Problems with safety valves (there’s a reward!)
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The upper drum of the boiler is equipped with two safety valves. Why are two installed? Do these two safety valves serve the same purpose? (Do they both serve to relieve pressure?) Thank you. Also, as a safety manager who checks whether the safety valves function properly, the boiler operator said that one should not touch them casually as it could cause an incorrect water level reading. Is this statement correct? Thank you all. This post was last edited by nanbo888 on 2008-11-27 at 17:00
The poster is referring to the safety valve of the steam drum, with one such valve installed at one end along its length. In my opinion, this allows for even vapor release and pressure relief; the size of the openings in the steam drum wall is related to its strength. The two safety valves serve different purposes – one is a control safety valve and the other is an operational safety valve, with different set pressures. The set values are 1.04 times and 1.06 times respectively.
One is 1.06 times the operating pressure at the set pressure, and the other is 1.04 times. I think it’s all for safety, to prevent overpressure. As required, the safety valve must be opened periodically. If it is turned on, causing the drum pressure to drop rapidly, the water level will first drop and then rise. If the pressure in the drum fluctuates little, then the water level also fluctuates little. This post was last edited by Qin Yu on 2008-11-27 at 16:50.]
Here’s a link for you; the principle is basically similar. You can refer to this: handshake http://bbs.hcbbs.com/viewthread.php?tid=296517&page=1#pid1445584
Each boiler shall be equipped with at least two safety valves (excluding the economizer safety valve). Meeting one of the following requirements. Only one safety valve can be installed: 1. Boilers with a rated evaporation capacity of 0.5 t/h or less ； 2. Boilers with a rated evaporation capacity of less than 4 t/h and equipped with reliable overpressure interlock protection devices. Safety valves must be installed at the outlet of the fractional economizer, at the outlet of the steam superheater, at the inlet and outlet of the reheater, as well as at the start-up separator of the once-through boiler. p
The two safety valves on the steam drum are designed to release pressure safely in case of overpressure; having two of them serves as a backup in the event that one fails. As a double safety mechanism, these safety valves must be tested under pressure once a month and inspected annually
The purpose of installing two is to provide a dual safety mechanism. Additionally, the set pressures of the two valves are different; thus, when one valve begins to release pressure and the pressure continues to rise, the other valve also releases pressure, which helps to ensure a proper rate of pressure release. As for the second question, to check whether the safety valve can operate properly, it is necessary to use a boiler to increase the pressure (usually by adding water to create pressure); alternatively, the valve can be removed for a dedicated inspection. Therefore, using steam pressure alone for testing is not standard practice, and it can also cause false readings on the water level gauge.
Yes, one is the safety valve and the other is the root valve of the safety valve; generally, there is a root valve in front of the safety valve. The root valve is usually kept in an open state to ensure the proper functioning of the safety valve. By closing the root valve, it becomes possible to remove and install the safety valve while it is still in use, which facilitates its annual calibration. Last edited by cad0518 on 2008-11-27 at 18:40.]
In my opinion, the purpose of installing two safety valves in a steam drum is as follows: 1. It relates to the amount of steam that can be released in case of overpressure; when one safety valve activates and is no longer able to handle the excess pressure, the other safety valve takes over； 2. Ensure that if one safety valve becomes rusted and unable to open, at least another one can function properly ； 3. Safety valves should be regularly calibrated and manually activated, usually once every quarter.
It might be a mutual backup arrangement; the steam drum is relatively dangerous, so two safety valves are installed to ensure reliable pressure relief – one can still function during maintenance while the other remains operational
Everyone has said such great things; in fact, all the functions are covered in what the others have mentioned, so there’s no need to say more! I just want to add that in some cases, 3 or even 4 safety valves are installed, but some of them come in pairs as valve assemblies! Everyone should think more about it