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Old 10-12-2009, 12:44 PM   #16
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Can I use a 750 millivolt generator on a 250 - 500 millvolt Gas Valve


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Originally Posted by Plumber101 View Post
I would just put it in. Not a real big deal and I don't see it doing any damage.

Thanks for everybody's opinion. I just phoned Burke's Engineering who only sell Heating and A/C stuff to contractors. They confirmed that since I was using the B-60 gas valve, that a suitable replacement was the PG-9 even if it produces 750 millivolts. I will do the install and let you know how it works.

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Old 10-12-2009, 01:05 PM   #17
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Can I use a 750 millivolt generator on a 250 - 500 millvolt Gas Valve


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Originally Posted by log_doc_rob View Post
the manufacturers say that the stat should not have a wire run of more than 25 feet....that means the stat cannot be more that 12 1/2 feet away.
This assumes some wire gauge. If they tell you what gauge they assume then you can back out the max. series resistance, which makes a difference with low resistance valve coils and not much voltage to play with.
With ~twice the circular mils you could go to 50'.
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Old 10-14-2009, 02:19 PM   #18
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Can I use a 750 millivolt generator on a 250 - 500 millvolt Gas Valve


I purchased the PG-9 and the instructions actually say that it is a replacement for the PG-1.

I finally installed it and it works perfect. However, it was hell installing it. The PG-9 is bigger and there are no adapter made to make it fit like a PG-1. In other words, you have to be "creative" to make it work. Although it works fine, I don't think it will pass an inspection. It is obvious that this PG-9 doesn't fit the way the PG-1 did.

I haven't kept the furnace on for more the a few minutes. I think for the first few hours when I do use the furnace, I want to watch it to make sure all goes well. It just worries me that the instructions say this is a replacement, but there are not parts sold to make it fit properly.
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Old 10-14-2009, 03:16 PM   #19
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Can I use a 750 millivolt generator on a 250 - 500 millvolt Gas Valve


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Originally Posted by stanlam View Post
I purchased the PG-9 and the instructions actually say that it is a replacement for the PG-1.

I finally installed it and it works perfect. However, it was hell installing it. The PG-9 is bigger and there are no adapter made to make it fit like a PG-1. In other words, you have to be "creative" to make it work. Although it works fine, I don't think it will pass an inspection. It is obvious that this PG-9 doesn't fit the way the PG-1 did.

I haven't kept the furnace on for more the a few minutes. I think for the first few hours when I do use the furnace, I want to watch it to make sure all goes well. It just worries me that the instructions say this is a replacement, but there are not parts sold to make it fit properly.

hey glad to hear it worked for you. MV valves and pilot generators are quite forgiving if you have mismatch ratings.

Back n the day we carried one valve and one 500MV pilot generator. That and a roll of perorated metal straping and you could fix any MV system in the neighborHood.
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Old 10-14-2009, 05:04 PM   #20
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Can I use a 750 millivolt generator on a 250 - 500 millvolt Gas Valve


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I finally installed it and it works perfect.
I haven't kept the furnace on for more the a few minutes. I think for the first few hours when I do use the furnace, I want to watch it to make sure all goes well.
So, what voltage is your valve seeing?
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Old 10-14-2009, 11:18 PM   #21
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Can I use a 750 millivolt generator on a 250 - 500 millvolt Gas Valve


I'm glad that it worked out for you. I prefer to use manufacturer specific parts. When you alter the appliance in ANY way, you then become the manufacturer of an illegally installed and unrated appliance which is not allowed to be installed according to most local codes. You also accept all liability associated with this appliance.

Yoyizit, manufacturers state their recommended stat wire sizes. Check the owner's manual.....your mileage may vary.
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Old 10-14-2009, 11:20 PM   #22
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Can I use a 750 millivolt generator on a 250 - 500 millvolt Gas Valve


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So, what voltage is your valve seeing?
As I stated in my earlier post, I was losing some some through the wire that is connected to the thermostate. I'm not sure if it's because the wire is old, or to long. Either way, the valve is only seeing 500 millivolts. The other 250 millivolts gets lost in the wire. Which works out perfect because the valve actually says it was made for 250 to 500 millivolts. For once, something that is bad (losing the 250 millivolts) worked to my advantage

Thanks again for everybodys help..
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Old 10-14-2009, 11:31 PM   #23
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Can I use a 750 millivolt generator on a 250 - 500 millvolt Gas Valve


You do lose a little voltage thru the wire and stat, but the voltage drop comes from activating the the main circuit coil.

Last edited by log_doc_rob; 10-14-2009 at 11:36 PM. Reason: Cuz Drac said so !!!
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Old 10-14-2009, 11:33 PM   #24
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Can I use a 750 millivolt generator on a 250 - 500 millvolt Gas Valve


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Old 10-14-2009, 11:37 PM   #25
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Can I use a 750 millivolt generator on a 250 - 500 millvolt Gas Valve


I fat fingered that one....could have been worse, could have been a go nad stat.
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Old 10-15-2009, 04:57 PM   #26
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Can I use a 750 millivolt generator on a 250 - 500 millvolt Gas Valve


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Originally Posted by log_doc_rob View Post
I'm glad that it worked out for you. I prefer to use manufacturer specific parts. When you alter the appliance in ANY way, you then become the manufacturer of an illegally installed and unrated appliance which is not allowed to be installed according to most local codes. You also accept all liability associated with this appliance.

Yoyizit, manufacturers state their recommended stat wire sizes. Check the owner's manual.....your mileage may vary.
Affirmative on the liability, although all DIYers are taking on more risk than someone who hires a pro. At least they should be because that is what they are paying for, but it depends on who you hire.

IMHO,
a valve with zero volts on it is closed, so there is no safety impact.
A valve with rated voltage on it is open, so there is no safety impact and the valve will have a limited life while it is powered.
A valve with a resistor in line is somewhere between these two extremes so the worst that can happen is that the valve doesn't open reliably if the resistor is too large. With a right-sized resistor you'd get longer valve life and still have reliable opening.
I don't see any possible increase in risk by using a resistor but I also don't design or test these these things for a living.

While I'm waiting on the library to cough up "Fundamentals of Gas Utilization" by Dutton, do you have any links to the specs for typical generators and valves and wire recommendations?
I know 750 mV and 30 mV are common [open circuit?] voltages and at least one 750 mV generator that I've seen has 3 ohms internal impedance.
Probably they're all spec'ed at a 1500C flame temperature.

I'm sure my gas appliances are just waiting for the worst possible moment to fail on me.

Last edited by Yoyizit; 10-15-2009 at 05:05 PM.
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Old 10-15-2009, 08:31 PM   #27
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Can I use a 750 millivolt generator on a 250 - 500 millvolt Gas Valve


My Gawd, this is so complicated. We used #18 bell wire for up to 50 feet with PG9 750 millivolt generators on every type of furnace, conversion burner etc and had no problems. Never use anything less than #18 for HVAC equipment as it can screw up the thermostat and circuit boards. Smaller wire is for telephones not HVAC. KISS. Keep it simple xxxxx.

Last edited by yuri; 10-15-2009 at 08:38 PM.
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Old 10-15-2009, 08:41 PM   #28
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Can I use a 750 millivolt generator on a 250 - 500 millvolt Gas Valve


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My Gawd,

Keep it simple xxxxx.
Yes, my son?

xxxxxKeep the wiring resistance to 0.6 ohm or less.
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Old 10-15-2009, 10:02 PM   #29
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Can I use a 750 millivolt generator on a 250 - 500 millvolt Gas Valve


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My Gawd, this is so complicated. We used #18 bell wire for up to 50 feet with PG9 750 millivolt generators on every type of furnace, conversion burner etc and had no problems. Never use anything less than #18 for HVAC equipment as it can screw up the thermostat and circuit boards. Smaller wire is for telephones not HVAC. KISS. Keep it simple xxxxx.

Hey Yuri, how about those calls where an HO put a high resistance anticipated stat on the wall and wondered why the MV wouldn't work?

I thought we put Yoyzi in Time Out for not replacing his furnace? Who paroled him?
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Last edited by hvaclover; 10-15-2009 at 10:07 PM.
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Old 10-15-2009, 10:06 PM   #30
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Can I use a 750 millivolt generator on a 250 - 500 millvolt Gas Valve


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My Gawd, this is so complicated. We used #18 bell wire for up to 50 feet with PG9 750 millivolt generators on every type of furnace, conversion burner etc and had no problems. Never use anything less than #18 for HVAC equipment as it can screw up the thermostat and circuit boards. Smaller wire is for telephones not HVAC. KISS. Keep it simple xxxxx.
Tell that to the guys who work for the phone company.

Found a 100 ft length of 30 pair run for stat wire. Must have been 30 AWG.

Gave his new 90% furnace a nervous break down.

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