Can a valve be installed below the safety valve?
Thread Content
Recently, the special inspection team visited our factory and required corrective actions regarding the installation of ball valves beneath some of our safety valves. However, some safety valves in our factory are equipped with stop valves, yet no correction was required. I checked, and it says that to install the stop valve it needs to be fully open, with a seal applied. Is it not allowed to install ball valves? Is it a problem to install a short circuit below the safety valve?
1. Whether it is permitted to install isolation valves between the container and the safety valve can be found in TSG 21-2016, Regulations on Safety Inspection of Fixed Pressure Vessels, section 9.1.3 Requirements for the installation of overpressure relief devices; item 4 states that such installation is allowed provided that it does not affect the safe operation of the safety valve, and provided that the valve has been sealed or locked with the approval of the person responsible for safety at the facility. 2. The term “shut-off valve” as specified here refers to valves used for cutting off flow, and does not specifically denote only gate valves. Ball valves are also shut-off valves, so it is permissible to use them. 3. Regarding the inspection items and requirements for safety valves specified in Procedure 7.2.3.1.1, item 4) refers to globe valves; it should not be interpreted as stop valves. 4. Shut-off valves include process valves such as gate valves, globe valves, ball valves, and butterfly valves.
Additional note: Ball valves have better flow characteristics than globe valves, but the advantage of globe valves is their ability to provide forced sealing. In terms of service life and reliability, globe valves are superior to ball valves; therefore, many root valves use valves with forced sealing capabilities, such as globe valves or gate valves.
Ball valves do not have as good sealing properties as gate or globe valves; if it is necessary to remove them for inspection during production, it may be impossible to do so, so ball valves should not be used – that’s my personal opinion.
In terms of durability, globe valves are somewhat better
We have been using ball valves, and we haven’t noticed any problems with their sealing performance
Regardless of the type of shut-off valve installed in front of the safety valve, it is crucial to prevent any possibility of accidental operation (manual shutdown) once it is in place. So try not to install it.
The reality is that if we don’t do it, regular inspections become a hassle; we have over a hundred safety valves here that need to be inspected every year.
The conflict between ideals and reality... In theory, it’s supposed to work well without any installation, but even when tested, it can’t be produced for testing, right? Haha, it’s impossible to handle this
It is best to use a stop valve, keep it fully open, and apply a lead seal