Discontinued Gas Valve for RV Wall Furnace
I've recently acquired a 1969 Aristocrat Lo-Liner travel trailer. The heater was experiencing "Flame lift", so I pulled the burner assembly out thinking it was a blockage in the venturi. There were bug carcasses and a bit of rust dust. I was pretty confident that was it. I cleaned everything up and reassembled it. Now the heater will come on when moving the 'safety' valve from pilot to on, but it does not shut off until I return it to pilot. So gas valve it is. But...the valve is nowhere to be found. So here I am. I am fairly sure there is a suitable replacement, I just don't know enough about gas valves to find it. We went to some HVAC places in town, but there is no gas lines in town so they were clueless.
Here's the info I have:
It is a Kresky Safti-Flame SSFT-100.The valve is stamped with TV17AA19 and below that is 1/2psi.
The heater says output is 7000btu/hr and max input is 10000btu/hr. It has a 3/4" inlet that has been reduced to 1/2". Outlet is 1/2".
Fuel: LP
Pilot: Standing
Voltage: none
Opening: unsure, 60yrs old, probably slow?
Stages: unsure, but probably single stage
Comments
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you could certainly replace it with a millivolt valve , thermopile, and thermostat. probably should have a limit and rollout and spill switch. might be a valve in that format for a fireplace. might cost about the same to replace the furnace with modern safeties as to replace the valve.
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https://www.supplyhouse.com/Robertshaw-710-205-1-2-X-1-2-Low-Profile-Combo-Gas-Valve-70000-BTU
looks like it doesn't have a lp version but you need to use a conversion kit for the regulator, then you'de need to set the manifold pressure
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Hi, From the valve @mattmia2 showed you:
It looks like it's designed to be convertible to propane. I might skip the type of valve you presently have and install the type in the lower picture than can take a thermostat, instead of that big copper bulb. Probably better control and easier to test. All sounds like an interesting project 🤠
Yours, Larry
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Looks like that valve modulates the flame size based on temp ike a cooking valve used for an oven but at a different temperature. I agree it will probably cost more to fix than replace.
You could use a millivolt gas valve with a remote thermostat and would have to install a powerpile as @mattmia2 suggested. But you will only get 1 constant firing rate
May not be a DIY job and your going to have to do some research to cobble the stuff together. I don't think you will find a direct replacement.
@Tim McElwain would know you could PM him.
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Sorry for the late reply. In limited cell area. Definitely looking for a suitable replacement. Pretty sure this one has gone the way of the dinosaur. I'm trying to avoid having to do any funky remodeling in the trailer, which is why I'm trying h to fix the existing one.
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Going to look into the 710 series valves. Robertshaw has a cross reference for the old valve but the specs say it's rated at 160,000btu, seemed wrong since the furnace is max 10,000btu. Am I wrong about that? Is it adjustable? Or is that just a max type of spec?
The Robertshaw cross reference # is: 700-204.
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So with the 710 models, it says the max capacity is 70,000. What would an RV LP regulator output? And just because it is 70,000 doesn't mean it won't work with less, correct? Pretty cool stuff, I was surprised at the LARGE number of valves available and many different specs. Learn something new everyday. Thank you guys for the help and advice.
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@Larry Weingarten By the way, what is the "large copper bulb" actually called?
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The large copper bulb is basically the thermostat. That is why the valve handle has #s on it. The thermostatic bulb measures the return air temp (which is the same as the room temp) and modulates the gas valve between high and low fire.
I don't know if any valves like that are available.
Robert Shaw makes gas valves for commercial ranges that are like that, but they would operate an oven at 300-500 degrees not 70 deg return air.
Maybe you could call a Robert Shaw rep and they could help you out.
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That copper bulb is called a sensing bulb, it is connected with a capillary tube to some bellows inside the valve. It is filled with some sort of liquid, usually some sort of refrigerant or alcohol. I wonder if you broke the capillary tube while servicing the burner. If whatever was inside it escaped then it won't exert increasing pressure on the bellows with increasing temp and turn the valve off.
The specified output of the valve is some maximum flow rate of gas and some energy content and pressure of that gas picked somewhat randomly.
The actual firing rate of the appliance is set by setting the pressure of the regulator built in to that combination valve and the size of the orifice on the burner. There probably is a minimum firing rate at which the regulator in the valve works properly, someone that knows gas controls better than I do will know how to read that rating (it may be on the spec sheet or the spec for the LP regulator accessory). Ideally the valve replacement would be done by a good gas tech.
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Ah! I knew it was a thermometer of sorts, just didn't know exactly what it was called. I also thought it was some sort of thermocouple. Absolutely could have buggered that up, I suppose. Something to check on.
@EBEBRATT-Ed probably call them or supplyhouse.com next. Yet another question is...will a tech install a valve without a cross reference #? So far all the techs have said it's discontinued, there isn't one. UT it looks like the Robertshaw 710 series might work.
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A thermocouple (which is what the pilot safety that screws in to the valve is) is 2 different metals that produce a current when heated. The thermocouple is electrical, the cap tube and sensing bulb is mechanical. Once you break it, there isn't really any fixing it unless you can find a new actuator module for that valve. Usually you need some special tools and skills to repair and re-charge a sensing bulb which is generally only done for antique restoration where there isn't a suitable substitute available.
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Make sure the heat exchanger isn't rusted out before you go too far down this path. Get a good unlisted low level carbon monoxide monitor for the rv too.
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@mattmia2 Not too much rust at all, I was surprised. A bit of surface rust but by no means rusted out. Even if the bulb broke, it's still the same prolem, basically, gas valve. Still, definitely useful info though.
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Hi, It looks like you can install the 710-502 valve (with propane kit) along with a thermostat on the wall, and be happy. It seems the heat exchanger is sound, but couldn't hurt to install a low level CO detector anyway. 🤔
Yours, Larry
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Gonna go with the 720-502 and CO detector. Trying to get as much info as possible here, I appreciate it.
Hopefully you guys can answer another question. Robertshaw has a cross reference for the original valve as model #: 700-204
To me, except for the size, shape and 'snap throttle', the specs look almost the same, what's the difference between that and the 710's?
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the 700-204 is modulating, it varies the firing rate based on how close the temp is to the setpoint on the dial.
it also does not have a built in regulator so you will need to put an appliance regulator ahead of it to control the pressure to the manifold pressure for that furnace.
EDIT:
Unless RV systems are different and the tank regulator brings the pressure down to the appliance manifold pressure.
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Good info, appreciated. If my current valve is modulating will it make much difference if I put a non-modulating valve in? Seems like maybe a bit of efficiency would be the only downside?
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And I would guess the lp regulator is bring the pressure down, other than that I don't see anything else that looks like it would be a regulator for the valve.
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normally the valve has a regulator built in to it but i'm not sure if yours does because it is for rv applications.
the big caution between valves is i don't know if the modulating valve is slow opening. if the burner needs a slow opening valve to light smoothly and you replace it with a fast opening valve it will light with a small explosion.
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