Can the liquid in the pump outlet pipe flow back to the inlet pipe?
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I have a question for everyone: There are manual valves at both the inlet and outlet of the pump. Between the manual valve at the pump inlet and the inlet pipe of the pump, there is a drain valve that allows the liquid behind the valve in the inlet pipe to be drained into the gutter； My question is: when the centrifugal pump stops operating and its impeller ceases to rotate, can the liquid in the pump’s outlet pipeline flow through the pump’s volute and be discharged to the drain via the pump’s inlet discharge valve?
After the centrifugal pump is stopped, if the valve at the outlet is not closed properly or the device designed to prevent backflow is damaged, the liquid in the outlet pipeline may flow back through the pump body into the inlet pipeline, and then be discharged to the drain via the discharge valve. A check valve is usually required to prevent this from happening. .
If there is no check valve at the outlet of the centrifugal pump, and the DCS indicates that the pump has failed and is no longer operating, should the personnel in the control room use walkie-talkies to inform the production/inspection staff? Upon arriving at the site, should they first stop the pump and cut off the power supply, then close the pump’s outlet valve, followed by closing the inlet valve, and finally opening the drain valve on the inlet pipeline? Is this the correct sequence of operations? Does the liquid in the pipeline from the pump outlet to the pump outlet valve also flow out through the pump inlet drain valve?
Yes, in winter, when liquids are prone to freezing, it is by emptying them that such measures are taken.
If you follow the sequence you mentioned, that is, turning off the pump first and then the outlet valve, the liquid in the pipeline from the pump outlet to the outlet valve will not flow out through the pump’s inlet drain valve. Because the pump had already stopped operating before the outlet valve was closed, there was no pressure inside the pump to push the liquid toward the drain valve. This liquid can only remain inside the pipe, unless the pipe itself is tilted or the liquid is manually drained. .
It would be best to send a flowchart for this issue; it’s more intuitive to understand things by looking at a diagram. Regarding the process from when a problem occurs with the pump to when it is handed over for repair, the standard sequence is pump inlet valve – pump – pump check valve – (some electric butterfly valves) – pump outlet valve. Following this procedure, in the event of a fault, the power is first cut off (the circuit is disconnected), and then the pump inlet valve and outlet valve are closed. If it is a low-temperature saturated liquid, the fluid within the pump must be removed promptly to prevent vaporization-induced overpressure. Generally, for liquids at normal temperature, it can be decided whether to discharge the liquid based on the nature of the fault. Such as electrical faults. For pumps that require disassembly for maintenance, the liquid inside the pump should be drained, the power should be turned off, the necessary maintenance procedures should be followed, and the pump should then be handed over for repair. Regarding this, companies have relevant operating procedures; just follow those procedures as a reference.
If it is understood simply as material discharge, it is possible to carry out discharge using the impeller at the inlet drain valve; simultaneously, the outlet drain valve is slightly opened to reduce the negative pressure inside the pump, thereby facilitating the discharge of the material.