HVLP spray gun recommendations

[Patrick Chase]

I am somewhat confused over the LVLP and Reduced Pressure guns now. By reading the descriptions of both, there does not appear to be a clear winner between the two. Both look like they would work quite well for my needs and my current compressor. If there was one thing that I interpret to be a pro for the RP gun, is it might possibly be a better choice for using water-based poly?

LP and RP are designations based on tip pressure and transfer efficiency, respectively. "LP" means that the tip pressure is 10 psi or less. "RP" means that the tip pressure is greater than 10 psi, but the transfer efficiency (percentage of finish that ends up on the work as opposed to in the filter) is greater than 65% for some standardized test conditions. In theory an RP gun should require somewhat less cfm to deliver a given amount of finish than does an LP gun.

See this page for information about the regulatory framework that created both classes of gun. HVLP guns are always permitted for commercial use even in high-air-pollution areas. RP guns are only permitted if the vendor has demonstrated 65% transfer efficiency. It's probably worth noting that top-quality LP rigs can have transfer efficiencies in excess of 80% depending on finish and conditions, so there is an efficiency (blowback, overspray, etc) downside to RP. The "RP" branding just tells you that it isn't any worse than 65% under standardized conditions.

LV vs HV is less clear cut as it doesn't have a legal/regulatory definition as LP/RP do, though the breakpoint is generally around 6-8 cfm depending on vendor.

There is huge variation within both LP and RP guns. My RP gun (a Fuji MPX-30) takes ~13 cfm at its max inlet pressure, so I suppose you would call it "HVRP". It's *really* fast at max pressure and can atomize most anything I care to spray without thinning. The RP gun that Jeff sells takes 6 cfm, so that would be LVRP.

IMO for woodworking finishes including waterborne clears a good HVLP gun is more than sufficient. I seldom work at the full rated inlet pressure even with those. It's probably worth noting that for an LP gun the rated inlet pressure is the highest pressure that produces <10 psi at the tip, after conversion. For an RP gun the rated inlet pressure is the highest pressure that the maker certifies will produce >65% transfer efficiency under standardized conditions. There's no magic here :-).

[John TenEyck]

I think you are going to want to add at least one larger N/N set for the 5008 gun if you want to spray many WB products, especially any pigmented ones, without thinning. When I was using gravity guns I mostly used a 1.8 mm N/N for the GF WB clearcoats I sprayed, and had to thin every pigmented product. That was a primary driver for why I went to a pressure assisted setup.

Of course, you could modify the 5008 gun to run a pressurized PPS cup as an alternative to using a larger N/N.

John

[Patrick Chase]

Of course, you could modify the 5008 gun to run a pressurized PPS cup as an alternative to using a larger N/N.

I asked Jeff about that about exactly that a while back (just after the last time this topic came up) and he suggested using the 6008's cup regulator with a PPS-equipped 5008.

Note that the "HGP" version of the 3M dispose-a-gun also has cup pressurization built into the gun body. It's just about the only conversion gun I know of that can do that (the 6008 relies on the aforementioned external regulator, as do the CATech guns with cup pressurization).