Vince Pitelka on sat 22 oct 05
my curiousity...
> Since I have not had the opportunity to compare these two respective kinds
> of Paint sparying Guns for having taken them apart to see the
> engineering-mechanical-design difference, can you maybe explain them to
> me?
> The 'conversion gun' is what, a regular one which has ( merely? ) a little
> larger diameter metering rod
> and a slightly larger oriface?
Phil -
As I understand it, standard high-pressure guns (usually running on 25 to 50
PSI) have the smallest passages, nozzle orifices, and spray needles, and
thus the greatest spray velocity, giving the lowest transfer-rate (the
amount of glaze that actually ends up on the ware) and thus the highest
overspray and waste. It doesn't matter how expensive the gun - a Binks or a
Speedaire or a cheapo Harbor Freight - if it is a high-pressure gun there
will be a lot of waste from overspray.
Far better are the so-called HVLP conversion guns like the Geil, which run
off a standard compressor but have a step-down regulator attached to the
spray-gun input, reducing the pressure to 9 or 10 PSI. That regulator is
critical, because standard high-pressure air hoses will not carry sufficient
volume of air if you try to step down the pressure at the compressor. These
guns have larger internal passages and larger nozzle orifice and spray
needle than a high-pressure gun, and the transfer rate is far higher, with
much less overspray and waste.
But by far the highest transfer rate is with true turbine-driven HVLP
systems, which have a turbine to create a high volume of very low pressure
(6 or 7 PSI). Those systems have a large-diameter hose between turbine and
gun, and the gun has much larger passages, nozzle orifices, and spray
needles. Some of the cheapest HVLP turbine systems like the $60 Harbor
Freight system are modeled after those old spray guns sold as accessories
for an Electrolux vacuum cleaner. They have huge internal passages and
spray orifices and do not incorporate a normal adjustable needle. I like
the slightly-more-expensive Wagner and Campbell Hausfeld turbine HVLP
systems. They have interchangeable nozzle orifices and spray needles for
different spray viscosities.
Hope that answers your questions
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
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