Flushing a hot water loop & bleeder valves

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Old 12-14-15, 03:26 PM
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Flushing a hot water loop & bleeder valves

Hello all. This is my first post but I have been reading countless articles regarding hot water heat on this great site. I recently moved into a 1928 home with baseboard hot water radiators. The boiler is from the 1990s and functions properly. All zones have heat. I found all the bleeder valves, which clearly had not been used in years, and bled them all. Luckily, no air present at any of them.

When pumping, there is only your typical occasional bubble or moving water noise. At least, I assume this is typical and that these systems are not fully silent. The system does not appear to have a air relief valve in the basement.

That said, I have one location with loud air noises. 2nd floor loop, where it returns and goes back down inside the exterior wall. The bleeder valve is on the opposite end of this loop, 30' away, and does not release air. The loop is not air locked and still gets plenty hot.

This gurgling can be also heard on the main floor by pressing my ear against the wall where the return pipe is. Clearly, it is a noise similar to turning a 2 liter bottle upside down, part rushing water but mostly a "glug, glug, glug."

My questions would be what the best next steps are. Being winter, is it even worth flushing this loop? And if so, should I also be installing a bleed valve at this location? Or should I try raising pressures? System currently runs around 15 psi. The pump is on the supply side, not the return side. I have a steel expansion tank as well. The pressure relief valve does not blow and pressures stay very stable.

I am not concerned about loss of heat - this pipe just happens to turn down next to my head where I sleep, and the "glug, glug, glug" wakes me up. Thanks in advance.
 
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Old 12-14-15, 03:58 PM
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The air can be a result of a few things.
First I would make sure the system pressure is at least 15 PSI and reads accurately.
Old gauges sometimes can't be trusted.
If the bleeder valve is not releasing air, does it release water ?
 
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Old 12-15-15, 09:58 AM
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Sorry for the slow reply; we had warm weather (60°+) and didn't trip the boiler yesterday. What is a good way to double check the pressure and accuracy? I can do so this evening with cold weather. Yes, the bleed valves all bleed water when opened.
 
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Old 12-15-15, 10:08 AM
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Old 12-26-15, 08:00 PM
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Update

Sorry for the slow reply all, it took some time for parts to arrive. The pressure dial on the boiler reads 16 PSI (on the return, inside the boiler enclosure), but I attached another 0-30 psi meter to my release valve, just past the supply side of the pump, and it registered 20 psi.

In addition, I looked up my pump and found it is a Grundfos UPS15-58FC/FRC. Part number 59896341. It is a 3 speed, and set to the highest speed 3. I plan to measure the pipe diameters to somehow calculate my water velocities, but I don't know how to estimate the GPM this pump provides. I found charts but would have to somehow estimate the head on the loop.

I've noticed when the pump kicks on, I tend to hear water noise for 15-30 seconds in most pipes, but I assume that is normal. They go silent after that, so it may not be velocity related. It is still my goal to eliminate the glugging sounds described in my first post.

To reiterate before, all bleed valves did bleed water when open, tested since my original post. Thanks!
 
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Old 01-05-16, 07:03 PM
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Bump

This is just a bump to the thread as it has been awhile. Is this allowed, or should I start a new thread with the same information? Thank you,
 
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Old 01-05-16, 08:51 PM
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Can you post some pictures of the boiler and the piping around it?

Those bleeder's aren't going to help much. You need to actually purge the system. I just did it to mine and it wasn't terribly difficult.
 
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Old 01-06-16, 09:14 PM
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Sure thing, here are a couple photos. It's a pretty straightforward system. The 4 loops are at the top, with the flush valve at the bottom. Can I close the 3 loops and flush the problem loop only? I would think some air could get in via the return pipes. I've also attached a photo of the water reducing valve. I should also note I don't seem to have an automatic air vent that I can see.

As it is mid-winter, I am not sure I want to flush the system in case something goes awry. But if I am going to do so, I am looking to make other changes to make the system function properly, such as adding air vents and bleed valves.

Thoughts?

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Old 01-07-16, 08:34 PM
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This should be pretty easy. Close the ball valve on the bottom, the one with the yellow handle, attach a hose to the drain spigot. Once you've done this, also open your fast fill valve to increase the water pressure coming into the boiler, at the same time slowly open your spigot but just a bit. The idea is to throttle the spigot to build the pressure enough to force the stubborn air bubble/bubbles out.

Keep a close eye on your pressure gauge, most relief valves will blow at about 30 psi. If you keep your hand on pipe right above the spigot as your opening it, you will feel the air coming out. You may or may not have to throttle the spigot as I mentioned, but the general idea is to force the psi up as needed to get that air out - the fast fill valve may accomplish this on its own, but since you can't isolate the returns you may have to throttle a bit.

So yes, it's a bit easier if you have shutoffs/spigots for each return, but not necessary. This is an easy winter project, and the WORSE case senario is you blow your relief valve - so keep an eye on that pressure gauge. Let me know if you have any more questions!
 
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Old 01-07-16, 08:43 PM
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Also, your pictures are a bit to close to see the whole system. What's that blue thing there? Is that water heater or an expansion tank? And your sure their are no individual shutoffs further up the return side piping that I'm not seeing? Also, i forgot to ask but do you have zone valves or zone pumps?
 
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Old 01-14-16, 02:56 PM
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Additional Guidance

Thanks, You are correct, the blue thing is the expansion tank hanging between the joists. The fill valve line connects to the expansion tank line as the photo shows, and both go into the boiler housing outside of the photo limits. I have not yet opened that housing, so I don't know how that connects to the boiler loops. And yes, the relief valve is set at 30 psi. There are several valves in the photos. The yellow valve at the bottom (below the spigot) you mention controls the entire supply coming from the boiler. The pump is just outside of the photo below that. The 4 zones at the top, with white tags labeling each, also have their own zone valve each. No zone pumps. There are also no return valves that I am aware of, so I cannot completely isolate zones. Should I close the 3 zones and only leave the problem zone valve open?

If I am to understand correctly, by closing the main supply valve you mention, I will be flushing the pipes "backwards" against the flow of regular operation, correct? Is that so I don't have to flush through the pump (which could prevent flow when off)? And flushing at a higher psi and flow rate should be enough to push air from the system?

As a separate question, my pump is set at Speed 3. Is there a downside to stepping down to speed 2? Worst case is that the ends of some loops could deliver less heat, correct? But could reduce noise?

Thanks for answering all my questions. Besides fixing this noise issue, I am just trying to learn about my system and maintenance in general. And sorry for the slow reply, I screwed up my subscription settings and was not notified of your response. It's much appreciated.
 
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Old 01-14-16, 03:10 PM
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As a secondary question, I know I don't want to go flushing this system often per guidance on this site. I just moved in, and am pretty sure the system hasn't been flushed in years. Should I wait until spring when I can drain the system and splice in a bleed valve at the problem location upstairs? Or is that overkill? I also don't have an air vent that I can find, which is something else I Should probably add to the system. Thoughts?
 
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Old 01-15-16, 08:34 PM
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Do not purge/flush air from your system.
You have a compression tank.
Air control systems have a compression tank.
Air should be returned to the bottom of the tank, never eliminated.
If you bleed the air from the system the compression tank will become water logged.

"Proper Air Management in a Hydronic Systems[sic]"

CounterPoint How Hydronic System Components Really Work [pdf]

TECHNICAL BROCHURE FHD-501A
[page 12, pdf] Air Separation
[page 15, pdf] Compression and Expansion Tanks
[page 17, pdf] Expansion tanks

Installing Expansion tank using B&G ATF [PDF] See drawings starting on page 4
ATF and Drain-O-Tank Air Charger

Most likely you system has inadequate air separation or low flow velocity due to improper pump selection.
Taco (TD09)Understanding Pump Curves [pdf]
Taco (TD10) Selecting Circulators [pdf]
 
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Old 02-09-16, 02:29 PM
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Update

HeatWorm, thank you for the links and information. Very good and informative. I will investigate to ensure my air separation is working properly. I do hear occasional gurgles and bubbles throughout the system, so this could be a likely culprit if it isn't getting sent to the bladder properly. Regarding low velocities, I was beginning to suspect the opposite. I will be taping some pipes and taking water temperature readings to see if the pump speed can be reduced from the current top speed setting of 3 down to 2, without creating too large of a supply/return temperature drop. However, if you are correct, there may be more work ahead in selecting a new pump since mine is already at its top speed.

As an aside, I have air trapped in the top floor (but not airlocked), where the return pipe turns vertical and goes down the wall. I have a 4 zone system with 4 valves, and only one pump. Would temporarily closing 1-2 of the other zones, thereby increasing velocities, potentially eliminate that trapped air? Or is increasing velocities over 4 ft/sec unwise, even temporarily?
 
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Old 02-09-16, 08:33 PM
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Compression tanks have NO diaphragm or bladder and are used in air control systems.
Expansion tanks have a diaphragm or bladder and are used in air elimination systems.
 
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Old 02-09-16, 08:50 PM
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In the absence of BMS load aggregation, thermostats cycle the zone valves randomly,they do not talk to each other.
 
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Old 02-09-16, 08:59 PM
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The valves are just manual for each zone. The single pump is on the main supply line before the valves. I figured if I closed 1-3 zones manually, the flow would be forced through less cross sectional area, increasing velocities. Hoping this could push any trapped air back downstairs and into the compression tank.
 
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Old 02-10-16, 12:01 AM
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Maximum flow for a given zone occurs when only one thermostat is calling for heat, no need to close isolation valves.
 
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Old 02-17-16, 07:34 PM
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Mysteries Continue

So I have continued research and would like some opinions on this matter and others. HeatGlow, to respond to your last post, I only have one thermostat for the whole system. The 4 "zones" are only controlled by manual valves, so I may be using the term "zone" incorrectly. There's one zone and 4 loops of pipe. I've uploaded a couple photos of my system. My random questions are:

1) If I have air trapped upstairs in the return pipe, where it turns down the wall, and I close 2 of 4 manual valves, flow in the remaining zones would double. Could that potentially push the air out? Where does air go if I don't have an air separator (see #4 below)?

2) Are bleeder valves typically installed on the supply end of a slant fin radiator where pipes come up, or the return end where pipes go down? Does it matter?

3) I used black electrical tape and an infrared gun to measure some temps. Though the boiler thermostat says 190°, I was getting 200° on the supply line. I only have a 10° drop at the return down to 189°. Should I lower this temp and pump speed? (I am at speed 3 of 3 on the pump) I should note 1 of 4 zones does have a temp drop of 20°, as it has the most radiators (34 linear feet) which are all open.

4) The pipe from the blue compression tank goes directly down into the boiler housing as shown in the photos. This pipe does NOT have positive slopes up to the tank, it's basically flat. Unless there is an air separator inside the boiler housing, it appears I do not have one. Is it common to not have a separator, or for it to be inside the boiler housing? I haven't opened the boiler since it has been running.

5) The 4 manual zone values are on the return pipes, just before the pump (red in the photos). The main supply pipe splits off into the 4 zones without valves. The pump is pumping downwards, directly into the boiler. For some reason this is surprising to me, as I assumed the pump would pump upwards directly to the 4 zone valves.

This system has functioned acceptably during my time with it (2 years), and has many years behind it. However, if I choose to make a project for myself, I am looking to understand how this SHOULD be designed.

Thanks.

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Old 02-18-16, 12:38 PM
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RE: Mysteries Continue [First reply]

There's one zone and 4 loops of pipe.
Yes, one zone with four "circuits", each with a isolation valve.

1) Flow increases some yes, double likely no -- head loss rises as the square of flow, and system flow is limited by the pump curve.
_ Air not returned to the compression tank will go round and round the system.

2) For Air control systems: Air vents -- high point in the system -- are only used when the system is being filled to eliminate excess air.

3) Boiler has a Temperature and pressure "Gauge" -- Tridicator
_ Emissivity of Specific Materials
_ Leave the aquastat setting where it is for now.

4) Read post #13 again.
_ Compression tank line: [ how it should look ]
_ _ Pipe: 3/4 inch diameter. Horizontal:Pitch not less than 1 inch in 5 feet.
_ _ Valves: None in horizontal sections, full port ball or gate.
_ _ Some --not all-- boilers can be used as the air separator.

5) The pump can be where ever you want it to be but the direction of flow in the boiler is dictated by the Aquastat needing to "see" the outlet flow. When a circuit serves multiple rooms (series loop), it may have a preferred direction of flow because rooms on the end of the circuit need more radiation due to lower inlet temperature.

TECHNICAL BROCHURE FHD-501A
[page 28, pdf] Job description... [ Pump ]
[page 28, pdf] “Pump head” is not height!
[page 29, pdf] Pump pressure and static pressure
[page 30, pdf] How circulators work in closed systems


_ The to do list:
_ _ Increase system pressure --cold to 19+ psi-- and see if that reduces your noise problem.
_ _ Determine circuit return flow required to entrain air -- 2 ft/sec for downward vertical flow.


Q: What is the system pressure and temperature when hot -- at burner off on aquastat high limit.
_ Pressure when cold.
Q: What is A.G.A Input and D.O.E. Rating (output) of the Boiler.
Q: Pump model number -- so we know what pump curve to use.
Q: Square footage of heated space, building length and width.
Q: For each "circuit": Square footage, heat loss, installed radiation -- feet of active element.
 
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Old 02-18-16, 02:16 PM
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This may be a multi-part post as I am not home to test some temps, but when reading other sites, I learned my Lennox boiler is actually a Dunkirk PWB-5D sold as a Lennox. A link to the boiler brochure is below.

Boiler Brochure

This brochure taught me a couple things already:

1) My pump is circulating the right way per the boiler drawings.
2) The connection to my compression tank is directly off the relief valve pipe coming out of the boiler. There is no air separator unless this boiler somehow provides it. I am not sure if any flushed air would make it into the tank or not.
3) AGA is 140,000 BTU. Output is 113,000 BTU (81%)

I have element lengths for each room and circuit totals but need to calculate heat losses. It's an 1800 SF house, with 120 total linear feet of slant/fin baseboard radiators. I know the boiler is pretty over sized based on this load.

I will have to grab the remaining information when I am home and the boiler is in operation.
 
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Old 02-18-16, 03:46 PM
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Why is the pump on the boiler return, Old Manual.
see figure #5 PWB REV 3.0 IOM [PDF]

Some history: See all of Furd's posts RE:repeated air problem in hot water baseboard #55/#57 Furd
 
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Old 02-18-16, 04:03 PM
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Thanks. I recall reading Furd's original posts when I first joined the forum; I wonder if the same issue is possible here. Though I am not having extreme air noise, just occasional. I have not needed to flush and the noise has not worsened. I do not know why the pump is on the return; the system was installed years before I purchased the home. It appears the pump is in the wrong place and that I should have an air separator on the supply line pitching up to the compression tank.

If the system is functioning properly with occasional air noise, is it really worth taking apart all the pipes this summer to fix these issues?
 
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Old 02-19-16, 10:10 PM
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If the system is functioning properly with occasional air noise, is it really worth taking apart all the pipes this summer to fix these issues?
No, not by its self.

Moving the pump to the supply riser/main will help but does not address the uneven heat distribution. And low air separation efficiency, in addition to poor air transport could still remain.

Nice to have if the system is already open:
- B&G ATF-12 on the compression tank. Reduces gravity circulation with system.
- Move compression tank connection to -- eg. Taco 1-1/4" Cast Iron Vortech Air Separator on -- supply main.
 
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Old 02-23-16, 06:34 PM
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Additional answers to your questions:
1) Cold pressure is 14 psi. Hot is 18-19 psi.
2) Pump is a Grundfos UPS 15-58 FC, set to the highest of the 3 speeds

I am going to measure all rooms and estimate losses, but place the results in my other thread regarding the heat imbalance I have. Given that I know I don't have an air separator, and that none of my loops are air locked, I am tempted to let sleeping dogs lie for now. Increasing pressure and moving air pockets would just end up circulating bubbles around the loops endlessly. I would be curious to see if my pump is sized properly, because if I am repiping things this summer to add the air separator, I may as well put the pump on the supply line anyways. If doing so, I would consider adding a 5th short loop in my basement, which doesn't have heat currently (but stays at 58° in winter).
 
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Old 02-25-16, 03:09 AM
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The temperature differential from room to room is only relevant if measured with all registers open.

Add radiation to the basement by extending a return with bare element at ceiling.


A UPS 15-58FC can not deliver design flow to all four circuits, that is why air is trapped out in the system, and one circuit has a large delta-T. You need a pump matched to circuit flow at design head loss.

. . . when the pump kicks on, I tend to hear water noise for 15-30 seconds in most pipes . . .
That much air blocks flow. Given the "steep" pump curve a 15-58 can clear big air pockets from the system, just set the pump to low and close three isolation valves and run for ten minutes each. You should start hearing glug-glug at the compression tank.
 
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Old 02-25-16, 06:22 AM
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Will do. Since my compression tank is attached at the relief valve with no air separator, will air actually make it into the tank?
 
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Old 02-25-16, 01:54 PM
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Yes, the boiler is the air separator.
 
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Old 02-25-16, 03:11 PM
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because if I am repiping things this summer to add the air separator, I may as well put the pump on the supply line anyways. If doing so, I would consider adding a 5th short loop in my basement, which doesn't have heat currently (but stays at 58° in winter).
Your getting some mis information here... Stand by
 
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Old 02-25-16, 03:21 PM
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You do not add air seperators to your boiler with the type of expansion tank you have... No No No NO!!!!


Your air issue is probably because you need to isolate and drain the expansion tank... That tank needs to be emptied completely...

Your psi in the system is fin at 15 psi...

The expansion tank you have is what removes the air, but if its waterlogged its not going to work as intended...

Close the valve going to the exp tank from the boiler and drain it from the boiler drain thats on the exp tank... You have to make sure its totally empty..

Read here please comfortcalc.com.. And post any questions you have...

Comfort Calc


Also I take it you have radiators on your system correct? You bleed them only on initial start up usually ...

And if you keep trying to purge the system from the valves at the boiler you are oonly intoducing more water into your system.. Water contains air.. And your just making matters worse..

Your pump is fine where it is too..

Like I stated your not getting the best advice from previous replys IMO...
 
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Old 02-25-16, 07:55 PM
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Hold on there, this boiler is using a top port to act as the system air separator/scoop for the compression tank.
A air separator (eg. Taco Vortech) would go on the supply riser/main not on the boiler. The compression tank line connects to the air seperator's 3/4" top port. Do not drain all the water from the compression tank. The system has not discharged from the pressure relief valve.

Equipment Room Piping Practice[PDF]
[ page 2, pdf] Figure 1.
 
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Old 02-25-16, 08:26 PM
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Hold on there, this boiler is using a top port to act as the system air separator/scoop for the compression tank.
Huh? I dont see a top port... Im not sure what your talking about...

So tell me with no air vents what device other then the expansion tank removes the air?

Systems like this have been in service forever... The OP has no reason to change anything on his system. Placement of pumps, adding seperators etc AFAIK...

https://www.youtube.com/watch?v=YpLJYCMCgGk
 
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Old 02-25-16, 09:00 PM
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This is a air control system.

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Note, only some air separators have a large (3/4") top port to connect a compression tank.
And if you do one thing to the system:
Rule #1) Pump away from PoNC (Point of No Pressure Change -the compression tank connection.)
Rule #2) Connect the compression tank where the system temperature is highest.

Rule #3 If you can't do both see rule #1.

HeatWorm
 
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Old 02-26-16, 03:10 AM
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what device other then the expansion tank removes the air?
In this case the boiler does, it has a dead space that is above the level of the supply tapping where air can collect.

I think of a Tank as a receptacle, reservoir, repository to "trap" or store or receive. And air directed into the tank is not lost, cool water from the tank transports air out of the tank and back into the system (by Gravity flow.)


I will always use the term "Expansion tank" when I am talking about air elimination systems that have a bladder or diaphragm separating the water and air, and vent free air to the atmosphere.

And for air control systems I will always use "compression tank" Think "closed steel compression tank."


I had this very same setup until I moved the compression tank connection to a air separator on the return main. See rule #1.
HeatWorm
 
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Old 02-26-16, 03:27 AM
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The boiler is from the 1990s
I doubt the air problem was always there....
 
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Old 02-26-16, 07:18 PM
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Thanks for all the assistance. This weekend, I am going to run the pump at speed 1 on each circuit individually as suggested to flush air back to the tank. I will see if that resolves most air sounds. If I am not adding element this summer, would you still recommend draining the system and repiping around the boiler to move the pump, and add the air separator and ATF? Is it worth it? And if my pump is undersized, whats a good method to estimate the head in the system to select a proper pump?
 
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Old 03-03-16, 01:33 AM
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. . . if my pump is undersized, whats a good method to estimate the head in the system to select a proper pump?

Caleffi Idronics16 January 2015: Circulation in Hydronic Systems[PDF]
[pp 29-31, pdf] Using a pump curve to Estimate Flow Rate: See Figure 5-8

Measure the in circuit pump Head directly: Winters-Instruments-PCT329-4.5-PCT-Contractor-Pressure-Gauge-30Hg-0-30-PSI

For circuits that are accessible you can calculate head loss for each circuit.
[page 19, pdf] example 4-5
[pp 16-21, pdf] "4. Head Loss In Hydronic Circuits, Equivalent Length"
[page 18, pdf] Tables: Figure 4-2, 4-3, and 4-4
[page 13, pdf] Table Figure 3-12 [Flow velocity]

You can measure or calculate the head loss of each circuit, build a system curve and then select a pump. You balance the system to the circuit with the highest head loss.
 
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