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Old Bryant Gas furnace question
QUESTION:I'm a landlord who has often had to service furnaces and boilers in
the middle of the night. Generally, I've been quite successful, as I
was again last night.
However, one thing bothers me about an old Bryant furnace.
I've got 4 Bryant Series PB-C Model 100-393U gas furnaces installed
in apartments. They date from around 1965 but show no sign of heat
exchanger failures, so I keep them running. These exchangers seem to
be made of welded steel 3/8" plate.
They have a pilot flame NOT controlled by a safety shutdown.
The pilot is fed by a tube teed to the main gas line. Also, the main
gas control valve is an oil filled unit, with its pilot safety being a
bimetalic relay, not a thermocouple.
When I examined the malfunctioning furnace, the pilot flame was around
3 inches high, bright yellow and not hitting the bimetallic relay,
thus the shutdown. It turned out that the air holes in the base of the
pilot tube assembly were clogged. A simple fix.
However, while reinstalling the assembly, I broke the tip off of a
narrow aluminum tube that ran back to the gas control valve.
It apparently had been previously pinched and straightening it caused
it to snap.
While cycling the furnace on and off, I noticed that this tube
actually has gas jetting out of it, when the value is on, which is
ignited by the main flame. After 2 minutes or so, the gas stops coming
out of this tube. It seems to act almost like an oil refinery retort,
burning excess gas from the valve. Does this tube somehow vent gas
backpressure in the valve? It seems to have no other purpose.
It certainly doesn't effect or aid pilot ignition or effect the main
burners.
I reinstalled it, took the stainless steel end cap off the broken tube
stub and force fitted it back onto the tube, realigned the tube near
one of the main burners and watched as the tube gas flow properly
ignited.
Should I try to get a new or make up a new tube?
If I were certain of its function I'd be more at ease.
ANSWER: You've used several words/phrases of concern. They are:
Old, Landlord, 1965, keep em running, oil filled unit, simple fix,
broke the tip, previously pinched, caused it to snap, gas jetting out,
seems to have no purpose, etc., etc.
Its quite apparent you shouldnt be messing with what your messing
with. You outta stop before you get someone hurt. The line you broke
is the vent for the gas valve. It relieves pressure from the backside
of the gas valve during the slow opening process of the oil filled gas
valve. If you pinch it shut, the valve wont open. If the line breaks,
or isnt vented properly, it spews raw gas.
You could try junking the old gas valve and installing a new
combination gas valve but you'll need to install a new pilot that VERY
closely resembles the pilot flame pattern of the old one. You'll need
to remove the regulator too. Its called "rigging" but something tells
me you're good at that.
Better yet, why not call in a professional and get all 4 units
replaced with something efficient? You might even get a good deal on
replacing them all at the same time. "I can see the sharks circling
already".
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