Water Hammer - Boiler Call for Heat off - Press Diff Bypass Valve or boiler setting???

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Philtrap

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Hope all is well with you guys... I have a quick question...

Here's the deal. See photo for piping set up... Ignore the closely spaced tees and the buffer tank since they're not the problem.

What happens is when the call for heat goes off the zone valve turns off, but the two pumps stay on (system pump and zone circulator) for a little while. Right when the zone valve shuts off there is a banging noise. I'm thinking there it may be one of these two problems:

1) The Diff Bypass valve may need to be adjusted (I did follow the installation instructions when it was installed by waiting for the outflow side to get hot and finding the tipping point). or,

2) the SC pump shown in the diagram should shut off when the call for heat goes off. This may be programed in the boiler...

Any help would be greatly appreciated.

Thanks,
 

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Philtrap

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Guys - So here's what I did to fix this. The factory reset for the CH post pump time was 1 minute. I changed it to zero. I'm pretty sure that will fix the water hammer bang. My next question is what's the reason for the on minute post pump time other than a cool down for the boiler? If I have a buffer tank, I don't need a cool down period, right? It can be set from zero to twenty minutes.

Triangle Tube Solo 110
 
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Dana

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Guys - So here's what I did to fix this. The factory reset for the CH post pump time was 1 minute. I changed it to zero. I'm pretty sure that will fix the water hammer bang. My next question is what's the reason for the on minute post pump time other than a cool down for the boiler? If I have a buffer tank, I don't need a cool down period, right? It can be set from zero to twenty minutes.

Triangle Tube Solo 110

The post purge is to take the residual BTUs in the boiler's thermal mass and pump it into the zone rather than abandon it in the boiler. The boiler's output temp would be 20F or more than the buffer tank's temp so without the post-purge you are leaving a bunch of heat in the boiler that could be put to better use than standby loss, either by storing it in a buffer tank or pumping it into the zone. At the end of the post-purge the temperature of the boiler will be the same as the buffer or zone water.

If it was purging into the zone radiation you'd want to let it run a bit longer, but a minute would enough if purging into a tank. With low-mass radiation the radiation would also be cooling off, and by continuing to pump you'd park the boiler at the lower cooled-off radiation temp. But with a buffer tank it would not be cooling off, so as soon as the boiler temp reached the tank temp, there is nothing further to be gained.

I'm not sure why or how setting the post-purge time to zero would stop the water-hammer issue unless the zone pump is still full-on when the zone valve closed, and there is no hydraulic separator. A less problematic way to configure a buffer tank it to make it the point of hydraulic separation:


PME_0907_Feat2Fig10Lg.jpg


This way the radiation circulation pump can halt when there are no calls for heat from any of the zones, but the primary loop pump can still purge the boiler's heat into the buffer tank.
 

Philtrap

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The post purge is to take the residual BTUs in the boiler's thermal mass and pump it into the zone rather than abandon it in the boiler. The boiler's output temp would be 20F or more than the buffer tank's temp so without the post-purge you are leaving a bunch of heat in the boiler that could be put to better use than standby loss, either by storing it in a buffer tank or pumping it into the zone. At the end of the post-purge the temperature of the boiler will be the same as the buffer or zone water.

If it was purging into the zone radiation you'd want to let it run a bit longer, but a minute would enough if purging into a tank. With low-mass radiation the radiation would also be cooling off, and by continuing to pump you'd park the boiler at the lower cooled-off radiation temp. But with a buffer tank it would not be cooling off, so as soon as the boiler temp reached the tank temp, there is nothing further to be gained.

I'm not sure why or how setting the post-purge time to zero would stop the water-hammer issue unless the zone pump is still full-on when the zone valve closed, and there is no hydraulic separator. A less problematic way to configure a buffer tank it to make it the point of hydraulic separati

This way the radiation circulation pump can halt when there are no calls for heat from any of the zones, but the primary loop pump can still purge the boiler's heat into the buffer tank.

Thanks Dana - You're right. The post-purge time had nothing to do with the hammer noise. I set it back to 1 minute as per the factory settings. My layout is very similar to the diagram you posted with the exception the there is a Diff Bypass valve connecting the zones out and return. When the Call for heat shuts off, the zone valve shuts off but both pumps stay on for a minute. The internal Boiler pump and the zone pump. Once the zone valve shuts the flow from the zone pump changes from going up to the zone and now goes thru the differential bypass valve. At the moment when that happens the pipes shake and make a banging noise. Could there be air in the line that causes this? Or could it be the Diff Bypass valve is set too high? Any suggestions?

Thanks again.
 

Dana

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Air in the lines would not cause this symptom, but excessive flow on the radiation loops could. What kind of delta-Ts are you getting out of the radiation?

A low temperature difference between the outgoing & returning water would be an indication of high flow. Under 5F would be too much, 10-15F deltas would be fine, even 25F would be fine as long as the system still keeps up with the heat load, and without too much room-to-room temperature imbalance on a zone.
 

Philtrap

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Thanks Dana - My delayed reply has to due with travel and the holidays...

The Delta T is greater than 5. It's more like 8-9.

When the Zone valve shuts and I'm by the boiler it doesn't sound that bad. It sounds bad on the first floor. Kind of like the pipes a being shaken. It's almost like the pipes are just shaking. Could this be resolved by installing hangers or clamps? Or do you still think it's a high flow issue.

Thank,
 

Philtrap

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What manufacturer are the zone valves?

Hope all is well Tom

Zone valves are Honeywell. At first I thought the problem may be due to the differential bypass valve being set too high but no one comment that that may be the issue.... I have a 1" Cliffy DBV as shown in the sketch I posted in my first post above. I would think when the zone valve closes, the water changes directions thru the DBV and keeps flowing back to the boiler until the pump shuts off. If the DBV is set too high, it may cause what I'm experiencing??? But then the noise or bang comes from further down the piping, almost like the pipes get a sudden surge. FYI, I have a Taco 077-F4 circulator.
 

Tom Sawyer

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It's because Honeywell zone valves are fast closing and when the close they are being slammed by the flow. Where is the expansion tank in the system?
 

Philtrap

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It's because Honeywell zone valves are fast closing and when the close they are being slammed by the flow. Where is the expansion tank in the system?


The expansion tank is right before the circulator pump. This was where it was shown in the system piping diagram from Triangle Tube. Is that wrong?
 

Tom Sawyer

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That's where it should be. I like to put fast closing zone valves on the return because they tend to hammer less but unless you want to get into controls that stop the pump before the valves close you probably have to live with it. You might try slowing the pump speed down.
 

Philtrap

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That's where it should be. I like to put fast closing zone valves on the return because they tend to hammer less but unless you want to get into controls that stop the pump before the valves close you probably have to live with it. You might try slowing the pump speed down.
Thanks Tom. I'm not sure if the Taco 077-F4 circulator can be slowed down... Do you know of a way to do it?
 

Tom Sawyer

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Can't but you can swap it for a VFD pump. Either the Taco bumblebee or a Wilo
 

Philtrap

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Can't but you can swap it for a VFD pump. Either the Taco bumblebee or a Wilo


Tom,

I was thinking of installing another zone valve that doesn't close so fast. Do you have one to recommend? I was thinking of abandoning the Honeywell, keeping it open and installing a new ZV a little further down the line. I could do this pretty easily or just swap the pumps...
 

Philtrap

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Can't but you can swap it for a VFD pump. Either the Taco bumblebee or a Wilo


Happy New Year Tom. On this topic, I'm thinking of trying swapping the pump since it would be easier. From what I've researched, the Taco Bumblebee should be able to be swapped out without doing any flange replacement. Do you agree?

Also, there is a pump in the boiler unit that is set to high. Do you think I should lower this one too?
 

Tom Sawyer

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Direct swap. Most circulators are. They standardized flanges 40 years ago or so. Bumblebee is a good choice
 
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