How can I build a better pulsed pressure generator?

Do the old type Wagner vibratory paint sprayers only eject paint? I always thought that they pushed a lot of air to carry a small bit of paint. You described how much paint they move but are you 100% certain that they don't move any volume of air to convey the paint?

The Wagner "Power Painter" sprayers have an "airless" design. The reciprocating driving piston is directly immersed in liquid paint, and forces the paint out through an atomizing valve via direct pressure. The chamber is refilled from the paint cup (or an external paint can) via suction - the paint cup is pressurized by the gun.

There might be a very small amount of air occasionally suctioned upwards into the driving chamber along with the liquid paint (e.g. small bubbles from the paint cup), but this isn't either necessary or desirable... it's just a side effect.

The result is a spray of atomized paint from the nozzle. This spray will of course "entrain" some exterior air after the paint leaves the nozzle... but it's the paint moving the air, not the other way around. The spray of atomized paint is quite powerful... Wagner warns that the sprayers are quite capable of injecting paint through the skin if you get your hands near the nozzle, and that this can have dire consequences for your health!

High-pressure-air paint sprayers move a lot more air, and the newer "high-volume low-pressure" sprayers move even more. Both of these depend on the pressurized airflow to atomize the paint and/or carry the atomized paint to the work surface.

Whups... missed a word there. The paint cup is *not* pressurized by the gun... only by exterior atmospheric pressure. You can use longer suction tubes to pull paint directly from a gallon or 5-gallon can... I think the painter will pull paint upwards 3-4 feet or more, once the pump has primed and the suction has started.

But those things clog up a lot if you use sturdy paint, plus the cleaning is such a lengthy hassle. Those are the main reasons why my Wagner sits parked in a cabinet for around 15 years now and we have gone back to brush and roller.

Mine has been sitting on a shelf, in its original box, unused, for over thirty years.

So, didja get it working yet? Wha'd you do?

(Please let the curious know what your solution was, once you get there).

I was tempted to use it when we painted our house earlier this year but then decided to use ye olde brush and roller. I think the Wagner would have had a hard time with the rather thick Sherwin-Williams Duration paint. 9 gallons later ... done :-)

I don't think I've ever had mine clog up during a project. On the other hand, almost every paint I've ever used it with, has had to be thinned at least slightly to meet the Wagner's viscosity requirements. I've sprayed oil-based primer, latex primer and finish coats, and Kelly-Moore "Dura-Poxy" waterborne acrylic enamel successfully.

I understand that some paints are of the "Do not thin before application - really!" They probably wouldn't be a good choice for this sort of sprayer.

Those tend to be the best paints for the house, though.

I did exactly one project with this Wagner, a lattice fence. It clogged up about every 20-30 minutes. The Wagner may be good for thin paint but IMHO not for robust outdoor Latex paint.

Well, that's just the point. I do not wish to compromise the specification of the product just to make a tool work.

The Sherwin-Williams can be thinned but they recommended not to do that. Plus it might compromise the warranty. In the end doing the whole house with roller and (small) brush was less onerous a job than I thought. Considering that the pros want $6-7k for this job we came out ahead financially as well because that would have been after-tax money.

We wanted the best paint there is and this one seemed to come really close to that requirement. Of course, we waited for the 40% off sale :-)

I will. Right now a much more pressing issue has come up plus a client needs support, so the pressure generator will likely be on ice for 5-10 days. It is not something super urgent, I won't need it until spring

So far I am still using the rat-tat-tat-tat compressor and a makeshift valve for the pulsing (excenter in drill chuck hits valve switch handle).

Joerg, go to Home Depot or Grainger and get a 26dB Multi-Position Earmuff.

They are lightweight and the headband is adjustable so you can get the optimum position for maximum noise reduction and comfort. I got a pair at Home Depot and was amazed at the attenuation they provide. They are light and very comfortable and you can wear them for long periods with no problem. They should really help with the impact noise from the air compressor.

Here's a link. Note how the headband presses against the center of the earmuff. This allows it to tilt properly to fit your ear and the side of your head.

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$11.77 is very cheap for the comfort they give.

Contrast that with the Leightning Hi-Visibility Earmuffs. They use a steel band which may be hard to adjust when the earmuff is on your head. Almost 3 times the price, although you certainly can spend a lot more and get a lot less. Note also they do not state the amount of attenuation provided:

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JK

Titanium piston, and they specify the throat to be a little under an inch. Can you connect a dozen of them to a single plenum to make up enough volume moved?

Yeah, it's a long shot: basically, I was suggesting a slow-filling tank followed by an abrupt loss-of-pressure, and trying to get high frequency harmonics from a fast-release-of-pressure valve. You'd get a pressure rise as the tank filled, and a pressure drop as the tank vented, and you could servo it to make a sawtooth, with F, 2F, 3F... harmonics.

Even a longer shot, use a tuned organ pipe on the outlet, and let the ventpipe resonance be your pressure modulation.

Yes, but at some point the whole enchilada will get too far in the direction of yet another science project. I was looking for something simple.

That's essentially what I am doing right now. Slow filling reservoir tank, abrupt pressure loss via a switch turned into a makeshift motor-driven valve. That works. But it isn't very exact and repeatable. Plus the compressor for the tank replenishment is very loud.

The next church with a pipe organ is around 40 miles away and they probably won't let a Lutheran mess with the innards of their organ :-)

Then I'd also need earmuffs for all the others in the house, tell people not to call between 8:00am and 6:00pm, put a note on the doorbell to forget about ringing it, and get custom-made earmuffs for two labarador retrievers :-)

Anyhow, it's also that the current scheme does not produce a very repeatable pressure pulse. Often I need umpteen attempts to get it close to what it was yesterday.

I used the Wagner once to paint cinderblock. I had to thin too much, poor coverage, and the drips !! I also used Wagner ?, roller pump. That worked well, but a pain to clean.

Greg

Sound is attenuated by distance and closed doors. You are sitting right next to the source. If it is loud enough to be annoying, it could be damagng your hearing. I never worried about loud sounds before, and now I have lost all frequencies above 8KHz.

The 26 dB earmuffs do not completely shut out all sound. They merely attenuate it. Hearing is logarithmic. You can still hear things like the phone and doorbell, but the sharp impact noise will not be as severe.

I still do many things that generate a loud noise, often enough to be painful. After a few minutes, I ask myself why am I doing this. I put on the earmuffs and lo, the noise is much more reasonable. For only $11.77, you should give them a try. You can always take them back and get a refund!

By the same token, you should be wearing eye protection around machinery. If a part fails, a chip could destroy sight in one eye. I am also a bit lax in this area. I tell myself my glasses will stop any stray missiles.

But I am only fooling myself. I have a pair of high impact safety glasses that will fit over my regular glasses. They are not expensive. I really need to get into the habit of having them handy so I can put them on whenever I am working on anything that could break. You can only lose your sight once.

The labarador's hearing can also be damaged by impact noise. They should not be exposed to it regardless if you are wearing protection or not.

Put them in the back yard and tell them to chase any chickens that try to get in.

JK

HVLP is "newer technology?" I've got a 40+ year old electrolux sprayer accessory in the shed.

Joerg, I am not following exactly what viscosity fluid you want to pump but your s pecs of pressure are too low and there is no flow rate.

Again an expresso pump works from a half wave rectified line voltage operat ing a spring loaded solenoid with an iron core piston and nylon valve. It pumps cold water up to 150 psi and up to 2 cups/ minute. This may not be su itable for high viscosity fluids or your desired flow rate but is tiny (thu mb size).

Can you revise your specs for pressure vs flow rate and viscosity of fluid? Without these, it is guesswork.

Tony