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Re: Generac natural gas generator - gas pressure/hard start kit question

S

SQLit

Jan 1, 1970
0
Bruce Demske said:
Hello,
I have a generac 12kw natural gas generator (model #4456) and the
manufacturer specifies 11-14 psi and at my location I can get only 6-8
psi without installing a pressure booster (according to my local
utility anyhow). I was talking to a guy that used to install these
units (he is not local so I can't just have him do it) and he told me
that they would install these on a fairly regular basis in 'standard'
pressure locations and that they worked just fine with the addition of
a 'hard start' kit. So.... I have 2 questions:
1. Has anybody ever done this or is my guy smoking crack?
2. What kind of hard start kit do I need for this generator and where
would be a good place to look for it?
Thanks,
Bruce

I contacted my gas utility here in AZ and they said that I had a 1/4 to 1/2
of a pound of pressure on my side of the meter. My take on that, was the
genset will starve for fuel and I would be screwed.
I suggest you check again with the utility.
 
B

Bob M.

Jan 1, 1970
0
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.
======
 
W

William P.N. Smith

Jan 1, 1970
0
Bob M. said:
while the unit cranked fine, it just refused to come up to speed.

Are you using, or have you considered a lighter (maybe synthetic) oil?
I'm using 5W30 Mobil-1 in my Superior Power Sentinel 9 (B&S Vanguard
18, 8.2KW on NG), and it spins up just fine with normal residential NG
pressure, though I can't say for sure exactly what that is in Eastern
MA...
 
B

Bob M.

Jan 1, 1970
0
Yes, I'm already using AMSOil 20W40, specifically made for natural gas
engines. It doesn't seem to be a cranking problem, as the engine actually
"almost" runs at a speed that's just a bit faster than the starter motor
would run it. But turning off the fuel, or covering the air input on the
carb, slows the engine right back down to cranking speed. A slight
adjustment to the carb and it comes right up to speed.

Bob M.
======
 
D

daestrom

Jan 1, 1970
0
Bob M. said:
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?

I'm curious about this. I thought the pressure in the home was set by a
pressure reducer right at the meter (large, disk-like device in the line),
not by the distribution line. The 'street' pressure almost *has* to be
higher than the few inches WC used inside the home, otherwise how could a
single pipeline supply hundreds of homes in a neighborhood?

Now, if the pressure reducer *is* at the meter, maybe you could have yours
adjusted to supply a slightly higher pressure. These things look like just
a large diagraph/spring type of reducing valve, A screw adjustment on the
spring tension would seem simple to adjust. Utility *might* even be willing
to do it within a certain 'range'. Of course, what affect this has on other
gas-appliances needs to be considered. The few I have specify a range of
gas pressure like 6-12 WC, so there might be some room to maneuver.

daestrom
 
D

Dale Farmer

Jan 1, 1970
0
Bruce said:
Thanks for all the replies thus far. I talked to the utility again
this morning and, as everybody said, the pressure was in inches of
water and he said that all they could deliver was 7. He advised me
that I should get a pressure booster. I asked him if they (Cinergy -
my utility) could supply such a thing or if he knew who could and he
said that he had no idea. I looked around the web and all the
pressure boosters that I could find were for much higher boost than I
needed and they look to cost nearly as much as the generator. So...
do you guys know of a comparable (10-15kW) generator that will run on
7 inches of water? If not I think I will try this one and see what
happens (and post a follow up). It does seem to me that generac
should feature a warning somewhere in their literature or something.
Hopefully (if indeed the generator doesn't work on this pressure)
others can learn from my mistake.
Thanks again,
Bruce

One thing you may try is to increase the size of the gas feed line to the
generator. You may be getting 7 inches of pressure at the meter, but
when the generator is running, you may only have four or five inches of
pressure at the generator from flow losses. I don't really know how
much this is an issue with natural gas, I know it is a significant issue with
liquid flow.

--Dale
 
W

William P.N. Smith

Jan 1, 1970
0
do you guys know of a comparable (10-15kW) generator that will run on
7 inches of water?

Call Superior Power at 508-226-3410 and ask about their Sentinel 9,
I've got one, with a 1" feed from my meter, and it works just fine.
It's only 8.2KW, but it's so quiet I can't hear it inside the house!
I don't have a good spec on pressure requirements, (I wrote in "4.5-9"
and "4-6" under NG requirements, but I'm not sure why...), but they'll
know for sure.
 
D

daestrom

Jan 1, 1970
0
Dale Farmer said:
One thing you may try is to increase the size of the gas feed line to the
generator. You may be getting 7 inches of pressure at the meter, but
when the generator is running, you may only have four or five inches of
pressure at the generator from flow losses. I don't really know how
much this is an issue with natural gas, I know it is a significant issue with
liquid flow.

This is a good point. Most people don't realize it, but halving the pipe
diameter will increase pressure losses (for the same flow) by *eight*.
Using a 3/4 inch vs 1/2 pipe for the same flow rate will reduce the pressure
drop through the pipe by (1.5)^3 or 3.375.

Go the next size bigger than you think you need and you won't be sorry.

daestrom
 
G

George

Jan 1, 1970
0
daestrom said:
I'm curious about this. I thought the pressure in the home was set by a
pressure reducer right at the meter (large, disk-like device in the line),
not by the distribution line. The 'street' pressure almost *has* to be
higher than the few inches WC used inside the home, otherwise how could a
single pipeline supply hundreds of homes in a neighborhood?

Now, if the pressure reducer *is* at the meter, maybe you could have yours
adjusted to supply a slightly higher pressure. These things look like just
a large diagraph/spring type of reducing valve, A screw adjustment on the
spring tension would seem simple to adjust. Utility *might* even be willing
to do it within a certain 'range'. Of course, what affect this has on other
gas-appliances needs to be considered. The few I have specify a range of
gas pressure like 6-12 WC, so there might be some room to maneuver.

daestrom
I live in E PA and some street gas mains here are low pressure. They have a
single regulator that might feed one section of town. Individual services do
not have regulators in this case. In one nearby city the entire system was
low pressure because a small local company owned the system. A big utility
bought the system and it is being upgraded. The lower pressure systems are a
real pain. I remember one battle that went on for years in the nearby city.
They extended the main into a new development. Things were great until
heating season and then users could't get adequate output from furnaces
because of the drop in the main.
 
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