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Constantly purging air in hydronic system (32 Posts)
Constantly purging air in hydronic systemI keep having to purge air from one of the 2nd floor circuits of my hot water heating system in order to get adequate heat out of it: I purge the system, then several days later I hear gurgling (although the noise "seems" like its coming from a different circuit upstairs), then the heat output starts to diminish in the convector over time. I bleed and everything's fine for a week or so. Let me give you details of my system...
I have a pump circulated hydronic system (circa 1950's) in my old colonial (circa 1910's). The boiler is a gas fired (80,000 BTU?) 80% efficiency New Yorker unit (circa 1990's) and the house is ~1,300 sq.ft. There is a single pump on a single zone feeding all circuits which have a mix of newer baseboard radiators (living room & bathrooms) and original-to-the-system fan-coil hydronic convectors (bedrooms, dining room, kitchen). The electrical circuits for the hydronic convectors, however, are split into two zones: 1st floor convectors on one thermostat & 2nd floor convectors on the other.
All the radiators/convectors on both floors have manual air purge valves that are pretty much in useless condition. As such, after I moved in, I had a good plumber/heating guy install shut-off and boiler drain valves in the return risers of each radiator/convector in the basement for easy purging. At the same time, he installed a city water make-up pressure-regulating device set to ~15psi, an automatic air purger (w/automatic purge valve) on the supply side of the boiler, and finally he re-routed the expansion tank to the supply-side. In addition, there is one automatic purge valve in the baseboard of one room upstairs that was there when I moved in (not the unit that needs constant purging, though). There is a file attached showing the layout of my system as I know it (there is only one shut-off/boiler-drain valve shown on the bathroom loop, but they are actually installed on every circuit in the basement risers).
My question is, where is the air keep coming from? I don't see any signs of leaking water anywhere in the system? Could it be air coming in from the city water makeup and there's nothing I can do about it? Any help would be appreciated.
Oh, one less important side question: The boiler is running with a Honeywell L8148E1265 aquastat and it's set at it's lowest setting = 180degF. However, I noticed that it very rarely (only really cold days here in SE Michigan) gets to kick off at it's 195 upper set point (15 deg differential). Would I benefit from lower set point aquastat (say, a Honeywell L8148E1299) or should I leave the system as designed?
Thanks!This post was edited by an admin on April 21, 2011 1:18 PM.
No file attachedBut I do not like remote automatic air vents as a general rule. Photos would be helpful of the boiler piping. The city water should only be adding water when the system pressure drops due to the gases bleeding out of the air scoop.Cost is what you spend , value is what you get.
cell # 413-841-6726
I can't seem to successfully attach a file...I pick my Visio drawing to upload, but when I hit submit, it's not there.
Anyway, I just thought the city water itself might have air in it, so as the pressure in the system drops, air is introduced to the system from the city water make-up. I'm trying to attach the Visio drawing of my system (hopefully it's attached to this post).
I will try and take a pic of the boiler piping tonight, though, if someone could help me point out what I'm doing wrong when trying to attach a file to my post.
Thanks.This post was edited by an admin on April 21, 2011 1:28 PM.
Save the Visio as a jpegThen attach the jpeg.
reply to air in systemI am thinking: In order for air to enter your system it has to be pumped in or let in. I find it unusual to suspect the utility water supply as a source containing air unless a problem exists on their system. It takes a certain amount of pressure to makes sure a leaky air vent will not allow air into the system and although a pressure gauge at the basement may read 12-15PSI, it most certainly will not be that at the top of the system. With 12 PSI on a gauge a pressure of 3 PSi could be found at the top of a system. and even though parts are new, pressure devices & gauges can lie, so it is important an accurate test gauge measure the pressure to make sure the fill valve is on and properly performing its job. The science of air in hydronics is that water under pressure will contain entrained air until its pressure is reduced and temperature increased where it will tend to change into free air bubbles you may be accumulating at high points. In order to prevent entrained air from being released into a lower pressure zone, a certain pressure must be present. Also it is known that an air cushion device such as an expansion tank can be siphoned of air in a cool down cycle to be later redistributed to a lower pressure area in the system. This is why steel expansion tanks without sealed bladders loose their air charge. New filled systems contain a lot of entrained air. So it is important that a tight properly pressured system with a bladder expansion tank be used. The older the water the better. Pressure changes can also occur with pump action, but normally are insignificant when system is properly pressurized.
Possible solutions: Verify pressures and the fill valve operation. Verify a check valve and or some type of back-flow protection exists to keep the system from draining into the supply water should pressures there drop. ( usually a code requirement). You could change the expansion tank to a bladder sealed type that keeps air and system water separate. This has proven to prevent call backs the next year from many customers. Properly pressurized and maintained if a leak occurs it should show water and not be a hidden leak sucking in air. You could also raise the pressure to 20 PSI. Just don't exceed the expansion pressures that might trip a 30 PSI relief valve which is standard. Just so you know many residential boilers used in commercial application are re-rated with no change other than adding a 50 PSI relief valve when higher pressures are required like in a four story building. Also there are superior air removing vents that handle the tiny entrained bubbles, there is however many opinions on many brands.
Hope this helps. By the way AMTROL made an extensive study of air in hydronics. Steel tanks can remain, bladders are better until they fail. some are made for potable water higher pressure and others for hydronic low pressure heat systems. They are sized on volume and btu input and summer winter v cold start.
Best regards, Lance
Pics added...I will try and get a test gauge on at the auto purge valve in that second floor baseboard and take a reading. I do know the fill valve is doing it's job because I can hear it fill when I'm purging a line with the shut-off and drain valves and the pressure drops below ~10 psi (indicated). After purging, I always manually fill the system until the pressure hits 25psi (there is a 30psi blow-off presently on the boiler), but I believe the valve itself is permanently set at 15psi from the factory as there doesn't look to be a set screw on it.
Does my expansion tank shown in the pics look like it's a bladder type? The water is about 5 years old (not including the constant purging and filling. But the last time the system was drained was when I moved into the house and had the drain valves put in.
I do not, however, see a check valve on the city water side. Could that be integral in the pressure regulator?
Thanks for your advice,
Follow-upThanks Lance. It turns out the issue was the automatic purge valve in that upstairs baseboard.
When I opened the baseboard sheet-metal and carpet underneath, I noticed it was indeed leaking (slowly). On system cool-down, it must have been sucking in air through the purge which made it's way to the problem circuit, because once I removed the automatic valve and plugged it's connection it has been fine.
The expansion tank is at the supply sideand the circ is at the return side. For the circ to be at the point of no pressure change it mu7st be down stream of the expansion tank. Why was it hung on the wall?Cost is what you spend , value is what you get.
cell # 413-841-6726
Still having some problems with air in the systemLast winter I had to purge the system not as frequently as before, but it was still a problem (about once a month). Later this summer, I'd like to tackle what other previous commenters had recommended: The fact that both the city water make-up and the circulator are on the return side of the boiler, while the automatic air purger is on the supply side with a rather unorthodox routing to the expansion tank (hanging on the wall upside down).
I'd like to take the expansion tank off the wall and re-route it's piping so that it hangs directly under the automatic air purger, then re-route the city water line to tee in-between the two. That I can do that myself, but I'm not too confident moving the circulator to the other side of the boiler downstream of the air purger, myself.
My main question is if I do re-route the rest of the equipment, but am unable to get a plumber to move the circulator before it gets cold, will having the city water piping moved to the supply side of the boiler while the circulator is still on the return side be making things worse for myself?
Air:Three years ago, you brought this up. It was suggested that you didn't have enough pressure in the system. You found that there was a "leaking" auto vent on the second floor because the floor/rug was wet. You changed the vent and the problem went away.
But you still have air. Did you increase the system pressure to a pressure that when the system is cold, that you get water squirting out of the second floor vent? Because if you didn't raise the pressure, you just put a band aid on the infection. The Infection is the lack of system pressure and the bladder/expansion probably not having enough pre-charge pressure. That Watts 1156F is as useless as boobs on a chicken. Air isn't going in through the valve, because the valve probably barely passes water. If it was disconnected, I doubt it would pass water. Or little water. That is a cast iron valve because it is painted the same color as the top. If it was a brass body valve, the body would be bare brass color. The top would be painted the same color as yours. There is a stainless steel screen on the outlet side of the valve, Because the valve is cast iron, and both ends are connected with copper tube, the screen plugs solid with iron particles. I'm not even sure that Watts sells those CI 1156's anymore. I think a lot of boilers died because of them and they did a GM key thingy. They just dropped the price of the brass valve to the CI one and the brass valve was the only valve available. Replace it with a Watts 9-11 with the backflow. Then, no one can ever suggest that water is coming in from the street with air and contaminating your system. The only possible way that can happen is of your system has a massive water leak.
In my experience, I have never seen an old cast iron Watts 1156 that would pass water.
You can doo all the expensive and time consuming work and change the fill valve, and the problem will go away. You can change the valve and the same thing will go away. And you can go to the beach instead.
I have NEVER, EVER, EVER, EVER HAD AIR APPEAR IN A SYSTEM ever IN MY LIFE, once I filled a system. As long as the system pressure was maintained high enough with the system cold, the expansion was properly sized and not too small. That #30 Extrol might need to be changed to a #60 or have a #60 added somewhere. If that is a cold start boiler/system, there isn't enough expansion room. Don't ever believe what the pressure reads on the Tridicator gauge unless you have proven it with a gauge of known accuracy. Just because it might read 15# doesn't mean it does.This post was edited by an admin on July 17, 2014 9:29 AM.
You need a check valve where the city water enters the system.The watts reducing valve you have is often sold with one attached.Yours does not have one.
The pressure reducing valve can be adjusted. You spin the nut under the lever. Chances are it should be in the 15# to 18# range. How high is it from the boiler to the highest radiator?
The expansion tank (yours is a bladder style) should be charged to the same pressure. You do this with a bike pump with the tank drained.
I do not hang pressure tanks below the air eliminator. Air eliminators also make great dirt separators. The dirt will sit on the bladder of the tank and shorten it's service life. Yours look good on the wall.
The expansion tank and fill valve do not have to be connected to the air eliminator. They are often done this way out of convenience.
The circulator can reside on the return side of the boiler, It just should not pump towards the expansion tank and prv.
The quickest way to solve your problem would be to install a tee between the return pipe and the boiler drain (hose connection) just above the circulator and tie the expansion tank and fill line in there. You could then leave the circ and air eliminator where they are.
Yes the the air eliminator would work a little better if it was installed in the area of slightly lower pressure behind the circulator, oh well...
air is a nuisance, but.......While the presence of air will impede flow, detract from system performance, and cause annoying noise, there is a much greater harm caused by continuous, fresh make- up water.
Oxygen is the arch enemy of all the ferrous components found in most heating systems, and often, there can be other water condition issues that will affect flow rate, and heat exchange.
I have seen upside down expansion tanks corrode due to O2 issues................
Good point...Mike makes a good point. At the end of the day, where is the air coming from?
Low system pressure is a likely one.
Is the pressure relief valve dripping?
What happens if you turn off the fill valve?
I think the tank corrosion Mike is talking about would not occur in a truly closed system with no leaks.
Answers and next steps...Firstly, I’d like to clear up something that icesailor pointed out since it's been so long since my last post on this subject: While, yes, the 2nd floor’s autovent was indeed leaking, I was mistaken in the effect of its removal. While it did help the frequency of my having to purge the system, it did not solve the problem entirely. I just hadn't had the time to research and diagnose it further until now (or I haven't gotten fed up with purging air until this past rough winter).
What is the distance from the boiler to the highest point in the system? About 18'.
What happens if you turn off the fill valve? I don’t actually know. That’s a very good question, I will try that.
Does the pressure relief valve leak? No, it’s normally as dry as a bone.
As for the system pressure, I will adjust the pressure reducing valve up to ~18#. It’s currently at an "indicated" 10# or so. As for using my Tricator for the “indicated” pressure readings, I have noticed that the Extrol only starts to flow when manually filling the system past its set 30# indicated on the gauge. So, while it certainly isn't a great gauge (and needs to be changed out since the temp needle had gotten itself stuck last winter), it's at least in the ball park.
Once that is done I will properly check and adjust the air pressure in the expansion tank to match the system pressure.
I will also install a check valve at the water make-up valve and consider swapping out the Watts 1156 entirely for an all-brass model.
Thanks for the advice regarding all the re-routing I was considering and I will hold off doing so until I do perform the tasks and checks above and will post my results.
T. J.This post was edited by an admin on July 17, 2014 5:58 PM.
Expansion tank pressureNeeds to be set isolated from the system. Set that pressure then bring the system pressure up to psi to match tank psi in this case 18psiThis post was edited by an admin on July 17, 2014 8:26 PM.
Expansion tank checkSo, if I got the process correct:
I isolate the expansion tank from the rest of the system via the ball valve shut-off in the line.
Drain the water side of the expansion tank with the ball valve's integral bleed screw.
Check the pressure and, if needed, fill the tank with a bike pump to, in my case, 18 psi.
Then finally open the valve and start a heating cycle.
Once the system is up to temperature, set the Watts fill valve to 18 psi (indicated).
Is that the correct sequence?
Fill Valves:If you buy a Watts S1156Fbrass fill valve only, it is possible that it is a direct replacement. The union on the fill/inlet side may be the same union. If not, you will have to change just the copper union part. Because the adapter is on with Teflon tape, it will screw right off.
If the pressure gauge says 10#, it doesn't have enough pressure. You have a auto vent on the second floor. When the system is off, and not running for hours or overnight, check the pressure on the top floor. If when you open the top floor vent, water will squirt out, if it doesn't, the system pressure isn't high enough.
Fill valve & auto ventThanks for the info on the fill valve.
I ended up removing the auto vent altogether. Should I re-install a new one? I just heard they were more trouble then they were worth and I shouldn't have a system that needs constant bleeding anyway, so I capped it off. But, having a way to check pressure in it's highest point may be a good reason to have one.
Higher Pressures:Yu don't need to check the pressure at the top of the system. Just maintain adequate pressure in the system. If the pressure gauge on the boiler is reading less than 10#, either the fill valve isn't filling, or the gauge is bad.
Do you understand what happens to a underwater diver when he/she dives below the surface? The oxygen and Nitrogen in the blood get compressed by the increasing pressure of the surrounding water. The bubbles become smaller and smaller the deeper you go. When you arise to the surface, the compressed gasses expand when the pressure drops. Causing "The Bends" which is just air bubbles forming in different places in the body. The higher the pressure, the more the higher pressure will hold the air in compressed and absorbed suspension.
The same thing happened to the passengers and crew of the two Malaysian Airliners. The cabin pressure is maintained at about 8,000' by using high pressure compressed air from 35,000 feet and heated by the friction of the compressed air between the first compressor stages of the engine. There isn't air/oxygen at 35,000' but if you can compress enough 35.000' air to equal 8,000'.or sea level, the later stages of the engine that burn the actual fuel for thrust, will be happy. When you get into a jet passenger aircraft, your body is set for Sea Level atmospheric pressure. You become uncomfortable when you take off and you finally become comfortable. Once you get past the 8,000' or whatever elevation the crew decides they want to maintain the aircraft. If the aircraft is flying at 35,000' and rapidly decompresses, the compressed air in the body will rapidly expand. Especially in the lungs. When the aircraft drops below the set cabin pressure, all air starts to compress to the actual altitude.
You MUST keep the pressure at the top of the system at a high enough pressure to keep from forming air bubbles. The pressure keeps gasses compressed and trapped.
auto ventsauto vents should be valved off after initial start up, they can draw air in if you have low system press. If your exp tank is on the supply side (not seeing point of no press. change ) ,your NPSP (net possitve suction press. could go into a negative press.causing air to be drawn in.RJ
System AirSo Icesailors explanation of how pressure effects keeping air in solution is a good one. There is one other thing, and that is temperature.
The hotter the water in the system the more air comes out of solution. So upon filling a system with fresh ambient water the system is brought up to operating temperature air will come out of solution. The pressure helps keep the air entrained in small bubbles to get back to the air seperator, or auto vents as Ice explained.
So every time your adding fresh make up water to the system your adding more air to.
make the correctionsas suggested. Then assure the system is leak free, make sure you have 5 psi at the high point, and purge the system.
I'd suggest adding a good micro bubble type air eliminator. it's possible that entrained air and micro bubbles are not being eliminated with a scoop type air purger..
Water will absorb and release gasses as it heats and cools. The hottest point in the system is the best loaction for a micro bubble eliminator.
Some good reading on air and dirt removal in this tech journal.
Auto Vents:If you have this type of air vent on emitters at the top of the system, it absolutely will not vent air if the system is full and only water is there. If the system goes negative, this type of valve will absolutely let air into the system, and you will never know it. The one I have the most experience with is the Taco #417-3. Taco has re-done their web site and the only thing I can find is this PDF and there is one on page 2. If you have one of these on a system, and you don't have adequate pressure, it will add air into the system.
https://www.google.com/search?q=coin+air+vent+for+hot+water+baseboard&tbm=isch&tbo=u&source=univ&sa=X&ei=_cDKU5_APMeLyATmsID4BQ&sqi=2&ved=0CEoQ7Ak&biw=1093&bih=434#facrc=_&imgdii=_&imgrc=naSMbHLcXok8nM%253A%3B6XqnajgrV6ogkM%3Bhttp%253A%252F%252Fs3.supplyhouse.com%252Fimages%252Fproducts%252Fzoom%252F417-3-2.jpg%3Bhttp%253A%252F%252Fwww.supplyhouse.com%252FTaco-417-3-Coin-Vent-11389000-p%3B500%3B500This post was edited by an admin on July 19, 2014 3:05 PM.
more optionsThis Hydroscopic vent is both manual and auto. It's used on panel rads and radiant manifolds installed in finished spaces. A bit more features compared to a coin vent. They do not need pressure to seal and can handle dirty fluids better as there is not a seal inside.
Also this check valve cap allows air out, but not in, if you think you have a vent sucking in air, this is a good way to solve or troubleshoot the problem until corrections are made.
You can also add a hydroscopic cap to the check valve.
Hydroscopic Vents:HR, those may work well when first installed. Every type of air elimination device I have encountered, sooner or later, fouled in the venting mechanism. Even like Taco #400 float vents. You put them on top of a boiler or on the top of a heat system and they vent air like a bandit. After time though, when there isn't enough pressure in the system (and even if there is), sooner or later evaporating water/air gets under the seats and they start leaking small amounts of water that evaporates and leaves that white stuff behind. With float vents, you can crank the cap and stop them from leaking. Any air will be absorbed. I used to change many. many every year that were leaking. Like every few years. I started cranking the caps and I never had another problem with leaking air air problems. I put Taco 417-3 vents on a few radiator systems and when I refilled the systems in the Spring, I never had to vent them. In the fall when I drained the system, I never had to open the vents. They automatically added air onto the radiators and broke the vacuum.
It was all part of the theory I developed about heating systems not having enough water pressure in them.
Look at the average float vent on a boiler or an old air scoop where the cap is left loose to vent air. It is all white and nasty. I've had micro bubble eliminators that leaked out the end and got all white with the nasty's. I don't know if you ever stood on a 6' step ladder with a couple of 3' pipe wrenches fit between pipes to unscrew that micro bubble cap to replace it, but it's safer to just put a 1/2" IPS coupling and a reducing ell with a float vent and a tight cap.This post was edited by an admin on July 19, 2014 9:46 PM.
I agreeall air vents fail or leak at some point. The mechanism inside is sensitive to dirt, debris, and just plain wear. Those hygroscopic do have a ball check below them, just un-screw the head to remove and shut off, or replace the consumable cap.
Another option is to put a small service check below the air vent. The majority of air vents we sell to wholesalers go out with that check. It allows you to remove and service, or replace the vent without lowering pressure or draining down.
There is one brand of air eliminator that can be disassembled by hand, or at most a 10" channelocks :) both the top cap and belly seam. It is assembled with fine, straight threads and an o-ring seal. Easy to get under the cap and clean out the needle valve, it is also a replaceable cap. If ever you need one, let me know.
Also you can get and adapter that allows you you put a drain tube on the air vent. so when it does give up the ghost, the drip will be on the floor, or near a drain, not through the ceiling.
Air eliminator brands:I'm quite familiar of the brand you mention, made in Europe and now sold by an American company. Whenever I replaced one, I always unscrewed them (by hand) and put some silicone grease to the threads and O-Rings. So I could get them apart later to clean the seat. Experience has shown that the seats don't clean easily and just replacing them was cheaper in the long run. They are sold cheap anyway. I used to replace more than 12 but less than 60 (I think) in the course of a year when I found them leaking. When I started to crank down on the cap, it didn't change anything. It stopped the white stuff from forming, and the system still worked as usual. And customers weren't getting charged for lots of leaking vents. I used to pipe an air chamber above the PR valve to collect air bubbles out of the boiler. They leaked first and I didn't have all the 30# Pressure relief valve replacements.
automatic ventingWorks better and longer if it is high enough, & if pressure is controlled. For example,some antique open tank systems are trouble free for generations. Air always gets into every hydronic system and water always disappears. Trouble free venting requires a device at a high enough location with low enough pressure so that water doesn't touch the device. In buildings with elevators automatic vents are installed in the penthouse.There they operate for decades until somebody or something(stupid PRV) blows the thing right off.
High systems:That's true. In open tank gravity systems, the overflow tank in the attic to a place where the system level was below the entrance of a radiator was long and the water volume was high. In a closes HW BB system that is series looped, had very little extra water in it. As long as someone kept the boiler/system filled to the red mark on the altitude gauge, the system was always full. Who ever checks system pressures and adds water.
Weekend work on system pressureI thought I'd update you on some checks I was able to do thus far.
I started by loosening the lock nut on the Watts pressure valve and adjusting the system pressure from an ~10 psi to ~18 psi. The valve worked properly and raised the pressure almost instantly with each turn of the adjusting screw.
My next step was to check and set the expansion tank pressure accordingly. I shut off the valve to the tank, drained the water side of the tank using the valve's integral bleeder, and checked the air pressure on the other side. 0 psi. Nothing. Well, that's not good, I thought. So, I pumped up the tank to 18 psi using my bike pump (took a lot of pumps), waited a few minutes and and checked pressure again. 18 psi.
I then opened the valve, bled the system to get any air out that has been there since its last winter, and started up the system. I let it run until the aquastat kicked off the boiler and, knowing that it was fully up to temp, I checked the pressure. 23 psi.
Letting it fully cool, the next day I checked the pressure again. 18psi and no water out of the air side of the expansion tank so far. Next weekend, after having it sit for a week, I'll check the pressure again and the expansion tank for water on the air side.
I'm hoping the tank isn't bad, but it not having any air pressure is not a good sign, right? BTW, the pressure relief valve did not flow throughout the entire test (I did lift up the lever to ensure it does indeed flow, so I think it's working).
if tank is badEventually bladder fails. People with foresight then replace with old fashioned gas water tank. At least that tank will never need replacing. Some people with even more foresight pressurize with nitrogen.
waterlogged?often when the bladder fails, the tank fills with water. And water may come out when you push in the air stem.
The tank will be very heavy, use care if you un-screw a waterlogged tank, Shake the tank or rap with your knuckles to see if it is waterlogged.
If the tank has failed I would replace with the correct side, bladder style expansion tank. Add an isolation/ drain valve if you plan on servicing this down the road.
Hydronic bladder tanks, like bladder well tanks are very dependable and should last many years if the fluid quality is correct, they are sized and installed properly, and no O2 is getting into the system.