Gas Conversion NG to LP

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Gas Conversion NG to LP

Postby dbksearay » Wed Jan 25, 2012 2:13 pm

I am converting a Munchkin 80M Rev 2 from NG to LP. It has a DUNGS gas valve. The conversion kit instructs me to turn the fuel screw "3 1/2 turns clockwise" to change it from NG to LP. I did this and fired up the boiler. Using an UEI C75 Combustion Analyzer to make the CO measurement, it exceeded 1000ppm at low fan speed. Range is suppose to be 0 to 20ppm. So assuming high CO means too much fuel I turned back the fuel screw (clockwise) 1/4 turn and re-measured. Still off the scale. I have repeated this process 6 more times turning back the fuel screw 1/4 turn each time and still get off scale readings. Is this normal? I can't get the CO level under 1000ppm. Would have thought the DUNGS valve to be more sensitive than I am experiencing. The UEI C75 was also just calibrated so I believe it is accurate. Just wonder what others have experienced?
dbksearay
 
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Re: Gas Conversion NG to LP

Postby ron.gajdos » Fri Jan 27, 2012 6:22 pm

hello
you should be turning the short brass regular screw with the + - beside it etched into the aluminum (throttle screw)
after that you would go to high fire and adjust the same screw to achive the parameters in the manual
you would then ramp down to low fire and check combustion readings, if they are off a little we would then use the offset screw to dial in the low fire watching our combustion analyzer
you only turn the offset screw a little at a time and give appliance time to stabilize
on the throttle screw clockwise leans it out
on the offset screw clockwise richens
ron.gajdos
 
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Re: Gas Conversion NG to LP

Postby MeeksHeat » Sat Feb 04, 2012 7:22 pm

I'm not familiar with your CO analyzer, but it looks to me that you have your meter set for NG and not LP fuel setting.
I'm assuming that the secondary LP regulator is set to 11" W/C by the LP service provider.
MeeksHeat
 
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Re: Gas Conversion NG to LP

Postby Josh Cayea ES » Mon Nov 12, 2012 10:31 pm

dbksearay wrote:I am converting a Munchkin 80M Rev 2 from NG to LP. It has a DUNGS gas valve. The conversion kit instructs me to turn the fuel screw "3 1/2 turns clockwise" to change it from NG to LP. I did this and fired up the boiler. Using an UEI C75 Combustion Analyzer to make the CO measurement, it exceeded 1000ppm at low fan speed. Range is suppose to be 0 to 20ppm. So assuming high CO means too much fuel I turned back the fuel screw (clockwise) 1/4 turn and re-measured. Still off the scale. I have repeated this process 6 more times turning back the fuel screw 1/4 turn each time and still get off scale readings. Is this normal? I can't get the CO level under 1000ppm. Would have thought the DUNGS valve to be more sensitive than I am experiencing. The UEI C75 was also just calibrated so I believe it is accurate. Just wonder what others have experienced?


When doing a startup, I check the following in order:
1. Verify fuel being used (NG or LP)
2. Verify inlet gas pressure in in range (see boiler data plate for range allowed)
3. Verify inlet gas pressure drop off from static to dynamic is less than 1.0" WC (otherwise gas line or pressure regulator sizing is incorrect).
4. Verify -.01" WC manifold pressure at low fire
5. Tune boiler at high and low fire until CO2 numbers are correct using throttle screw.

If the boiler is not new, then it should be cleaned and serviced first. Otherwise your CO numbers will not look correct. I use the Wohler A400 combustion analyzer with great results.
Josh Cayea
Emerson Swan Applied & Distribution Products Outside Sales

Central Massachusetts
MA and NH Licensed Gasfitter
MA Licensed HVAC Sheetmetal Installer
Josh Cayea ES
 
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