【Daily Question 20090215】Orifice plate fault analysis question
Thread Content
On a horizontal pipeline whose process medium is liquid, a differential pressure flow measurement system is installed vertically. The differential pressure transmitter is installed after being calibrated; however, once the instrument was put into use, the indicated values turned out to be low. After verifying that there were no issues with the process operation conditions or the design and manufacturing data of the orifice plate, analyze the possible causes and suggest solutions. Give at least three reasons. Answer: ① The orifice plate is installed in the wrong direction – in this case, the distance between the flow constriction and the orifice plate is greater than when it is properly installed, which results in an increased reading at the negative pressure port of the orifice plate and a decrease in the pressure difference; therefore, it needs to be reinstalled correctly. ②The presence of gas in the positive-pressure pressure measurement pipeline, or the fact that the highest point of the negative-pressure pressure measurement pipeline is higher than that of the positive-pressure pipeline, results in an additional static pressure error, causing the instrument reading to be lower than the actual value. ③If the gas in the positive pressure chamber of the differential pressure transmitter has not been completely exhausted, the exhaust valve in that chamber can be opened; once liquid is seen flowing out, it should be tightened again. ④The balance valve in the three-valve assembly is not closed properly, or although it has been tightened, there is still internal leakage; it needs to be closed tightly or replaced.
1. Leakage on the high-pressure side. 2. The pressure tapping pipe on the high-pressure side is low. 3. The high-pressure side drain valve is not closed.
1. Internal leakage in the balance valve of the three-valve assembly. 2. The primary valve in the high-pressure chamber is not fully open, resulting in a low pressure in the positive-pressure chamber. 3. Gas is present in the pressure guide tube of the high-pressure chamber
My answer: 1. Leakage on the high-pressure side. 2. The pressure tapping pipe on the high-pressure side is low. 3. The high-pressure side drain valve is not closed.
1. The zero point of the differential pressure transmitter is too low; solution: recalibrate the zero point； 2. The balance valve of the differential pressure transmitter is leaking. Solution: Replace the balance valve or address the cause of the leakage ； 3. The screws at the output terminal of the square root circuit in the flow regulation system are loose; solution: tighten the screws again.
1. Internal leakage in the balance valve of the three-valve assembly. 2. Gas present in the pressure guide tube of the high-pressure chamber. 3. Whether the high-pressure pressure guide tube is blocked. 4. Whether the orifice plate is installed in the wrong direction
1. The orifice plate is installed backwards； 2. Internal leakage in the balance valve ； 3. The high-pressure chamber is blocked or contains gas that has not been completely removed ；
Orifice plate quality. Installation quality ； Check the high-pressure side, the balance valves of the three valve assemblies, etc. Usage.
1. The normal-phase pressure guiding tube is not unobstructed； 2 Positive phase drain valve leakage ； 3 Internal leakage in the balance valve on the three-valve assembly ；
1. The orifice plate is installed backwards. Solution: Reinstall the orifice plate. 2. Leakage in the balance valve. Solution: Replace the balance valve. 3. Leakage in the high-pressure side drain valve. Solution: Replace the drain valve.
1. Internal leakage in the balance valve of the three-valve assembly. 2. The primary valve in the high-pressure chamber is not fully open, resulting in a low pressure in the positive-pressure chamber. 3. Gas is present in the pressure guide tube of the high-pressure chamber. 4. Leakage in the positive-phase drain valve
Such measuring elements are widely used in engineering. Based on your question, I think the main issues are related to installation as well as poor sealing, which leads to leakage
1. The orifice plate is installed in the wrong direction – in this case, the distance between the flow constriction and the orifice plate is greater than when it is installed correctly, which results in higher pressure readings at the pressure sensing holes located behind the orifice plate. This leads to a decrease in the pressure difference, and the plate needs to be reinstalled properly. 2. The presence of gas in the positive-pressure pipeline, or the fact that the highest point of the negative-pressure pipeline is higher than that of the positive-pressure pipeline, causes an additional static pressure error, resulting in a lower indicated value. 3. If the gas in the positive pressure chamber of the differential pressure transmitter has not been completely removed, the exhaust valve in that chamber can be opened; once liquid begins to flow out, it should be tightened again. 4. The bypass valve in the three-valve assembly is not closed properly, or although it has been tightened, internal leakage still occurs; it needs to be closed tightly or replaced. 5. There is air leakage in the instrument output circuit (pneumatic gauge).
1. Internal leakage in the balance valve of the three-valve assembly. 2. The primary valve in the high-pressure chamber is not fully open, resulting in a low pressure in the positive-pressure chamber. 3. Gas is present in the pressure guide tube of the high-pressure chamber. 4. Leakage in the positive-phase drain valve