Vent Hiss on Shutdown

AnthraciteEnergetics

I've found a few posts before about this however they all seemed to involve additional underlying issues (poor main venting, excessive pressure, etc).

This will be the second season with my 331 sq. ft. 1-pipe counterflow system. New Peerless 63-03 118 MBH(in) last October, dropped header with 2x2" risers feeding 2" mains. Steam quality appears to be good and all radiators get steam at roughly the same time and the system is balanced and makes ZERO noise during the heat-up cycle. No pressure build on the 0-5 PSI gauge at all except on recovery from setbacks.

I initially had NO main venting (it was a coal conversion). It worked "OK" but response time was slow on second floor. I tapped the ends of the mains directly for 3/8" and put in 3" nipples. I had two Vari-Vents that I bought early last season and found they were no good for radiators (too fast, threw off balance). But they were basically an open 1/8" pipe (that's what it felt like when I blew into them). So instead of wasting $40 I decided to try them as main vents - bushed the nipple down to 1/8 and screwed them in. They work great, time for live steam to get from header to 2nd floor rads might be 2 minutes. The 2nd floor risers are vented through the rad vents - only one radiator per riser.

I have all-new Gorton 5's and 6's on all radiators except one, which has a 4. No problems at all during heat-up.

It's when the heat call is over and vacuum forms in the system, that one or more of the Gortons open up and make a loud sucking hiss sound. I actually went as far as countersinking the Gorton orifice to improve aerodynamics and putting a thick sock over the vent to try to dampen the airflow/noise, none of which worked too well. Which radiator opens first seems to be random. This becomes annoying when the bedroom is up for the draw at 4:00 AM.

Is this a main venting issue? I feel this should be happening in the basement on the main vents, not in the living space. Do typical main vents (Gorton #2's, etc) normally perform the vacuum relief function? I don't want to buy them and change out the Vari-Vents, which otherwise are serving me well, if it won't help.

Any experience or suggestions?

Fred

The sucking noise at the radiators is the direct result of the radiator vent being pulled open by the vacuum before the main vents open. I suspect that while those Vari-vents may (or may not) be enough to vent the air out of the mains, the orifice isn't large enough to suck enough air in, at the end of a cycle or they don't open fast enough or as fast as the vents on your radiator(s).
I had a similar situation with Hoffman #75's on my mains. Installed the B&J Big Mouths and the sucking went away.

Jamie Hall

Various makes of vents open at various temperatures. I'd suggest Gortons on the mains, or a Big Mouth.

RomanGK_26986764589

I have Gorton #2s on my main and they are really slow to open. My radiator vents do most of the sucking.

AnthraciteEnergetics

Thanks!

@Fred

The Vari-Vents dont open at all to relieve vacuum.

I have a Gorton C laying around, i'll try putting a tee on the main vent nipple and gang it up with one of the Vari Vents on the end of a longer nipple (to try to keep it cooler and maybe open sooner) and see if it will do most of the vacuum relief duty before buying anything new.

Fred

Depending on the length and diameter of your main(s), I suspect you need more venting capacity than a Veri-vent and/or a Gorton C can provide. Size matters when you are trying to vent air out, at the beginning of a heat cycle or allow enough air back in at the end of a cycle so that your radiator vents don't have to collectively do those jobs.

JUGHNE

I also have the sucking hissing in a church on shut down.
A vac breaker at the boiler will not stop it.
I was considering moving the vac bkr to the venting antler that has 4 G2's and 1 75. 2 branches same set up on each.
Has this worked for anyone??

PMJ

@AnthraciteEnergetics,

You seem like a great candidate to try some vacuum on a one-pipe.

Try to envision your system with no sucking noise at all anywhere. What good is coming from letting all that air back in anyway, only to have to push it out all over again every cycle which requires pressure over atmospheric? Try to picture what is happening to the steam still in the system right when the burner goes off and you start letting the air back in. You will see that what the steam does then is the opposite of what you want it to do when you are heating. When you don't let air back in the forward motion of the steam to the rads never stops. I have found that what the steam does in my system in vacuum (even a slight one) is way more important to my end result than what it does with the burner on and slightly above atmospheric. And typically my system spends 80% of the total time in vacuum during each call for heat - and 100% between calls. By the way, the system is still in vacuum during the first 4 minutes of each average 8 minute firing.

How about you install an inexpensive check valve outside of your vent on that bedroom rad and start there. I am not familiar with them but are there any rad vents with threaded outputs? If you did this at least then there will be no hiss in the bedroom which as I understand it is your biggest complaint right now.

Give it some thought.

AnthraciteEnergetics

1 pipe Vacuum would be great, basically a giant heat pipe. I like the idea of vacuum but not pumps or expensive valves.

Burner will shut off and boiling point drops as vacuum develops, turning sensible heat of water & iron into steam which goes into the system instead of heating the boiler room.

Can the check go between the rad and vent? That's easy to fit with a 1/8 check valve. Grainger, etc sells them and not expensive. I still have to be able to vent air but keeping steam in, but not allow air back in on shut down.

MilanD

There was a discussion here on this check valve business a few months back. You need a check valve with 0 psi cracking pressure. I think Apollo 61-100/200 valves are like it. However, smallest thread on it is 1/4 so you'd have to use bushings.

PMJ

The check valve @MilanD mentions is still showing 8oz cracking pressure which is probably still too high. I began this way in my system and it worked because I only needed one valve for the whole system. In your case this would make the pressure required to fill that one bedroom rad higher than all the rest and not what you want.

I ended up with a solenoid valve to get all the way to zero and I might see 2oz positive as the peak in my system for 2 minutes each cycle.

This would just be a test on one rad for starters. I would be doing a small locally controlled rig there with solenoid valve and pressure sensor just inside your vent just to see how it went. Valve opens whenever the slightest positive pressure over atmospheric is seen - closed otherwise.

Kahooli

Don't forget that in the warmer season your rad valves generally dont close because they never fill fully with steam. As soon as the system shuts off they will suck from the higher pressure end which almost always is the atmosphere, not the system (it turns to vacuum extremely fast).

My system does the same thing you describe. I have not been able to fix it yet (but I've only been here a year).

PMJ

Kahooli said:

Don't forget that in the warmer season your rad valves generally dont close because they never fill fully with steam. As soon as the system shuts off they will suck from the higher pressure end which almost always is the atmosphere, not the system (it turns to vacuum extremely fast).

My system does the same thing you describe. I have not been able to fix it yet (but I've only been here a year).

Even a partially filled rad - as soon as the steam supply stops the condensation in the rad will create a vacuum there and close a check valve on it immediately if there is one. The rad will then continue to pull new steam from the main as opposed to air from the room.

EBEBRATT-Ed

I would put a check valve teed in with (not in series with) the main vents. Cheap and effective way to break a vacuum

Kahooli

PMJ said:

Kahooli said:

Don't forget that in the warmer season your rad valves generally dont close because they never fill fully with steam. As soon as the system shuts off they will suck from the higher pressure end which almost always is the atmosphere, not the system (it turns to vacuum extremely fast).

My system does the same thing you describe. I have not been able to fix it yet (but I've only been here a year).

Even a partially filled rad - as soon as the steam supply stops the condensation in the rad will create a vacuum there and close a check valve on it immediately if there is one. The rad will then continue to pull new steam from the main as opposed to air from the room.

Again, check valves have a cracking pressure. To do this you must have the same check on all rads and accept a higher initial system pressure Pcrack+Pnorm and steady state Phold+Pnorm.

On a system that used to operate at a low pressure, the result of this will most likely be system imbalance. Airflow will not be predictably controlled by vent orifice anymore as the first check valve opening will drop system pressure enough that other checks will not open. The first one open will get a blast of steam and continue to draw in more. I believe you will end up with a Russian roulette of "which radiator overheats this cycle?"
Or, in the case that check pressure has a tolerance (it does) you'll have a predictable few that will play that game.

PMJ

Kahooli said:

PMJ said:

Kahooli said:

Don't forget that in the warmer season your rad valves generally dont close because they never fill fully with steam. As soon as the system shuts off they will suck from the higher pressure end which almost always is the atmosphere, not the system (it turns to vacuum extremely fast).

My system does the same thing you describe. I have not been able to fix it yet (but I've only been here a year).

Even a partially filled rad - as soon as the steam supply stops the condensation in the rad will create a vacuum there and close a check valve on it immediately if there is one. The rad will then continue to pull new steam from the main as opposed to air from the room.

Again, check valves have a cracking pressure. To do this you must have the same check on all rads and accept a higher initial system pressure Pcrack+Pnorm and steady state Phold+Pnorm.

On a system that used to operate at a low pressure, the result of this will most likely be system imbalance. Airflow will not be predictably controlled by vent orifice anymore as the first check valve opening will drop system pressure enough that other checks will not open. The first one open will get a blast of steam and continue to draw in more. I believe you will end up with a Russian roulette of "which radiator overheats this cycle?"
Or, in the case that check pressure has a tolerance (it does) you'll have a predictable few that will play that game.

I don't think there will be a blast of anything. If I learned one thing about natural vacuum it is that all transitions are slow and easy - nothing happens fast. I also think one pipe will end up solenoid vent/check control like I did.

Perhaps no one pipers will try then. All I heard when I started was that there would be multiple mystery problems with vacuum on 2 pipe too. Not one shred of it turned out to be true. All I got was dramatically improved performance. A few other brave souls here have too.

Kahooli

Maybe If I get bored this winter I'll make a system model in comsol to prove my point.

The problem I am describing has nothing to do with vacuum operation, it's at positive pressure startup. My argument is not about the natural vacuum at the end of a cycle. The local dynamic pressure changes due to a check valve opening and the local dynamic pressure changes due to collapsing steam are both fast transients.

To argue that the one pipe system will work the same way as any two pipe system is probably being myopic. You get to control when the system operates in vacuum from a single solenoid (or one per dry return. A mechanical check will never give you that option. I would agree with you that a solenoid controlled check that closes at the end of a burning cycle would be a nice way to continue with the system in vacuum, but that is a very different concept with very different overall operating characteristics.

AnthraciteEnergetics

Cracking Pressure - dont know how big of a deal it is but might be worth a try. Worst case the valve gets relocated and turned around beside the main vent

Solenoid valve - I actually have one laying around for 1/8 thread. Dont think it would last on steam (its designed for control pneumatics) but I already have t-stat cable to the radiator as part of a hi-lo fire scheme, so getting a firing signal to it is easy.

Reverse check valve in parallel with main vent - sounds like a quick system wide solution. Great insight on that one.

The natural vacuum is always slow to develop, as the steam takes time to condense.

MilanD

61-100/200 - data sheet. A1 cracking psi = 0.

PMJ

> @MilanD said:
> 61-100/200 - data sheet. A1 cracking psi = 0.

I see. I hope someone tries it.

PMJ

@Kahooli ,

I would argue that it was myopic of many to discourage my pursuit of natural vacuum in two pipe. And over many years now I am well past the theory stage.

I think a one pipe system on timed cycles like mine with checks that are truly 0 cracking pressure like the one @MilanD proposes would run beautifully. The check on each rad would open just as the pressure inside the rad equaled the pressure in the room it was in and there would be no rush of anything just as there is no rush when my one valve opens.

I bet someone out there will have at it - one rad at a time.

Steamhead

Are your steam pipes insulated? If not, steam will condense in them very quickly and will form lots of vacuum..............

PMJ

> @Steamhead said:
> Are your steam pipes insulated? If not, steam will condense in them very quickly and will form lots of vacuum..............

Trying to run any of these systems vented or not without the delivery lines insulated doesn't make much sense does it?

Assuming they are then runaway the rads condense the most and create the most vacuum. When you then prevent air from filling them when the burner goes off steam from the mains continues to fill them instead. The boiler continues to make steam as the pressure drops. When this happens every cycle it is just plain a lot of steam delivery where vented there is not only no delivery but negative delivery to be recovered next cycle.

The difference overall is really quite amazing.

Motorapido

I am not familiar with them but are there any rad vents with threaded outputs?

Maid-O-Mist radiator vents have removable orifices. The body of the vent has a threaded female opening to accept the threaded male portion of the interchangeable orifices. Would it be possible to install a check valve into the body of such a Maid-O-Mist vent? I will volunteer to be the first one-piper to try this experiment if somebody can find me a source for a check valve that would thread into a Maid-O-Mist radiator valve. The check valve would need to have a female threaded boss at the top of the diameter of the interchangeable orifices for the Maid-O-Mist, so you could put the orifice on top of the check valve.

PMJ

Motorapido said:

Maid-O-Mist radiator vents have removable orifices. The body of the vent has a threaded female opening to accept the threaded male portion of the interchangeable orifices. Would it be possible to install a check valve into the body of such a Maid-O-Mist vent? I will volunteer to be the first one-piper to try this experiment if somebody can find me a source for a check valve that would thread into a Maid-O-Mist radiator valve. The check valve would need to have a female threaded boss at the top of the diameter of the interchangeable orifices for the Maid-O-Mist, so you could put the orifice on top of the check valve.

Great.

I don't have any rad vents so I'm no help on this but I'm sure others here can. The zero cracking pressure on the check valve you try would be pretty important so I hope what the paper says about the one @MilanD showed us is true.

AnthraciteEnergetics

My pipes (2 inch mains) are insulated. Still working on getting some of the fittings done and a few feet where I have to crawl over the pipe for crawlspace access but its more or less totally covered. The copper pipe is part of a hot water zone I'm adding (kickspace heater - bathroom).

Kahooli

Sadly there is no such thing as zero (0.0000) cracking pressure check valves. Surely they can print 0, because they denote no precision beyond the decimal. You can only be assured that it is less than 0.5, which is still 8 ounces.

Mechanically speaking there will be some mass and friction on the piston that will require some pressure to provide the force to move it. That 0 is a marketing number, not an engineering number.

PMJ

Kahooli said:

Sadly there is no such thing as zero (0.0000) cracking pressure check valves. Surely they can print 0, because they denote no precision beyond the decimal. You can only be assured that it is less than 0.5, which is still 8 ounces.

Mechanically speaking there will be some mass and friction on the piston that will require some pressure to provide the force to move it. That 0 is a marketing number, not an engineering number.

I tend to agree with you on this which is why my search led me eventually to solenoid valves. The good news is that for this application they can be small and inexpensive.

Longer term I would be thinking run tubes all the way to the boiler room to a manifold where the valve management would be much easier.

Fred

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