Adding air storage tank to DA400 airbrush compressor

I don't know about the perfect size but I used a 3 gallon tank. I use an Iwata Sprint Jet and ran it to the tank from an old compressor I had on hand that the motor had died on. Works great with the bonus of being a large water trap. Yes, I still use a separate water trap too. It also alleviates any pulsing. The Iwata isn't bad about pulsing but did at very low pressures. I still run the compressor a lot, 3 gallon of air doesn't go far. At least not for me...

Tony

Tony,

Thank you. How long does it take to fill the 3 gallons tank? Do you drain the tank between uses? With the 3 gallons tank, how often does the Sprint Jet kick in during AB?

I have a 3 gallon tank hooked up to my compressor. The system fills the tank up to 100 psi and then the compressor turns off. It stays off until the pressure in the tank drops to about 80 psi, and then the compressor kicks in.  I seem to get about 15 minutes of spray time (not constant release) before my tank pressure drops to 80 psi and the cycle starts again.

I also have a pressure regulator so that I can adjust the psi to the AB and keep it between 12 and 20 psi - depending on the work being done. I have also installed a water trap after the regulator, as well as in in-line trap nearer to the AB.

I only empty my storage tank when I'm doing work on the system, such as draining a water trap. I haven't installed a shut-off valve because it doesn't take my compressor too long to refill the 3 gallon tank. 

I would try and go with at least a 3 gallon tank and up to 5 if you can. More stored air means greater time between you compressor cycling on. Regardless, use a tank to avoid the air pulsing that is common. 

scrambler8 wrote:

I would try and go with at least a 3 gallon tank and up to 5 if you can. More stored air means greater time between you compressor cycling on. Regardless, use a tank to avoid the air pulsing that is common.

I disagree with a tank that large for a small compressor like he is using as he is going to exceed the 50% duty cycle the air compressor needs to run at in order to avoid overheating.

How big is your compressor Scrambler8? 

That Paasche DA400 is a 1/6 hp motor, my Badger Million Air is a 1/5 hp and it has a .45 gal tank, not even a half gallon and there is a reason why, it is the 50% duty cycle I mentioned before. The Badger Billion Air has a larger air tank than mine (1.06 gal) but they upped the size of the compressor motor to 1/3 hp. If the compressor takes 10 minutes to fill the tank and then shuts off and you can spray for 5 minutes before it comes back on again then you are over stressing the compressor motor and shortening it's life quite a bit.  

I also recommend that everyone try and use some sort of fan aimed at the compressor to keep it cool and lengthen it's life, especially the oil less ones that get much hotter than oil bath silent models like my Badger, Silentaire, Jun-Air, Iwata, Werther, etc.  

Good question. I'll have to confirm, but I think it's a 1/2 hp motor. My compressor does have a cooling fan that runs for several minutes after the compressor motor shuts down. As stated, I get approx. 15 minutes of painting time (the trigger is not engaged 100% of the time) before my gauge drops to 80 psi and the compressor engages. The run cycle is only a few minutes to bring the storage tank back to 100 psi. So for my system, at least, it stays well within the comfort range of its duty cycle.

Another factor to consider is the psi capacity of the system.  While model painting rarely requires high psi, the ability of a compressor to pump more air into a storage tank will reduce the amount of time the compressor operates. Obviously, a lower psi capacity will limit the amount of air you can get into a tank. (Also have to consider the safety rating of the storage tank before too much air is pumped into it.)

My question is this: if you're assuming a 50/50 duty cycle and a compressor is charging a 1 gallon tank, or smaller, that compressed air will be used very quickly by the AB. Doesn't that result in the possibility of the compressor spending more than 50% of its time running under load to recharge the rapidly depleated tank?

The point seems to be that the compressor has to be properly sized to the storage tank. A small compressor trying to fill a big tank will cause the compressor to run more than it should. Likewise, a small tank won't hold sufficient air to prevent the compressor from cycling on to avoid its 50% duty cycle.

scrambler8 wrote:

My question is this: if you're assuming a 50/50 duty cycle and a compressor is charging a 1 gallon tank, or smaller, that compressed air will be used very quickly by the AB. Doesn't that result in the possibility of the compressor spending more than 50% of its time running under load to recharge the rapidly depleated tank?

That would depend on the compressor motor as was stated.

A 1 gallon tank with a 1/5 hp compressor would be great as the Billion Air compressor is that I mentioned earlier. Now if you had a little 1/8 hp compressor connected to that 1 gallon tank I would assume the compressor would run about 70-75% of the time to keep up which would result in an early death for the compressor.

The point seems to be that the compressor has to be properly sized to the storage tank. A small compressor trying to fill a big tank will cause the compressor to run more than it should.

Yes that is exactly right.

Likewise, a small tank won't hold sufficient air to prevent the compressor from cycling on to avoid its 50% duty cycle.

No that is not true as the small tank is filled very quickly and to a high enough psi to allow the compressor's off time to be sufficient. Now if the air tank was only being filled to say, 60 psi then you would be correct and the air would be depleted very quickly.

My Badger Million Air has a small tank but the compressor runs maybe 15 seconds to fill it and then it is off for about a minute or more of regular painting. With spraying out the airbrush with cleaner it cycles much more but it is still in the 50% duty cycle as it was designed to be.

Now the initial turning on of the compressor will take longer to fill the tank but after it is up to pressure the 50% or better duty cycle comes into play.

I just timed my 1/5 hp Million Air and it took 43 seconds to fill the small .45 gal tank to 126 psi (specs).  Spraying at 20 psi holding the trigger down constantly it comes on again after  11.3 seconds and takes 11.6 seconds to refill.....that is a 50% duty cycle and actual painting is even longer as the trigger is not always down.

As long as the compressor is off as much as it is on you are in the 50% duty cycle and good to go.

Mike and Scrambler,

Thank you for the inputs. The duty cycle is function of the compressor capacity and required AB flow. It is also affected by the tank size. With a larger tank, it would take longer to drop from the shut-off pressure to the kick-on pressure. So my main consideration is how long does it take to reach max (compressor shut-off) tank pressure (filled the tank).

My decision to go ahead with the tanking project was actually made after I saw what Mike did and read the web articles. Of course, I do not have the size of compressor that Mike has. The DA400 is spec at 1.48 CFM (42 L/min) and supposed to support 2 airbrushes. The recent July FSM article showed that it has the highest steady pressure (45 psi) among all units tested. If I assume an average flow of 0.5 CFM, it would take about 80 seconds to fill a 3 gallons tank. I don't want it to take much more than that for the initial filling. Unfortunately, the flow spec of most small compressor is meaningless. I don't have a good prediction approach until I have the tank to measure the filling time.

As is, the DA400 runs when I brush and stops when the AB is shutted off.

keilau,

Read my post above again as I timed it and edited my post.  

These are good discussions. At my company, we deal regularly with discharging compressed gas and charged chemicals out of various size tanks. The chemicals are stored typically at 360 psi and the compressed gas systems range from 150 to 200 bar. There are a number of factors that come into play including, elevation, temperature, required discharge time, pipe size and discharge nozzle orifice. Many of the same things apply to airbrushing.

Good luck with adding your tank. I believe you'll find it very helpful.

Let us know how it goes. 

Mike,

Another thing to consider regarding this matter is the frequency of cycling the compressor. Coming close to a 50% duty cycle is important. However, if your cycling on and off frequently - even if it is close to the 50% ratio - it will still cause wear and tear on the compressor components. For most of us, this frequent cycling doesn't come into play very often given the relative infrequent use of the compressor for model painting. However, it could be an issue if the compressor is being used regularly through the day on a regular basis during the week.

For me, and my model painting, I think my compressor will last a very long time.

keilau,

If I run the tank down to 20-25psi it takes maybe 10-12 minutes to build back to 100psi. That's without spraying while it's filling. When I'm painting a lot continuously I leave the compressor on. Most of the time I'm spraying at 20-25psi and the compressor will maintain 40-50psi in the tank. It isn't the ideal set-up but it works.

Mine is the SprintJet so it's manual on and off. The SmartJet has the auto switch.

The biggest reason I hooked it to the tank was the amount of moisture I was getting in the line. It's very humid here in the summer and these little compressors generate a lot of heat. There was more moisture than two water traps could handle. Not a problem now. I don't drain it every use, maybe once a month if I'm painting a lot. At very low pressure there was enough pulsing to notice, not now. Also, the air hissing from the bleed valve was annoying. Now it all goes to the tank. I did away with the regulator on the compressor and ran it straight to the tank and use a regulator on the tank. I suppose if I were electrically inclined I may have been able to use the pressure switch on the tank to turn the compressor on and off. I'm not.

Oh well, I've used and abused it for three years. It may die tomorrow but it's still working fine now. When you consider I went through two Campbell Hausfeld and one Craftsman in less than three years I think it's doing pretty well.

Tony

Thank you again, everyone. My final decision may depend on what I can find. The likely source of the air tank are auto parts store that caters to custom Jeep or truck. 3 gallons tank are cheap and plenty of choices, including some aluminium ones. 1-2 gallon tank are more difficult to find and actually cost more. I am trying to find it locally to avoid high shipping. If I have to go net shopping, I will likely get the 1 gallon Viair with 4 ports.

 If I have to pay more than $60, I may just go down to Habor Freight, get a compressor with tank and replace the noisy compressor with mine.

I will come back to post my result on a later day.

Keilau,

Another thing to remember is how is that auto on feature of that compressor going to affect how it runs if a tank is added? 

I remember someone on here had that problem a few years back and I am not sure what the solution was.

This is where I bought the 5 gallon tank for my Jun-Air silent compressor.

http://www.kmwperformance.com/products/AirTanks.aspx 

MikeV wrote:

Keilau, Another thing to remember is how is that auto on feature of that compressor going to affect how it runs if a tank is added?  I remember someone on here had that problem a few years back and I am not sure what the solution was. This is where I bought the 5 gallon tank for my Jun-Air silent compressor. http://www.kmwperformance.com/products/AirTanks.aspx

Mike, thank you. I learned a lot from you old posts. I already checked out KMW site last week. The price is very good, but their shipping is expansive. I like their 3 gallon Aluminium tank too, but nothing smaller in AL.

I added a three gallon tank to my Iwata Smart Jet. It takes about 1:45 for the initial fill and kicks on around 35psi for about :30 to run the tank back up to 50psi. Got the tank off of ebay for $10. Another $10 to ship it. Spent about $7 on fittings at the hardware store. I never shut it off. It kicks on about three times a week for thirty seconds and is always ready.

hkshooter wrote:

I added a three gallon tank to my Iwata Smart Jet. .... Got the tank off of ebay for $10. Another $10 to ship it. Spent about $7 on fittings at the hardware store. I never shut it off. It kicks on about three times a week for thirty seconds and is always ready.

hkshooter, you lucky guy. After shopping for a week both locally and on Ebay, I am giving up on getting the tank and fittings. Some parts, such as the check valve, is impossible to find at local hardware store. The total mail order bill including a 1 gallow tank with 4 ports, fittings hardware and shipping added up to over $60.

Checking recent sales on local craigslist and Ebay, I am convinced that I can get a complete oilless compressor with 1-3 gallon tank for less than $60 shipped. If I am lucky, I may even find one of those "as is", "not working" or "broken" one for $20-40 in very good condition. After throwing away the noisy compressor, I will get the tank, all the necessary fittings and a nice platform. My first choice will be this Sears compressor.

This re-manufactured Campbell Hausfeld looks good too at $69.

Wish me luck finding what I want on the used market.