- #1
Minghan
- 17
- 2
What is the reason making this sound?? ( Rotary lobe pump)
anorlunda said:Cavitation is my first guess.
On Youtube you can find numerous audio examples of cavitation noise. It is described as a sound like rocks going through the pipes.
You said lube pump. Is it pumping oil or water? Cavitation is most often associated with water pumps, but it is not impossible in oil pumps, such as in this video.
Thank you!Asymptotic said:Cavitation is my first guess as well. What are the pump specs, and what type of fluid, temperature, motor speed, pump input shaft speed, pump outlet pressure, and (if known) motor power?
I've encountered similar issues with gear pumps used for gearbox lubrication (ISO 320 oil) that were prone to cavitation until the oil warmed up. If you have one handy, as a troubleshooting step run the motor from a variable frequency drive to determine if it quiets down when operated at reduced speeds.
View attachment 223925
Is this the suction run? If so, overall length and fittings conspire to create a decent amount of flow resistance, and could be starving the pump suction inlet (especially so if the fluid has high viscosity).
Air entrained into the pump suction both causes symptoms akin to cavitation, and makes true cavitation more likely. The course of action required is installation dependent, but often involves the strategic placement of baffles and increasing liquid level height.Minghan said:And I just wondered if this setting could cause "Aeration" and make bubbles into pipe which make "Cavitation" easier to happen??
Minghan said:Thank you!
And I just wondered if this setting could cause "Aeration" and make bubbles into pipe which make "Cavitation" easier to happen??
"Air entrainment and recirculation will also cause the same rumbling/rattling noise and high vibration as cavitation, as well as the recognizable impeller pitting damage."Asymptotic said:Air entrained into the pump suction both causes symptoms akin to cavitation, and makes true cavitation more likely. The course of action required is installation dependent, but often involves the strategic placement of baffles and increasing liquid level height.
Do a Google search for "difference between entrained air and cavitation". This return hits the high points. http://www.pumpscout.com/articles-expert-advice/am-i-experiencing-cavitation-or-not?-aid102.html
I'll inquire again, what are the pump specs, and what type of fluid, temperature, motor speed, pump input shaft speed, pump outlet pressure, and is that the suction run outlined in yellow in the photo in post #3?
This is a major contributor to your problem. I recommend thoroughly documenting your installation (a drawing with pump size/model number, pipe diameter(s), run lengths, fitting details, etc.) and consulting with the pump manufacturer's engineering department.Minghan said:Is that the suction run outlined in yellow in the photo in post #3? : Yes!
Do you mean by throttling the pump outlet valve as is common to reduce flow in a (non-positive displacement) centrifugal pump installation? A rotary lobe pump is positive displacement, and although to some small extent outlet throttling reduces flow (mostly, by increasing slip), the increase in outlet pressure at the operating point where flow rate has been reduced enough to prevent cavitation may exceed pump and/or pipe pressure ratings, it puts more wear and tear on the pump, and is a very energy inefficient way to reduce flow.Is increasing pressure of pump outlet a factor to reduce cavitation in rotary lobe pump??
Asymptotic said:Do you mean by throttling the pump outlet valve as is common to reduce flow in a (non-positive displacement) centrifugal pump installation? A rotary lobe pump is positive displacement, and although to some small extent outlet throttling reduces flow (mostly, by increasing slip), the increase in outlet pressure at the operating point where flow rate has been reduced enough to prevent cavitation may exceed pump and/or pipe pressure ratings, it puts more wear and tear on the pump, and is a very energy inefficient way to reduce flow.
When outlet pressure is too high, discharge cavitation can occur.Minghan said:Minimizing discharge pressure to ensure bubble won't implode at the outlet side??
No. Unless the pump is badly worn only a small percentage of flow is expressed as slip.Minghan said:1.Could the slip which is caused by higher pressure at the outlet side add pressure to the inlet side and minimize the cavitation ??
Asymptotic said:No. Unless the pump is badly worn only a small percentage of flow is expressed as slip.
Minghan said:1. Increasing clearance could minimize cavitation because of adding more slips and more pressure to inlet side ??
Minghan said:2. And another question making me confused : If the liquid viscosity is too high and rotary PD pump's speed still do not slow down ,then severe noise and vibration will happen. Why?? How to explain this phenomena??
No. Cavitation occurs when NPSHa (Net Positive Suction Head Available) in the system a pump is a part of is lower than NPSHr (Net Positive Suction Head Required) by the pump. One of the contributors to pressure drop in the suction line is flow rate (more flow >> more pressure drop).Minghan said:1. Increasing clearance could minimize cavitation because of adding more slips and more pressure to inlet side ??
I'm not certain what you are asking here. You've indicated this is a water pumping application, and water viscosity doesn't change very much (from about 1.9 to 0.32 cSt) between 0°C or 100°C.2. And another question making me confused : If the liquid viscosity is too high and rotary PD pump's speed still do not slow down ,then severe noise and vibration will happen. Why?? How to explain this phenomena??
ChemAir said:PD pump systems need to be evaluated pretty carefully, there is usually a pressure relief system integrated to address the discharge pressure spikes they can generate. I have seen pumps cavitate (or at least exhibit cavitation like symptoms) when relief or minimum flow control systems weren't working properly.
Regarding your original question: "What is making this noise?" Many have a relief valve that can dump excess discharge pressure back to the inlet. It may be internal or external. If flow usage is below what the pump can deliver, the relief valve will vent the excess back to the suction. A relief valve operating at just slightly above its set point can chatter on its seat and make a nice rattle.
Minghan said:Pump specs: 120 L/min
Type of fluid: Water
Temperature: 25°C
Pump input shaft speed: 400 rpm
Pump outlet pressure: 0.5 kg/cm^2
Asymptotic said:I'm not certain what you are asking here. You've indicated this is a water pumping application, and water viscosity doesn't change very much (from about 1.9 to 0.32 cSt) between 0°C or 100°C.
The pump is starving.Minghan said:At the full speed, severe noise and vibration happened.
Troubleshooting said "The liquid viscosity is too high. The pump is starving. "
After I tune the frequency inverter, motor speed slows down and transporting liquid become smooth.No noisy and vibration!
Why?? How to explain this phenomenon??
@Tom.G has covered the phenomenon better than I, but allow me to add that cavitation in your case appears to be due to restriction in the suction line caused by a combination of a long run in smallish diameter pipe, and fitting placement.Minghan said:Sorry to make you confused.
I made this rotary PD pump to suction another high viscosity liquid and I used frequency inverter to change the motor speed.
At the full speed, severe noise and vibration happened.
Troubleshooting said "The liquid viscosity is too high. The pump is starving. "
After I tune the frequency inverter, motor speed slows down and transporting liquid become smooth.No noisy and vibration!
Why?? How to explain this phenomenon??
A Rotary lobe pump is a type of positive displacement pump that is commonly used in various industries to move fluids. It works by using two or more rotating lobes that trap fluid and move it through the pump's chamber.
The sound produced by a Rotary lobe pump is a result of the movement of the lobes and the fluid inside the pump's chamber. As the lobes rotate, they create pressure differences that cause the fluid to move, resulting in the characteristic humming or buzzing sound.
The sound produced by a Rotary lobe pump can be affected by various factors such as the speed of rotation, the type and viscosity of the fluid being pumped, and the condition of the pump's components. Other factors like the pump's installation and surrounding environment can also contribute to the sound produced.
The sound produced by a Rotary lobe pump is generally not harmful. However, prolonged exposure to loud noises may cause hearing damage. It is important to wear appropriate ear protection when working in close proximity to the pump.
Yes, the sound produced by a Rotary lobe pump can be reduced by implementing proper maintenance and lubrication, using sound-absorbing materials in the pump's installation, and adjusting the speed of rotation. You can also consult with a professional to determine the best ways to reduce the sound in your specific situation.