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Hydronic Pump Cavitation - Pump cavitation can cause severe problems to a pump if not addressed and corrected. To understand the cause of cavitation you need to understand the pressure-temperature relationship of the liquid in the loop. Whether it is water or water/glycol mix. As the water passes through the pump it changes the pressure from the suction side to the discharge side of the pump.
If the water’s static pressure drops too much vapor is created causing tiny bubbles in the water or fluid in the loop passing through the pump. These bubbles are unstable and collapse causing severe turbulence inside the bearing assembly and can damage the impeller.
Hydronic Pump Cavitation | HVAC Water Problems
Cavitation is often occurring when one hears popping and crackling noises passing through the pump. Cavitation can also sound like the pump is pumping rocks through the impeller. These abnormal noises are the result of these tiny bubbles collapsing.
As these bubbles are forming the pump loses its ability to create the necessary head to continue circulating the fluid through the loop. Solve the problem of and the noises go away along with the extended life of the pumping system.
Aside from the damage to the impeller inside the cavitation also causes the decreased life of the pump. Cavitation causes accelerated wear of bearings and seals increasing downtime for maintenance and repair. This coupled with increased operating costs makes cavitation a serious problem if the pump is left in operation without solving the problem for whatever reason.
Always address cavitation by solving the core issue and avoid quick temporary fixes. When cavitation is unavoidable special pumps, bearings, and impellers should be used along with strengthened pump foundations and fasteners to deflect vibrations caused by cavitation. This can be more costly than resolving the issue.
Hydronic Pump Cavitation | HVAC Water Problems - Causes of Cavitation
Poorly designed hydronic loops, oversized pumps, and operating the loop fluid at higher than designed temperatures are common causes of cavitation in water loops. Typically cavitation occurs at high flow rates but it can also occur at low flow rates. These issues occur when the suction head pressure drops below the vapor pressure of the fluid being pumped. Problems that cause cavitation are:
- Fluid temperature is too high
- The hydronic loop is clogged or plugged up. Check strainers (especially on the suction side), manual valves, or other problems that can impede flow in the hydronic loop.
- Over-sized pump
- Air in the loop
- Internal recirculation - this is a problem inside the impeller where internal recirculation patterns develop inside the bearing assembly. The velocity of the fluid in recirculation patterns increases until the fluid vaporizes causing cavitation.
- Turbulence - too much turbulence has the same effect of internal recirculation noted above.
The most prevalent form of pump cavitation is referred to as NPSHa or Net Positive Suction Head available. The solution to this problem may be to change out the pump however, consult with an engineering professional to find other possible solutions that may be less costly. Never allow the problem to go unresolved. Replacing impellors and other parts of the pump will be more costly than resolving the issue.
If you have an issue with hydronic pump cavitation work your way through the list to solve the issue. Increase the suction pressure or lower the temperature of the fluid and check the impeller for unusual wear or problems. Solve the issue of hydronic pump cavitation and avoid severe damage to the hydronic loop and pump system.
Hydronic Pump Cavitation | HVAC Water Problems
