Adding another air tank

[Owen]

Hi everyone,
I'm planning on getting an upright compressor in the near future. I also want to get a hold of an old non-working compressor and connect the two tanks together. I've read on this site about people using two working compressors in tandem, but how about just adding another tank?

Where would I plumb the outlet of the main compressor in to the old one? Do I need to remove the cylinder block and then make a block off plate? I'm thinking of just disconnecting the copper hard line that goes into the tank and hooking the new compressor up to that. And then I would use the old tanks outlet/regulator like normal? Sound OK?

Is there anything else I would need to ensure proper operation?

Also, does this increase my CFM? Or is that not based on the size of the tank(s)?

Thanks

 

[PAToyota]

I'd just put a tee in my airline and connect up the second tank. Existing and new tanks on the two legs of the tee and then the third leg would run to the rest of the airline system.

 

[CRAZYASTRO]

in my old hall i just conected one tank to the other - that's it...

 

[nissan_crawler]

in my old hall i just conected one tank to the other - that's it...

I'm not a fan of using two tanks. Yes, it takes more time before the pump to kick in, but once it does, you have to wait that much longer for the damn thing go pressure up again, not much gain.

CFM has to do with the pump, not the tank.

High volume, low cfm = Longer use time until pump kicks in, but once it does, you're waiting twice as long for it to build up pressure again.

Low volume, high cfm = pump kicking in more often, but always keeping needed pressure.

I went with a high CFM (18 @ 100 p.s.i.) pump and only a 30 gallon tank. Yep, it'll run more often, but it'll keep up.

If you want to joint them together, I personally would keep everything on the existing tank (regulator, etc., and just run a single line from new tank to the old tank. That way, if you get rid of the second tank later, you stick one pipe plug in a hole, and your existing compressor is back to normal.

 

[Uncle Buck]

I think you ought to forget adding the extra tank for the reasons outlined by nissan.

 

[JB740i]

Could you use some ball valves going to each tank like we frequently do with the drain valve? One going to each tank?

 

[Owen]

Thanks guys,
I've heard of the longer charge-up times as well. If it bothers me, I guess I can always get rid of the second tank. Or maybe go ahead with ganging them and repair the motor one day in the future.

PAToyota, wouldn't my copper lines have to be rated at the same psi of the tank in order to prevent damage? I know I previously had my external regulator set to 90psi or so feeding the lines. I have no idea what copperlines are rated at.

CRAZYASTRO, how did you do your connections?

 

[nissan_crawler]

regular box store copper line is fine for the pressure, HOWEVER, you will want a flex line (at least for part of the run) between the two tanks, due to vibration.

 

[russlaferrera]

I think you ought to forget adding the extra tank for the reasons outlined by nissan.

I second that. More storage will not improve anything.

 

[Lyaec350]

Actually, if you have a big shop and a long run between where the first compressor is and your outlets, it might be advantageous to have a 2nd tank because it will act as a water separator when doing high CFM tasks.

 

[nissan_crawler]

or, you could do a separator and not bandage the problem.

 

[SteveU]

Hi everyone,
I'm planning on getting an upright compressor in the near future. I also want to get a hold of an old non-working compressor and connect the two tanks together. I've read on this site about people using two working compressors in tandem, but how about just adding another tank?

Where would I plumb the outlet of the main compressor in to the old one? Do I need to remove the cylinder block and then make a block off plate? I'm thinking of just disconnecting the copper hard line that goes into the tank and hooking the new compressor up to that. And then I would use the old tanks outlet/regulator like normal? Sound OK?

Is there anything else I would need to ensure proper operation?

Also, does this increase my CFM? Or is that not based on the size of the tank(s)?

Thanks

No, it will not increase your cfm, that is a function of your pump size & speed. The thing about doing something like this is the pump/motor combination of the new compressor is sized to work within a certain duty cycle during which it will fill the tank it is mounted on. Doubling the tank size will double the amount of time it needs to run to get up to pressure and shut off which may or may not exceed the duty cycle of the pump/motor combination. Think of it like a 350 motor which works well in a car doing about anything, now take it out and put it in a full size school bus and drive it in a mountainous area, it will not perform very well nor will it last very long because it is being overworked doing something it wasn't designed for.

 

[scurvy]

Depending on what Owen needs compressed air for, it may or may not be OK.

Like everyone else has chimed in, the pump (and its rated duty cycle) is what determines the overall SCFM of compressed air available. The tank acts only as storage so the pump doesn't have to run every time you need a little air.

If your needs are for short bursts of air, a secondary tank may be just fine for you. I have a tiny 1hp/3gal Craftsman oil-lubed direct drive compressor which does everything I (currently) need a compressor to do. I also have an external air tank which I will be plumbing into the garage along with a hose reel to give me bursts of air for using an impact or air ratchet for light wrenching.

On the other hand, if you need lots of volume for painting or sanding, all the tanks in the world won't make up for your lack of airflow.

Figure out your needs and size your tank appropriately based on those and your compressor duty cycle.

scurvy

 

[rsanter]

what did you need the air for? depending on the application this may be good for you...depending...
first thing is if this is a garage then you are wasting your time. if this is a commercial application then there may be some benifit if you are going to have the compressor going all day long and intend to store at a higher pressure and use a demand expander going out to areas of the shop.
if you are going to fire the thing up for short jobs now and then, you will be nearly doubling the cost of generating conpressed air.
if you need added reserve for some jobs then you will want to get a smaller (portable) tank that you can put in line near the point of use

bob

 

[Owen]

Thanks everyone,
The duty cycle issue makes sense, I may not do this after all. The usage is for a home garage with occasional automotive spraying, nothing bigger than a hood. But I do intend to spray gelcoat (for composites) once in a while, again, nothing bigger than a hood. Plus some ratcheting, etc.

If you've seen my other posts, my budget forces me to go with the Home Depot 60gal Husky.

Just a question on the cfm, why are tools and such rated at cfm if they're only used when the motor is not running? At least in the painting I did, I would wait til the motor stopped in order to avoid any chance of moisture getting to the gun. I simply carried that habit to my impact wrenches, etc. Is there no need to do this?

If tank size doesn't matter, I guess the ideal setup be a constantly running motor (that was quiet) and that increased cfm with speed?

 

[nissan_crawler]

Thanks everyone,
The duty cycle issue makes sense, I may not do this after all. The usage is for a home garage with occasional automotive spraying, nothing bigger than a hood. But I do intend to spray gelcoat (for composites) once in a while, again, nothing bigger than a hood. Plus some ratcheting, etc.

If you've seen my other posts, my budget forces me to go with the Home Depot 60gal Husky.

Just a question on the cfm, why are tools and such rated at cfm if they're only used when the motor is not running? At least in the painting I did, I would wait til the motor stopped in order to avoid any chance of moisture getting to the gun. I simply carried that habit to my impact wrenches, etc. Is there no need to do this?

If tank size doesn't matter, I guess the ideal setup be a constantly running motor (that was quiet) and that increased cfm with speed?

I have never heard of anybody stopping air tool use because the compressor kicks in. If you have a moisture problem, take care of it, don't bandage it. Get an intercooler, water separator, motorguard filter, all of the above, whatever. I can't believe you're painting without these measures anyway.

My 30 gallon I'm building is setup to run like normal via pressure switch, or with the flick of a valve, the pump runs continuously, and head unloaders controller whether the air goes into the tank, or back out the intake of the pump to cool the heads. Ideal? Eh, I don't think you can get an "ideal" compressor for everything, but it's the best compromise I could do. For most use, it will run on the pressure switch, for sandblasting and such, it will be on the continuous run setup.

 

[djjsr]

I was involved in an engineering project to install very large air tanks in several manufacturing plants. The object was to reduce the number of compressor starts, which reduces power consumption and saves money.

Typically each plant had four 300 hp compressors, so it's not quite the same as your home workshop, but the principle still works on a small scale.

The 1000 gallon tanks were installed both near the compressors and several hundred feet away in various places on the piping loop.

Not only did this reduce the number of compressor starts but it also resulted in fewer pressure drops when there was a sudden high demand for air.

Yes, the compressors ran longer when they ran, but reducing the starts saved about $35,000 per year at each plant in power consumption.

Just something to think about if you've already got a spare tank.

 

[PAToyota]

I was involved in an engineering project to install very large air tanks in several manufacturing plants.

One question - were they reciprocating compressors or screw compressors?

With screw compressors, it makes sense to have a metric buttload of storage space, fill it all up, and then let the compressor sit idle longer. This is due to the output characteristics of a screw compressor and also the time it takes to "spool up" to full output. In the case here - with a smaller reciprocating compressor - it doesn't make as much sense because the compressor is already going to be running quite often to keep everything topped off.

 

[Owen]

I have never heard of anybody stopping air tool use because the compressor kicks in. If you have a moisture problem, take care of it, don't bandage it. Get an intercooler, water separator, motorguard filter, all of the above, whatever. I can't believe you're painting without these measures anyway.

My 30 gallon I'm building is setup to run like normal via pressure switch, or with the flick of a valve, the pump runs continuously, and head unloaders controller whether the air goes into the tank, or back out the intake of the pump to cool the heads. Ideal? Eh, I don't think you can get an "ideal" compressor for everything, but it's the best compromise I could do. For most use, it will run on the pressure switch, for sandblasting and such, it will be on the continuous run setup.

Cool, so I won't have to stop at least when using normal tools. As for painting, I do have the separator and filter, water drops and all that. I just read somewhere to wait for the compressor to stop.

 

[VDubJoe]

I have 2 120 gallon tanks but they are both running units. Nice to have a spare. Otherwise i wouldnt do it.

Joe

 

[SteveU]

Cool, so I won't have to stop at least when using normal tools. As for painting, I do have the separator and filter, water drops and all that. I just read somewhere to wait for the compressor to stop.

The only time you would actually have to wait is if you were using a tool that used more cfm's than your pump made to the point where you depleted your tank to a pressure that would no longer run correctly. A good example of this is a die grinder which needs a 20+ cfm compressor to run constantly, you can run one with a smaller compressor but will have to take frequent breaks to let it catch up or it will start running poorly then not at all until you stop & let the pressure build back up.

 

[Micscience]

I'm thinking of adding a second tank myself. I have read the points that Nissan mentioned and SteveU which are really good points however, nissan has an 18scfm compressor most people who want to add a second tank are not even half that cfm. And in response to what SteveU said compressor engine's are built to be on for a long time. To me a long time is 50% duty cycle. A lot of compressors sold at retail stores don't even mention the duty cycle probably because it is irrelevant. That doesn't mean it should be ran to the max but a lot of compressors can handle 100% duty cycle. Most manufacturer's will ask you to run your compressor with the drain open for 30 minutes to break it in and some are even longer. I'll most likely use my compressor for automotive repair stuff mainly so I think adding a tank is perfectly fine. I have a CH 15gal 200PSI compressor which has only 3.8 cfm @ 90psi so you can see how it would help me out. The motor will run longer to fill up the 2nd tank but the motor might only go on once or twice instead of six times. The problem I face is finding a 200psi tank.

edit: If you are worried about the duty cycle put a fan on the motor to keep it from overheating.

 

[kc-steve]

Interesting comment about duty cycle Mics, but I have never heard of a 200psi tank, whew! I would also worry about the compressor wearing out sooner than usual.

I think someone mentioned this, it really depends on what you are going to use with the compressor. I calculated my needs before I purchased my compressor and things have worked out fine for me.

Steve

 

[cheechi]

CH's most recent line of compressors is boasting smaller tank equivalents because they're 200psi, so they store the same mass of air in a smaller volume. Not exactly the same in the real world but I haven't seen one in use to know much more about it than the box in Lowe's.

 

[larry_g]

so I think adding a tank is perfectly fine. I have a CH 15gal 200PSI compressor which has only 3.8 cfm @ 90psi so you can see how it would help me out. The motor will run longer to fill up the 2nd tank but the motor might only go on once or twice instead of six times. The problem I face is finding a 200psi tank.

edit: If you are worried about the duty cycle put a fan on the motor to keep it from overheating.

lots of 200psi tanks here tanks It sounds like you have thought all this out so go for it. Let us know how it works out for you.

lg
no neat sig line