I'm going to be putting my haskel up on the wall to get it out of the way, I thought I saw there was a preferred orientation. Being vertical with the outlets pointing down.
Can anyone confirm?
Yes if its not a problem: PUDD
Piston drive Up. Driven gas Down and out
In general the answer is for a non condensing gas wall mounting piston up vertical.
But for a scuba application its not that important so mount it as you feel.
The reasons why are way too complicated for an open forum but general principles apply.
Condensing and non condensing gases are obvious but a couple of lesser known considerations
are piston slap or sag, and torsional load flexing.
The Haskel I have assumed is the small single stage sports version it has a very large piston (4 inch) for a very long stroke 2.5: inches) for its small size.
Air gas driven the 4 inch piston will flex during compression and to compensate Haskel increase the piston rod larger in diameter to reduce side load on the seal rings and rider ring that would create uneven wear (called washboarding)
The Haskel also is driven back to front that is it is driven piston down to rod rather than rod up to piston. Now also the weight of the piston causes sagging when left extended in a horizontal plane and although this is compensated by using a light weight piston on a thicker rod. The long stroke length to piston diameter ratio will also cause additional distortion on the concentricity (roundness) of the soft polymer seals and 0-rings. When idle as well as during the compression stroke.
Hence why located or left dormant or running in a vertical plane you achieve minimum sag and minimum ring seal distortion.
To the average sports diver you don’t have enough experience with the product or see enough of them to see the difference and for most sports divers they are used so little and for such a short life expectancy it is of little interest or matter.
Seals will wear regardless over time you just get a little longer life if you don’t wear one side out more than the other. Iain