O/A Torch Question

[BrentD]

A couple of years ago I bought one of those Harbor Freight Oxy/Acetylene kits that has the two bottles in a little red plastic carrier. Wasn't planning on using it very much so I didn't want to spend a fortune on a professional rig.

I've used the rig maybe twice since I've had it and it seemed to work OK for what I was doing. Until today. I needed to do a quick braze on a part that I had to modify so I got out the torch and opened the acetylene valve 1/4 turn and set the regulator to about 10psi. I opened the Oxygen valve and set the oxygen to about 20 psi. Tried to light the torch and it was a no go and I couldn't smell any acetylene. I thought maybe I had forgotten something and had the valves reversed so I opened the other valve and got the same result.

Then I looked down at the gauges and noticed my Acetylene gauge was now up around 20PSI. I quickly shut off both bottles and bled the lines, then turned both regulators fully off and started over. I opened the acetylene bottle 1/4 turn again and this time set the regulator to only about 5 PSI. Then I opened up the Oxygen bottle and started to slowly turn up the regulator. I had already double checked to make sure both torch handle valves were fully closed. Once the Oxygen passed 5 PSI I noticed that both the Oxygen and Acetylene gauges started increasing as I increased the oxygen pressure. At that point I decided that maybe I wasn't understanding something so I decided to come ask the experts what's going on with my torch.

Am I correct in assuming that the oxygen and acetylene aren't supposed to mix until they pass the valves in the torch handle and enter the mixing chamber in the tip? Is it possible that there is a crack somewhere inside my torch handle that is allowing the oxygen to feed back into the acetylene line?

I'm also guessing at this point I should maybe disconnect the lines from the regulators and bleed them out in case the acetylene line has an Acetylene/O2 mixture in it that might be unstable.

 

[wushaw]

Turn both of the valves at the base of the torch off and see if the regulator still increases.

 

[Scotty370]

Do what Wushaw said first! When I braze, I typically run #5 and #5. Light the Ace first, then slowly add the Oxy. Your right, that the gases shouldn't mix until they clear the torch handle. ~S

 

[BrentD]

Turn both of the valves at the base of the torch off and see if the regulator still increases.

This torch only has 2 valves on it, and they are right below the couple where the torch tip attaches to the body. With both of those valves off turning the oxygen up increases the reading on the Acetylene gauge.

Another interesting thing... When the O2 pressure is say 20 psi and the Acetylene pressure is 10 or less, opening the valve on the torch marked "Fuel" releases oxygen instead of acetylene, and no I don't have the hoses on the wrong ports because opening the oxygen valve also releases oxygen.

 

[Scotty370]

I'm wondering if over the years, you Ace bottle went 'flat'. When you first tryed it, your Ox tank pressurized the Ace bottle with Ox! I can't imagine how it would back feed it to do that! Do you have double gauges so that you can read tank pressure and feed pressure? Did you 'crack' the Ace bottle and smell Ace?

 

[BrentD]

I'm wondering if over the years, you Ace bottle went 'flat'. When you first tryed it, your Ox tank pressurized the Ace bottle with Ox! I can't imagine how it would back feed it to do that! Do you have double gauges so that you can read tank pressure and feed pressure? Did you 'crack' the Ace bottle and smell Ace?

Yep. Separate gauges on both regs. The Acetylene bottle is only about 2 years old and it's still showing plenty of pressure in the bottle.

I'm betting that the two valves in the handle are machined from one piece of brass. If there was a flaw in the brass that separates the valves and that flaw turned into a crack, that would allow the gasses to mix inside the torch body.

 

[Cap-n-Cray]

Sounds like the Acetylene regulator is bad. The same thing happened to me the other day. I had not used my Smith torch for some time. I turned on the Oxygen tank and adjusted the pressure, but the pressure kept increasing. It finally started blowing the safety release so I closed the tank valve fast. Rebuilt the regulator and all is well. The seals went bad over time.

Cary

 

[BrentD]

Sounds like the Acetylene regulator is bad. The same thing happened to me the other day. I had not used my Smith torch for some time. I turned on the Oxygen tank and adjusted the pressure, but the pressure kept increasing. It finally started blowing the safety release so I closed the tank valve fast. Rebuilt the regulator and all is well. The seals went bad over time.

Cary

But in my case, if I turn the acetylene bottle main valve off and just leave the regulator set where it was then turn on the oxygen the acetylene pressure immediately starts going up.

Did another test and the opposite is true. Turning the oxygen bottle valve off and leaving the regulator set, bleeding the Oxygen line then turning on the Acetylene and turning the pressure up gives a rise on the Oxygen pressure gauge as well.

Bottom line is that the Oxygen and Acetylene are somehow mixing inside the torch body between the hose connections and the control valves.

 

[Cap-n-Cray]

That doesn't sound good. Does the torch body have two valves on it? My torch you open the Acetylene first, light it and then add Oxygen. The gas are mix but only in the torch body and tip. Could your tip be blocked? Can you blow though it?

Cary

 

[BrentD]

That doesn't sound good. Does the torch body have two valves on it? My torch you open the Acetylene first, light it and then add Oxygen. The gas are mix but only in the torch body and tip. Could your tip be blocked? Can you blow though it?

Cary

Tip is definitely not blocked and yes there are two valves. What started was when I tried lighting it and it wouldn't light, so I checked for that distinct Acetone/Acetylene smell at the tip and realized it was blowing oxygen. Thought the hoses were maybe reversed so I opened up the Oxygen valve and still got oxygen. That's when I checked the regulators and discovered that the pressures start cross-feeding when both torch valves are closed.