Read this about HVLP. It gives some good insight as to the differences from conventional equipment. Regardless of what you have heard about HVLP being able to spray higher viscosity than conventional air, it may be necessary to thin your primer the same as you did before.
_____ _____ _____ _____ _____ _____ _____ _____ _Ask Doctor Gun
Is it Time to Switch to HVLP? Are you thinking about switching from non-HVLP to HVLP spray equipment? If you are, then you should take a few moments and read over the following questions and answers. These questions have been submitted to me over the last few years by painters like you. The answers may help you make up your mind. If this doesn't cover all your questions about HVLP and you wish to ask me another one, then just head on over to the Ask Doctor Gun Message Board and send yours in. I'll get back to you as soon as possible. Q: Will I have to change my spraying technique?
Doctor Gun: Yes, and here's why. A non-HVLP spray gun's 50 PSI inlet gives you 50 PSI out at the cap. Depending on the brand you choose, an HVLP spray gun may require 18-80 PSI in to produce the mandated 10 PSI at the cap. Since the paint exiting the gun at 10 PSI will not carry as far as at 50 PSI, the gun must be closer to the painting surface. The recommended 8" distance for most non-HVLP spray guns should be cut by 2-4" for HVLP depending on the painter's technique. Q: Will I lose my production speed?
Doctor Gun: No. Transfer efficiency on HVLP should be about 65% compared to 25-30% for non-HVLP. This, along with the fact you are spraying closer to the surface requires that you spray faster. The closer to the surface, the faster the stroke; the further from the surface, the slower the stroke. Q: Will I need a larger compressor?
Doctor Gun: Maybe! Be sure to check the CFM on the gun you are considering and don't be fooled by the low inlet PSI on some HVLP guns. The CFM requirement is very important and can range from 7.5 to 24. Rule of thumb..... . a good 5 HP compressor should produce 3.2 - 3.6 CFM per HP. Q: Is HVLP really a good investment and will I see any material savings?
Doctor Gun: Yes and yes. A 30-50% material savings is easy to obtain and at that rate your equipment pay-back period is short. As your HVLP technique improves, so will your savings. Q: Is temperature range choices for reducers and hardeners more critical with HVLP?
Doctor Gun: No and yes. No for small areas and yes for larger ones. Medium and slow reducers and hardeners should be used to allow for good solvent escape and flow out. Q: Can I still use one gun for most refinish materials?
Doctor Gun: Not likely and expect to stay in compliance. The inlet pressure is critical to maintain 10 PSI at the cap and this does not allow increasing the atomizing air to compensate for higher viscosity materials. However, if you are not in a compliant area, don't worry about the 10 PSI at the cap and increase the inlet pressure. The maximum inlet pressure marked on most HVLP spray guns is in reference to the pressure at the cap, i.e.: maximum 50 PSI equals 10 PSI @ the cap. Spraying at a higher pressure will not harm the gun. Just put your gun out of the 10 PSI @ the cap range. Here's a recap when spraying with HVLP — Depending on the brand of spray gun, you will see a wide range of inlet pressures to equal 10 PSI @ cap. — Having enough CFM is critical. — Spray at a closer distance. — Use a faster stroke.
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