Questions about liquid ring vacuum pumps
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I have heard that liquid ring compressors are prone to surge when the inlet flow rate is insufficient. I wonder if liquid ring vacuum pumps are prone to surge. (For example, the inlet valve is closed when in standby mode; at that time, the inlet flow rate is definitely low.) Additionally, there is a return line from the inlet to the outlet of the liquid ring vacuum pump in my plant, and a control valve is installed on this line. What is the purpose of this line then? During the training, a teacher explained that it is used to regulate pressure in order to prevent cavitation, when the vacuum pump is running in standby mode without being connected to the system. Personally, I think this pipeline is used to prevent surging when the pump is on standby. I would appreciate expert advice on these two issues. Thanks.
Surge should occur; for example, when the machine is in operation and the inlet pump is not turned on, there is a lot of noise and vibration. As for the control valve used across the pipeline that you mentioned, it is used to adjust the system pressure during production – the valve opens when the system pressure is low and closes when the pressure is high.
I would be extremely grateful if all the experts could share their opinions freely and offer their guidance!
A liquid ring vacuum pump should experience cavitation; it is not called surging. A high vacuum level is achieved when the inlet valve is closed and the outlet valve is opened. If the sealing fluid is water, it may reach the boiling point of water, causing the water to vaporize and resulting in cavitation. The inlet and outlet with bypasses are used to adjust the level of vacuum. A high vacuum level is not required; the bypass valve can be opened a little. Additionally, this valve is also used to operate the vacuum pump; it is open before starting the vacuum pump.
Surge will not occur. Our company has two water ring vacuum pumps; the required vacuum level for the system is above –90 KPa, and the higher the actual vacuum level, the better. Since the actual gas extraction volume is very low, surge will not happen either. Furthermore, the return line of your company’s vacuum pump is used to regulate the vacuum level.
You should first understand the principle of surge, and then you will realize that a liquid ring vacuum pump cannot experience surge. As for the outlet check valve, it is used to control the outlet pressure of the pump, and it also prevents cavitation caused by rising water temperature at very high vacuum levels.
Please also share your views and opinions. Thank you
Surge should not occur. Before starting the vacuum pump, the outlet valve should be opened while the inlet valve should be closed. If the outlet reflux valve is closed, the motor may overload and shut down after startup.
It shouldn’t happen in a short period of time. A reflux control valve was added, right? It’s hard to say for a long time
It’s unlikely that a liquid ring vacuum pump will experience cavitation. Because the liquid ring vacuum pump itself has a limit vacuum level, and it can operate at extremely low pressures. (Saturation vapor pressure is not applicable here.) Water is the working fluid, and it can be replenished; water that is continuously being added cannot evaporate. As for whether surge will occur, that’s what I was thinking just now as well. Concept of surge: The air flow alternates between being supplied and flowing back from the piping system to the vacuum pump; this phenomenon is known as surge. I haven’t really heard much about water ring vacuum pumps experiencing surging, nor have I seen any surge prevention devices for such pumps. The final correct answer – well, professional vacuum pump designers can probably provide it.
Surge can occur; for example, when the pump at the inlet is not turned on while the machine is running, there is a lot of noise and vibration