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If it isn't loosening, then you might want to just leave it for now to avoid accidentally damaging or deforming the tube. You certainly don't want to crimp it out of shape. As you said, it is already working better than before.

I guess you can't heat the tube too much to assist freeing it. You don't want the spring to loose its temper.
Nevetheless, boiling it in citric acid or lye solution might help and won't alter the spring's tension.

 

I could remove the main tube off OK, and the spring and rod all checked out, it was the inner air tube with the slot going down the side I could not get off.
The citric acid idea could work OK, is it safe to use on brass? I always find you will see it dissolve the zinc out of the brass and leave the copper residue behind, I dont know if this weakens it or only removes the top layer at an atomic scale.

Im ordering a bunch of spares that I will need from OCP, im hoping that the tube inside the generator may address most of the trouble, if not, I will give this air tube another crack.

 

In most instances, the citric acid attack on brass would be largely superficial. Unlike ammonia or ammoniacal products.
When very hot or boiling, the attack is faster but you wouldn't be leaving it that long in the solution anyway. It might make the brass look reddish or pinkish but you could polish it down to brass again. Even lye would similarly attack brass when hot or very concentrated.

On instances where I can't apply the aggressive dull red heat-&-quench method for freeing up seized parts or when merely squirting some penetrating oil at non-elevated temperatures wouldn't do the trick, I'd use an alternative solution.
I'd just heat the parts in DOT 3 brake fluid which, is quite penetrating itself. Most such brake fluids wouldn't start to boil or evaporate before approaching 200°C. Therefore, a combination of elevated temperature plus penetrating fluid action at the same time. I might also include some ATF in the 'high-temp' penetrating fluid in improve its lubricity. Most ATF wouldn't start to boil unless its over 200°C.
The boiling of fluids is a rough indicator, which also keeps the temperature in check. As long as you don't allow it to fully boil and evaporate off, the temperature wouldn't rise further to dangerous levels. In a rough sense, I'd be keeping the temperature somewhere just below 180°C without needing a temperature probe for indication.
I might also use a drill check to clamp on round tubes where the absence of flats rules out the use of a wrench. However, even with a chuck, there is still a risk of crimping delicate, thin walled parts.

 

Thanks, I will give those methods a go if i get stuck, I think if i use a good pair of pliers and padding I should be OK, I was trying to be extra careful naturally, the citric acid may help penetrate into it too possibly.
The fact that someone has attacked this with pliers suggests to me that the last owner was having some issues, so i think its worth investigating further.

 

Wish you good luck with it. Perhaps you can also combine it in your Ultrasonic bath to enhance the effect.

 

Yeah I was thinking that might be a good idea. I'm sure i will be able to get it apart.