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Why add another air tank to your air compressor? This is page two of an article about I need more air! Page one about I Need More Air is here. Page one begins our discussion about the benefits of adding another air tank and this page continues that theme.
If an air tool draws more air than the air compressor can deliver even when running full out the supply and pressure of compressed air to the air tool will decrease. At a certain point, dropping air flow and pressure will not allow the air tool to do the job it was designed to do. Ultimately, the air tool will stop as the tank pressure continues to drop.
Adding another tank will help resolve that by providing an additional reservoir of already-compressed air for the air tool to draw against too.
An additional tank will help… certainly, but, if the air tool demands more air supply than the compressor can delivery, even the second air tank will run down as well.
When you add another air tank
When you add another air tank, when you are not using compressed air, your air compressor will run and fill both tanks – the one that came with the compressor and the one you have just added.
This means that the air compressor motor will run longer before reaching cut out pressure and stopping. The compressor pump is now filling a larger volume.
Increased compressor run time
Note that you must make sure that your air compressor will handle the increased run time. If the duty cycle of the air compressor is too low – that’s the maximum run time allowable to avoid compressor overheating – then adding a tank may make your compressor run too long at any one time, and that may damage the compressor motor.
The manuals for the lower cost DIY air compressors may not even show you what your compressor duty cycle is. If your air compressor manual does not indicate the duty cycle of your brand and model, then our rule of thumb is that your air compressor should only run for a maximum of ten consecutive minutes. If it needs to run longer to fill the tanks, the we shut it down and let it cool for fifteen minutes before running the compressor again. After the compressor motor has cooled down, we will run the compressor again for the maximum ten minutes or until both tanks are full to the cut out pressure setting and the compressor stops automatically, whichever comes first.
Having the extra tank, means that you now will have a much larger reservoir of pre-compressed air to use when you next run your higher demand air tool.Just watch out for compressor overheating.
Plumbing the new air tank
You can use one similar to the “air pig” shown in the image.
Plumbing would need to be modified so that air from the compressor pump would flow both into the main tank on the compressor and this new tank at the same time.
Plumbed this way the one pressure switch on the air compressor would monitor the pressure in both tanks and shut the air compressor off when the pressure reached in both tanks reached the normal cut out setting of the original compressor and tank.
To add a tank to your DIY type air compressor, the simplest way is to add a tee to the tank. See the sketch below.
- The first air line is plugged into the discharge coupler on the compressor
- The other end of that air line has a coupler
- Plug that air line coupler onto the connector on the secondary tank
- Since the coupler on the other side of the Tee on the portable tank is checked, air will not flow out until a mating connector is inserted into the coupler on the secondary tank
- When you need air at the job, plug a second air line into the discharge coupler on the secondary tank, and air from both compressor tank and secondary tank will flow down the line to your air tool
Place Second Air Tank Near Job
Another benefit of having a secondary tank is that the secondary tank can be placed nearer the job site more easily.
To use an air nailer for shingles on a roof for example, it would be so much more convenient to leave the heavy air compressor at ground level, run an air line from it up to the secondary portable tank on the roof, and then run an air line from the secondary tank to the nail gun. More convenient to move around and more air supply closer to the nail gun are significant benefits.
If you add another air tank to your air compressor, you will be able to use higher demand air tools for a longer period of time. If, however, the air supply and pressure diminishes still, and your air tool starts to wind down, then stop, take a break, and let the air tanks come back up to cut out pressure.
Just be mindful of the duty cycle.
If I add a second tank to my air system does it matter if I add the tank before or after my air dryer?
Thanks
The dryer, if not a refrigerant type, will dry air by cooling of the air stream from the pump. If the tank is after that dryer, air idle in it will continue to lose water if the air inside the tank is warmer than the air outside it. So in that sense it’s beneficial, as long as the tank gets drained regularly.
If the compressor has a refrigerant dryer, then putting the tank before it might, and that’s exactly that, “might”, overload it in terms of air flow through it if the piping allows that, and the air exiting the dryer may not be as dry as selected.
Hope this helps. In both cases, the tank needs a drain.
Hello, Can I put a T at the drain valve on the first tank to add a second tank instead?
Not quite sure what you mean. If you put a T in the drain of a tank, you could plumb in the drain from another tank, and on the other outlet install an auto-drain. That would effectively drain both tanks. Or, a manual drain valve could be used, and that, too, would drain both tanks. Does that help?
Hi, this is what I am trying to do. Will it work?
Vincent, with the setup you’ve drawn (thanks for the drawing by the way, it makes it so much easier to understand the intent) the added tank would eventually fill with water up to the point where it would drain out of the line on the side of the tank. This is not good.
Any reason why you cannot bring the line from the bottom drain on the added tank to the T?
Yes the drain lines will T and plumb together. However, in the second thought I probably hook up the second tank as your post above because the only time I need more air is when I do some painting 🙂
I am wondering if I permanently plumb in a second tank does it need to have a drain valve also if it is higher than the compressor mounted tank? Or would the water naturally settle in the lower tank only? The air line would run into the side of the vertical tank and out the top.
As far as I’m concerned, as long as all tanks have a direct path to the main drain, which should be located at the lowest point in the bottom tank, then all tanks will drain via gravity to the lower. Of course, each tank must have a drain portal at the lowest point in the tank, or water will simply build up in the tank to the level where it can escape, and the remainder of the tank will be under water in time, depending on service life, atmopheric humidity.
With multiple tanks I’d sure recommend an auto drain for the bottom tank. Good luck.
My only concern is that the secondary tank fills from the side & empties from the top so theoretically water could collect in the bottom of that tank? Or would it only collect in the lowest point?
Hey Michael. Water flows with gravity, so yes, it will flow to the lowest part of the tank. If there is no way for water to get out of the tank from the bottom, over time, that tank could fill with water.
Hi there. I know this is an old post, but I’ve just stumbled on it and its exactly what I want to do.
I have two compressors, one is a harbor freight 1.8HP, 26 gallon, 150psi max.
The other one is a campbell hausfeld 4hp, 13 gallon, 120psi max.
I intend to make both tanks run off the 4hp motor, but, use the pressure switch of 120psi. That way, I don’t over pressure the smaller tank because the larger tank can accept more psi. I’ll default to the lower pressure for safety.
Having said that, there is a brass/copper hard pipe that has compression fittings, appear to be 3/4″ from the motor to the tank itself. Then from there, the air goes through the pressure gauges, safety, regulator as most do.
On the larger tank, the whole gauge/regulator, etc. setup is directly mounted (no pipe) to the tank itself on a 3/4″ male nipple.
My first idea was to find piping, ‘t’ it the smaller tank and run the pipe to the larger tank. Then, I thought, why do I need piping when hoses will do?
So, I plan to run a female 3/4 fitting with a quick disconnect nipple with a hose (short, about 17″ or so-found a swivel end hose that should work) to the ‘t’, and then of course ‘t’ from there with a 3/4″ male to to 3/4 quick disconnect fitting.
I’ll do the same on the opposite side with the quick disconnect fitting, plug in another hose run of 25′ hose (shortest I found) to the larger tank.
At that tank, I’ll use a 3/4″ female to male adapter, screw it onto the nipple of the tank, then insert a quick disconnect nipple there to plug onto the hose.
For use, it will be primarily to support air tools for automotive work, but it is a home setup, not professional use so load on the system won’t be that much. The reason I’m doing this is it seems like I can’t get a full run down of the lug nuts (16 in total) before the compressor comes on. I then have to wait for recharge, and check the tightness again just to make sure I’m good.
Unless you tell me all this is a horrible idea and it will only end up to being a lot of work for the coroner to locate all my body parts. lol
I realize the run time of the motors too that you mentioned and I believe the 4hp motor will do fine to power both tanks.
Thank you for taking time to help.
The concept is sound. Know that with the compressor off, the pump is open to atmosphere, meaning that if one pump is running and the other is not, air being generated will simply go out the unloader valve on the other compressor. That needs to be addressed in your design.
It’s hard to visualize your set up as you’ve written it, but simply, regardless of what air lines you use to plumb (assuming they have the correct pressure rating) running a line from the tank output on the running compressor to the input of the tank on the second compressor, and air from the second goes to the air line to your tools will work just fine.
Wow, thank you so much for that quick reply! That is so helpful.
One last question if I can trouble you further:
I’m having a hard time finding a 3/4″ female tee fitting. Seems like whats available is either in the U.K. or ‘not found’ on ebay once I click the pic.
Any recommendations on websites to get exactly what I need, like, THE place to find air compressor fittings/hoses, etc.?
Google “brass fitting manufacturers” as I just did, and you’ll find lots of sources.
Not sure if you require extra information hopefully this is correct.
Wanting to know if installing a 50L Receiver is large enough for a Compressor that operates but with power surges will stop that compressor however want to continue the pressure flow with the Receiver?
Question is how long to hold above 1bar when releasing pressure at 2 ltrs per min? Do we need a bigger Receiver than a 50Ltr?
Sorry Q, but I have no idea what this means… “Wanting to know if installing a 50L Receiver is large enough for a Compressor that operates but with power surges will stop that compressor however want to continue the pressure flow with the Receiver?”
Also, I cannot tell you that, even if you provided the PSI (bar) requirements of the application. I am happy, however, to post this in the event some nice air engineer wants to comment. Cheers.
I have a 75 ltr tank can i ad a 50 litr auxiliary tank
Sure you can. Just make sure you read this page too: https://fix-my-compressor.com/add-another-air-tank/
Thanks for a very informative and useful set of articles. The information assisted in updating a couple of small portable hobby and light work compressors. Attaching a manifold to a couple of small volume air storage tanks have really improved the output and increase productivity on some projects. The recommendation to factor in the duty cycle and tool CFM can often be overlooked and are very valuable points as required to extend service life on these small compressors. Thank you again for providing this information. It will be well referenced and passed on.
I have a pump and motor that work great. But the tank is rotten. I also have another complete compressor. Can I hook up the two pumps to the same tank to get the boost in CFM?
Bryan, I moved your question to this page since it seemed be more applicable here.
Can you run two pumps to the same tank? Yes.
Typically, will one pump/motor bear the brunt of running most of the time? Yes.
As long as you have the two pressure switches getting an air reading from the same tank, then both pumps/motors should be off when the tank pressure (assuming both have upper pressure settings that are safe for that tank) when the tank is full.
Whichever pressure switch has the higher cut in setting will always go on first when the tank is drawn down. That may or may not be bothersome, depending on the compressor use.
If the secondary pump/motor has a cut in pressure setting above the cut out pressure of the first, then when the tank pressure drops to the cut in of the secondary pump, it will start and add air flow to the tank.
But, assuming both compressors have an unloader valve, if one compressor is on and the other off, air from the running compressor will flow out the unloader valve of the second. You will need to put a check valve in the air-delivery line from both compressors before you join the lines in a tee to the tank to prevent this.
Could be fun. Enjoy. Be safe!
Hi I am a bit confused and hope you can help. I have 50ltr compressor with a discharge pressure of 115psi/8bar but the tank fills to 10bar , firstly what’s the difference, and can I use an 8bar tank as a secondary tank. Hope this makes sense.
What happens when the tank fills to 10 bar? Does the compressor stop or keep running? Not sure what you mean by what’s the difference? About 2 bar, 30 PSI I’d say. Also, I wonder why the PRV isn’t cracking since I doubt that it’s normal that the PRV allows the tank pressure to exceed the cut out pressure by 30 PSI?
The tank fills to 10 bar and stops. I meant what is the difference between discharge pressure which is 8 bar and the tank pressure which is 10bar. What is PRV?
I want to connect the two tanks together but not sure if the smaller 8bar tank will stand the pressure.
PRV is pressure relief valve.
The tanks should have a plate on them somewhere indicating the rated pressure. Sometimes lower cost compressors don’t, however. If you have a compressor rated for a pump output pressure of 10 bar, and another with an output pressure rates for 8 bar, that’s a 30 PSI difference in pressure. Can you put, then, 10 bar into a tank that is designed to safely handle 8 bar. Maybe, but I wouldn’t.
When you say discharge pressure, are you referring to the pressure coming out of the discharge coupler, the one downstream from the regulator? If so, that pressure can be set by the user, and is typically set below the tank cut out pressure to help ensure that downstream air pressure is constant, which can be critical for some uses.
Thank you very much for help much appreciated.
You are welcome. Cheers.
Hello, great idea. I have a Rhyas 50l V-Twin 3HP 14,6 CFM engine which would probably (?) suit a twin tank set up. On the basis of aesthetics alone, I have seen very visually similar motors used on 100l tanks and, therefore, have some grounds to believe the motor would be sufficiently capable…?
Is a spares or repair compressor the only avenue for obtaining a candidate for additional expansion 50l tank? Or could used automotive LPG tanks be suitable (only where they have been emptied by qualified LPGA fitters as the gas expands 20x by volume at room temperature and is extremely flammable!)
I hope you may be able to help but superb idea you have suggested.
Regards,
Matt
I’ve uploaded an image of this type of compressor for folks that aren’t familiar with the make and model. It looks to me like a rotary pump, similar to one made by Thomas… is it rotary?
As long as due regard is paid to duty cycle, you can add any number of tanks you wish. Remember that doubling the tank capacity will make the compressor run a lot longer to fill multiple tanks.
LPG tanks? Not keen on those unless there is a plate on them indicating their pressure capacity, and that capacity is under the potential high output pressure of the pump. How would you drain the water from the LPG tank?
Like this idea. I have a 90 PSI compressor and want to add my 100 psi portable tank to it to increase volume. I’m going to try this so my pneumatic tools will run better, but like you said the cycle time is critical so you don’t cook your compressor.
Would you need a pressure regulator at the outlet of the reserve tank, of would the regulator at the compressor serve that function?
That’s an excellent question, Neb. Here’s how I would address that. If you add a tank and feed that tank with air from an upstream air regulator, the pressure in the downstream tank will only get to whatever is set on the upstream regulator.
I would remove the regulator between tanks, and add it to the downstream side of the reserve tank, and then, if you are plumbing air to your air tool from that outlet, you can set the pressure to the optimum for the tool and still have lots of reserve pressure in the two tanks.
I’m looking to build a 300 psi system and I want to know if I could run 2 air tanks rated at 150 psi to meet my 300 psi goal. Thanks.
Nope. Though I suppose it really depends on what you man by “running two tanks rated at 150 PSI to meet my 300 PSI goal”? A tank that is rated for 150 PSI should never be exposed to pressure over that level. Two tanks filled with 150 PSI outputting flow into one line will net out at 150 PSI in the line, with longer flow available due to the two tanks having more volume than the one. Can you expand on what you are looking to do, please?
I figured It would have more flow and volume, but I am trying to start on a project wich is a work truck with a on board air system, and I would like to have a 300 psi system, but might have to go down to a 250-200 psi system instead, but I’m just getting some planning done so I know what all I want, and I’m also quite new to the air seen so just looking for some pointers. Thanks.
What would you estimate a Kobalt 8 gal compressor maximum extra tank size be?
Can’t estimate as I’m not quite sure what you mean? Are you saying the largest tank possible for a Kobalt compressor? If so, what model, and if not that, what HP is the motor?
Another issue is how long will it take to fill the two tanks, and will that run time exceed the duty cycle specs of the compressor, or will that cause an overheat and the compressor to go off on thermal cut out?
Any size tank can work, as long as you can be sure that the compressor is not overworked to fill it, or to re-fill it if you are using an air tool with a high CFM demand.
I have a Werther TC-108 Special compressor with an 1.5liter air tank. I want to add a second tank in order to achieve higher air brushing times without the need of turning on again the compressor. Is it possible to auto switch to the second air tank when the 1.5L gets full? What kind of materials I’ll need and the second air tank how much pressure must withstand ? Thanks
Compressor
Bar 3.8/psi 55
L/min 23/cfm 0.74
The information on the page explains the process of adding a second tank, Thanassis. I don’t know what you mean by “auto switch”? If the discharge coupling is connected to the second tank, and you are drawing air from the second tank, as you draw air, more will flow from the compressor tank until such time as the compressor tank drops to the cut in pressure, and the compressor will start. Any tanks you use must be rated to withstand higher pressures than the maximum pressure the compressor can deliver.
I want to connect and use both tanks to the same compressor. So i will use a 1/8 T connector. By saying “auto switch” I mean a valve (if there is any) to automatically stop the air from the air tank.
I’m trying to understand why this is important? If you have air running to both tanks from the same compressor, with a check valve in each line from the tank before it gets to the Tee, the compressor will still run the same length of time as if it were filling two separate tanks? What is the need to isolate one tank with an “automatic valve”? Yes, you can do it, provided you have power and a signal, or perhaps with air logic devices, but how come this is necessary, please?
Okay so I have 2 compressors both 30-40gal. Compressor a had bad motor good tank. Compressor b has good motor and tank.
If I take compressor b line from motor and put a tee coupler with a line going to tank a and b and the two going into shut off regulator, and then put my quick connect on compressor a, I will have doubled my capacity, correct?
If by capacity you mean available pre-compressed air, when both tanks are full, and the compressor is off, then yes. Of course, the motor and pump and compressor B will run twice as long to fill the two tanks.
In my effort to add a tank, i want to tee off just before the check valve threaded into the tank.
What i am finding is that while it is a compression fitting, the discharge line is NOT a true 3/8″ or 1/2″ line, and the nut is 3/8″ PIPE threads!
So, based on the pic i included with this question, how would i still be able to use a compression fitting tee for both the discharge line AND the Auxiliary tank line AND thread the third tee opening onto the check valve inlet?
Is the threaded port to the left is the metal air line from the pump to the tank, and the larger threaded boss at the bottom of your photo is threaded into the tank? And you need one more line to pull air from the tank to a secondary tank? I wouldn’t install it here, it were me. I’d install a Tee at the port for the discharge coupler, removing the coupler, installing a tee there, reinstalling the coupler on one leg, and the additional air line to the new tank on the other. That line should have a one-way valve in it.
I have a porter cable pancake 6 gal for jobs on site. But I want a bigger and more powerful compressor in my basement workshop that will be static.
Somebody gave me a porter cable compressor 20gal 135psi 5.3cfm@90psi with a cracked tank. The compressor is almost brand new(he didn’t drain the tank and wasn’t using it often).
And I have an other porter cable 6gal pancake which the compressor is busted.
My question is is it possible to build a station in my workshop using 2 portable 10 gal tank with my 6gal pancake tank plugged on my compressor who was on the 20gal tank. That would give me 26 gal. I’d use it for nail gun and spray paint etc wich I guess would be plenty enough.
Short answer… yes! See the info on the page I’ve moved your question to: https://fix-my-compressor.com/add-another-air-tank/. As noted in response to our other question, without knowing the demand of the spray gun in CFM at the 30-40 PSI it requires, you will not be able to determine if the compressor 5.3 CFM will be enough.
will my compressor run less by doing this with a smaller compressor to larger tank
Raymond, there is no “free energy”. If you connect a small air compressor to a larger air tank than came with it, then the small air compressor will have to run longer to fill that larger tank. The larger the tank, the longer the small compressor will have to run. If the new tank is too large, that threatens the small air compressor, as it may surpass its duty cycle, and that may damage the compressor. On the other hand, if you can fill the larger tank with a small compressor, and give the small compressor lots of time to cool before it runs again, then you will have a larger reservoir of compressed air to draw from for your air tool. Whether you can fill that larger tank with your small air compressor will depend on make and model of compressor, and size of the tank.
So i have an old twin tank compressor with the motor shot. I ripped the motor off and ran a line in from the compressor at the bottom and a line out at the top to the gun. The piggy back tank is in series with the compressor. That probably will not give me the desired affect will it? What i need to do is cap off the bottom and then put a tee at the top for air in and out so it can use the same pressure switch? Or should it work the way i have it set up?
The way to install a second tank is as it’s recommended here: https://fix-my-compressor.com/add-another-air-tank/ . If you have problems with that, please advise. We certainly do NOT recommend taking a feed from the bottom of a compressor tank, as you will get a great deal of water and sludge along with the compressed air.