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Air Compressor filter/regulator & LVLP setup

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Forum topic by richardatkinson posted 02-21-2017 06:05 PM 2367 views 0 times favorited 19 replies Add to Favorites Watch
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richardatkinson

12 posts in 295 days


02-21-2017 06:05 PM

Topic tags/keywords: air compressor filter regulator lvlp hvlp spraypaint airhose compressor setup

Hi All,
After years of working with wood I now want to set up a small paint shop to paint some of my furniture… After reading loads of articles online… I am confused if anyone could help with my setup that would be amazing :)

I have a 14gal compressor with 2 outlets one with a regulator. So I though it best to keep the air tools on one line (A) and paint on one line (B).

Line A seams straight forward compressor / hose / air tools

Line B I confused what is best. A lot of people seem to recommend having over 50ft of hose or hard pipe before the regulator/water filter… something about the air from the compressor needing to be cooled so it can be separated by the filter so you don’t get water/oil coming out of the spray gun.

As I have a small spray room (workshop room 2) I thought I could loop the hose around first, would I be best to have 32 or 64ft of hose to cool the air? or is this no good and I need hard pipe like cooper to cool the air?

-- Love wood


19 replies so far

View EarlS's profile

EarlS

602 posts in 2183 days


#1 posted 02-21-2017 06:20 PM

Keep your regulator and filter as close to the point of use as possible. There are a couple of reasons for this.

First, the same amount of air (weight) at a higher pressure air occupies less volume than it would at a lower pressure (remember PV= nRT from HS chemistry class?)

Second, you will have some pressure loss as the air travels through the line. If you lose pressure after your regulator then your delivery pressure at the gun will not be correct and the spray will suffer.

Third, any impurities that might be in the lines (dust, shavings, whatever) will be removed in the filter (as well as moisture or oil from the compressor) You want the air cleaned just before it is used to reduce the chance of impurities getting back into your air.

Your main line should be one size bigger than the line after the regulator so you don’t wind up with an undersized supply line restricting your sprayer. You should be able to find flow rates at various pressures for different pipe and hose diameters so you can make sure that the lines are big enough for your sprayer capacity.

One last thought. Make sure you don’t try to spray while someone else is using an air tool unless your compressor can handle the flow rate and pressure to supply both at the same time.

Other questions?

-- Earl "I'm a pessamist - generally that increases the chance that things will turn out better than expected"

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richardatkinson

12 posts in 295 days


#2 posted 02-21-2017 08:58 PM

Thanks Earl, very helpful.

Just to go into a little more detail. with the hose/equipment I have already purchased for line (B) the paint line.

Firstly all my hoses have 1/4 BSP nuts, so my hose length are fairly fixed (apart from adding two together if needed)

I have: two 32ft fairly stiff hoses with a (9mm) 23/64 bore – which I was going to use either 1 (32ft) or both (64ft) joined together before the filter/regulator

one 16ft more flexible hose with a (8mm) 5/16 bore – which I thought would be good from the regulator/filter to my spray gun. (I do have a regulator on my gun so I can see if there is a pressure drop from the wall mounted regulator/filter).

so my main question now (in more detail) is should I use: one of the 32ft hoses before the filter/regulator both 32ft hoses to make 64ft in total neither hoses at all and splash out another about $150 on copper piping?

Also I did read somewhere that looping the system was good for no pressure drop, but I didn’t think this suited my equipment/layout!

No problem with using multi lines at the same time as its just me using the whole system.

Thanks again for any advice in advance :)

-- Love wood

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OSU55

1423 posts in 1825 days


#3 posted 02-21-2017 09:59 PM

You dont need copper pipe. Here’s my set up, which has never given me an issue in years of use: 50ft 1/2” air hose connected to compressor reg and gauge, hose sits on reel. Have a 3ft long piece of 1/4” air hose, one to the gun, other end to gauge/reg/filter for the gun, which connects to the 1/2” hose. Tried it with the filter/reg/gauge right at the gun but it always got in the way – not an issue with the 3 ft 1/4” hose. I just hold the filter/reg in one hand and the gun in the other. Typically run the compressor reg at ~75 psi and never have an issue with enough pressure at the gun A 14 gal tank will have your compressor cycling a lot. You couls plumb in an extra tank using quick connects to use only when you spray

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EarlS

602 posts in 2183 days


#4 posted 02-22-2017 06:30 PM

Richard – I would go with 1 length of the 9 mm hose to the regulator, then the 8 mmto the gun. No need to go around the room to get to the sprayer. Shorten up the distance from the compressor to the regulator and mount it on the wall if you can.

You don’t really want to have both hands full with a gun and regulator in a tight spot when you are spraying. Keeping the hose length to a minimum helps keep the pressure loss in the hose down. As OSU mentioned, run the compressor at a higher pressure and drop the pressure to the gun with the regulator just before the 16’ hose.

If you can’t get away from a regulator on the gun, eliminate the filter/regulator on the main line and just use one hose to the gun from the compressor.

Looping would only help if you had an oversized line and an oversized compressor. Ultimately, the compressor is the limiting factor. Having said that, I think you should be OK. I’d give a it a try before spending $$ on a more complicated system.

-- Earl "I'm a pessamist - generally that increases the chance that things will turn out better than expected"

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richardatkinson

12 posts in 295 days


#5 posted 02-22-2017 07:13 PM

Thanks Earl, you been very helpful :) also thanks to OSU55

-- Love wood

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Bill_Steele

217 posts in 1567 days


#6 posted 02-22-2017 07:29 PM

I’m glad you posted this. I recently purchased a smallish compressor (IR Garagemate – 20gal/2hp) for my use in my garage (impact wrench, air ratchet, fill tires, etc.) and I would like to perhaps use it someday to spray paint/finish on woodworking projects. I’ve done a little research, but admittedly I’m a noob so take that into consideration.

With regard to the 50ft length of hose before the tool—it’s my understanding that the reason this done is to give the hot moist air in the system a chance to cool down and allow any moisture in the system to condense out. A copper pipe will provide better transfer of heat than a rubber hose. If hot condensed air (full of moisture) goes through a water trap, it will only pull out the water that has already condensed. You should build in drain leg(s) to release any moisture in the system past the compressor tank. To much moisture in the air can negatively affect air tool life and paint/finish quality.

I saw a video where a guy took an inexpensive 50ft air hose (HF) and coiled it into a 5 gallon bucket filled with ice water. This helped cool the air and condense out moisture—still need to get the condensate out of the system before the tool.

I’ve read/seen where people use an automobile AC condensor or soft copper tubing or rigid tubing to create an after-cooler. I’ve thought about maybe getting a wort chiller and trying to incorporate that into my air system.

When I’m at the point where I’m serious about the spray finishing I’ll try to figure out how much of a moisture problem I have.

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richardatkinson

12 posts in 295 days


#7 posted 02-22-2017 07:35 PM

Hi Bill, I will let you know how I get on when I’ve set mine up!

-- Love wood

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EarlS

602 posts in 2183 days


#8 posted 02-23-2017 01:32 AM

Bill,

The humidity in the air is condensed out as a consequence of the compression. With little air compressors, the amount of water and heat from compressing the air should not be a significant issue. As long as you de-pressurize the air compressor occasionally and pull the drain out to drain any accumulated water you should be OK. Ultimately, the only water in the compressor comes from the humidity of the incoming air. On a normal day that shouldn’t amount to much. On a hot humid day you get a lot more moisture. A rule of thumb is that for every 10 degrees increase in temperature the air can hold 2X more moisture as humidity. Yet another reason for not spraying on a hot humid day. In a reasonably climate controlled environment this is a non-issue.

By compressing the air to a higher pressure then using a regulator to drop the pressure the air you are using will not be saturated with humidity. Also, water droplets in the air hose are a result from the condensed water in the receiver being carried into the hose with the compressed air which would also mean you are using a lot of air and it would be moving very fast to entrain the water droplets.

-- Earl "I'm a pessamist - generally that increases the chance that things will turn out better than expected"

View Bill_Steele's profile

Bill_Steele

217 posts in 1567 days


#9 posted 02-23-2017 05:17 AM

Earl,

Thank you for taking the time to post that excellent explanation! When I get around to spraying finish, I’ll pay attention to the weather (lower humidity days are preferred) and open/close the drain on the compressor tank periodically to release any moisture. Sounds like an after-cooler is not really necessary.

The compressor I have has finned copper lines going from the pump heads to the tank. I assume this is to help dissipate heat? If the air is cooled as it is entering the tank does that help with regard to reducing moisture content? I would think not. My guess is that it’s sort of a closed system past the pump head….right? Any moisture in the compressed air is still going to be there even if it is cooled. Maybe the cooling helps reduce pressure so that the pump doesn’t have to work so hard?

I have so many questions. Just ignore me if I become irritating :)

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OSU55

1423 posts in 1825 days


#10 posted 02-23-2017 12:52 PM

The compressor I have has finned copper lines going from the pump heads to the tank. I assume this is to help dissipate heat? Yes

If the air is cooled as it is entering the tank does that help with regard to reducing moisture content? Yes

My guess is that it’s sort of a closed system past the pump head….right? Yes

Any moisture in the compressed air is still going to be there even if it is cooled. No. As the air is cooled water vapor condenses and falls out of the air as liquid. This is how water gets in the air tank and needs to be drained.

Maybe the cooling helps reduce pressure so that the pump doesn’t have to work so hard? No. More heat transfer occurs the larger the temperature differential. As air is compressed it heats up (heat of compression) and friction of the compressor moving parts adds heat, The air is hottest at the compressor discharge and in the pipe going to the tank. The finning increases the hot surface area (another major player in heat transfer) and increases heat dissipation. Once the hot air gets to the tank it mixes with cooler air, and the lower temperature of the air reduces heat transfer. It’s also expensive to fin the air tank.

Air will “hold” more moisture with temperature, and less moisture with pressure. The compressor adds pressure but also heat, then the air cools in the tank and moisture “falls out” as liquid water in the tank, which then needs to be periodically drained.

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EarlS

602 posts in 2183 days


#11 posted 02-23-2017 06:18 PM

OSU – as I read your comments I figured you were an engineer. Sure enough, and you also worked on compressors (bonus for this conversation). I’m currently commissioning a 7,000 HP, 2 stage compressor that delivers 35,000 cfm at 50 psig.

-- Earl "I'm a pessamist - generally that increases the chance that things will turn out better than expected"

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OSU55

1423 posts in 1825 days


#12 posted 02-23-2017 07:32 PM

Earl – what’s the compression design? Never worked directly with anything that large.

View EarlS's profile

EarlS

602 posts in 2183 days


#13 posted 02-25-2017 02:56 AM

OSU – Centrifugal, and it is 20 years old so it isn’t going well.

-- Earl "I'm a pessamist - generally that increases the chance that things will turn out better than expected"

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pontic

500 posts in 444 days


#14 posted 02-25-2017 04:59 AM

If you are doing hi end lacquer jobs then get a Devilbiss dessicant(sp) dryer. If you have a big compressor that has an oil sump to lube the crank and pistons then you will need a coalessor in the line as well. Small oil free compressors still need a dryer if you want good results with oil based paints and lacquer.
There are two types of dryes systems pre coolers or intake refrigerators and output dessicaters.(sp)
If you don’t have a good quality HVLP and use a compressor for painting then get a dryer at leastIMHO.

In dentistry we had to use very tight tolerances to keep oil out of the lines. When you are painting a large project with a small compressor on a humid day the compressor is cycling while you are spraying and much of the moisture doesn’t have time to fully condense into the bottom of the tank and gets into the lines.

-- Illigitimii non carburundum sum

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pontic

500 posts in 444 days


#15 posted 02-25-2017 05:04 AM

Ever seen a nested screw compressor?

-- Illigitimii non carburundum sum

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