Hey everybody, just wanted to add some information to this very interesting thread.
After reading about this question of excess volume and/or pressure in the feed line and whether or not to move/mount the final stage of the regulator closer to the back of the welder I decided to try to sort out my own problem.
About a year ago I purchased a small DC welder – a
Weco Discovery 171T Max. This has been a great little unit I might add: brilliant HF starts, smooth arc, pulse adjustments and never a moment's trouble.
- Weco Discovery 171T-Max.jpg (79.02 KiB) Viewed 1710 times
The only fly in the ointment has been a puff of gas every time I trigger the start. Note that I work on small art pieces. How small? Check out the quickie test piece in the photo. I use nails as my metal source and my torch is usually running at between 15 and 25 amps using a number 4 ceramic nose piece (sometimes regular, sometimes gas lens) and I'm real happy with a gas flow of 4 liters per minute (approx. 8.5 cfh). But that initial puff of gas upon triggering the torch has tended to blow my little workpieces right of the table. I've gotten around that by using little weights on the nails, but the extra fuss of placing them on my work prior to initiating a small weld is a pain in the b*tt.
- nail welds.jpg (66.04 KiB) Viewed 1710 times
Anyway, inspired by this thread I took a trip over to the local welding supply shop which had sold me the unit. The salesman marched me into the back work area for a discussion with their repair technician. The tech admitted that this condition could sometimes be a problem. He went on to say that they had also encountered the same phenomenon, especially at trade shows where it was sometimes necessary to hide the argon cylinders behind curtains and then run extra long feed tubes to the demo welder units on display. Having said that, he then told me how to fix it. Read on.
In my case, my feed line is a transparent tube with integrated woven reinforcement having an inner diameter of something like 3mm (0.118 inch)… about 1.5 meters long (5 ft). I'm using a flowmeter regulator made by the Swiss company,
Gloor (primary stage = 3000 psi, secondary working pressure = 4.5 bar (about 65 psi)).
- Gloor regulator.jpg (30.83 KiB) Viewed 1710 times
So anyway, when one stops welding the pressure in the feed line will trickle up to that 4.5 bar pressure regardless of the flowmeter setting. That pressure in the line creates the puff of gas upon triggering the welder. The solution is almost stupidly simple. One fits a small flow-restricting orifice at the end of the feed tube where it meets the back of the welder. In my case I purchased an additional length of tube with an additional screw fitting for my welder. To this screw fitting I added a small, turned brass insert (soldered in) with a tiny hole drilled in it. How small of a hole, you ask? I used a
#75 drill to make mine (0.021 inch in diamter = 0.5334 mm). This little restriction orifice prevents the higher back pressure in the feed line from running out through the solenoid valve into the welding torch hose all at once. And believe it or not, even acting as a flow constrictor that small hole allows me to push anything up to almost 9 liters of gas a minute (up to 19 cfh)… good enough to use up to a number 9 ceramic. End result: Puff of gas all gone!
I can now light up on my tiny nails with only a tiny, discrete 'snap' as the arc initiates. The nails don't move a hair. And the flowmeter at the regulator still indicates the gas flow as expected.
You might have to experiment a bit with hole sizes for your own combination of regulator pressure and feed lines, but this might be really useful for those of you with similarly sensitive welding needs.
