banging hydronic heat system

[Anonymous]

we have a hydronic heat system with taco 570 gold line zone valves. when the valves open or close the baseboard heaters slam terribly. we have checked for air in the lines with little to no succcess all the diffrent zones in this area do this. this is a commercial building and this heat is in an office area.the fintube is literally jumping up and then coming down onto there brackets. any help?

[Harold KestenholzParticipant]

If you have installed a manual vent valve at a possible air trap in a riser to vent air from the tubing when the zone valves are closed – then found no air coming out look for something else.

There may be an expansion tank or bladder type device in the pipe somewher besides the expansion tank near the boiler. There needs to be a place that a large slug of water can follow an air pocket to slam against an elbow.

Also the system pressure may be below that needed to keep water pressure at the top of the loop. If there is an automatic air bleed there, air can enter the upper pipe while the zone valve is closed to permit the slamming and then the air can exit while the pump pressure forces air out.

[Harold KestenholzParticipant]

You will also hear a bang when hot water turns to steam at a restriction. A strong pump can create enough suction to boil water at a lowered pressure. The steam collapses at a cool place to make the banging.

Look for a pump pumping toward the expansion tank and away from zone valves. The drop in pressure can cause cavitation. This is explained in the system design lesson called “Create a positive pressure” at: http://www.hydronic.net

[Author]

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