Regarding the pump automatic start-up design scheme

Does your system use different signal interfaces for starting and stopping the pump? Is pressure control achieved by using pressure sensors or electric contact pressure gauges to provide the start signal, with the outlet valve opening automatically after the pump starts? And for stopping the pump, is a level switch used to send a shutdown signal when the liquid level is low, causing the outlet valve to close automatically after the pump stops? That’s what I’m asking – I just don’t understand why the inlet shut-off valve needs to be closed

Haha, I didn’t explain it clearly. The logic is in place to protect the pump; if the inlet shut-off valve closes, an interlock will activate to stop the pump. The process requires the pump to remain operational without interruption; therefore, a backup pump is designed to start automatically when the outlet pressure is low.

There’s a logical issue; it’s too simple. It needs to be decided after thorough discussion with the process engineering team. For example: What should be done if the outlet pressure is low and the liquid level at the bottom of the tower is also low?

In that case, the equipment itself should be protected first; the pump should stop operating when the liquid level is too low

It is not advisable to use a check valve to close the inlet valve. Stop the pump and turn it off. The pump is started. Right?

The process conditions need to be described more clearly. If the pump is a feed pump, ensuring normal flow in the process requires a sufficient supply of material at the inlet; if the pressure of the main pump drops or flow is insufficient for other reasons, in the case of a centrifugal pump, the standby pump’s inlet valve remains open while its outlet valve is closed. When the main pump fails, the standby pump starts up, and its outlet valve opens after a few seconds. When the flow rate is normal, the outlet valve of the main pump is closed and the power supply to the main pump is cut off; simultaneously, the inlet valve is also closed. In the case of a positive-displacement pump, the standby pump should be used first: open its outlet valve and start it; once the flow rate is normal, close the inlet valve of the main pump, then cut off the power supply to the main pump and close its outlet valve.

In fact, this is the first time I’ve seen such a interlock system; I hope colleagues who work with similar interlock devices will share their insights! To add to what was said above, there is also a manual valve at the pump inlet. The so-called interlock cut-off valve is also known as a fire valve; this type of valve is usually located near the outlet of the tower, for safety reasons. In recent years, large design institutes have adopted a design approach in plant design that involves installing shut-off valves on the outlet lines of vessels and towers. :D :D :D

Pumps that start automatically like this are of the centrifugal pump type, and they have only a manual valve at the outlet. To achieve automatic startup, the outlet valve of the standby pump must be in the open position. I was also puzzled by this: when a centrifugal pump starts with its outlet valve open, both the starting current and the load it bears are very high, and its flow rate is already high to begin with. Later, I consulted experts in electrical engineering, who said that the starting current would be high, but it wasn’t a problem; it depended on the design of the substation. :hug: :D

Hehe. The problem wasn’t clearly stated. Under normal circumstances, when the liquid level at the bottom of the tower is low, the outlet flow rate of the pump should be reduced, and this can be achieved using an inverter-driven motor. If the operating conditions change frequently, running the pump constantly can cause significant damage to it. Based on your flow rate requirements, the motor power required for this pump will be high; therefore, using inverter control allows for better regulation of the flow rate, helps save electricity, and also provides good protection for the pump.

I think the interlock on centrifugal pumps is not intended to protect the pump itself; it is usually for safety reasons, to ensure that the material inside the tower can be removed promptly, thereby preventing an increase in concentration due to accumulation, which could lead to high risks. Or it is something provided in unsafe conditions for emergency situations, and it needs to keep running without stopping.

Concentrated sulfuric acid is highly corrosive; ordinary centrifugal pumps suffer from severe leakage, which poses significant problems regarding the environment and safety. And now I’m facing another problem: I only need a flow rate of 15 kg/h, but for some reason the design specifies a pump with a capacity of around 100 m3/h. Most of this flow is wasted as return flow – I’m not sure what the purpose of that is Also, I want to change the material of the pump – how should I choose?

Regarding the automatic start-up of centrifugal pumps, the following points should be noted: 1. Pump configuration: Each pump should be equipped with a check valve and a manual valve at its outlet, and an adjustable valve should be installed on the main outlet pipe where the outputs of the two pumps meet; this setup is more economical (however, it is not suitable for media that tend to crystallize or in which solid particles can accumulate). 2. Startup procedure: (1) When the main pump stops operating, the outlet adjustable valve should be closed via interlock; after a few seconds, the pump should be started, and then the outlet adjustable valve should be opened after another delay； (2) When the liquid level before the pump (tower) is high, the standby pump is started via interlock (this applies only when the main pump is still running but its flow rate is insufficient, resulting in an increase in the liquid level before the pump (tower)).