Negative boiler pressure?

bdugan

I'm going to try to keep this short, if possible.

First: what I see now: My two pipe steam system is heating the house fine, not hammering or hissing or making any real trouble. When it turns on, if I feel the headers start to get hot, then the main vent starts venting, the radiators get hot, the traps close (I assume) and the main vent stops venting, and usually a little while later the thermostat shuts off the furnace. I think that is all normal and seems like it must mean there is pressure driving the steam around the system.
But what is making me a little crazy is that the pressure gauge I recently installed is never showing a pressure. I put it on a tee next to a new pressuretrol above a pigtail. The pigtail is not clogged.

I can tell there is pressure in the boiler by fiddling with the pressure safety valve -- it releases some steam if I lift it slightly.

I removed the gauge to check it and it shows pressure if I blow into it, and it doesn't take much, so I think it is a functioning gauge. I realize this basically does not add up.

As the boiler cools off there is some suction in it. I can see how that might happen if the traps stay closed and the rest of the system cools. But is that right? I can see this (again) by lifting the safety valve lever slightly: now it pulls air in instead of blowing steam out. (That's why I made the title here negative pressure.)

I have been thinking there was a leak somewhere that keeps the pressure very low. But the vacuum in the boil lasts a long time -- maybe an hour -- so that seems to say there is not a leak.

Now a brief background: I have 11 radiators that have never had new traps since I have lived here starting in 1988. This fall when I started the furnace there was banging and water audibly moving around the system so I decided to replace all the traps and while at it, pack all the valves (some were hissing). I have replaced 9 traps. One I could not get open so far, and I have one more I have not yet tried. But those two I have turned off the valves on. So the system should be running with all new traps. After doing that basic maintenance I decided to replace the pressure switch with a pressuretrol. And since the old original gauge on the boiler is dead, I added a gauge too. Like I said, the system is working well but I am confused about the pressure readings.

Also, for what it is worth: I would love to have a pro in the Philadelphia area come and look. I just have not been able to find anyone.

Thanks in advance for any help. Sorry I could not keep it shorter!

Ben

ethicalpaul

Consider yourself fortunate. You don't want pressure (why does it drive you crazy that you don't see pressure?).

And the vacuum is normal, even desirable. I wish my 1 pipe system could hold a vacuum.

ethicalpaul

PS: If you want to see the pressure, get yourself a Dwyer Magnahelic gauge, something with a range of like -10 to +10 inches of water.

What is the scale of your current gauge?

bdugan

Thanks very much @ethicalpaul. My current gauge is 0 to 5 psi. I don't know what the pressure should be but I thought maybe an ounce or two. It doesn't really leave the zero pin. But I am glad to know the vacuum is normal. I'll try to get a gauge like you suggest! The old gauge read - and + pressure so I should have taken that as a cue.

Here is the old gauge (its on a Weil Maclean 57!). I can't read psi or inches on this gauge -- do you suppose it is inches of water?



Should I try to take that old gauge off? I am guessing it is stuck to the tank with tons of rust.

bdugan

Also, in case it helps, here is how the vaporstat and new pressure gauge are connected:

PMJ

@bdugan, you are well on your way to a great system. Since you show no pressure you are in great shape - you don't need any pressure ever. Vacuum is absolutely desirable and the more the better. Your conclusion that if it will hold vacuum it does not have any leaks is quite accurate - take comfort in that.

Your one vent must then be a vacuum vent. Is it on the dry return? Don't let anyone talk you into removing it and letting all that air back in.

The vacuum will continue to deliver steam from the mains after the burner goes off. It will also keep all the piping warmer between firings shortening the time to steam on all new firings. It will also do a lot of balancing when the boiler is off due to the fact that the colder areas will create slightly more vacuum that the warmer areas steering more steam to them.

Vacuum is great stuff. I have a two pipe system I have run in vacuum for many years. Contact me with any questions.

Jamie Hall

To follow up one o @PMJ 's comments -- i you have just that one vent location, the Hoffmann #76 is an excellent choice. It's one of the very few with decent capacity -- if you ever needed it -- and will hold a vacuum.

SteamCoffee

Wow, I kinda prefer the old one!
1)Download a copy of the Dunham book, circa 1937, great discussion on vacuum vs pressure. The vapor/vacuum was simple and effective. 2) the tread around this time ultimately was toward sub atmospheric, the Great Depression killed R&D, post WW2 the need was speed, steam was too labor intensive to install. 3) the #76 is a tank, will last forever...4) there are some great threads about this topic, a quick search will give you hours of reading enjoyment about this topic.

bdugan said:

Thanks very much @ethicalpaul. My current gauge is 0 to 5 psi. I don't know what the pressure should be but I thought maybe an ounce or two. It doesn't really leave the zero pin. But I am glad to know the vacuum is normal. I'll try to get a gauge like you suggest! The old gauge read - and + pressure so I should have taken that as a cue.

Here is the old gauge (its on a Weil Maclean 57!). I can't read psi or inches on this gauge -- do you suppose it is inches of water?



Should I try to take that old gauge off? I am guessing it is stuck to the tank with tons of rust.

EBEBRATT-Ed

@bdugan

Sounds to me like your system is running like it should.

There is no need to build steam pressure in a residential boiler.

If you want you can install a tee next to your pressure gauge and put a 0-3 lb or 0-5lb gauge on there. Leave the 0-30 gauge and leave your old gauge on the boiler it's not hurting anything

EricBaisch

I agree with @ethicalpaul and his suggestion of the Dwyer gauge.  They are pricy but come up for sale used on EBay quite often.  I have a 0-6” H2O Capsuhelic and it’s been working well for 4 years now although it does not have the brass housing.  My system runs where I have the mark between 2 and 3 inches which is .1 PSI.  It’s a 2 pipe Webster system.  This would not register on a 5 PSI gauge.

bdugan

I took my vent off to photograph it -- it's a Hoffman 76:

PMJ

That old and still working. Nothing on the market today can touch these old systems on an all in annual cost basis.

100 year old technology outperforming today's in total bang for the buck. In a word - ridiculous.

WMno57

@bdugan Welcome to the Old Number 57 Club! It's a very exclusive club, you and I may be the only members. Does anyone have any details on our boilers? How old, wet base, wet leg, wet back?

bdugan

Wow @WMno57, your is in beautiful shape! So clean! The silver & red nameplate is very readable: mine is completely corroded. Mine has an extra "box" over the end you are showing here. It looks like yours runs on gas (mine runs on oil). Did you convert it? I never thought of doing that but maybe I should. I will send a few more photos when I get a chance -- they'll make you glad you have yours!

WMno57

My boiler was converted from oil to gas about 50 years ago. I might replace my gas burner this summer with a new gas burner.

Although we both have hydronic heat, mine is hot water and yours is steam. These old boilers are not as efficient as new boilers, but they probably last longer than anything that can be bought today.

WMno57

I did not do the conversion 50 years ago. 50 years ago one of my teachers told my parents "He is obsessed with taking everything apart. He does manage to get everything back together, and it usually works."

I've been a DIYer longer than most of today's techs have been alive.

bdugan

I've been searching online for information about the Weil Mclain No. 57. Not finding much so far. Did find this, which I'm sending as a screenshot because it shows where to find it and what the name of the source is:


Would it be better to start a new thread about this furnace? I am new to the group and want to do what is considered right here.

WMno57

bdugan said:

Would it be better to start a new thread

Excellent idea. I have gone ahead and done that here.

https://forum.heatinghelp.com/discussion/182299/weil-mclain-no-57-series-boilers#latest

WMno57

You may want to check out this thread:
https://forum.heatinghelp.com/discussion/169027/steam-boiler-replacement-in-order-to-save-system/p1

@johnnygreenham had an old Weil McLain boiler supplying a steam system. He replaced the WM with a new Burnham boiler. Lots of good pictures, old and new. The steam trim on his old WM boiler looks just like the trim on your boiler.

bdugan

Thanks @WMno57 for pointing me at that thread about @johnnygreenham 's boiler replacement. There is a lot of good information there! But I don't see the new system. The thread seems to stop before that. I will search for it. I have had an experience like what his where a few contractors have come and looked at my system and gotten spooked by it being steam.

Dan_NJ

Try page three on that thread, here's a direct link:

https://forum.heatinghelp.com/discussion/169027/steam-boiler-replacement-in-order-to-save-system/p3

WMno57

Page 3 near the bottom of the page. Photos may take a while to load depending on your bandwidth. I have DSL so sometimes I have to click "reload current page" a couple times to get the photos.