Steam Controls

Chancellorred

My home heating system is a Burnham IN-7-I steam boiler with a MM-67 low water cutoff and a Honeywell Pressuretrol Controller PA404A-1009, installed in 1994.  The Pressuretrol is connected to the low water cutoff by a curled pipe.  Lately, the burner will go through four or five stop-start cycles while in the middle of a heat run (not a full shut down but the burner cuts off and immediately relights).  The water in the site glass is above the low water cutoff level and the MM-67 is reguarly drained. 

My contractor stopped by and removed the Pressuretrol from the curled pipe, rotated the curled pipe to drain water from that pipe and reinstalled the Pressuretrol.  The burner then completed a full heat run without cutting off.

The stop-start cycling came back within several weeks.  I repeated the fix performed by the contractor, and the curled pipe was full of water.

My question is: should the curled pipe have trapped air pressing on the Pressuretrol switch or should it be filled with water.  If the pipe should have a column of air is the Pressuretrol switch failing or is it more likely that the seal between the Pressuretrol and the curled pipe is water tight but not air tight. 

Thank you for any information.

BobC

Sounds normal

The pigtail should fill the bottom of the loop with water, that water protects the pressuretrol from the steam in the boiler. Only the bottom of the loop should be filled with water, if you remove just the pressuretrol you will see the top of the pigtail is empty.



The boiler may be shutting off because the pressure is reaching the pressuretrols cut out, when the boiler pressure gets below the pressuretrols cut in the boiler will restart. This will repeat until the thermostat is satisfied.



This may indicate that the boiler is larger than the load it is supplying so it is creating more steam than the radiators can condense.



Bob

nicholas bonham-carter

stop-start

this may be a main [not radiator] venting problem. one of the advantages of having a good low-pressure gauge is in being able to see how effective your main venting is. if it is adequate the back-pressure will be about 1 ounce [at the start of steaming]. when all the main vents have allowed the air to escape without the cost of extra fuel being used to force it out, and the mains are full of steam, then the radiator vents will allow the riser air to escape at a back-pressure of about 2 ounces.

if the main vents are not capacious, then you are waiting for the air to be paid to get out, and that is always slower.

the other cause of short-cycling as bobc says is boiler over capacity, but that is separate from the venting problem.--nbc

Abracadabra

damaged pressuretrol?

If the contractor drained the pigtail of water, the pressuretrol was now no longer protected from steam. What is the pressuretrol cut-in and cut-out set to? What does the gauge say at cut-out and cut-in?