Noisy circulator pump

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Ricardo Villamil

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Hey guys, I just bought a 20y/o house with an oil boiler and three heating zones. From what I can tell, there's one circulator pump for all three zones and three zone valves (there's another circulator pump which I'm not sure what it does. It is also a bit noisy but not much). One of the pumps makes a loud grinding noise through out the house BUT only when one zone is active, as soon as a second or third zone activate, it quiets down. I'm not super familiar with these systems so please bear with me!

Here's a quick video I shot:
20201226_134712.jpg 20201226_134728.jpg 20201226_134740.jpg

What do you guys think? Thanks!
 

Dana

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The pump is probably cavitating, something that can happen when it's starved for flow by serving only one zone. Try dropping the speed down to low where it isn't trying to pump as hard. Does the sound when serving just the one zone improve? (If yes, leave it there. Most systems are over pumped anyway.)

Cavitation is also more common when the system pressure is on the low side. What is the pressure on your system at the pump's elevation (measured when the system is not pumping) ?

If the pressure gauge is on the boiler that's good enough as long as the pump is only a few feet above or below the boiler. If the pump is several feet above the gauge on the boiler, subtract 0.433 psi per foot of elevation difference to estimate the pressure at the pump. eg: say the gauge on the boiler is say 3' above the floor, the pump is 7' above the floor, and the static psi at the boiler reads 12 psi. The 4' difference in elevation means the pressure at the pump would be 4' x 0.433= ~2 psi lower than at the pressure gauge, or about (12 psi - 2 psi=) 10 psi. Any lower than 8 psi can make the pump significantly more prone to cavitation.
 
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