Issue with the switch status of the three-valve assembly in the differential pressure transmitter – urgent
Thread Content
Recently, a Rosemount differential pressure transmitter with a three-valve assembly was installed on the equipment. Once installation is complete and before shipment, should all three valves in that three-valve assembly be closed, or what? How should one proceed when going to the customer’s site for a briefing? When I arrive at the customer’s site, my main task is to figure out how to operate the equipment before and after introducing air flow. Thank you!
I checked online and understood it as follows: during debugging, before introducing air, the positive pressure valve and the negative pressure valve are closed while the balance valve is opened. After allowing air to flow for a while until the pressure in the pipes stabilizes, both valves are slowly opened simultaneously, and then the balance valve is closed. I’m not sure if my understanding is correct; this is my first time using a pressure difference transmitter, and I’m worried about damaging it and facing criticism. I hope someone experienced can help me out. Thank you!
In the past, differential pressure transmitters had a relatively low resistance to pressure in one direction, in order to prevent damage to the instrument due to pressure applied in that direction; when operating a three-valve assembly, it was necessary to follow a specific sequence. Modern transmitters have a high one-way voltage tolerance and come equipped with one-way pressure protection, preventing damage to the instrument. It is common to see gauge technicians turning on and off the positive and negative pressure valves simultaneously while operating.
Take a look at the instrument technician* question set; there are correct answers**
At startup, first open the positive pressure valve, close the balance valve, and open the negative pressure valve.
At startup, first open the positive pressure valve, close the balance valve, and open the negative pressure valve.
Oh my God! Please don’t bring up questions like that.
The startup sequence for the three-valve assembly is (assuming all three valves are in the closed state): open the balance valve, open the positive pressure valve, close the balance valve, and open the negative pressure valve. The shutdown sequence is: close the negative pressure valve, open the balance valve, and close the positive pressure valve.
The question posed by the original poster is a bit strange. “A Rosemount differential pressure transmitter with a three-valve assembly is installed on the equipment. When installation is complete and the equipment is shipped, should all three valves in that three-valve assembly be closed, or what?” " Could it be that the poster installed the transmitter and the three-valve assembly before sending them to the site? These are usually installed on-site. If it is indeed installed properly before being sent to the site, it doesn’t matter what position the three valves in the three-valve assembly are in (since there is no pressure on the transmitter before it is used at the site); the correct procedures mentioned by others earlier should be followed before it is used there.