I have a Cummins/Onan 12kw natural gas generator (model RS12000) at my
house. The utility told me they provide 6-8 inches WC pressure (1 psi =
about 28 inches WC). The genset spec says 7-15 inches WC pressure. The unit
seems to run fine in the summer, but is very hard to start, or impossible to
start, in the winter. Just the other day it was 15F here in southern CT and
while the unit cranked fine, it just refused to come up to speed.
After speaking with several people, I was informed of a carb adjustment,
which I played with. I was able to get the unit to start immediately, but
the carb stayed at wide open throttle, just to maintain 3600 rpm, at one
"lean" setting, but by setting it a bit richer once it started, the throttle
was barely open to maintain 3600 rpm, but it would not start. I eventually
came up with a middle-of-the-road setting but I'm not happy with it yet.
I measured the fuel pressure feeding the carb, and it's 6.5 inches WC, the
same as what comes in from the street. I played with the fuel pressure
regulator adjustment somewhat and was unable to change the outlet pressure.
I was also told that the engine only needs 5 inches WC pressure to operate,
so I may have a regulator problem that's affecting the cold weather starting
ability. It seems that NG engines can be flooded with excess pressure the
same way as gasoline engines with too much liquid fuel.
The gas company around here seems to consider 6-8 inches WC a standard
residential pressure, so I wonder how Generac and Onan manage to get their
residential units to operate successfully on such low pressures, when their
own installation requirements are for higher pressures which just aren't
available at residences? In some areas there is something known as a 2psi
gas line system, where higher pressure gas comes into your house and through
the meter, then is regulated to 11 inches WC for generators and 6 inches WC
for other household appliances. But that service is not available on my
street, as they feed the entire neighborhood with 8 inches nominal and you
are stuck with whatever you get.
I was almost ready to convert to vapor propane, which my genset can run on
after a slight conversion effort, due to all the problems I've had with it,
but maybe if I can prove that the pressure regulator is malfunctioning, I
can replace that and get the unit to start and run during the colder months.
Unfortunately this weekend's blizzard has temporarily halted all genset
experimentation.
Bob M.
======