My Pressure Woes Continue - Pigtail Edition

merikus

Hi all, I’m back with a question on my ongoing problem to make my boiler turn off on pressure rise. In previous episodes we learned that my pressuretrol was not wired at all into the system for 30 years. Since learning that and rewiring the thing, I’ve been still unsuccessful in trying to get it to turn off on pressure rise. 

My newest theory is that my pigtail is flooding with water. The hole for the pigtail is clearly right around the waterline for the boiler, and it is installed in such a way that the pigtail loop dives below the water line. My theory is that when the waterline bounces up and down, it’s going into the pigtail and then settling in the loop. 

In looking at pictures here on The Wall, it appears the pigtail should be installed in such a way that a nipple comes out of the boiler pigtail hole, then connects to a 90 degree elbow, then the pigtail connects to that straight up and down with the loop well above the waterline. 

Given how close my boiler pigtail hole is to the waterline, I’m worried about water surging into the nipple before it turns 90 degrees and sitting there too long, preventing steam from getting to the vaporstat. 

I’m wondering if it’s possible to put a 45 degree elbow on the boiler pigtail hole, then a 3 inch nipple running at 45 degrees, then another 45 degree elbow to get us back to up and down, then the pigtail. The reason I’m thinking of doing this is that, in theory, that should encourage any water that surges into that nipple to flow out of it and not clog things up. 

Or am I totally overthinking this and a straight nipple out of the boiler pigtail hole to a 90 degree elbow, and then the pigtail well above the waterline? To be very clear, my boiler doesn’t surge a lot. It does what I would consider to be normal bouncing of the waterline due to boiling, but nothing crazy. I just think the boiler pigtail hole is too low and I want to be sure it’s not filling with water and continuing my problem. 

Thanks as always, fellow steam heads!

ethicalpaul

I can't picture what you are proposing, but I doubt that water is splashing "through" the pigtail and hitting your pressuretrol.

Even if it did, I don't think it would hurt the performance of the pressuretrol.

If you want the pigtail higher, by all means make it be higher, or utilize a trap scenario as some installers do (maybe this is what you were trying to describe)

gerry gill

Perhaps you are condensing what you are making and you are not building up any pressure. 

Fred

Steam does not get to the Pressuretrol/vaporstat. That loop is always filled with water (condensate) to protect the Pressuretrol from steam temps.

Jamie Hall

The boiler shouldn't turn off on steam pressure until all the radiator vents (or main vents and traps, for a two pipe system) are closed. If the boiler is reasonably close to the correct size, this may take anywhere from half an hour to an hour.

While your connection to the vapourstat isn't ideal, it won't affect that.

merikus

Thanks for your thoughts, @Fred, @gerry gill, and @ethicalpaul. The issue is that I know I'm reaching an unsafe pressure in my system. I've had multiple radiator vent failures and have had the boiler keep firing well after every radiator was hot fully across and their vents are closed. I've confirmed if I physically detach the vaporstat/pressuretrol wires that the burner will cut off (confirming that the burner controller limit circuit is working properly).

I installed a 5 PSI gauge on the pigtail as well and the needle barely dances around even when it's obvious due to how my radiator vents are behaving that the system is overpressured. I've attached a few pictures of the current setup in case that will help.

Thanks!

EBEBRATT-Ed

Pressure is pressure doesn't matter if it is water or steam when it comes to a pressure control.

It is better to have it mounted in the steam space because it is less likely to get plugged up if you have a tapping available.

Jamie Hall

Can I ask why you have the vapourstat main setting cranked all the way up to the top? At that setting, the mechanism may be jammed and it can't shut off at any pressure -- it's locked on. Try setting it about half way down -- say at 8 ounces, with the other scale set at 4 ounces. If the mechanism hasn't been damaged by setting it all the way up, it just might work...

ethicalpaul

Sorry I said Pressuretrol but you indeed have a Vaporstat. No real difference in terms of what we're talking about here though...

I'm with Jamie, why is it all the way to the top???

Also, did you verify that the pigtail is not clogged with gunk? The fact that your pressure gauge doesn't register anything has me concerned. That would be normal for a 30psi one from the factory, but not normal for a 0-5psi one that you installed later.

If it were me, I'd remove them both from the boiler, and test them with my breath or with a low-pressure source like a squeeze bulb (not a tire pump) to see if they work off of the boiler. This will let you know for sure if they are working.

merikus

Thanks for all your comments here. I'll admit, I'm pretty confused now, but I'll try to answer some questions and hopefully get unconfused!

@Jamie Hall: It's to the top because I got the wrong scale. According to everything I've read it needs to be 1.5 psig cutout with a 1 psig differential. On this unit, it tops out at 1.1 psig, so that's where I've put it. As for the pressure issue, agreed on that--it shouldn't shut down until all vents are closed. But I'm reaching that point and it's continuing to push with no indicating on the 5 psig gauge that any pressure at all is making it to the vaporstat.

@ethicalpaul: I'm 100% in agreement with you. The pressure gauge should register something. And it does--but very little. When the boiler is on, it bounces around a little from about 0 to 0.1 psig. But it never gets above that, despite the fact that I know for a fact that I'm getting high pressure at my radiators due to the fact that the vents are failing and spraying steam everywhere. This leads me to think the pigtail is clogged, but I've done two tests to prove to myself it isn't: 1) I've poured boiling water into it at a high rate of flow and it's gone through with no problem and 2) I've put a wire down there and managed to get it fully through into the boiler with no resistance. Which is why I keep coming back to this "flooded pigtail" idea.

I feel like my next step here will be to try to take the pigtail off and install a new one. The only reason I haven't yet is because the DHW makes it impossible to take off. I'm going to have to cut it off, then unscrew the remaining part, and then install a new pigtail.

Thank you all!

KC_Jones

Just to be clear on pressure, because by this statement: "According to everything I've read it needs to be 1.5 psig" You may not be understanding how things should work.

First, pressure should be as close to zero always. You aren't trying to get up to a pressure, the 1.5 is to limit and keep things below that.

Second, the pressuretrol is a safety, there is differing opinions on here, but on a properly sized boiler, piped properly with proper venting, it should never activate unless some other actual control is running amuck. IMHO the vaporstat is in the same category, some don't agree. You most likely have an oversized boiler. It also isn't piped properly and by what I see is probably sending a ton of wet steam into the system.

As far as the pigtail, it's supposed to have water in it to isolate the steam from the pressure safeties, they aren't supposed to see the steam.

How have you determined that the vents are seeing too much pressure and it's not a failed vent? Vent's close on steam, if they don't they can be failed and not due to pressure, just a simple failure. It can also be that the vent can't close because of too much water being pushed into the system. They work on steam heat, water cools them and can prevent closing.

Are you getting steam or water? Remember steam is invisible for the most part, so if you are actually seeing "stuff" I'd suggest it could be a water issue.

Long Beach Ed

Easy way to test this all out. Reduce the setting to 6 Oz with a Diff of 3 Oz. See what happens as the boiler runs on a very cold day. If it cycles on a cold day, you know everything's working as it should. Then get into finding the optimal setting and straightening out your venting.

If the system never turns off on pressure, check that the siphon isn't plugged with rust and dirt.

ethicalpaul

There's no need to replace the pigtail if you are able to successfully pour water into it and into the boiler. It's not magic, it's just a pipe.

But the far easier and faster test is to just blow through it

JUGHNE

IIWM, I would cut the pigtail off so you could unscrew the remaining part.

Then, make sure the port is open to the inside of the boiler, add a nipple with tee, a plug in the end of the tee so you can check that the port is open later, Then on the branch of the tee add a pigtail that will go straight up, loop and then straight up again. (make sure the first nipple you add is long enough to rotate the p-tail and vaporstat) Then tee on top for your controls and gauge.

Many will add the original ptrol on the p-tail as back up. Wired in series with new control.

Does your 0-30 gauge ever move or always stuck there. You could unscrew it and check that port also.

merikus

Thanks for all the responses. Some thoughts:

@KC_Jones: I mistyped on that--I intended to say "the pressuretrol/vaporstat should be set a 1.5 psig with a 1 psig subtractive differential." I've determined the vents are getting too much pressure because the boiler is continuing to run after all vents are hot all the way across and I am not getting any more sounds of air escaping the radiator vents. Then, as the boiler continues to run for awhile after that has happened, a vent will make a very loud sound of air escaping it, like it's releasing all of the pressure at once. I am down 8 vents now, so I can't imagine that it's just bad luck. Also, I don't think it's a wet steam issue--I'm not getting any sort of wetness at my vents, and I've had several folks here take a look and tell me the near boiler piping looks better than most. I've attached near boiler piping photos to the end of this post if you'd like to take a look.

@Long Beach Ed: By the "siphon," do you mean the loop on the pigtail? I think it should be fine due to my boiling water test, but I do need to get that thing off and take a look.

@JUGHNE: Thanks--that is a good idea. I think I'll go in that direction. The 0-30 gauge does move. I frequently see it getting to approx. 5 psig during a longer burn after all the vents are shut down and the radiators are hot.

Jamie Hall

It does NOT need to be 1.5 psi. 4 to 6 ounces is all you ever need -- the 1.5 is the maximum pressure, not the operating pressure.

Before you start unscrewing stuff, take about 2 minutes and try what @Long Beach Ed and I have said. Turn that main scale down to 6 to 8 ounces and the sub scale on the left to 3 to 4 ounces and see if it works. I can absolutely guarantee you that it will never work the way you have it set now. The way you have it set the mechanism is jammed at the top, and can't trip at any pressure.

Much as you like the idea of it being the pigtail, it isn't. It's a mis-set vapourstat.

JUGHNE

Looks like you have a tankless heater for hot water.

That means the boiler is kept hot year around?

Is it possible that the aquastat running the boiler for this purpose is set wrong or malfunctioning?

It could be calling for the boiler to fire all the time, and driving the pressure up to that 5 PSI until the P-trol shut the burner down. It could then start again on the low cut in temp of the control and run up to pressure cut out.

Just an idea.

KC_Jones

If the boiler is firing for a while and the rads are fully hot the vent can and will release air again during that time as the end sections cools and heats.  That isn’t an uncommon phenomenon and could indeed seem loud even at relatively low pressure.

How loud it is depends on the vent.  The ones that came with my house would click and vent loudly, click vent, click vent, click vent.  It was annoying.  Downsizing the boiler to a proper size solved it all, that and changing to Gorton vents, which honestly just got rid of the clicking part.

What I’m getting at is venting during a cycle doesn’t necessarily mean you are over pressure, it may just mean the vent cooled slightly and it’s releasing more air like it’s supposed to.

merikus

@KC_Jones: Interesting. The reason I keep thinking I have a problem here is that (for example) yesterday morning was quite cold and my boiler ran for 1 hour and 45 minutes. All radiators were hot fully across by 45 minutes, and it continued to run for an additional hour because the thermostat was calling for heat. 

Am I wrong that once all radiators become hot fully across pressure should build and the vaporstat should break the circuit? Or am I mistaken about that? I got that impression from Dan’s books, but maybe I misread. It would seem logical to me that once all radiators are full no more heat can be given to the radiators and it should shut down. 

@Jamie Hall: Sounds good. I will try it as soon as I’m home (away for business for a few days). Fingers crossed that works out!

ethicalpaul

Am I wrong that once all radiators become hot fully across pressure should build and the vaporstat should break the circuit? Or am I mistaken about that? I got that impression from Dan’s books, but maybe I misread. It would seem logical to me that once all radiators are full no more heat can be given to the radiators and it should shut down.

You may be mistaken. The radiators don't fill like a bucket and just sit there full...they are constantly radiating heat which comes from the steam they are condensing. In a correctly-sized system it is very possible for the radiators to be condensing everything the boiler is creating--maybe with a small pressure increase--but still below the cut-out pressure.

merikus

@ethicalpaul: Thank you so much for that information. I guess I was misreading Dan’s book—my impression was that once they filled they needed to reach the drop off pressure to open and lose their vapor lock, and that wouldn’t be possible unless the boiler stopped running. That could explain things here!

ethicalpaul

I'd have to be referred to the specific section of the book to see for sure, but IMO "vapor lock" or "vacuum lock" or radiators having to get to a certain pressure or down from a certain pressure in order to release condensate is mythological (at least in residential steam)

Condensation doesn't care if there is a partial vacuum in the air it's sitting in...it will flow regardless.

merikus

@ethicalpaul: I’m out of town for business this week but when I’m home this weekend I’ll get the book and tag you on the page. It’s from the Lost Art Revisited and I can see it in my mind, it’s in the one pipe steam chapter and there’s a graph of pressure peaking, then falling off about 1/3rd down the page. Can’t remember the page number but I’ll get you that cite! Thanks!

Jamie Hall

Perhaps a bit of refresher here on vents for steam radiator systems and mains.

Almost all such vents (there are rare exceptions, such as the "Big Mouth" maim vent) close on either one of two conditions: there is enough liquid water present in the vent to raise a small float, or there is steam present. If either of those conditions are true, a properly functioning vent will close. Otherwise, with the exception of a very limited number of "vacuum vents" (unless I am mistaken, the only one currently on the market is the Hoffman #76 main vent) they will open, unless they have been seriously overpressured.

(to briefly look at the two exceptions: the Big Mouth has no float, and so will not close with water. The Hoffman #76 will close if the pressure in the main or radiator (it's never used on radiators) is less than atmospheric pressure).

Now let us look at a one pipe steam radiator. Starting from cold, with the system at atmospheric pressure, the boiler will create steam. This steam will move -- at very low pressure -- through the pipes to the radiator. It can move to the radiator because the vent is open, allowing the air to escape while the steam comes in. Once in the radiator, the steam will condense back to water. If more steam can come in than can be condensed by the radiator (the usual case in one pipe steam), eventually the steam will reach the vent -- at which point the vent will close. Note that in no way is this related to pressure -- only the presence or absence of steam. Now so long as the boiler continues to provide steam -- regardless of the pressure -- the vent will stay closed. The radiator will condense steam at a rate controlled entirely by the size of the radiator -- again, pressure has nothing to do with it. When the boiler stops firing, it can no longer provide steam to the radiator, and the vent no longer senses steam -- and will open. And again, this has nothing to do with pressure.

You mention "releasing" condensate. Condensate is continuously released, by gravity, though the inlet pipe. This will occur whether the vent is open or not. This assumes that the vent is operating properly. There are VERY rare conditions where the vent is damaged or stuck shut, always because of serious overpressure in combination with poor piping, in which a vacuum can form in the radiator; there are even rarer conditions where the combination of this vacuum and poor piping might cause condensate to be retained.

There is, then, no such thing as a vacuum lock or vapour lock in a one pipe steam radiator.

To recap: a radiator vent will be open, and allow air to escape and steam to enter, unless steam is present at the vent. Otherwise it will be closed. To further recap, pressure has no influence on this. The only way pressure affects a vent is if it is too high. This may prevent the vent from reopening, but this high pressure can only be maintained so long as the boiler is operating. If the pressure for some reason got much too high -- say 10 psi or so for most radiator vents -- however, the vent itself may be damaged, and not be able to operate properly (it may fail either to close or to reopen).

ratio

merikus said:

The 0-30 gauge does move. I frequently see it getting to approx. 5 psig during a longer burn after all the vents are shut down and the radiators are hot.

Sure looks like a smoking gun to me. I've seen many gauges read too low, & I've seen gauges out of cal & reading high, but it seems somewhat unlikely that the 30# gauge is reading ≈5 lbs high with the low pressure gauge reading ≈0.

Check the piggy tale by pouring water into it, or blowing into it. It looks like it's brass, so you should be able to clean it out if (because?) it's clogged.

ethicalpaul

Thanks for that summary, @Jamie Hall, I couldn't agree more!!