Popular Woodworking 2001-12 № 125, страница 54
High Pressure vs. HVLP What's the difference between a conventional high-pressure system and a low-pressure system? In a nutshell, it's the speed of the air and the amount of finishing material you waste. HVLP systems produce no more than 10 pounds of air pressure per square inch (psi), and the amount of finishing material that lands on the work piece (also called the "transfer efficiency") is 65 percent or higher. Conventional high-pressure systems generally operate at around 35 psi and have a transfer efficiency of about 35 percent. There are two types of HVLP systems: conversion and turbine. Conversion guns are similar to a conventional high-pres sure system, working with a compressor but using a regulator to step down the pressure of the air at the gun. Though this is a good system and it produces less waste and overspray, it requires a fairly large compressor, which is expensive. One advantage of a conversion system is it applies finishing material faster than a turbine system, making it a favorite choice for production shops. Turbine units operate by producing air through a series of turbines (spinning fan blades, or a squirrel cage). The air produced is fed continuously to the gun at a lower pressure, but is capable of producing a high volume of air. This produces a gentle (but slower) application of fin ishing material to the project. Air flows from the turbine through the gun and into a plastic tube running to the cup to pressurize it enough to push the fluid into the fluid passageway of the gun. Unlike a conventional or conversion system, the air is not stored in a compressor's tank, but is a continuous stream. In bleeder-style guns, the air passes continuously through the nozzle, causing a constant hiss. Non-bleeder guns evacuate the unused air near the turbine, giving the gun a more conventional feel and reducing the chance of blowing dust around with the air stream. When speaking of HVLP, most people are referring to a turbine system (as we will be here). For most readers a turbine sys- |
