I would like to ask experts in compressors about the issue of motor vibration
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This post was last edited by fyswan8 on 2016-4-12 at 15:41. There is currently one motor-driven single-stage double-cylinder piston-type hydrogen circulation compressor in use; its designed normal operating pressure is 11.4 Mpa for the inlet and 12.2 Mpa for the outlet, with a motor rated current of 408 A. After installation, leak testing is carried out using nitrogen; hydrogen valves are also used. The manufacturer was consulted, and it was stated that using nitrogen for a short period of time is acceptable. However, during the leak detection, regardless of the pressure of air being introduced, the exhaust pressure increased slightly; the compressor vibrated normally, but the motor experienced significant vibration and produced a loud noise, similar to that of a tractor. When the manufacturer arrived at the site, they accidentally reduced the outlet valve, resulting in a pressure difference of over 8 kilograms between the inlet and outlet. Instantly, the motor stopped working, and both the noise and vibration ceased; it operated as stably as when tested individually. The manufacturer was unable to explain what caused this phenomenon. There are several sets of data: Inlet pressure at 3.3 Mpa, outlet pressure at 3.8 Mpa, current around 205 A, horizontal vibration level at 6.8 mm/s; the noise from the motor was present. Inlet pressure at 3.3 Mpa, outlet pressure at 3.9 Mpa, current around 215 A, vibration level at 4.5 mm/s; the noise from the motor decreased. Inlet pressure at 3.3 Mpa, outlet pressure at 4.1 Mpa, current around 225 A, vibration level at 3.9 mm/s; the noise from the motor decreased again. Inlet pressure at 3.3 Mpa, outlet pressure at 4.23 Mpa, current around 235 A, vibration level at 3.5 mm/s; the noise from the motor was lower. Inlet pressure at 6.2 Mpa, outlet pressure at 7.1 Mpa, current around 280 A, vibration level at 2.8 mm/s; the noise from the motor was low as well. After that, nitrogen was used to increase the pressure: inlet pressure at 9.5 Mpa, outlet pressure at 104 Mpa; motor vibration was low. With such high pressure differences, the exhaust temperature increased. The manufacturer could not explain why this happened; they said that using hydrogen would help. Hydrogen was introduced into the system while it was running, but no matter how much the outlet valve was adjusted, there was still noise from the motor, and it was not possible to reduce the motor’s vibration and noise levels. Currently, the operating conditions are as follows: hydrogen inlet pressure at 8 Mpa, exhaust pressure at 8.1 Mpa, current at 220 A. The inlet and outlet valves are fully open, while the reflux valve is fully closed. The compressor vibrates normally; however, the motor exhibits significant vibration and noise, at a level of 8-9 mm/s. I would like to ask experts: why does increasing the backpressure at the outlet when using nitrogen help reduce motor vibration, while this approach doesn’t work with hydrogen? What is the impact of the molecular weights of nitrogen and hydrogen? (It’s possible that there is a problem with the outlet valve; the valve itself might be too large, making it difficult to adjust properly.) Are there any solutions available?
First, the original poster should clarify: how many stages does the 1-pressure compressor have?； Does the temperature of the intake and exhaust valves change when the compressor vibrates? ； 3 Has the outlet pressure changed when adjusting the return valve? ； My first impression is that the compression ratio of your compressor is very low, and this could well be the root of the problem.
For a first-stage two-cylinder piston compressor, when the outlet valve is adjusted to be closed, the exhaust temperature rises; the pressure at the outlet of the return valve also changes. The pressure ratio is low because it is a circulating air compressor, whose sole function is to circulate air within the system
The motor load is unstable; the rule is that the greater the work done, the less vibration there is
The cycle gas compressor should not require much work to operate
The compressor with a single motor experiences greater vibration, while one with multiple motors has less vibration; if the pressure still remains the same in such cases, it’s necessary to check the motor itself. Based on the description, it seems that the issue lies in improper installation of the motor itself. The poster should check the vibration distribution at various points of the motor base and the pump when the motor vibrates heavily; it shouldn’t be a difficult problem to resolve.
Firstly, the motor performs well in all aspects when tested individually. Secondly, increasing the outlet pressure can bring the motor to its optimal operating condition; of course, it is normal for the motor to suffer damage due to prolonged operation under vibration
From a mechanical perspective, the operating condition of having a pressure difference of 8 kg as specified in the design is essential to maintain the proper operation of the entire unit; this pressure difference is very important. The pressure difference is too low; this results in the balance of forces that keeps the equipment operating stably being disrupted. Put more vividly, it is to maintain a rated pressure difference that precisely balances the impact forces generated by the piston’s back-and-forth movement, thereby stabilizing the crankshaft and ensuring the stable operation of the motor. Conversely, the greater the deviation from the rated pressure difference, the smaller the impact force on the balance piston, and the more unbalanced it becomes; as a result, the impact force on the crankshaft increases. This vibration is reflected in the motor, causing it to function more abnormally. ---Just personal opinion
The 8-kilogram pressure difference applies to nitrogen; no pressure difference has been set for hydrogen
What you mean is that there are certain issues with the design; in other words, the designed operating load is 120 kilograms, but operating it at 80 kilograms may not be feasible
Is it a mismatch in the motors, or is there something wrong with the motors themselves?