low pressure gauge

ToddB

After having my boiler serviced two weeks ago and finding that the pigtail was partially clogged I decided to add a low pressure (0 to 3 psi) gauge as discussed on this site to keep track of what my pressuretrol is seeing.  The boiler is a Lennox/Dunkirk with the pigtail attached to the glass gauge upper fitting.

For some background - my system does not cycle on pressure.  I have the pressuretrol set at 0.5 psi cut in and 1.5 psi cut out.  The boiler typically runs for an uninterrupted 18 to 22 minutes regardless of the outdoor temperature to satisfy the thermostat.  On warmer days the frequency of cycling is about 1.5 hours, on colder days about 50 to 55 minutes.  On average the boiler runs for 18 minutes every hour on a day in the mid 30s to mid 40s.

My question.  I found that the gauge only reads 0.05 psi after the boiler runs for 18 minutes.  One cycle after turning off the thermostat and letting the temperature drop 2 degrees resulted in a 30 minute run time and a 0.15 psi gauge reading.  Do these readings make any sense?  Are they unreasonably low?  I also found that the gauge reads below 0 after the boiler shuts down, but zeros out as air re-enters and condensate returns to the boiler.  Is this vacuum harmful to the gauge?  I was thinking about adjusting the gauge 0 point to compensate for the vacuum that I am seeing.

Thank you. 

BobC

Low pressure is usually good

It sounds like your boiler is very well sized for your steam radiators. Is the water in the gauge glass perfectly still? that could indicate your pigtail is clogged, it's normal for the water in the glass to rise and fall a little as the boiler steams, if it is perfectly still I would be concerned about a clog.

As long as the heat is satisfactory and your satified the pigtail is clear, that low pressure is good and it's saving you money on fuel.



The vacuum you see after the boiler starts to cool down is probably quite normal and i would not worry about it. It's caused by collapsing steam forming a vacuum before the vents open to admit air into the system.



Bob

ToddB

pigtail is clear

I know that the pigtail is clear based upon the boiler servicing.  The water level does rise and fall a bit while steaming (+1/4"/-1/4") and the gauge needle vibrates a bit and follows this movement.

ChrisJ

pigtail

I also run very low pressure 99% of the time in the area of 0.05psi or less.



I am curious though,  I have seen others also mention a clogged pigtail causing the water in the gauge glass not to move.  Why or how would a pigtail being clogged have any affect on the water in the gauge glass?

BobC

Error, error

I meant to say a clogged gauge glass port would isolate the water column from the glass and from any gauge or pressure device taken off the gauge glass fitting.



sorry bout that,



Bob

ToddB

vacuum

I am concerned that the vacuum will damage the low pressure gauge.  I was thinking that I could either do one of two things:

1.  Set the gauge zero to be at some point greater than the vacuum that I am seeing.

2.  I have a ball valve on the gauge now, not knowing what kind of pressure that it would be subjected to.  Could I add some time of inline vacuum breaker?

Hap_Hazzard

Sounds familiar.

After I'd been in my house a few years, I realized that someone had cranked the burners up too high on my boiler. The pressure was about 5 psi, some of the vents leaked, and at times the pipes were noisy. So I turned down the burners and started insulating the pipes so I could get more steam to the radiators without burning as much gas. The pressure was much lower, but some radiators didn't heat as well as others, some rooms were cold when it was really cold outside, and I started wondering if I'd turned the gas down too far. Then I found this place and started reading what these guys were saying about main venting and balancing radiator venting, and gradually I started understanding the principles involved and playing around with my venting. Now the pressure is really low, all the radiators heat up evenly, and I can hardly tell the boiler is on even when I'm downstairs. It's like the whole house is just magically warm and cozy.



Having grown up in a house with forced hot air, where the blowers rattled and the downstairs vents made loud slapping noises when the plenum filled up with water every time it rained, and the air that came out was never really warm, I have to laugh when people tell me forced air heating is quieter or "more efficient."