I've talked (email) to a couple of the guys that have built their own HVLP turbine from a 3 stage vacuum motor and they both seem quite pleased with the results. So I was wondering if anyone has taken this to the next level of 'frugal'. I already have a central vac in the garage where I want to spray, so I got to thinking that I could run my gun off the central vac. Yes, I've read about the Harbor Fright ghetto gun. A few problems spring to mind though, burning out the motor, dust in the spray and possibly low PSI. I'll stick a pressure meter on the vac's output to test #3 and a cloth over the output to check for dust and use a bleeder gun to prevent #1. The CV is fairly powerful though and I've never seen any dust on the car, plus it's dead quiet compared to my blower or Shop Vac.
I know the purists will hate this idea, but has anyone actually tried it? Any other problems I've overlooked?
You would have to have a pretty strong CV to power your HVLP. I am assuming that you are also talking about hooking up to exhaust, not reversing the motor.
You should be able to find some specs somewhere to get started, but again, I don't think you will get enough (but I have been wrong about other things) to get a good gun going. Find the gun you want first, then find out what the requirements are for the gun. Make sure you allow for more since all of the manufacturers of HVLP guns lie like hell about how little airflow their gun requires.
In understanding HVLP, you should be aware that pressure means very little to the gun. What you are looking for is HV (high volume) LP so when you spray you have lots of continuous air. You only need about 5
- 10 pounds of pressure to pressurize the gun so again, airflow is the key. I am not sure that a well used, dust/hair/dirt would be a good source of clean air to get you the finishes you want. The filters on a turbine are very dense and the air that comes out of the is really, really clean. The air that comes out of a vac has been cleaned by a paper filter of some sort. If you are spraying latex that would probably be fine, but for lacquers and polys, I wouldn't.
So I think I would look at either buying some inexpensive unit to goof with, or something expensive that would last.
Of you could build your own turbine.
Some of the systems are cheap enough for three stage you could hardly build for the cost when you look at a good gun ($300+), the proper supply line ($50), and a whip ($25). And still you have no turbine. But if you are so inclined to build, this is the only book I know of with detailed plans:
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that the book can be had used for about $5 plus shipping. Whether you use the plans for an HVLP turbine or not, this book has some good discussions on spraying in general and also CAS HVLP compared to turbine HVLP. Good info on general finishing, too.
If you're turned off by the Harbor Freight sprayer then I'd suggest you pick one up, try it and then return it if you don't like it. I think everyone is biased against their tools because we know they sell junk. The HVLP sprayer they offer works really well though. I can tell you there is no dust in the air that comes out of that sprayer. I'm spraying gloss finishes and not getting any dust or lint. I had that issue before I made a spray booth but now the issue is gone. If you're paranoid about the air quality you can add some more filtration to the turbine, keeping in mind that too much filtration will kill the motor. The low PSI is by design and is tuned to the system.
So here are my thoughts on your central vac question. The first is that the exhaust air from your central vac is likely a lot dirtier than you think. A single spec of dust will show up in a glossy finish and will drive you nuts. You would also have to tune the PSI and air throughput so you don't burn up your central vac. The large diameter output of the vac, constricted into a smaller hose for the gun would further increase the pressure and further stress your motor. Too much pressure at the gun is a bad thing also. The air emitted from a bleeder gun with actually blow the paint after it hits the surface you're painting. It creates an orange peel effect. This also causes the paint to dry sooner, making it harder to get wet droplets onto the surface and allow them to join together. Think about the process of how paint gets onto a surface; it has to be atomized, fly through the bleeded airstream, land on the surface while still wet and then flow together with the other droplets. Too much PSI in the airstream dries the droplets mid-air.
My summary is that you'll have all three issues you mentioned if you try to use your central vac. HVLP turbine systems are tuned for optimum air flow. You'll eventually have a turbine motor burn out if you use your sprayer heavily or for long periods of time. That's the nature of turbines but you have the same problem with an air compressor wearing out. I don't know which is more durable but my bet would be on the turbine.
Thanks, I've seen the book mentioned, but hadn't bothered to track it down yet. I'm in no hurry to start anyway, as it's too cold to spray outdoors now.
No real aversion to HF, I buy plenty of cheap tools for items I won't use much. But I must admit the closeup of the sprayer did look a little cheesie. I also wanted to spray some heavier finishes, so I wasn't sure the HF gun would do. Perhaps I'm better off getting an airless sprayer + the HF gun.
I was planning on buying a decent bleeder type gun to alleviate the back pressure. Although the one guy who built his own turbine bought a non bleeder gun, but used some sort of 'bleeder' control valve to accomplish the same result. I suspect you're right about the dust, but I plan to check this before I start. The CV will likely only be a temporary measure, until I can build a turbine. But who knows, if it may be good enough for my limited use.
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