Flow meter

You’d better explain the operating steps of the valves clearly: what is the normal closed state of the three-valve manifold, and what is the state when the positive pressure valve is activated? Does your balance valve malfunction often? What you said is too vague; please be more specific. Although we’re using smart transmitters now, we still should try to avoid subjecting them to prolonged unidirectional pressure

Presence/absence of internal leakage; whether the valve group has been disassembled for inspection; diaphragm box inspection

Hehe, this completely defies logic. Either that, or you’ve misunderstood how positive and negative interfaces work

It is necessary to clearly describe the status of the three valve assemblies in order to conduct an analysis

State of the three-valve assembly before operation: positive pressure and negative pressure valves are closed, while the balance valve is open. During one-way pressure testing, the positive pressure valve is opened while the balance valve is closed; at this point, the display panel shows negative pressure ； Using the same method later on, I tested it under negative pressure; it indicated positive pressure instead ； Finally, the three-valve assembly was put into normal operation: negative pressure was enabled, the balance valve was closed, and positive pressure was enabled; the gauge readings were normal, as was the flow rate display. Installation of the transmitter and piping: In the transmitter, H corresponds to the upper pressure tap along the steam flow direction, i.e., before the throttle element; L corresponds to the lower pressure tap along the steam flow direction, i.e., after the throttle element.

This is the situation of viewing the transmitter three-valve assembly online. It’s not necessarily possible to follow the theoretical discussions exactly. Logically, when you switch to the positive pressure side to balance it, it should be at positive pressure. Pressure buildup may also occur during the switching process. The negative pressure drain port of the transmitter can be used for drainage while only positive pressure is applied, to check whether it returns to normal operation.

Based on my 40 years of experience as an instrument technician, I can say with full responsibility that this issue cannot be resolved through discussion. We have discussed with technical personnel from both the transmitter manufacturer and the valve manifold manufacturer regarding the phenomenon where the output of the differential pressure transmitter is not zero when the balance valve is open. No definitive conclusion has been reached; however, the only possible causes for this phenomenon are related to the structure of the balance valve’s valve core and piping: even when no flow passes through the balance valve, there remains a pressure difference between its two ends (caused by factors such as air resistance, fluid resistance, capillary action, the weight of the valve core, temperature changes, etc.) ； Changes in the static pressure state of the transmitter caused by stress-induced deformation of the valve assembly ； Changes in the static pressure conditions of the transmitter caused by unequal temperatures in the two measurement chambers ； Measure the amount of fluid/air in the chamber ； ………… Conclusion: When adjusting differential pressure transmitters on-site, never rely on the open balance valve. If you want to confirm that the pressures on both sides are equal, the correct procedure is to open the vent valves/drain valves on both sides simultaneously. .

There seems to be a problem with the steps for operating the one-way pressure testing valve in your case. You see, before the three-valve assembly is put into use, the positive and negative pressures are shut off while the balance valve is opened. During pressure testing, the positive pressure valve is opened; at this point both the positive and negative pressure chambers are filled with the medium. Then the balance valve is closed, which in turn traps the medium inside the negative pressure chamber. If there is additional heat tracing, then the pressure in the negative-pressure chamber will definitely rise. . . . . . . . .

During one-way pressure testing, first close the balance valve, then open the positive pressure valve to test.

Don’t I think this is abnormal? ? Is there a problem?