is no flow – or in other words, when the process system assumes that the valve is closed and thus no flow exists, even though in reality the valve might not be sealed properly and flow is actually present – it displays a certain value. At that time, a technician adjusts the transmitter to zero, in order to satisfy the operators. When flow does exist, even if it’s at a low level, the value might still be negative
It’s very possible! ! ...
The daily zero-check is carried out in this way, but to determine its accuracy, calibration with standard instruments is still required.