Switching sequence of three-valve assembly

The sequence for opening the three-valve assembly should be: (1) Open the positive pressure valve； (2) Close the balance valve ； (3) Open the negative pressure valve. The sequence for closing is the reverse of that for opening: (1) Close the negative pressure valve ； (2) Open the balance valve ； (3) Close the positive pressure valve.

Before cutting off, open the balance valve (pressure equalizing valve); after connecting, close the balance valve (pressure equalizing valve). In principle, it is possible to reduce damage due to excessive pressure difference caused by high pressure on one side. In fact, it is about minimizing the pressure difference before/after the variable input is applied.

This post was last edited by jlshnlhj on 2018-10-23 at 16:04. “The three-valve assembly of the pressure transmitter is closed; it needs to be opened. The procedure is as follows: first open the middle balance valve, then open the valves on the left and right sides respectively, and finally close the middle balance valve.” Steps to shut down the three-valve assembly: First, open the middle balance valve, and then close the two valves on the left and right respectively. .....” Does the pressure transmitter have a three-valve assembly? It should be a differential pressure transmitter. “The steps to open it are: first open the balance valve in the middle, then open the valves on the left and right separately, and finally close the balance valve in the middle. ” Wrong: When the three-valve assembly is closed, the balance valve is already in the open position. “Steps to shut down the three-valve assembly: First, open the middle balance valve, and then close the two valves on the left and right respectively. ”That’s not right either. First close the positive or negative pressure valve, then open the balance valve, and finally close the other valve. I agree with what was said on floor 2; actually, the order of opening and closing in steps (1) and (3) can be swapped. The key point is that when the balance valve is opened, only one of the positive pressure valve and the negative pressure valve can be opened. The other one should be off. Why? Think for yourself.

Differential pressure transmitters for measuring steam flow – What are the precautions to follow during the operation of the three-valve assembly when starting up or shutting down the meter?

Here’s how I do it: 1. Use a differential pressure transmitter with the orifice flow meter; for the 3 valves, I operate them arbitrarily (the differential pressure across the orifice is low, right?), without regard to any order. 2. Used on ordinary level gauges; I follow the sequence of turning it on by opening positive, closing negative, and then setting it to neutral. Before operating, check whether the balance valve is in the open position (sometimes it may be forgotten to open the balance valve when turning the gauge off). If it is in the closed position, open it first; when turning the gauge off, follow the sequence of closing negative, setting to neutral, and then closing positive. 3. If it is a double-flange silicone oil level gauge, there is no three-valve assembly on the gauge head – only a root valve. I’ll ask someone to help me; we’ll give a signal, 1, 2, 3, and then open the root valve at the same time (it might sound a bit funny).

Which one is correct? Generally, I do it this way: first turn on the negative pressure, close the balance valve, then turn on the positive pressure. To turn it off, I first turn off the positive pressure, open the balance valve, and then turn off the negative pressure. Which method is correct? Please advise