Are shut-off valves needed before and after the control valve?
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Our nitrogen cylinder outlet is equipped with a pneumatic pressure regulator, in parallel with a manual shut-off valve. But many pressure relief valves I’ve seen are equipped with manual shut-off valves both in front of and behind them, with another manual shut-off valve connected in parallel. Therefore, I think we should also install two stop valves before and after our pneumatic control valve.
Generally, a gate valve is installed before and after the control valve, and a stop valve is installed on the bypass line. To facilitate adjustment in the event of an accident, the gate valve can be closed and the bypass line used, with the flow rate being manually regulated via a stop valve.
I have also seen control valves equipped with gate valves at the inlet and globe valves at the outlet, with globe valves installed in the bypass as well
It is mainly to facilitate maintenance in key locations; if a location isn’t changed for a hundred years, regular maintenance is sufficient, and there’s no need for anything more.
In process design, there are usually valves before and after the automatic control valve, along with bypass lines. The purpose of these bypass lines is to allow for manual adjustment in case the automatic control valve fails, which is why globe valves are typically used on these bypass lines. As for the selection of valves before and after the self-regulating valve, it can be determined based on the medium; generally, gate valves are used for gaseous media, while globe valves are used for liquid media.
Generally, there are valves before and after the self-regulating valve, to facilitate the removal and adjustment of the valve.
Hehe, control valves generally operate frequently and are prone to failure; therefore, there are shut-off valves at both the beginning and end for maintenance purposes, as well as a bypass line that serves as a backup.
If it is possible to park the vehicle to service the control valve, there is no need for auxiliary line valves or front and rear valves. However, it's still better to add it in most cases.
No, we have never done this before, nor have we seen such a P&ID. The control valve already has the function of a shut-off valve; it’s sufficient to add a shut-off valve in the bypass line.
Valves must be installed before and after the control valve. As the fellow sailors mentioned earlier, when the control valve needs to be maintained, the valves located before and after it can be used to shut off the flow of material, allowing for manual adjustment via a bypass. A shut-off valve must be installed in the bypass to ensure stability in flow regulation. As for the valves at the inlet and outlet, I don’t think it matters much, but to prevent internal leakage, it’s better to have a shut-off valve there as well.
Gate valves can be installed before and after the pneumatic control valve； Cut-off valve for the bypass line. If it is convenient to install valves on the pneumatic control valve, it is recommended to add two gate valves before and after the pneumatic valve, as this will facilitate the maintenance or replacement of the pneumatic control valve