Problems with chain-driven self-priming pumps
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Problem with interlocked self-priming pumps: For interlocked self-priming pumps (centrifugal pumps), how should the opening degree of the outlet valve be controlled when the self-priming interlock is activated? (If it is too large, the pump is prone to tripping during startup.)
For pumps with an auto-start function, a large margin is usually applied when selecting the motor (generally extending to the end of the curve). And it generally does not involve valve adjustment at startup. So if this situation occurs, I think the motor is probably too small
From the perspective of centrifugal pumps, if the motor is large enough, the valve opening can be set to the level required for normal operation； If the motor is not large enough, then the valve must be closed a bit more. This should be determined comprehensively by taking into account aspects such as process, control, and equipment.
The outlet valve of the standby pump is generally fully open
Here, the outlet valves of the interlocked automatically-starting pumps are fully open; this applies to both high-speed pumps, and they did not get bypassed during the interlocked automatic start-up； I think on the one hand, there is sufficient margin in the motor selection, and on the other hand, the electrical delay protection settings have been appropriately extended; it’s just a guess, though, and it needs to be verified.
There used to be self-priming pumps, but I didn’t pay attention to it; presumably the motor chosen was too large. I had intended to find the documentation for a related pump today to compare it, but unfortunately I couldn’t locate it.
This needs to be determined based on the pump’s performance curve and the actual process conditions. In other words, it depends on the pressure behind the pump at the time of startup, as well as the flow rate corresponding to the operating point of the pump at that pressure. As long as the opening degree of the valve behind the pump ensures that the flow rate does not exceed the motor power specified on the corresponding curve for either during startup or after it, then there is no problem. Haha, it’s a bit tricky to say.