Where To Install Automatic Air Vents

[velvetfoot]

Pumps are usually flood filled from the boiler base outlet which is
the best way to reduce cavitation to near zero and eliminate any
chance of pump damage and improve pump life span.

I'm pumping to the return and I don't think I can fill upstream (check valves). Anyway, the boiler pumps don't seem to be a problem, just the zones.

 

[velvetfoot]

Well, I think I got a good part of the air out. Starting up boiler now with zones still isolated. I figure it'll run through the air scoop a few times that way as it heats up. Who knows.

 

[BoilerMan]

I'm pumping to the return and I don't think I can fill upstream (check valves). Anyway, the boiler pumps don't seem to be a problem, just the zones.

Are these weighted flow checks? If so, you can open them with the handle on the top which will help get flow up and move more air to the elimination point.

You can try putting about a tablespoon of Liquid Dawn, yes the dish soap, into the system. It will cut the surface tension in the water allowing it to carry air bubbles down a pipe more efficiently.

TS

 

[velvetfoot]

Thanks. The zone checks are flo checks and there are a couple spring checks. Makes sense about the soap.

I just spent an entire boiler cycle down in the basement with it heating the tank to 176 and also providing some zone heat. It turns out there is indeed noise coming from the boiler pump plenty also from the zone circs. It was pretty darn quiet when cold. I went around with my stethoscope and could hear the bubbles in the pipe all the way from a short distance from the pellet boiler, past the air scoop, and then finally as they burped their way into the tank. I bet if that air scoop was a Spirovent or Caleffi, or like that, it'd be gone sooner rather than later. Right now, I'm hoping for eventually. Or, I might bust a move and install a new air eliminator. Then again, I busted a move with the auto air vents, duh.

 

[arbutus]

I put in a single Spirovent, right near the lowest part of the system (basement), at the expansion tank connection, and had very little trouble with air. After the initial fill and bleed for the radiators (second floor) and staple up loops (in basement ceiling) I had occasional air gurgles for a couple weeks, and darn near nothing after that.

There were some other discussions about air eliminators, with the Spirovent or Caleffi type solving similar issues for other folks here.

 

[velvetfoot]

I put in a single Spirovent, right near the lowest part of the system (basement), at the expansion tank connection

I wonder if you could be more specific. My current air scoop is just past the boiler protection recirc line and therefore sees flow from both boilers. The flow then goes to the tank and/or zones if they are running. I had thought that the zone pumps running from the buffer only and bypassing the existing air scoop would be a factor, but I'm currently thinking that just replacing the current air scoop with a Spirovent would do the trick. I had originally thought about putting a Spirovent close to the pellet boiler, but I was concerned about head loss and figured the existing air scoop would handle both boilers.

 

[arbutus]

It is very close to the PS setup in the sticky at the top of the boiler room. Rotate the picture 90 degrees and it will show the primary loop is at the bottom of the house, and all the zones are higher.


The odd bubble or two that have gotten into the radiators after the initial fill and bleed have been absorbed into the water and separated by the Spirovent. No gurgling like when I was filling and bleeding, and I have had various small portions of the system drained and refilled over the last year. Each time a few bubbles to the upper levels, but not enough to worry about, and no gurgling in the radiators. Tried bleeding the radiators again this fall and they were full.

I was able to isolate the boiler and pressure relief valve, use fast fill on the pressure reducer, and drain air from the zones with a garden hose during initial filling.


The Spirovent does a good job. I'm sure the Caleffi product is quality as well. I can't compare to an air scoop, because I don't have one.

 

[velvetfoot]

I might try to replace the air scoop tomorrow. Oh, wait, it's tomorrow already.

 

[Bob Rohr]

Are you sure you are not cavitating one of the pumps? Any flow restrictions upstream of the circs?

Cavitation forms, and will continue to form vapor pockets, not to be confused with air bubbles. Vapor pockets can form even in a system that has been purger 100% air free.

Vapor pockets form when you drop the fluid pressure below the vapor pressure, this can happen at the eye, or inlet to the circ under some conditions. So the key is to make sure the SUCTION side of the circ has enough static pressure to prevent this condition.

And the hotter the fluid the more apt to create or cause cavitation. Vapor pressure of water at 140F is 2.9 psia, at 200F it around 10psi. So be sure you have at least 10 psi at the circ inlet. This is the key to why so many OWF destroy their pumps frequently, not enough pressure in an open vessel to provide the vapor pressure to prevent cavitation.

Idronics 16 will be about pump sizing, selection, and troubleshootring.

Did you use a Caleffi 281 ThermoBloc? It has a gravity gate (check valve) inside. it ships with a screw locking it closed that needs to be removed for gravity circulation function.

Tips for avoiding cavitation

Run system pressure as high as possible (practical)
fluid temperature as low as possible
expansion tank at the suction of the circ pumps ALWAYS
mount circ pump as low as possible in piping, maximizes static pressure at the suction
no flow restriction devices on the suction side, valves, checks, mixers, etc
12" of straight pipe is ideal, not always possible on the suction side
Microbubble type air separators, the iron, scoop type vents are best for light boat anchors

 

[ewdudley]

And the hotter the fluid the more apt to create or cause cavitation. Vapor pressure of water at 140F is 2.9 psia, at 200F it around 10psi. So be sure you have at least 10 psi at the circ inlet. This is the key to why so many OWF destroy their pumps frequently, not enough pressure in an open vessel to provide the vapor pressure to prevent cavitation.

Vapor pressure of water at 200 degF is more like 11.5 psia, which equates to 6.5 inches of mercury vacuum or 3.2 psi below atmospheric pressure. So if your OWB pump has a static head of 2 psig at the bottom of the boiler, and the pump develops a pressure drop of 10 or 12 ft (~4.75 psi) you could easily be in trouble, especially considering that pressures within the impeller turbulence can be significantly lower that the pressure entering the volute.

But in a sealed system with 10 psig (as opposed to the '10 psi' mentioned above) you would need a hell of a pump to cause cavitation.

 

[Bob Rohr]

Vapor pressure of water at 200 degF is more like 11.5 psia, which equates to 6.5 inches of mercury vacuum or 3.2 psi below atmospheric pressure. So if your OWB pump has a static head of 2 psig at the bottom of the boiler, and the pump develops a pressure drop of 10 or 12 ft (~4.75 psi) you could easily be in trouble, especially considering that pressures within the impeller turbulence can be significantly lower that the pressure entering the volute.

But in a sealed system with 10 psig (as opposed to the '10 psi' mentioned above) you would need a hell of a pump to cause cavitation.

Thanks for catching and clearing that up, I need to be careful with my psi, psia and psig.

I believe Grundfos recommends 4 psi, suction side at 190F operating condition.

It is certainly easy to establish problem conditions with improper component placement.

From some old B&G training regarding expansion tank placement.

 

[velvetfoot]

Thanks guys.
I'm about to turn on the Bernzomatic to sweat on the Spirovent. One of those slip couplings sure came in handy.
I will buy a gauge I can thread onto the hose connection on the valve right before the pump. I should look for at least 4 psi at 190-190 won't happen? How about cold?

Bob, I have model 280975A. Does this have the capability you mentioned?

Gotta go. Have to also plug those darn air vents as well (long term leak concern) after sweating in the Spriovent.

 

[velvetfoot]

Used 50/50 solder. I had forgotten how easy it was.

 

[velvetfoot]

Did indeed plug the 1/8" adapter tees where the two autovents were; at least I got that nice one handed recip saw out of it.
I put the new Spirovent where the original air scoop was located.
The vertical pipe with the insulation,the supply riser from the oil boiler, is blocking the recirc line to the Thermomix (only a 280, no easy way to defeat it, far as I can tell).

I'll get a pressure gauge to attach to a hose connection tomorrow. It'd be a handy thing to have.

I wonder where I should set the pumps' speeds? First floor, second floor, boiler pump all have same Ecocirc Vario pump. I slowed them down some.
There's still pump noise, but I still think its air that has to get out. Time will tell; must be patient. At least there's warmth.

 

[Bob Rohr]

A heads up on that T&P valve in the tank. The probe needs to reach into the tank, by code, so it can sense the temperature. They do make extended probe types for use thru a fitting like that. Technically the valve should be right into the tank port, top or within 6" of the top if side mounted. If I'm not mistaken.

That should be plenty of "air scrubber". Not my favorite brand , but a nice quality 90% plus efficiency device.

 

[velvetfoot]

A heads up on that T&P valve in the tank. The probe needs to reach into the tank, by code, so it can sense the temperature. They do make extended probe types for use thru a fitting like that. Technically the valve should be right into the tank port, top or within 6" of the top if side mounted. If I'm not mistaken.

I believe it has an 8" long probe, but I still am not sure if it gets all the way past the 4" of insulation. Still, the valve is going into the 1.25" stainless dhw coil inside the buffer tank, perhaps a "tank within a tank, which snakes around inside it and goes in at the bottom and out at the top, so it is sensing the temperature. The tank side is protected by the boiler pressure relief valve. I'm not sure why the "T" part of T&P is even necessary, but this is what the distributor told me to do.

That should be plenty of "air scrubber". Not my favorite brand , but a nice quality 90% plus efficiency device.

Yeah, I know, but that's all the local place had, but it does seem nice. Was quite active when filling, Interesting that they gave me the contractor's price over the phone (even though I told them I wasn't a contractor) and I had to argue a little for it. The regular schmo price was $40 more! Although I got a lot of stuff on line for this project, I spent plenty at that place at the schmo rate.

Trying to figure out which valve to open for a complete fill as possible depending on the temperature of the boiler protection is a pain. Maybe I should have piped in a bypass. Perhaps some boiler vents as well: I burped them a little with the pressure relief valves. I inadvertanly left the oil boiler pump running with no heat on when we left the house for dinner and when we came back it was totally quiet. I'm hoping the zones clears up with time-I think the downstairs one is already on its way, but will check the pressures at the zone pump inlets tomorrow.

Any ideas on the pump speeds?

 

[BoilerMan]

Personally I'd leave the circs on "high" speed for a few weeks to move the air out. After that turn them on the lowest setting that will deliver the comfort to the zone.

From personal experience that is generally the "low" setting for the majority of residential setups. With the circs on the return it could be "med" but try low first for a few cold days, if the last BB in the loop is heating well then leave it on "low".

TS

 

[velvetfoot]

Thanks.

I am thinking of moving the separator to the outlet side of the buffer tank (see photo, above). That way the Spirovent will still see flow when the boiler pump is on and the zone circs will see flow even when the boiler pump is not on, but it may not see flow when the boiler pump is on and the zone circs are on. I could turn on the zone circs and let them run.

 

[velvetfoot]

Well, I relocated it. We'll see. Maybe should've just added it instead and have too. Or, be patient.
Also bumped up the pressure, cold, to 15 in the system and 17 in the expansion tank.
Couldn't see any hose bib pressure gauges around here with a scale of less than 0-100.

 

[velvetfoot]

Personally I'd leave the circs on "high" speed for a few weeks to move the air out. After that turn them on the lowest setting that will deliver the comfort to the zone.

From personal experience that is generally the "low" setting for the majority of residential setups. With the circs on the return it could be "med" but try low first for a few cold days, if the last BB in the loop is heating well then leave it on "low".

Would you have an opinion as to where I should set the boiler pump? All the pumps are the same and they pump to return and are infinitely adjustable.. Thanks.

 

[velvetfoot]

The Spirovent seems to be doing the trick. Very little noise from upstairs zone on high. Hope I didn't jinx it.

 

[Bob Rohr]

The Spirovent seems to be doing the trick. Very little noise from upstairs zone on high. Hope I didn't jinx it.

Run the pump on the lowest speed that will cover the load, start low, maybe bump up in design conditions if needed.

Air eliminators work best at flow velocities under 5 fps. Above that their efficiency starts to suffer. And above 4 fps you will start to hear "water flowing" when the system runs, and it can start eroding fittings and ells. The hotter the water the more aggressive, so keep the flow rates low.

Also flow rates below 2 fps will make it tough to get the air pushed back to the air eliminator, so 2- 4 or 5 fps is what you should design and size everything to.

Step one, determine the flow rate you need to run, step two, use a pipe sizing chart or software to select the correct size pipe to assure 2- 4 fps.

 

[leon]

I can tell you that in my case the B+G dumb as dirt three speed pumps are t'eed from the sump
outlet of my oil fired hot water Buderus boiler.

Water pumps work best when the installed with flooded suction just like hydraulic pumps. The water is always feeding the pumps at all times and the air scoop and vents are higher than
the pumps.

My pumps are at the numbe rone setting with zero problems except when I installed them as I had a large amount of air to bleed out at temperature with one zone of almost 250 feet of continuous base board(home perimeter including non living space/storage)

 

[BoilerMan]

Water pumps work best when the installed with flooded suction just like hydraulic pumps. The water is always feeding the pumps at all times and the air scoop and vents are higher than
the pumps.

In a closed loop system this is not the same. If you were pumping out of the bottom of a boiler like in a hydraulic tank it would be similar, like open systems such as OWF. The key is where the expansion tank is connected, most efficient tank location is as the air elimination device, which is most efficient at the hottest point of the system, which is at the boiler supply. Most efficient circulator (not a pump) location is closely after the point of no pressure change, which is the expansion tank, so on the supply.

Many book have been written on this, bottom line is all will work in an over-sized resi system, but when things are engineered in a large commercial system this comes into play. When we are talking about 10+ HP circulators capable of moving 100+ GPM and expansion tanks of hundreds of gallons.

TS

 

[velvetfoot]

To close the loop, I did slow the pumps down as well. Totally silent-like you can't hear them. I'm going to give most of the credit to the Spirovent, and of course, my advisors.