Gravity circulation in FHW system?

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Old 12-08-08, 09:28 PM
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Gravity circulation in FHW system?

I believe that I have gravity flow in one of the zones in my FHW heating system. The oil-fired boiler provides hot water (via an insert) and heat to three zones via circulator pumps. There appear to be no check valves on the individual zones, only air release valves above each of the pumps.

Each of the circulator pumps has an arrow pointing downward into the common large pipe that goes into the boiler. The arrows point away from the the pipes that head upward off to each zone.

I have a zone with the thermostat set VERY low, yet the zone is throwing a lot of heat. I suspect gravity-induced flow in this zone.

question 1: How can I prevent this flow w/o installing a check valve?

question 2: Where do I install a check valve? I would think that the circulating pumps would push water (upward) in the opposite direction than the arrows show and that I would install a valve above the pump. With the arrow on the pump pointing downward, I am confused.
 
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Old 12-09-08, 04:31 PM
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I think what you need are three "flow-control" valves. They are also referred to "flo-control" valves, the name used by Bell & Gossett (not the only manufacturer). They will stop both gravity flow (that you suspect) or reverse flow through and idle pump.

A flo-control is actually a "lift-check" valve. In the forward direction, they lift due to the pump head. In the opposite direction, the act like a regular swing check valve.

The way you described your system, you will have to install the flo-control valves somehere where the three zone lines are separate. Could be on the pumps' suction or discharge sides. Three flo-control valves required.

The flo-control valves I'm familiar with must be mounted in a horizontal run of pipe, not vertical.

If your pumps have an arrow, I would assume that is the direction of flow. You can also tell by feeling the temp of the suction and discharge lines.
Doug
 
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Old 12-09-08, 04:41 PM
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Gravity Flow

I would be surprised if there were not flow control valves arleady in place. Some pictures of the boiler & nearby piping would help. You can post them on photobucket.com or similar photo hosting site & provide a link here.
 
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Old 12-09-08, 09:27 PM
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Thanks for the feedback. I will post pics tomorrow; it's getting late tonight.
 
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Old 12-09-08, 09:34 PM
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here are the photos.

d-cubed/boiler - Photobucket - Video and Image Hosting

Clearly, I already have flow check valves. Could the valve for the zone in question be faulty?
 
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Old 12-10-08, 09:08 AM
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Originally Posted by d-cubed View Post
Clearly, I already have flow check valves. Could the valve for the zone in question be faulty?
Yes, they can start leaking after a while due to wear or internal build-up of crud.

You can try gently rapping the sticking valve with a plastic mallet - maybe the valve will start working again, temporarily (until spring).
Doug
 
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