seconding the whip line or old hose for a low-/no-cost solution. Hydraulic hose is massive overkill, unless you just happen to have it laying around to be sacrificed. It certainly isn't an application that 'needs' 2000psi+ hose.
And watch out for the 'flow' recommendations that mix things up with the fluid dynamics of uncompressible water, where angle of turns and pipe diameter really matter. Air, not so much. Particularly when you consider that QD air couplers have an ID of 3/16" and compressor hoses are typically 1/4"~3/8".
Same for the howling about using PVC for hard line piping. Its working pressure / burst rating falls off sharply as the pipe diameter increases, but the rating on the smaller pipes far exceeds that of the other typical components. A Schedule 40 3/4" PVC pipe has a burst rating of 480psi. A Sched40 1/2" pipe has a rating of 600psi. A 1/2" pipe has nearly 7x the area / flow as the restriction in a QD coupling.
Now I don't know what pressure you all run your air systems, or if you folks that like the old machines even use a pressure regulator. But all of my air tools run at 80-100psi so I set my regulator - which is at my tank - appropriately and rarely over 100. And my compressor tank has a pressure relief valve that blows at 150psi. And I leave my drain valve slightly cracked, so my system bleeds down when I'm done using it. And no need to remember to drain the water from it. So my system is only pressurized when I am using it.
All that put together and I really don't fathom the 'common wisdom'/lore that condemns using PVC.
And if you are really worried about it, Sched80 1/2" pipe has a burst rating of 850. ~3x the rating of your flexible hoses.
There are temperature and UV and damage factors to consider, but those are controllable.
For all that, I don't get why people don't just use rubber air hose for their runs, it's rated 250-300psi. It can be made as neat / presentable as any visible pipe.
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