the hp is only nessecary (sp) for blowback markers try a lp tank on a site rental or something to see what i mean, but the hp has a higher flow rate than lp so it wont drop off when shooting fast strings of paint, if straight hp air gets into a gun it can in theory blow it up, for instance ions run at about 160-180 psi, if much higher than 200 psi gets into the solinoid, it will blow the hoses off and mkost likely foock the noid up, this is why most high end markers have their own inbuilt vertical regs!