Pump Common Noise Problem

Let's take a look at a few problems in a building system that are commonly the cause of pump noises, and how to fix them.1. Air in The System
If you don't have an air separator installed, you will most likely have to deal with air in your system at some point. When this happens, it's important to inspect the water lines and bleed the system.
Modern pumps have bleeder valves that make the process very easy. Slowly open the valve until you start hearing a hissing noise. Once the hissing ceases, you will see a slight dribble of water, indicating that the pump no longer has air. At this point, you can close the valve.
After doing this, make sure that the pump has been installed correctly. Even a few degrees of inclination or misalignment will allow air to get locked in the pump.
2. Incorrect Pump Size
Both oversized and undersized pumps can lead to noises in the system, but the solution to deal with each case is different.
Pumps can be oversized for several reasons. It could happen due to a degree of error in the planning and design stage when engineers need to "guesstimate" piping length and fittings, or it could be purposely designed this way so the system can expand in the future and the "right-size" pump today would not be able to meet the future demand of tomorrow.
Sometimes a pump replacement is needed right away, and the supplier didn't have the perfect replacement in stock, or the engineers choose an oversized pump already considering an expected build-up of corrosion in the pipes that require more pump head.
Regardless of the reason that led to an oversized pump, having one can always cause excessive noise and vibration, loosing up connections and joints and causing piping fatigue.
To solve the issue, you can take the following actions:

• Throttle the pressure-side valves until the noises are eliminated
• Trim the impeller diameter
• Reduce pump speed
• Add a flow recirculation line
• Install a variable frequency drive and remove control valves

Under sizing a pump presents a more serious issue. That's because you, unfortunately, don't have much choice other than replacing the pump and installing a larger one.
If the system is undersized, it can't provide the duty needed, it can also lead to deadheading - when a pump's discharge is closed because of a blockage in the line or an unintentional closed valve. When this happens, the fluid churns inside the pump until it heats up into a vapor, causing noise and damage. Deadheaded pumps can lead to motor burn out, a damaged impeller, seal leakage, cracked bushings, and compromised elastomers, ultimately killing the pump.
In systems with undersized pumps, you can verify if the existing pump can handle a larger motor to avoid dead head. Even though it may be the cheapest way to handle the problem, it is not the best and the solution would just be temporary.3. Excessive Wear of Bearings
Only some pumps have bearing assemblies, not all. However, all electric pump motors have bearings, and the excessive wear of bearings - whether on the assembly or inside the motor - can cause pump noise.
The good news is that pump models with bearing assemblies usually have the components available for purchase, and they are inexpensive and easy to replace.
he bad news is that motor bearings are not sold as components, and when the bearings wear out in the motor, you need to replace the entire part.
The life of a bearing is determined by how many hours it takes for the metal to "fatigue," but many factors can affect this, such as static overload, corrosion, lack of excess of lubricant, overheat, misalignment, and contamination. So, the best way to avoid bearings from wearing out too fast is via preventive maintenance and a comprehensive inspection of your system.4. Clogged System
Water with rust and other sediments can wear out the circulating pump and clog the impeller. When this happens, noise is a consequence. To get rid of it, there is no magic bullet: the solution is in cleaning the system.
Many HVAC systems have dedicated filtration systems and dirt separators to prevent clogging from happening. Sediments can be easily removed from the system through water blowdown.
These systems protect not only pumps but all the other HVAC units in the system.5. Incorrect Speed Setting
High-quality and modern pumps usually have 3 flow settings, while older pumps may have only one or two. That's why older pumps are typically noisier than others. They are less efficient, and the energy loss is usually translated into a humming noise.
If your pump is making this noise and you have more than one option of flow setting to work with, locate the flow switch and turn it down one level. Then check the radiators and tower rails to verify if they are still getting up to the temperature they should. If so, then leave it this way.
If you operate with a VFD and your pump is still making a humming noise, check to see if you have a correct grounding of the motor to the VFD. In many cases, incorrect grounding allows the system to act as a noise transmitter.
6. Lack of NPSHa or Incorrect Install Causing Lack of NPSHa
To understand this, we need to take a step back and take a quick look at pump operation. Bernoulli's principle shows us that fluid flows from areas of high pressure to areas of low pressure.
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