Hydronic Cavitation Can Be a Serious Problem

HVAC 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 (typically water or water/glycol mix). As the water passes through the pump it changes pressure from the suction side to the discharge side of the pump.  If the waters 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 where the impellor is located and can damage the impellor. Pump cavitation is often occurring when one hears popping and crackling noises passing through pump. Pump cavitation can also sound like the pump is pumping rocks through the impellor. 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 pump cavitation and the noises go away along with extended life of the pumping system.

Problems Associated with Hydronic Pump Cavitation

Aside from the damage to the impellor inside the pump cavitation also causes 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 hydronic cavitation by solving the core issue and avoid quick temporary fixes.  When cavitation is unavoidable special pumps, bearings, and impellors should be used along with strengthened pump foundations and fasteners to deflect vibrations caused by cavitation.

Causes of Hydronic Pump Cavitation

Poorly designed hydronic loops, oversized pumps, and operating the loop fluid at higher than designed temperatures are common causes of hydronic 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
• 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.
• Oversized pump
• Air in the loop
• Internal recirculation - this is a problem inside the impellor where internal recirculation patterns develop inside the bearing assembly where the impellor is located. The velocity of the fluid in recirculation patterns increase until the fluid vaporizes causing cavitation.
• Turbulence - too much turbulence has the same effect of internal recirculation noted above.

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 impellor for unusual wear or problems.  Solve the issue of hydronic pump cavitation and avoid severe damage to the hydronic loop and pump system.

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