Balance valves in five-valve assemblies and three-valve assemblies

This post was last edited by ylb913 on 2015-6-18 at 15:08. Before activating the gauge and after deactivating it, it is necessary to ensure that the pressures on both sides of the pressure tapping are equal; this is done firstly to adjust the zero point and secondly to prevent excessive pressure differences from damaging the gauge. The sequence for putting the three-valve assembly into operation is as follows: open the positive pressure valve, close the balance valve, and open the negative pressure valve (what is not mentioned here is that before operation, the positive and negative pressure valves are closed while the balance valve is open) ； The sequence for shutdown is: close the negative pressure valve, open the balance valve, and close the positive pressure valve. Our instrument technicians, with over 20 years of experience, are used to closing (or opening) the positive and negative pressure valves with both hands at the same time, and then opening (or closing) the balance valve. I once gave an example: Suppose the normal pressure difference for a orifice plate is 50 kPa, while the pressure inside the pipeline is 1 MPa. If there is no balance valve, or if the balance valve is not opened in advance, then whether positive pressure measurement is carried out first or negative pressure measurement, the pressure difference acting on the diaphragm will still be 1 MPa. This will immediately cause the differential pressure across the diaphragm to far exceed the designed value, resulting in damage to the diaphragm of the differential pressure gauge.

Equalize the pressures on the high-pressure side and the low-pressure side

Thank you for your answer. It was originally intended to measure the pressure difference; it makes no sense if they are equal.

When starting up or shutting down, a balance valve is used to equalize the pressures on the high-pressure and low-pressure sides, thereby preventing damage to the instruments

It is useful; to prevent damage to the diaphragm during measurement by the differential pressure transmitter, one should first start the transmitter, open the positive pressure valve, close the equalization valve, and open the negative pressure valve. Conversely, it’s a flashback.

If there is a differential pressure at zero flow rate in the differential pressure transmitter, this pressure can be adjusted by using a balance valve to equalize the differential pressure on the high-pressure and low-pressure sides. The balance valve is used to equalize the pressures on the high-pressure and low-pressure sides, thereby preventing damage to the instruments

A pressure equalizing valve is either open or closed; using it for adjustment, can the measured values be accurate?

What I mean is that if, with no investment required, the high and low pressures at the transmitter are not equal, one can try opening the balance valve to make the high and low pressures equal, and then close the balance valve. It didn’t say to use a balance valve to regulate the flow rate

The balance valve is used during maintenance or when starting up and shutting down; its function is to equalize the pressures on the high-pressure and low-pressure sides of the transmitter, or to disconnect those sides from each other...

When installing and removing instruments, it is necessary to insert a balance valve between the instrument valve on the open side and that on the closed side; this valve functions to balance the pressures on the high-pressure and low-pressure sides, thereby preventing the instruments from being damaged by sudden pressure differences. And it is used only in this process, serving only that purpose.