Questions on Clocking

JHMartin

Hello,
A newbie here who could use some “schooling” on clocking and tuning the gas valve. Perhaps the answer is to go to school, that what I’m asking takes a semester to explain. I’m hoping there are some “Cliff Notes.”
I understand how to clock a gas meter, but I don’t understand what to do with the data: adjust the input side of the gas valve, the output, or both?
How can adjusting the input side get the clocking number to better match the manufacturer’s BTU spec? I would think that would only happen by adjusting the output side.
If adjusting the output side to better match the BTU spec, is it okay to adjust within the typical range of 3.2-3.8” of WC even if the appliance manufacturer specifies 3.5” and not a range?
How do I practically factor in our local, NG heating value of 829?
For what are we optimizing? Complete combustion? Maximum BTU output? Most closely matching the vendor’s specs? Efficiency? Longevity of the heat exchanger? Minimum production of CO?
If we are optimizing for minimal CO, why would one need to clock if using a combustion analyzer?
How important is clocking with 70-80% efficient appliances? I recently watched a vendor replace a 2-stage gas valve on an old boiler and he never even pulled out his manometer.
Again, I’m hoping I’m not asking too much. If this isn’t the place to get these answers, is there some other online resource to which you could send me?
Thanks much,
Jay

pecmsg

To measure for “Complete Combustion” you need a combustion analysis. 

EdTheHeaterMan

pecmsg said:

To measure for “Complete Combustion” you need a combustion analysis. 

Always a wealth of insight to the obvious.


I would always use a manometer to check the gas pressure when replacing a gas valve. especially the little residential valves that have the regulator included in them. Based on the orifice size provided by the appliance manufacturer and the pressure the manufacturer recommends the flame should produce the BTUh the appliance is rated at. Clocking the meter is a way to double check your numbers.

My mother was a bookkeeper. One of the principles of bookkeeping was to verify your numbers by adding up all the columns twice. That way you know you added them correctly if you get the same total twice. That is where the phrase Double Check comes from. Now if you get the pressure and the orifice dimensions correct, you have the correct rate of Gas CFM. If you clock the meter and it is within a small percent of the appliance rating, then you know you got it right. You got the same answer both ways.

When you have a problem… that is when you need to understand how to convert that clocked meter to BTU and the pressure and orifice size to BTU and make sure they match. If they don't, then you need to determine what is not correct. If for example you have an orifice that is too small and you believe it to be the correct size, and set the pressure accordingly, you may have a problem that clocking the meter will discover. Then you get your number drill index out and verify the orifice size and then say OOPS, I put the wrong orifices in there. and be able to make the necessary repairs.

There are those in this forum that will want the correct answer to the exact millimeter, ounce percentage and the like. Good luck with that! This is not Rocket Surgery! You get as close to the number as you can. Be sure the keep the CO to a minimum, a zero smoke, the least amount of excess air and still have an acceptable combustion process. That is all you can hope for. Every installation is different and you will not gt the same numbers as your neighbor or the guy across the state or across the country. If by chance that you can tweak another half percent efficiency out of an appliance, and at the end of the year there are no adverse effects, that is great. But you only saved $15.00 over that year, so if it took you 4 hours of testing and adjusting to get that savings, was it worth it? Even at minimum wage, that time could have been more productive elsewhere. Get the picture?

Tim McElwain

Send me an e-mail at timmcelwain@gastcri.com I run a training center here in Rhode Island which you may want to attend. In the meantime e-mail me And I can send you some helpfull literature for FREE!