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# Curious Piping on a Boiler

#1
12-16-18, 12:08 AM
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Curious Piping on a Boiler

I was working on a friends gas-fired boiler today. He said the pressure relief valve opened and won't stop running. A new 30psi relief valve and draining the water-logged expansion tank was a quick fix for a change. As I was looking at his setup I noticed a piping configuration that has me puzzled. He has 3 zones. Just after the circulators there are smaller diameter pipes, with valves, that connect to the returns on each zone. What is the purpose?
Also, what should be the static pressure be on a boiler? When the system cools the pressure drops to 0psi. I think the pressure should be higher than that, but I'm having a brain fart.

Thanks!

#2
12-16-18, 04:03 AM
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The required cold water system pressure is determined by the height of the highest radiation down to the pressure gauge (if it is reading the correct pressure) multiplied by .433, plus an additional 2 psi pressure above that reading. For example; if the measurement as previously described was 25 feet then the cold pressure would be about 12.8 or 13 psi when the number is rounded up. (25 X .433 = 10.8 + 2 = 12.8 or 13) However in the boiler business PRV controls are usually factory preset to 12 PSI , which is OK for most installations. When there was doubt we would use 12 psi for a 1 story home and 15 for a 2 story home and 20 psi for a 3 story home. as long as the expansion tank was sized correctly.

#3
12-16-18, 10:17 AM
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Welcome to the forums.

Pictures of your boiler and piping would be very helpful..... How-to-insert-pictures

#4
12-16-18, 12:01 PM
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Curious piping

Sounds like system bypass piping. It allows hot supply water to mix with cold return water so as to not shock the boiler and cause condensation or worse crack the boiler

#5
12-16-18, 04:56 PM
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I do have pictures, but I can see the detail really doesn't show enough detail. I'll get new pictures either tomorrow or Tuesday. Until then...

#6
12-19-18, 06:18 PM
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I didn't forget the pics. I took new pictures, but they don't identify the layers properly. I'm making a diagram to go along with the pictures. Hopefully I will have this done tomorrow.

#7
12-20-18, 09:27 PM
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Here is the diagram I promised. I also included a picture so that you can see the plumbing rats nest.

Attached Images
#8
12-21-18, 07:36 AM
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You need shut-off valves in the green and blue loops to isolate the loops for bleeding one loop at a time. Also the expansion tank should be relocated to the manifold or common return pipe (between furnace and first junction) to best sense system volume. Don't know why the bypass valves are installed since normally they all must be shut off to prevent flow problems whenever at least two loops are operating.

#9
12-22-18, 07:21 AM
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As I stated, system by-pass if, say the green zone was running and the boiler was already hot, and then the red zone kicked on, and had been off for a while , it would bring cold water into a hot boiler. The by-pass would allow tempered water to return to the boiler rather than very cold which could be detrimental to the boiler.

#10
12-23-18, 12:18 AM
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Now I see what you're talking about, poorplmbr. That makes perfect sense. I'll have to look at what position the valves are in. Beelzbob, I did notice that tank's position once I made the drawing and was thinking it was in the wrong spot, but since it was working, i figured I was thinking about it too hard. It's reassuring to find out my suspicions were correct. Thank you both for your your input!