There is no need to close the outlet valve first when shutting down a high-speed centrifugal pump

At what rotational speed in revolutions per minute is a centrifugal pump considered a high-speed centrifugal pump? Regarding the question raised by the poster, the part about stopping the pump without closing the valve is something I’ve heard of for the first time as well. However, this remains to be verified. In the second half, here’s what happens: the outlet valve isn’t fully closed to stop the pump. Currently, the main centrifugal pumps used in long-distance pipelines are started with the outlet valve set at 10% open.

Won’t leaving the outlet valve open damage the pump? Is a check valve installed?

A high-speed pump refers to a centrifugal pump with a rotational speed of around 10,000 r/min. A motor operating at 2,950 r/min drives the low-speed shaft; after speed adjustment via a gearbox, this shaft drives the high-speed shaft. To prevent cavitation that can occur at high speeds, an impeller is equipped with an inducer wheel. Three sets of seals—upper, middle, and lower—are used for sealing purposes. Auxiliary equipment includes an auxiliary oil pump (activated before starting the pump and before stopping it) as well as a seal buffer tank. Before starting the pump, the inlet valve should be fully opened, while the outlet valve should be opened to 1/3 of its capacity. The reverse flushing valve for the seals and the discharge valve of the seal buffer tank should also be fully opened. The rest of the procedures are similar to those for ordinary centrifugal pumps. There is no need to close the outlet valve first when stopping the pump, as claimed by the original poster. If you still have any questions, feel free to contact me.

Basically, high-speed pumps are available in almost every factory, but I’ve never heard of the opinion mentioned by the original poster; they are all operated using the methods applicable to centrifugal pumps. Please, the original poster, explain in more detail so that everyone can learn from it. Thank you. Stopping the pump without closing the outlet valve causes the pump to experience a sudden power outage while operating at high capacity, which can cause damage to both the motor and the pump. How can the original poster overcome this issue? Thank you:handshake

To be honest, I’ve only heard of this view recently as well. A few days ago, when testing the pump, the manufacturer’s technician said that, and it was the first time I heard such something. I wanted to share it and discuss it with everyone right away, and I’m also interested in hearing other people’s opinions. By the way, I’m talking about the propylene reprocessing pump.

We are a hydrogenation unit equipped with four high-speed centrifugal pumps, and during design, each of them was fitted with a minimum flow line so that it can be opened fully during startup and shutdown. So what the moderator said makes sense.

The motor rotates at 2,950 revolutions per minute, while the pump rotates at 9,918 revolutions per minute. With variable-speed gears. I checked again – the pump should be started as I said. I’m curious to hear what other opinions you all have. Thank you!

Is it the GSB type high-speed pump from Beijing Aerospace? We have been using it for over a decade; it is also an acrylic feeding pump, and the operation method is correct.

The operating procedures specify that the outlet valve should be closed first when shutting down a high-speed centrifugal pump; if such a requirement exists, the operating procedures should be revised

The pumps of the new units in our company are generally equipped with check valves at their outlets! In terms of operation, when starting the pump, the inlet valve is usually opened fully, while the outlet valve is first opened to a small degree! I’d appreciate hearing everyone’s thoughts upstairs! I would like to ask if there are any standard specifications or literature available for reference, as only these have authority and guiding value! If so, please provide it so that we can learn from it!*

The propylene feed pump on our unit is also a high-speed centrifugal pump; when it is in operation, the inlet is fully open while the outlet is open to 1/3； Shut down directly when stopped.

In the question bank, I outlined several levels of consideration for starting and shutting off the outlet valve of a centrifugal pump: 1. Close the outlet valve completely; 2. Close the outlet valve but leave 7-10% open; 3. Before starting the pump, open the outlet valve for a moment and then close it, as it is required that the outlet valve be closed within 3 minutes after the pump starts; there is concern that it might not close properly. In all three cases, the outlet valve is closed (the question bank does not specify that it needs to be fully closed), with the aim of reducing the starting current and preventing damage to the motor. If a variable-frequency drive is used to start the pump, it is not necessary to close the outlet valve (although this practice is not recommended). As for shutting down the pump, it is necessary to close the outlet valve primarily to prevent arcing in the motor when the pump is turned off; if the switch has an arc-suppression feature, it may not be necessary to close it. But Guan is still correct.

Currently, the operating procedures for pumps generally require that the outlet valve be fully closed when starting the pump, and it should also be fully closed first when stopping the pump. However, having used pumps for such a long time, I have always believed that for pumps with high flow rates, it is better to open the outlet valve slightly before starting the pump – the valve just needs to be open enough to allow fluid to flow out. When stopping the pump, the valve should be closed gradually; usually, closing it until the pump starts to vibrate is sufficient, after which the pump should be stopped immediately. I think this approach helps to prevent pressure buildup in the pump during startup and shutdown, as pumps with high flow rates generally experience high pressures during these processes.

One of the functions of closing the outlet valve when stopping a centrifugal pump is to prevent the medium from flowing back.

Answer to floor 15: A check valve should be installed at the pump outlet, so backflow of the fluid is not a problem. The main concerns are: 1. Stopping the pump under load, which can cause electrical arcing (primary concern); 2. Rapid changes in flow rate, which can lead to water hammer (secondary concern)

Here, we set the switches to 10% first. There was a time when, when the pump was running, it was **30%**.

I also think that the outlet valve should be closed first when stopping the pump