# Can I use a 750 millivolt generator on a 250 - 500 millvolt Gas Valve



## stanlam (Aug 25, 2009)

*Can I use a 750 millivolt generator on a 250 - 500 millivolt Gas Valve?*

I am working on a really old wall heater with a B-60 gas valve. I know the generator is bad. The problem is the generator is not made anymore. The B-60 gas valve has instructions on which generator to use. It says...

USE WITH G.C. 250 MILLIVOLT (YELLOW BAND) PG-1 PILOT GENERATOR 

it also says....

WHEN USED WITH T-70 HEAT ANTICIPATOR USE ONLY G.C. 500 M.V. BLUE BAND PG-9 GENERATOR.



So my question is, which replacement generator do I buy this is reasonable price? I know the PG-1 is not made anymore. I found a website that told me to replace it with a 750 millivolt generator. However, I don't want the extra millivolts to damage the gas valve. The replacement gas valve is really expensive.


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## yuri (Nov 29, 2008)

Is there a newer replacement wall heater available? At that age the valve may fail soon and is the heat exchanger safe? I always protect my behind first and won't retrofit anything even if there is the smallest chance of it not meeting some code or rating or design. Had a bad experience with a customer with lots of $$, and no brains try and sue me and my company. Do someone a favor and they stab you in the back.


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## stanlam (Aug 25, 2009)

*Gas Company said it's okay*



yuri said:


> Is there a newer replacement wall heater available? At that age the valve may fail soon and is the heat exchanger safe? I always protect my behind first and won't retrofit anything even if there is the smallest chance of it not meeting some code or rating or design. Had a bad experience with a customer with lots of $$, and no brains try and sue me and my company. Do someone a favor and they stab you in the back.



The Gas Company I use actually have technician that come out and do free safety inspections and diagnosis. The technician said the heater is in perfect shape with the exception of the generator that needs to be replaced. 

Therefore, thanks for your concern. Now I just need advise to know on which replacement generator to buy.


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## Yoyizit (Jul 11, 2008)

To drop 750 mV to ~400 mV at some unknown, small, current level you need a series dropping resistor. It costs less than a dollar.

Since the elec. specs. on the internal resistance of generators and valves are a State Secret, you'd have to try different resistor values unless you measure the resistance of the gas valve coil and post back with the value.

E.g., if the coil reads 10 ohms and you want 500 mV across it the current in the coil must be 500/10 = 50 mA.

(750-500)mV/50 mA = 5 ohms
If the gas valve has an internal resistance of 3 ohms then you only need a 2 ohm resistor but let's start with 5.

The resistor will be dissipating 5 (0.05^2) = 13 mW. Choose a 1/8w or 1/4 w, 5.1 or 4.7 ohm resistor from (yuck) Radio Shack.

If you use no resistor the coil power will be twice normal and that will shorten the life of the coil, somewhat.

How old is that heater?


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## yuri (Nov 29, 2008)

I think he needs a variable resistor as when the new generator starts to get weak the resistor needs to be variable or he will have no heat?:thumbsup:


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## Yoyizit (Jul 11, 2008)

yuri said:


> I think he needs a variable resistor as when the new generator starts to get weak the resistor needs to be variable or he will have no heat?:thumbsup:


A few fixed resistors, jumpered in as needed, are probably cheaper.
You have any measurements on what is considered "weak?" Open circuit output voltage goes down, internal resistance goes up, or both? How do these type of generators normally fail?


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## yuri (Nov 29, 2008)

They get old and lose voltage. I don't dissect em just replace em. :yes: They are a series of thermocouples in a daisy chain. Read Fundamentals of Gas Utilization for more info.:whistling2:


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## Plumber101 (Feb 25, 2009)

I would just put it in. Not a real big deal and I don't see it doing any damage.


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## log_doc_rob (Sep 5, 2009)

If the control valve is designed for 250mv, then damage will occur if you hook up a 750mv TP. That would be like hooking 300 volts AC to an appliance designed for 110 volts AC.

Does the TP make any voltage? I have seen people replace the TP only to find that the problem was only a clogged pilot assembly.


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## yuri (Nov 29, 2008)

Those ITT General B60s had a small steel vent line from the side of the gas valve to the pilot burner. Very common that the end of it would get burnt off/plugged and not allow the valve to open. Now you got the old bean thinkin "old school".:detective:


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## stanlam (Aug 25, 2009)

log_doc_rob said:


> If the control valve is designed for 250mv, then damage will occur if you hook up a 750mv TP. That would be like hooking 300 volts AC to an appliance designed for 110 volts AC.
> 
> Does the TP make any voltage? I have seen people replace the TP only to find that the problem was only a clogged pilot assembly.



If you measure the wires directly from the generator, then it produces 150 milivolts. However, if you measure it through the thermostate, which is on the other side of the room, then it only produces 75 millivolts. I guess it loses millivots since the wire to the thermostate is either to long or to old.


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## Yoyizit (Jul 11, 2008)

yuri said:


> They get old and lose voltage. I don't dissect em just replace em. :yes: They are a series of thermocouples in a daisy chain. Read Fundamentals of Gas Utilization for more info.:whistling2:


OK, book by Dutton.
OK, open circuit or closed circuit voltage decreases.



stanlam said:


> If you measure the wires directly from the generator, then it produces 150 milivolts. However, if you measure it through the thermostate, which is on the other side of the room, then it only produces 75 millivolts. I guess it loses millivots since the wire to the thermostate is either to long or to old.


#26 AWG is ~4 ohms for 50' [100' loop distance] so I = 75mV/4 = 19 mA, assuming the wire and connections are good. 

What's the voltage across the valve with this current? If it's 75 mV then the resistance of the valve should be 75/19 = 4 ohms. You may want to confirm this.


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## log_doc_rob (Sep 5, 2009)

I would try to disconnect the pilot line at the valve and blow the pilot assembly out with compressed air. Also, I deal mainly with gas fireplaces that use a 750mv TP and 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. Check the connections of your stat at the control valve and at the thermostat. I've seen a slightly loose connection cause voltage drops.


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## hvaclover (Oct 2, 2008)

:clover::scooter:


log_doc_rob said:


> I would try to disconnect the pilot line at the valve and blow the pilot assembly out with compressed air. Also, I deal mainly with gas fireplaces that use a 750mv TP and 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. Check the connections of your stat at the control valve and at the thermostat. I've seen a slightly loose connection cause voltage drops.



Aman to that brother!

back in the day the majority of MV furnace calls were tarnished terminals.

Do twenty calls in a 12 hour shift just polishing the copper withe a SOS pad (steel wool fine grade). You might still be able to knock out 20 calls in this day and age if all you have are dirty flame sensor cleanings.
Really have to get your motor scooter running;:clover::scooter:

get out on the highway; 

look for some adventure;

or what ever comes your way!

BORN TO RE-PAIR-AIR!! 
BORN TO RE-PAIR-AIR!!


WHERE'S THE BUSTED FURNACE?


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## yuri (Nov 29, 2008)

Cool dude. Was that you in your "Glory days". :laughing: Bruce wrote a song about them, you can sing along to as well.


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## stanlam (Aug 25, 2009)

*Burke Engineering said it's okay*



Plumber101 said:


> 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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## Yoyizit (Jul 11, 2008)

log_doc_rob said:


> 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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## stanlam (Aug 25, 2009)

*it works, but it was hell installing it*

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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## hvaclover (Oct 2, 2008)

stanlam said:


> 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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## Yoyizit (Jul 11, 2008)

stanlam said:


> 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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## log_doc_rob (Sep 5, 2009)

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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## stanlam (Aug 25, 2009)

Yoyizit said:


> 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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## log_doc_rob (Sep 5, 2009)

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


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## hvaclover (Oct 2, 2008)

Nad Stat:laughing:


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## log_doc_rob (Sep 5, 2009)

I fat fingered that one....could have been worse, could have been a go nad stat.


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## Yoyizit (Jul 11, 2008)

log_doc_rob said:


> 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.


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## yuri (Nov 29, 2008)

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.


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## Yoyizit (Jul 11, 2008)

yuri said:


> My Gawd,
> 
> Keep it simple xxxxx.


Yes, my son? 

xxxxxKeep the wiring resistance to 0.6 ohm or less.


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## hvaclover (Oct 2, 2008)

yuri said:


> 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?:ban::laughing:


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## hvaclover (Oct 2, 2008)

yuri said:


> 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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## yuri (Nov 29, 2008)

I may be creating a "Monster".  Yoyzie's reading "Fundamentals of Gas Utilization". Should have never gave him that reference. Goin to "reinvent " his furnace. BwaHahHa.:nerd:


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## hvaclover (Oct 2, 2008)

yuri said:


> I may be creating a "Monster".  Yoyzie's reading "Fundamentals of Gas Utilization". Should have never gave him that reference. Goin to "reinvent " his furnace. BwaHahHa.:nerd:


Oh Lord!

Now he's gonna dig up his gas line and put a tap valve on it:help::excl:


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## Yoyizit (Jul 11, 2008)

For the record, I had nothing to do with that balloon over Colorado. . .


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## guyinsb (Sep 24, 2011)

*Old thread, old pro's*

This thread is old, but the posters are obviously knowledgeable.
I want to have a replacement ready in case my old General Controls B60 valve fails:
https://picasaweb.google.com/112652995081934659158/GardenHeating#5660407623868116866

My HVAC expert who maintains the system notes that the replacement must be very similar to the original B60; otherwise we are creating a new, unproven system, and he is reluctant to take on that liability. The regulator/valve/boiler have been working very well for over 70 years; the only replacements have been the controls (aquastat, thermostat, thermopile, relay). Seems like there should be a way to replace the valve, rather than spend $10K or more to replace the whole system.


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## guyinsb (Sep 24, 2011)

*Replacement part for General Controls B60 valve*

I have an Ideal boiler system which is over 70 years old:
https://picasaweb.google.com/112652995081934659158/GardenHeating#5515080866385018386

I have or can get spares for all the control elements, but do not have a spare for the General Controls B60 valve. Can anyone recommend a replacement part?


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## bob22 (May 28, 2008)

Why 96 pictures of your heating system?


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## guyinsb (Sep 24, 2011)

*General Controls B-60 gas valve*

Better too many than too few?


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