I have been using a prest-o-lite acetylene/air torch for a couple of
years. Until recently, I have only used the smallest tip with no
trouble. I now need to use a larger one (size 3 or 4). I am having
trouble with flashbacks when turning off the torch with the larger
tips. I have increased the pressure to 10 lbs. Do I need to use more
pressure? I am using the gauge that reads and setting it
at this is ten pounds isn’t it? Help!
Also, where can I find check valves or flashback arrestors to fit
this torch?
The flash back and popping you are seeing and hearing is caused by
the fuel being burned off after you close the valve on the handle of
your prest-o-lite torch. This happened with your smaller tips but
is much less noticeable due to the smaller volume of fuel/air
flowing through the torch tip. The torch pulls air from the bottom
of the tip as the fuel travels through the tip. When you turn the
fuel off at the handle, the fuel stops flowing through the tip. The
fuel and air continue to burn for a second as well until all the
air/fuel burns up. It does start moving down into the tip and
continues till all the fuel is purned away. Since the fuel has
stopped flowing out of the handle, it starts to burn down into the
tip. This continues until there is just enough fuel/air to cause a
small explosion or pop as it burns up the last of the fuel. This
pop is the perfect air/fuel mix to cause a small explosion at the
base of the torch tip but also serves to burns the last of the fuel
in the torch tip. The small pop or explosion actually blows out the
flame.
Sounds dangerous and is kind of scary, but is part of the safety
features of the torch. When you turn the torch off, the torch blows
its self out. The larger the tip the larger the pop because there
was more fuel in the tip. When I first started making jewelry we
used to have contests seeing who could make their torch pop the
loudest or get the biggest flash comming out of the base of the tip.
It is nothing to sorry about, it happens. The main thing you want
to do is make sure that you turn the fuel off all the way when you
turn the torch off. These are very safe torches and have been used
for years around the country. We get calls every once and a while
on this feature of the torch. It is normal and happens with every
prest-o-lite or Smith Acetylene/air torch out there. It is nothing
to worry about and you will get used to it. Just know that it is
going to happen.
I hope this has helped.
Respectfully,
Phillip Scott
Technical Support & Sales
Rio Grande
1-800-545-6566
While the smallest Presto-Lite tips almost never flash, the large
ones almost always do. As a matter of fact, I would be worried if
the larger tips did not flash.
When you turn off the valve at the torch handle with a small tip on,
although there is still gas in the tip, it cannot continue to burn
for lack of oxygen. But in a larger tip there is enough open area at
the tip to allow air to mix with the gas to continue to burn. That is
what causes the flash at the base of the tip. It is one of the most
asked torch questions I am asked.
I always recommend flashback arrestors. You can find them at our
website or at any welding supply.