Operating pressure question

db_10

David,

Okay, I see what your saying, I went back via the search
function to dig up your prior posts/sketches, etc..

I,m going to dig out some reference material that
hopefully will explain the "static" 8oz.'s.

Every boiler "has this" including mine, I just don't
"see" it, if it were not, the condensate would never
be forced down the "A" dimension back up through the Hartford loop.

Most boilers with gravity return are "hydraulically
blind" to that (drop) differential between the main and
return, but it is there.

That said, the reason ( I believe ) you can see it on
your gauge is a result of how your system is fit up.

For lack of a better phrase "hydraulic shunt" or short
circuit, if you will, comes to mind.

If your other take off were fit up to the main on the left
and went round the loop to the return ( with vents there
instead of the middle ) you would only see those "other
few" ounces above the static half pound.

I'll dig up a sketch to illustrate the concept.

Later, db

Oh yeah, my other comment above was imparted to me by a
"Vapor Guy", I have also read it here, more than once, by
more than one person, I didn't make it up and quoted it
to the best of my recall. db

pessimist; half empty,
optomist; half full,
engineer; twice as big as it needs to be. ;)

David Nadle

Is this operation normal?

Today I installed a vaporstat and a sensitive compound pressure gauge. (I am dangerous on long weekends.) Pic attached. Cute little gauge.

After the installation, when I turned the power back on, the thermostat read 68 deg. and the setpoint was 70. I had the vaporstat set for 8 oz. out, 2 oz. in. As soon as the boiler started to steam the pressure shot up to 0.5 psi almost immediately and the vaporstat cut out. So I raised the cut out pressure to 12 oz.

The boiler operated at 0.52 +/- 0.04 psi for nearly an hour before making up the 2 degree setback. The peak pressure was 0.6 psi. When the boiler shut off the pressure was back to zero within 1 minute. I checked a few radiators, including the slowest one, and they were fully hot.

So, assuming it's not the gauge, what's going on? A leak? Maybe a vent not closing? I expected the boiler to cut out on pressure long before an hour elapsed. Any ideas?

Ken_51

How is the air

getting out?

Cute gauge,indeed! Where did you get it? Where is the sensor attached? How much was it?

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David Nadle

Wish I knew...

Gordo,

I wish I knew how the air was getting out. Any leak checking tips? Does soapy water work here? I hope it's not the 1/4" stuff I just added ;-)

The gauge is from Panasonic Electric Works, only $79 with lots of features. -14.5 to +14.5 range. The sensor is at the back of the gauge, with a male 1/8" NPT thread. The only catch is you need an external DC supply, anything between 12 and 24 volts. I used an old 12V wall transformer. There's a place called BAPI that sells small 24V converters for HVAC, this thing draws 35 mA at 24V so I bet you could easily run it off the transformer.

don_52

Air out as in...

David,

Air out, as in "venting", is what Gordo was referring to
I believe, i.e.; Main Vents, Radiator Vents etc.

Steam up, "Air out", Condesate back.

db

John Cockerill

long cycle


What is the insulation on the piping?

David Nadle

Answers

Insulation is 1". Near boiler and mains are insulated, takeoffs are not.

A single Dole #90 is venting approx. 73' of 2" mains. 8 rads vented with a mixture of Dole 1As and Gortons.

Since my original post I've seen some short cycling, so I upped the cut out to 16 oz and set the cut in to 8 oz. I think a Dole 1A on an upstairs bath is not closing. That will be the 4th one to fail on me.

don_52

Venting...

David,

Air "The Heat Thief", 73' of 2" main = 1.679'***, a Dole #5
with a capacity of .066 CFM would take 25.44 minutes just
to vent the main? (that's an "average" full cycle at 32^)

Put 2 Gorton #2's on a "vent tree" and you'll vent those mains in 46 seconds @ 1 oz.

Get a copy of Gill & Pajek's venting charts from the store,
10$, the proceeds go to charity, an excellent deal for all.

Get those mains vented good first, then mess with the rads.

Post some pics of your end of main(s) if you can.

Hope that helps, db

David Nadle

Headroom

I've got my Gill & Pajek. What I don't have is enough vertical space for a Gorton #2. According to the best information I could find (which ain't much) on the Dole #90 it's the equivalent of a Gorton #1. I have timed the venting and it's fast enough I suppose: 3 to 4 minutes. But as I learned today, this is at 8 oz. The vent seems to be operating well, closing when it should, etc.

I think the problem could be related to a rad vent, or more than one, not closing. Here's my hypothesis. On a normal 1/2 degree heating cycle the thermostat is satisfied before the vents become an issue. But if 2 degrees or more need to be made up, most rads shut, then get pushed on for 45 min. because one vent is stuck open preventing the pressure from rising to the cut out point.

David Nadle

Update

This is a bump/update because I am still confused. I gave the gauge one extra turn, but I don't think the joint was leaking before and I don't think it is now. I replaced the vent that was not closing with a Gorton #5. I let the thermostat sit at 69 for a few hours then bumped it to 70.

On this one degree makeup, I am pretty sure every vent closed. I wish I could figure out a way to be more than pretty sure. Yet the pressure never exceeded 0.58 psi and the system ran a long time, until the thermostat killed it. Then the pressure dropped to zero in under a minute.

Any guesses?

Steve Garson_2

Any steam going up the chimney?

Jon Held

I am having a similar issue with my steam system in my home. I have a 0-3 psi analog gauge and a plain old pressuretrol set to .5 cut in and a diff of 1 (the lowest possible settings).

From a cold start in the morning, she will fire for a while and I can watch the pressure slowly build in the system as vents begin to close. Eventually the pressure will get up to the 1.5 psi cut off but then drop back too quickly IMO. I think I have leaky air vent(s). My mains is fully insulated (as of this past weekend) and all rads get hot. The system just doesn't hold pressure. I have 2 new Gorton #2s on the way for the mains and I will be replacing the rads with appropriately sized Gortons within the next week or so.

David Nadle

Nope, but...

No steam up the chimney--thank heavens. The boiler is 2 months old by the way. I put the gauge in peak hold mode last night and this morning I got a peak reading of 0.90. Something happened overnight. Tried to recreate conditions today by getting the house down to 68 then setting the thermostat to 70; no dice. Peak pressure was 0.62.

Now I'm wondering if I'm just being impatient. If a vent or two is a bit late to close (but doesn't hiss or spit), then with present outdoor temps and a 1/2 degree swing the thermostat is getting satisfied first, then the open vent (plus maybe one or more vents dropping back too soon?) let's air rush back in and the pressure falls fast.

I'll keep watching...

mel rowe

Don't know how much of the pressure drop is due to steam condensing, but that is a significant factor to consider. By the way I've noticed the same thing on my system in the past. When the pressure got up to the cutoff, it dropped to the cut-in point in only about 25 seconds. Then the boiler would fire for about 45 sec. This usually lasted for only a few cycles before the stat was satisfied. Since installing a number of TRV's and balancing the system, it seldom gets above l0 oz. of pressure on the Vaporstat. FWIW

don_52

What's your...

David,

You mentioned that you have a Utica PEG(C), if
I may ask. What size boiler and what is the connected
load, radiation in EDR, just curious.

db

David Nadle

Boiler is

a PEG-112C. Connected load is 281 ft^2 EDR, which is pretty much an exact match.

don_52

Well..

David,

I'd say that's close enough, what I'm not getting
is why your "seeing" any pressure at all, esp. at the
fairly mild temps of late.

Got any pics of this rig?

Edit(1): Strike that, I found them.

Edit(2): Correction on the vent, I was looking at the wrong
one, The Dole #90 has a rate of .330CFM according to
Tunstall's, at what pressure, I don't know?

Okay fellow engineer, time to spin that propeller on the
beanie and get creative, got a pic of this problem main
vent area, I'd like to see it.

db

David Nadle

An earlier thread

has posted pics. Look here.

Wish I knew what you were looking for...

Matt_67

Yes, saw that....And

David,

Yes, saw that....And what hopefully is an optical
illusion.

Please tell me that takeoff next to the 45 "is not"
piped directly into the return, because it sure looks
like it.

If it is, it would explain a lot of what your seeing, your
feeding steam to the main on the left of the first photo,
that's fine. The other takeoff looks like its tied into
that 2x2x1-1/2 at the return, hence feeding steam in both
directions at the same time, against condensate, thus
closing your wee main way early leaving you nowhere to
vent "but" your rads.

Please say it ain't so, do you have another (close up)
pic of that.

db

David Nadle

No illusion

db, Both takeoffs are teed directly to the return. I beleive it's called a dry return. Steam does take off in both directions at the same time, against condensate. The mains then meet at the opposite corner, as piped when the house was built. I've read it's common in old coal fired systems. And there never was a wee main vent until I added it.

I'm still wondering why you're asking about all this and how it relates to my question.

db_10

The answer...

David,

If your original question was;

As soon as the boiler started to steam the pressure shot up to 0.5 psi almost immediately...

Is this normal..? In a word.. no.

A steam boiler properly sized, vented, balanced and fired to the connected load (EDR) should not (with rare exception) build pressure until it approaches, is at or passes design load, at which time the operating limit will cycle off-on
within it's differential setting to maintain pressure until the thermostat is satisfied.

db

David Nadle

OK, so?

We know the boiler properly sized. The main vent I have should clear the 73 feet of 2" mains in 3.1 minutes at 2 oz. Is that really so bad? The other radiators have vents chosen to fill the rads in around 3 minutes at 2 oz, except for the rad in the room with the tstat which has a #4, and the two upstairs BRs which have TRVs and slower vents.

The connected load, even with all vents open, has some non-zero backpressure. I don't have a problem believing it's 8 oz. What I don't get is why, long after all the vents should have closed, the pressure is still 8-9 oz and never exceeds 10 oz. That was my original question.

I do appreciate your interest.

don_52

Check your mail..

David,

Check your (hot)mail..

hope it helps, regards, db