Setting of the emergency valve position for the pump return switch valve
Thread Content
Dear sea friends, we have a tank whose bottom valve is a on/off valve, with the air cut-off valve set to FO. A return valve is installed at the outlet of the bottom pump, and this valve is also controlled by an on/off valve; it does not have any flow regulation function. The on/off valves on the pump’s outlet pipeline are all of type FC. So, should the on/off valve on the pump’s return pipeline be set to FC or FO? The feeding for this tank is carried out through a circulation line elsewhere, and the feed pipeline also uses FC.
FO But why are you using only on-off valves? Won’t that allow flow to escape unchecked?
What was said upstairs makes sense; if there’s no adjustment function, then how can the amount of material be controlled?
The reflux valve should be equipped with a flow-limiting orifice to allow backflow to the tank, and no on/off valve should be used.
Identify a closed system in which the overall control of the system is negative; positive action is not allowed. The discharge valve of the tank should be a air-actuated shut-off valve, while the feed valve should be an air-actuated open valve, ensuring negative action. The outlet gas valve should be a shut-off valve, while the reflux feed valve should be an open valve, that is, F.C.
Whether the valve should remain open, closed, or in its original state in the event of failure (loss of power or air supply): 1) based on safety requirements, 2) based on process operations. Safety requirements take precedence over process operations; in other words, it’s a matter of choosing the lesser of two evils, ensuring reliability and usability. The return line of the pump is usually designed with the pump’s normal operation in mind (to ensure a minimum operating flow rate for the pump or to provide overpressure protection); therefore, it is more appropriate to use FO (although this results in some waste of electrical energy). However, even if an XV is available, full reflux should not be used – instead, process valves are employed on the return line ； Some use process valves + flow-limiting orifice plates, some use control valves, while others use shut-off valves + flow-limiting orifice plates, etc.… It’s not possible to generalize