On-site instrument failure analysis (one question per week) – Question 3! (Reveal answers)
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This post was last edited by Yiding on 2009-10-11 at 12:47. A certain device uses a differential pressure transmitter in combination with an orifice plate to measure the flow rate of high-pressure steam. However, after the instrument was put into use, it showed no indication for a long time. After some time, the gauge readings gradually increased until they returned to normal. What is the reason? Answer revealed: When restarting the differential pressure transmitter used in the steam system, it is necessary to fill the positive and negative pressure chambers with condensate; however, the instrument technician overlooked this point and started using the instrument right away, resulting in an imbalance in the liquid level on both sides and no indication from the instrument. Once the condensate automatically filled the pressure guide tube, the instrument returned to normal.
When using a differential pressure flow meter to measure steam, no stable condensate is formed in the pressure tap pipes at the time of initial operation; as a result, the problems described in the question occur. After it has been operating for some time and stable condensate forms in the positive and negative pressure tap pipes, the pressure difference can be measured accurately, allowing the transmitter to indicate the flow rate correctly.
I agree with what was said on the second floor: generally, after the chamber is filled with condensate, it takes 12 to 24 hours before the pressure valves in the positive and negative pressure chambers can be opened. During this time, if the drain valve of the valve assembly is slightly opened, white bubbles will be observed escaping.
If there is no condensate, as the original poster mentioned, then the problem is resolved; I wonder what the steam temperature is, according to the original poster! But this is not good; using the steam gauge without any condensate can easily damage the diaphragm box! Since the original poster said that everything was normal after it was put into use, it’s likely that the steam didn’t damage the diaphragm box; as it gradually turned into condensate, the readings became normal
As long as the discharge valve is not open, no convection will occur and the gauge will not be damaged. The answer to this question is that no condensation is formed.
It is best to add water to the condensation tank before putting the gauge into operation, and then start using the gauge.
Personally, I think it was due to the absence of condensate in the pressure guide tube; things returned to normal later as the steam turned into condensate
No condensate formed in the instrument pressure guide tube, which is why the instrument did not display readings for an extended period of time.
When measuring steam flow, in addition to the methods mentioned above, it is also necessary to perform drainage before putting the system into operation; by opening the drainage valve when there is a certain amount of condensate, it can be seen that a lot of dirt can be removed. My device experienced a blockage in the pressure guide tube due to the lack of drainage from it.
Which teacher can help explain why the absence of condensation in the pressure guiding tube results in no reading on the instrument? Thank you
The absence of condensate does not necessarily mean that no reading will be shown. This might be due to the fact that, at the beginning, the condensate level on the low-pressure side was higher than that on the high-pressure side. As operation continues, the condensate levels on both sides increase; when the level on the low-pressure side reaches the overflow hole, it stops rising anymore, while the level on the high-pressure side continues to rise until the levels on both sides are equal, at which point the flow rate is displayed correctly