Why no vacuum on single-pipe?

ethicalpaul

mattmia2 said:

I assume you have tried this sort of thing:

https://www.mcmaster.com/2987K38/

No I haven't tried that one. Even it is .5 psi reported cracking pressure, that's way more than I want in my system. That much pressure would have to build before any of the radiators even started to vent air. Oh and the main also wouldn't be able to vent until that pressure were reached. The main needs a check valve too.

mattmia2

oh, i see, i didn't see a specified minimum opening pressure. Could try changing the spring in it to reduce the opening pressure.

mattmia2

Maybe you could modify that type of check valve to use a viton ball instead of a diaphragm.

EBEBRATT-Ed

Remove the radiator vents.

Vent every radiator into a new common dry return (say 1" just for fun) with 1/4" copper tubing.

Put 1/4" ball valves (to adjust the venting rate) where the 1/4" connects to the new dry return.

Then on the new dry return after all vents are tied in put a solenoid valve that opens and closes when the boiler fires and a big vent after the solenoid.

Ty the new return into a return pipe

ethicalpaul

Yeah I think that is basically what @PMJ is running with the solenoid. I'd hate to have to use ball valves for venting rate

It would be a challenge for me to get 1/4" tubing to all my upstairs radiators. One or two of them would be easy though.

dabrakeman

I present the most sophisticated low cracking pressure check valve ever conceived:D.  I know we don't talk cost here but understandably this may be out of most people's range.  Required:  1 cm^2 Press'nSeal (preferably used), 8mm^2 duct tape, a MoM or capless Hoffman 1a and digits on your hands that are not thumbs. 
Actually it has been working for a week now.  This is my purposely fast venting radiator in an under radiated room that would whistle dixie after the boiler shut down.  Tried this just to shut it up and works great.  Vents just as fast as it did before and the flap seems to seal down pretty well once the vent tries to start drawing air in. Not sure how many inhg it would hold if all the radiators were done this way, but, access to both sides of the vent orifice on the MoM's opens up a few simple design possibilities. 

SteamingatMohawk

@ethicalpaul Interesting, but if the system is operating properly there is no air in it because it has been essentially purged by the vacuum pump. For the return pipes to never see steam the pipe must be full of condensate, I would be very surprised if that is the case for all of the return piping.

neilc

dabrakeman said:

I present the most sophisticated low cracking pressure check valve ever conceived:D.  I know we don't talk cost here but understandably this may be out of most people's range.  Required:  1 cm^2 Press'nSeal (preferably used), 8mm^2 duct tape, a MoM or capless Hoffman 1a and digits on your hands that are not thumbs. 
Actually it has been working for a week now.  This is my purposely fast venting radiator in an under radiated room that would whistle dixie after the boiler shut down.  Tried this just to shut it up and works great.  Vents just as fast as it did before and the flap seems to seal down pretty well once the vent tries to start drawing air in. Not sure how many inhg it would hold if all the radiators were done this way, but, access to both sides of the vent orifice on the MoM's opens up a few simple design possibilities. 

I wanna see a tee and gage on that the next time you post it,
and the video,
#smiling

mattmia2

you'd need a more substantial diaphragm to hold the 14 psi or so of atmospheric pressure.

AMservices

Running air vent lines to a common vent is the best way to get a 2 pipe vapor vacuum systems performance, out of a 1 pipe system.  
What so wrong about ball valves for balancing? It's cheap, but more importantly, it works. 
I used 3/8" copper tubing from each radiator with a 1/4" ball valve for balancing. They run down to a 3/4 copper common vent line that follows the steam mains around the basement. 
Not having steam traps to prevent steam from getting into the air line, I piped the main vent line so it can drain and condensate back to the boiler. 
It also helps to arrange the vents from radiators as a reverse return, so the closest radiators to the boiler is where you start the main vent line. If a little steam makes it's way into the main vent, it has time to condense before it can vent out. With some steam condensing in the main vent it doubles as a condensing line. Just like the Moline system did with their steam ejector bleeding steam into a condensing line before the main vent. It starts making a vacuum (lower point of pressure) on the return that gives a little bit of suction on the radiators to speed up the venting. You just don't want to much steam in the main vent as it could block the other vents from venting. 
The reverse return will equalize the pressure drop and make balancing that much easier as well. 
What I've found playing around with check valves is it's best to double up. 1 never seems to hold as tight as I need it. 
The best check valves are a stainless steel ball sitting over a hole. Like what you'd find on an old hoffman or Websters or B&J vapor vac system. 
The cracking pressure shouldn't be more then the weight of the ball. So if your making a check valve don't use an 8 oz steel ball. 
If you find your boiler is running at +0.5 psi, don't panic. The difference in 212°F and 213° isn't going to blow the annual heating budget. And try to focus on all the time at the end of the cycle where the system is sub atmospheric. 

PMJ

I agree with @AMservices that .5psi at the end of the burns doesn't mean much in the big picture. I have a doubled up cheap check valve arrangement that is my safety vent should the electric not open for some reason. I am guessing it has a cracking pressure of like .5 or something. It is only at the end of the burns where you go over atmospheric anyway to push out the small amount of air that leaks back in. I have run using that check valve only hitting a lightly higher header pressure for a few minutes at the end of the burn. It means little with regard to total efficiency. The vent only ends up being open about 35% of the time the burner is firing and like 10% of the total time.

SteamingatMohawk

Yup, I just came back to this discussion and saw I incorrectly directed my question to you @ethicalpaul .

So, @PMJ can you explain your logic to @ethicalpaul and me?

PMJ

SteamingatMohawk said:

Yup, I just came back to this discussion and saw I incorrectly directed my question to you @ethicalpaul .

So, @PMJ can you explain your logic to @ethicalpaul and me?

The level of vacuum created is directly related to the percentage of the total air removed from a system. Two pipe systems have a higher percentage of total system volume in piping that never sees any steam. In operation then the steam pushes out a smaller percentage of the total air in the system in two pipe than one pipe. So when that steam collapses a larger void as a percent of the total system volume is created in the one pipe system and so a deeper vacuum results.

SteamingatMohawk

If the system is operating at a vacuum, presumably there is little to no air in it. That leaves steam and condensate. If some of the piping never sees steam, what is in it? I have a difficult time believing the return is "full" of condensate all the way from the radiator back to the boiler. What don't I understand?

PMJ

SteamingatMohawk said:

If the system is operating at a vacuum, presumably there is little to no air in it. That leaves steam and condensate. If some of the piping never sees steam, what is in it? I have a difficult time believing the return is "full" of condensate all the way from the radiator back to the boiler. What don't I understand?

A closed system in vacuum does not mean it has no air. It only means it contains less air than it would at atmospheric pressure. The more air you remove, the lower the pressure will be inside relative to outside the system.

So in my two pipe system let's say the steam fills 1/3 of the total volume and the other 2/3 is still air. When the steam completely collapses the system will again be all air. It will be filled by the 2/3 volume of air spread out in the entire system volume and the system pressure will be below atmospheric.

Gsmith

If the system is operating at a vacuum, then it contains steam, condensate and vacuum which is essentially air at a very low pressure, like outer space.

AMservices

People think of a vacuum as all or nothing. 
No one, in the history of man, has every made a perfect vacuum. 
The vacuum gauge has a scale from 0-30 HG. 15 HG is only 50% vacuum. Whats left is air. Air that has expanded to fill the space. 
Steam does the same thing. Under a vacuum steam molecules are larger. 
Having less air in the piping makes a lower pressure that allows steam to move in with less effort.  Steam does push the remaining air out of the radiators. But in a 2 pipe system there will always be air in the return.  

PMJ

See the attached pressure chart. I only get about -5"hg between firings because I rarely fill my radiators even 1/2 full. I believe one pipe systems will naturally pull deeper peaks than -5" because the steam fill will be a higher percentage of the total system volume than mine.

mattmia2

Also in a 2 pipe system, the devices that keep the steam out of the returns decide if something is air or stem by temperature, so if you get enough of a vacuum to depress the boiling point enough, it will affect their operation.

SteamingatMohawk

@mattmia2 You hit the nail on the head. My personal experience is with a single pipe system that has vents at the end of the return near where the returns go down into the Hartford loop, so my system vents almost the entire system.

I have been noodling on converting to a vacuum system and neglected to consider what additional devices are used in a 2 pipe system to prevent steam from getting into the vacuum pump.

Igor and AMservices materials for a one pipe system that I have been looking at have a separator between the return and the vacuum pump to prevent steam from damaging the pump.

Depending on the densities of the gases, they may eventually mix. Air is nitrogen and oxygen ( plus some other junk) with close atomic numbers, so they don't stratify, but water vapor (as a gas) and air might stratify, or as mentioned above, there are devices which prevent the steam from getting to some portions of the system.

Now it makes more sense to me. Sorry for the distraction from the main topic of the discussion.

dennis53

There is an Apollo check valve that claims 0 psi cracking pressure: Apollo 61-100-A1(fxf) or 61-200-A1(mxf). Smallest size listed is 1/4" npt.

ethicalpaul

It is spec’d .5 psi which is too high IMO. Plus it’s $50 or so 😬

dennis53

The -A1 option is listed at 0 psi cracking pressure. I agree it is expensive, but at least there is one available.

ethicalpaul

Thanks Dennis! I missed it in their other documents. They remove the spring. It’s still not zero in our terms of course. You’d have to orient it vertically so the weight of the stopper is the spring.

I wonder what true cracking pressure would be acceptable to steam heat folks. 

At our pressures one problem is that tiny variances in when a steam vent opens wreaks havoc on balancing.

I’m getting convinced that the check valve must be integrated into the heat activated part of the vent.

jumper

A hermetic container can contain only liquid & vapor. So maybe no air.
If there is air water has to get hotter to boil.
That is why boiling water is hotter at sea level than on mountain.
But do our radiators get hotter with air in system? I say no.
The less air the better. Plus any vent will let some steam escape.
So ideal is to plug vents; seal connections; and mechanically evacuate system.
Can't say how much improvement in real life?

mattmia2

It seems like a resilient ball and a hard seat or vice versa will have the least difference between cracking pressure and holding pressure. I think in any system they will all oscillate as other valves open and release pressure then the pressure drops as a result of the open valve and the close and this will repeat until the boiler makes enough steam to keep all of them under positive pressure.

Think about what you would do with a temp and pressure sensor and a solenoid valve, if there is a control point of temp or pressure or a combination that would tell you it is the right time to be closed or open as the system is heating and cooling. This eliminated the cracking and holding pressure from the problem.

ethicalpaul

A solenoid on each radiator? Clickety clack, don't talk back! And a temp sensor and pressure sensor too? $$$

I think the opening and closing is going to be hard to predict, but I don't really see a pressure drop as a result of an open check valve...pressure is required to keep it open so I see pressure rising in a given radiator until the valve cracks, then I see the pressure being generally stable (excepting pressure drops due to condensation). It's not like the check valve pops open and stays open letting the pressure drop...if the pressure drops the valve closes.

My fear there is that x radiators with the lowest cracking pressure will get all the steam (until they fill up) messing up balancing. Today my system sits at around .5" of water during a call for heat...with each of the radiators slowly oozing air out of their #4 and #5 vents. That can be affected by things such as a single drop of condensate sitting on the vent orifice. I think the check valves will prevent that even flow of steam.

I have a prototype with just a 5/32" brass ball sitting on a hard seat just to experiment with--it prevents all steam to that radiator. I have to make 6 more to see what happens then.

PMJ

Air lines back to the boiler room. Could be plastic. Vent side pressure of all rads would be exactly the same then just like 2 pipe. 

More effort up front but dramatically more possibilies downstream without all those moving parts in each room all of which must stay working.

I'd work on how to snake those lines. 

mattmia2

You can get viton balls from mcmaster-carr.

I was saying think about what you can do with a solenoid and pressure and temperature sensor to figure out if it is possible to figure out when the valve should be open or closed based on just temp and pressure at the radiator.

ethicalpaul

AMservices said:

...The best check valves are a stainless steel ball sitting over a hole. Like what you'd find on an old hoffman or Websters or B&J vapor vac system. 
The cracking pressure shouldn't be more then the weight of the ball. So if your making a check valve don't use an 8 oz steel ball. 
If you find your boiler is running at +0.5 psi, don't panic. The difference in 212°F and 213° isn't going to blow the annual heating budget. And try to focus on all the time at the end of the cycle where the system is sub atmospheric. 

@AMservices I missed this excellent post of yours in all the excitement.

Do you know if those old vacuum vents had a soft seat for their stainless steel ball?

The problem I see currently in my mind is that a light ball is necessary to keep pressure low, but a light ball may not make a good enough seal.

And regarding cracking pressure and the weight of the ball, I think the cracking pressure (let's say in ounces / sq in) will be more than the weight of the ball, unless the area of the ball exposed to the pressure is exactly 1 square inch. As the exposed area of the ball goes down, the pressure required to lift it will rise above the ball's weight. And I was certainly thinking of using a ball with less exposed area than 1 sq in

With these check valves in place on every radiator, building a little pressure in the system wouldn't be so bad, because unlike in my current system, the pressure would build fast (because at start of firing, all vents would basically be closed) and would max out hopefully still quite low (because cracking pressure would be reached, allowing steam to enter radiators).

I just received my tiny o-ring shipment so I'll let you all know how it goes. Stainless steel balls are on a slow boat from China, but I have brass balls on hand (haha)

What I've found playing around with check valves is it's best to double up. 1 never seems to hold as tight as I need it.

Why are you trying to make me sad?

AMservices

Recently I bought some 1/4" by 1/8" reducing couplings, 8 mm stainless steel ball bearings and some O rings to try an experiment. 
Cracking pressure was around 3oz.
Couldn't hold a vacuum  😖
The check valves on the old systems used a 1/2" ball (I think) and it was metal to metal.

ethicalpaul

Yeah I'm sure I'm destined to the same result with my experiments, but still I persevere Thank you so much for sharing your experience.

Wow, metal to metal, i wonder if they actually hold vacuum. I may have one in my possession soon for testing. One can buy a Hoffman 76 today from Supplyhouse.com but it's $149!!!

I might have to try one of those Apollo ones just to see what they are able to do.

Originally I was thinking of a slip-fit brass cylinder rather than a ball but I think it would get jammed/stuck and/or would just plain require too much pressure to lift.

mattmia2

It could be a metal disc rather than a cylinder.

There are many resilient plastics that can hold up to steam that were not available 100 years ago.

ethicalpaul

Yes but I don't have a metal disc design in my head to try

I'm not worried about the steam because mine is after the vent

dabrakeman

I have two simple devices as shown in the pictures here running for a few weeks now. One photo shows while boiler on and vent venting air and the other after boiler shutdown. I used a MoM and just cut the length of a standard ball tip pin so you can put a hook on the end that will catch the inner wall lip of the MoM orifice adaptor when venting yet maintain clearance to the internals of the vent when not venting (admittedly can be a little tricky to get right but doable). There are likely numerous ways you could keep the ball and shaft from flying out while venting while allowing it to fall back in place when system goes into vacuum. The plastic balls seem remarkably true to form. As far as cracking pressure it relates to the weight of the ball and pin shaft along with orifice size. I attached a simple calculation sheet. A plastic ball with some shaft length should allow it to crack at pretty low pressure (<0.2oz). A metal ball tip pin obviously would be higher due to the weight of the metal ball. I need to get a hand vacuum pump and see what kind of vacuum this can hold (unless someone else already has one) but this simple pin design opens at extremely low pressure and effectively diverts vacuum intake to another radiator. Only real reason for posting is if there was someone who had all their radiators with MoM vents and they had patience and some time it would cost nothing to see if could get the whole system into holding vacuum by doing this on each radiator. The two I have working are using a C and a 6 orifice so not sure how small of an orifice will work. The pin and ball I think do effectively reduce the overall venting of a given MoM orifice size a little bit. <img src="https://us.v-cdn.net/5021738/uploads/editor/hc/amos5vytb6iu.jpg" alt="" />

dabrakeman

dennis53

Great idea and data to back it up.
Now it's off to the craft shop.

ethicalpaul

Based on my tests that won’t hold. Here’s a good cheap test pump with a gauge on it: 

CARSC Hand Held Vacuum Pump... https://www.amazon.com/dp/B07D2B13DF?ref=ppx_pop_mob_ap_share

dabrakeman

@ethicalpaul
Thanks. What level of vacuum were you able to hold with your test?

dabrakeman

As mentioned I would suspect it might be less effective with smaller orifice MoM adaptors. The larger 6 or C gives a better incidence angle at the contact between the ball and orifice edge.