Regulators doing strange things

[Welderpaul]

I put a shielding gas bottle on earlier this week and set the regulator to 12 LPM. Later in the day the bottle ran out and after i swapped the bottle it was up to 30 LPM. I put it down to it getting knocked or something.

Same thing happened yesterday, i know i set it at 12 LPM, when i swapped the bottle it was 20-odd LPM. No one else is using this set so i know no one is altering it.

Do regulators creap as they get older? Any reason for this? This reg is not even a year old.

 

[Welderpaul]

Anyone?

 

[Hitch]

Been hanging your headshield on it?

 

[Welderpaul]

No. Done the same again. Bear in mind i'm emptying a cylinder in a few hours. Regs are wet through.

Somehow the flow rate is rising as pressure in the bottle drops

 

[Hitch]

Even with a fair leak aswell, thats rapid... tried a different reg?

 

[Jim Davey]

No. Done the same again. Bear in mind i'm emptying a cylinder in a few hours. Regs are wet through.

Somehow the flow rate is rising as pressure in the bottle drops

Tough one to get your head around but with all single stage regs this is what happens to some degree. Inside the body of the regulator there is a diaphragm, with bottle pressure one one side and a spring under the pressure adjuster (PA) screw on the other side. The diaphragm moves in or out exposing a port on the high pressure side and allows some gas through, how much it opens and how much gas you get is simply a case of balancing spring pressure against the pressure of the gas on the other side of the diaphragm. You will already know that winding the pressure off decreases flow until the gas stops.
As the pressure in the cylinder drops, the force acting on the gas side of the diaphragm drops but if the PA screw is not adjusted to compensate the diaphragm will open more as spring pressure will remain unchanged but the pressure on the gas side will be less, allowing more flow. This is why we sell multistage regs, as they have two pressure reducing stages, one fixed one adjustable, and this reduces the changing effect on flow that you get from full cylinder to empty.

For reference a good single stage reg should increase flow by 10-15% from full to empty if not adjusted, but as mentioned earlier its not uncommon to see a rise of more than double the gas flow if the regs are not regularly adjusted (this becomes increasingly more regular as bottle pressure drops to low levels) If this is the case now and it wasn't so noticeable before then the reg has started to fail and it needs replacing.

It takes people ages to grasp this concept as everyone thinks that as the bottle gets towards empty flow should be drop, but you get the exact opposite until the bottle is almost run out.

Hope this makes sense.

 

[backpurge]

Paul
Echo what Jim says, explained it far better than I could.
I would recon on a full size cylinder giving you round about 12 arc hours. With the reg being dripping wet it sounds as if you could be runninng at a fairly high flow rate as well

 

[Welderpaul]

Thanks fellas, some good info there. I'm starting off at 12 lpm, but the outlet pressure is gradually rising between me resetting the pressure 3-4 times a day. I'm probably getting 8 hours trigger time out of a 230 bar bottle? It is pretty much constant welding all day so a wet reg is pretty usual. I've had the Nevoc regs frost up on the serious stuff.
I swapped the reg tonight, its only six months old mind; see what the new one is like.

 

[dannyp]

some of the new regs one the arc shield we's had the flow rate double over a day as bottel pressure drops.

i usally set aound 15lpm. if doing a lot of welding the reg will need ajusting at least twice a day, thats from when they are new untill they give up.

quite easy to get them dripping wet when useing the torch latching and everything is ready tacked up. when doing a lot of heavy weling ( torch latching on )

a 50ltr @ 230 bar bottel of gas will last me 2 x15kg reels of wire. reel a day and 2 days for the bottel.