Velocity noise.....

PDB2

or at least I think it's velocity noise. I'm installing a replacement cold start boiler. The new boiler was shipped with a Taco 007 pump, and as I have two baseboard circulator controlled loops, I bought another 007 to use on the second zone. I kept the supply size at 1 1/4 in. to the pumps. The pump discharge is 3/4 in. , as is the zone piping. At the boiler return, each zone goes to 1 in. and then back to 1 1/4 at boiler. I didn't figure head loss on zones, but they should be fairly well matched as one one is 315' and the other 275'.

 I haven't fired the boiler yet, but circulating the system and bleeding air, I'm getting a lot of rushing noise at the pumps. I don't think it's an air problem as I have bled and bled.....When I choke each zone down with the return side balance valves, about 40%, the noise pretty much clears up. Is this an acceptable way to run, or am I going to have premature pump failures? If I do, what size Taco pumps would you replace the 007's with ? I'm too close to heating season to change any piping if I can get away with what I have for this season anyway.......Thanks for the help.

Mark Eatherton

Probably air in suspension...

Once you heat the water up, it should quiet down.



If the pumps are not pumping away from the expansion tank, you are guaranteed to hear cavitation noises, which choking flow will help negate.



How do you know that the are the right pumps without having done any hydraulic calculations?



You won't know if choking flow is a good thing or not until its too late (design temperatures outside).



Just curious.



ME

PDB2

the 007

was included with the boiler package and the efficiency specs seemed close enough to the old B & G 100's that had worked pretty well for 50 yrs.. I guess I figgered it was worth a try for the price of another 007.......The expansion tank is on the return side, so that doesn't explain it. With the old system, both zones were returned and combined to a 3/4 t back to boiler, so I guess they were choked down there as well. I'll let it run with the balance valves half throttle and see what kind of temp drop I'm getting and then decide how much noise I can live with. Maybe the air will work itself out better at the slower flow also.....

Mark Eatherton

So....

If the expansion tank connection is on the return, I assume the pumps are on the supply, and if so, what kind of pressure drop (boiler) is between the pumps and the expansion tank connection.



Ideally, the expansion tank connection should be as close to the pumps inlet as possible.



Another trick is to induce some Dawn liquid detergent to help in getting the bubbles out. It raises the pH as well.



ME