Relief Valve Popped Last Night

[velvetfoot]

The 30 psi relief valve popped last night when we were out. Not much water-probably just at the end of the cycle (oil boiler mode, 120 gallon buffer tank.)

I turned down the boiler 10 degrees and cooling things down by running circs with boiler off.

Expansion tank should be at 22 psi and autofill at 12 psi, or something.

I should check things when they are cold, ie 70*F, right? Or should I check it, and adjust it, at a higher temp? I could, say, reduce the pressure in the system to 12 psi at 100*F. Thinking out loud, if the system did cool off totally, the autofill would fill it back to 12 psi.

I'm thinking the 22 psi will provide some extra cushion, since the bladder won't start compressing until system pressure exceeds 22.

There's a possibility a little more expansion could be needed-maybe I'll screw a little tank to the bottom of the Spirovent at some point in future.

Suggestions/Ideas?

 

[Fred61]

I got my pressures where I thought they should be and then turned off my autofill. Check it daily. I've turned it on for a minute only once in the last two years. Keeps it from adding water when pressures are at their lowest.

 

[velvetfoot]

Tank is 109/95 (top/bot), and pressure is 23psi. Circs running constant-not much heat transfer across baseboards, apparently.

 

[maple1]

I also have my autofill valved off.

Your air pressure in your bladder tank should only be a pound or two more than the COLD pressure of your system, for a starting point. Your autofill may have malfunctioned (dirt?) and let in water when it shouldn't have - but if your system is cold now, I would bleed off water until system pressure got to 12 or so, then check the air pressure in your expansion tank. It shouldn't be more than 14 or so. If it is, let some air out too. There could also maybe be a possibility that the bladder let go in your expansion tank.

 

[velvetfoot]

Your air pressure in your bladder tank should only be a pound or two more than the COLD pressure of your system, for a starting point.

Wouldn't this give you LESS of a cushion, so to speak? At a low cold starting pressure, the bladder will be compressed to the max earlier.

but if your system is cold now

Define "Cold"? Top is 102, bot is 97, press is 23

I would bleed off water until system pressure got to 12 or so, then check the air pressure in your expansion tank. It shouldn't be more than 14 or so. If it is, let some air out too.

Again, wouldn't running the expansion tank at a higher pressure provide some more leeway?

 

[maple1]

I would define 'cold' as the coldest your system gets during the heating season. It could also be defined as the coldest it gets all year - which might be OK to go by too if you have lots of expansion room. The difference is that if you keep your fresh feed on all year, and the pressure drops when it falls from the first 'cold' to the second 'cold', it will let more water in to maintain 12psi - then when you fire back up again in the fall, system pressure may or may not get too high when up to temp. Again, based on expansion room.

Running more than 2psi air above minimum system pressure, will only reduce your expansion room. Should be lots to find on that aspect with some google-fu. 23psi of air on a cold system will cause earlier blow off, because there is no expansion room available at all until your system pressure gets above 23psi. My blow off valve blows off at 22psi.

 

[velvetfoot]

22 psi seems early-mine is 30.

I'm thinking the bladder will bottom out at the lower temp.

I'll definitely try it at 2 psi above the autofill.

I might as well do this now.

Back to the basement I go.

 

[maple1]

You want your bladder bottomed out at the low temp.

(If by bottomed out, you mean completely full of air, that is - - if you mean the opposite, it won't 'shrink' or 'collapse' at all as long as the air pressure is more than the water pressure, hence the 2psi difference at 'start up').

Once you get your cold starting point & pressures established, I would valve off the fresh feed, and observe until you get your system up to temp & pressure. Then open up your fresh feed & see if your pressures change - you still might have some unwanted flow through there from a malfunction. Actually, a malfunction should show up when you are bleeding off pressure on the start up stuff - it would keep letting water in & bring pressure back up before you even start heating. Mine will make a little noise when it is letting water in, if I get my ear right up against it - I can hear that, before I see my pressures rising on a guage.

 

[velvetfoot]

(reading about Watts autofill valve - I put a new one in about a year ago)

if you mean the opposite,

Yes I do. Thinking about it, if the ultimate system pressure is going to overwhelm the expansion tank, it's a 'wash', so to speak, where on the pressure curve this occurs-whether the bladder is full compressed at 14 psi, or 22 psi, if there isn't enough capacity due to a too-high start point, or lack of exp. tank capacity.

Autofill is currently set at 14 psi (can hear noise). I'll reduce it to 12 psi - that should be good for a two story building, right?
Then, I'll set the tank to 14 psi.

 

[velvetfoot]

Per Watts:
A.
Calculate the number of feet from the regulator to the top of highest radiation.
B.
Multiply this number by 0.43 and add 3 lbs. This will give the pressure required to raise the water to the highest radiator
and keep the system under pressure.

12 should do it for me. I think I get around 10 or so.

 

[velvetfoot]

Went down after a little while and pressure had drifted up to 19 because of the autofill.

Drain some more, autofill seems to stop at 12. Will go back down after awhile and see if it drifts back up.

I will indeed probably valve it off.

 

[maple1]

Might be some dirt in the autofill valve. Sometimes if you flip the quick fill lever up for a few seconds, it will purge the dirt out of the way. (Could also let more dirt in & make it worse too). It doesn't take much of a piece of dirt to hold it open & let water by slowly. If that doesn't work, you could isolate it & take it apart to clean. But - it might have just needed an adjustment. I kind of came to my own conclusion that the spring in those things weakens over time & need adjusting, but I might have been out to lunch on that one.

 

[NateB]

Is there any possibility that the DHW coil may have a small leak?

 

[velvetfoot]

Is there any possibility that the DHW coil may have a small leak?

I don't think so. I have a reverse indirect tank that has a 1.5" corrugated s.s. coil in it that's only a couple years old.

 

[velvetfoot]

I just started things. Exp. tank is at 14 psi. I used an air pressure gauge and checked it against the boiler gauge by opening the fast fill. Then I drew down the pressure and adjusted the autofill, which I no longer trust, to 12 psi, and then valved it off. The boiler was at 75F when I started, so that's low. We'll see how it goes.

 

[lotawood]

My blow off valve blows off at 22psi.

I got a 30 psi PRV that blows off a little higher than that. It certainly won't wait until 30.

I don't have any connection to domestic water for filling. Some systems count on having cold house water cooling an overheat situation by blowing hot water out the PRV and replacing it with cold.

Do you have a requirement to have the autofill always on? Or is it a good idea in your situation?

I set my pressure by guessing 11 psi at the expansion tank and getting the system as hot as it will ever be and keep it below "maple 1's" 22 psi. It is easier to add more water or even air if you think it is too low.

Also, I haven't needed to add water in the 5 or so years the system has been running, unless I re-piped something.

 

[velvetfoot]

I wonder if the auto fill might be better for steam systems. Do they have a tendency to lose water?

I'm writing this from the friendly confines, well confines anyway, of the basement. Will report on final numbers when it turns off.

There is a low water cutoff switch, which is required. If there was a loss of water incident, I wonder if letting the low water switch turn things off would be better than pumping in endless amount of water with the boiler continuing to run with water all over the basement?

 

[velvetfoot]

I set my pressure by guessing 11 psi at the expansion tank and getting the system as hot as it will ever be and keep it below "maple 1's" 22 psi. It is easier to add more water or even air if you think it is too low.

I guess that's an approach too. Let's see how the numbers turn out on this run.

 

[velvetfoot]

I wound up at 20 psi, filling the buffer tank to 188/top and 179/bot, which is good for me.
I think I'll keep it where it's at now, and keep the autofill isolated.
Thanks for your input guys.

 

[Bob Rohr]

Another option is a higher pressure relief valve ONLY if the boiler is rated for it. What is the boiler listing say?

The correct pre-charge is the fill pressure at room temperature. 12 psi fill pressure= 12 psi pre-charge. Any pressure above fill pressure in the tank will use up some of the expansion space.

I suggest highest elevation above the tank X .433, then add 5 psi. So a 12 psi fill is 15' elevation above the tank connection.

 

[velvetfoot]

Another option is a higher pressure relief valve ONLY if the boiler is rated for it. What is the boiler listing say?

The correct pre-charge is the fill pressure at room temperature. 12 psi fill pressure= 12 psi pre-charge. Any pressure above fill pressure in the tank will use up some of the expansion space.

I suggest highest elevation above the tank X .433, then add 5 psi. So a 12 psi fill is 15' elevation above the tank connection.

See above post. It peaked at 20 psi so I'll probably keep it where it's at.
However, I can see your point about gaining a couple of psi cushion by matching initial fill psi and expansion tank psi.

 

[velvetfoot]

Probably interesting to no one but me, but this morning boiler pressure was way down to 3 psi or something. What happens is that when the autofill is valved off, the boilers get isolated from the buffer tank AND the expansion tank by the protection valve when the boilers aren't running. The pressure is still up in the still-warm tank, while down in the cooled boilers.

I should say that the autofill valve can feed both sides of the boiler protection valve. I did that at the time to facilitate filling the system. I found since that leaving both valves open causes unwanted ghost flow so I had left only one valve open.

I wonder if the autofill valve being open to the boiler side of the protection valve might have added a little volume each cycle?

I'm sure this is much ado about nothing, but I'm letting it cool down again, and repeat the process, maybe take a couple psi out of the expansion tank as well.

Last time things were in the 80F range, as I recall. Not sure if it's worthwhile to let it cool down more. Again how cool? Room temperature in basement is 57, hah.

The point is moot probably, since I'll be turning off the autofill.

 

[maple1]

I'm not picturing how that is managing to happen. Thinking both sides of the boilers would need to be isolated - whereas the protection valve, if it can indeed isolate, is only one side isolated? Also not sure how valving off the fresh feed would isolate different parts of the system - although might depend how it's isolated & where the valves are for that. Mine is on the inlet to the fresh feed valve stuff.

 

[velvetfoot]

Mine originally was and still is on the return. So, there's no path back to the boiler unless the protection valve is bypassed (with a sectionor the protection valve is open (>130 or something). The path back via supply is blocked by check valve.

What's isolating things is the cold protection valve. I can bypass the protection valve by opening both paths for the autofill-the one before the protection valve and the one after the protection valve.

 

[velvetfoot]

Now, with the connected system originally, at a just slightly warm 12 psi, when the boiler cools down after a run, the boiler pressure reads around 3 psi. When things warm up the protection valve opens and pressure equalizes to to what the tank is, about 12, and rises to about 17 when the system shuts down.

The water is only recirculating at low pressure and not going to other floors.