air compressor question

since it's stupid question week . i have a 2 hp compressor with bad motor and a 2 1/2 hp compressor. thinking of fixing bad motor and twinning both compressors together, with a 80 gallon tank. will it be the same as a 4 1/2 compressor? stupid idea or not? what about adding more storage with a 40 gallon tank? can't afford a new 5 hp , just looking to make my small compressors think they are big.

 

Both can be plumbed into the same large tank but your output will still be 2 small compressors as for storage it will be much better. You could sand blast for a longer time but will take a longer time to recover. This is what I have and is sufficent for painting if Im careful. Blasting is slow. Air impacts are great, grinders run the air out fast. If thats all you can afford go for it. You can use it till you can afford a better setup. I been using my temporary setup for 18 years.

Ron

 

Not stupid at all. Good idea for a small shop, run the small compressor when you want to pump up a tire or blow off dust, plug them both in when you need more air for painting.

Good idea for a small hobby shop. Also avoids rewiring for 220v.

 

thanks guys. so maybe more storage is better?

 

To be clear, are you talking about having both compressors running, feeding the same air line?
That would not be exactly the same as having a compressor twice the size, but it would certainly work better than either one alone.

Now, if what you mean is to have one compressor filling both tanks, then you're not adding at all to your max CFM but you ARE adding more reserve air, meaning you could use it longer before it runs. But eventually it'll kick on and then it'll run for a long time to fill up both those tanks.

Either will work. I used (and used, and used) a portable compressor when building my car and ran it almost continuously by having a large box fan pointing directly at the motor and pump head. It used a ton of electricity and made my garage hot but it worked and the compressor is still working fine years later. Keeping them cool and changing the oil from time to time is critical.

 

i think you want to run both compressors at the same time into one large tank, that means one pressure switch, and thats where the wiring can become complex.

 

Yes, add the capacity of the individual compressors, that is your new capacity. Bigger tank. Some guys try to cover inadequate pump capacity with a larger tank. That works to a certain degree. But if you have adequate pumps, additional tank capacity just lengthens the time the pumps run as well as the non-run time. 80 gallons should work just fine.

The motors really should be on separate lines. Codes usually require motors over a certain size ( can't remember the exact size, but its less than 1 hp) to have a dedicated circuit. That would be especially true if they start at the same time. Maybe a 5 hp motor running two pumps. It ain't cheap, but you will have the motor when you decide to go with a better, bigger pump.

Bill

 

was thinking of running two motors at same time. they would fill the same tank. my compressors look like this only cheap used 2 hp and 2 1/2 hp with 20 and 30 gallon tanks. but i thought i would run them to 80 gallon tank. total storage would be 130 gallon. i would put the compressors on separate circuits.

 

If you are using a lot of air, more storage provides more time before the system pressure drops too low. Of course, it takes longer fior the compressor(s) to refill a larger receiver volume.

There are compressors that are manufactured with two pump/motor units mounted on one tank. That's not the most cost effective option, but it does provide some redundancy if one of the units fails. I had a 7 1/2 HP compressor and a 20 HP compressor with the receivers joined together. It works fine. If desired, you can set the pressure switches so that one compressor comes on only when the first can't maintain the pressure you select.

One thing to consider, if you are doing this at home some electrical work and/or upgrades may be needed to provide an adequate supply of power to both compressors.

 

my problem is with the 2 1/2 hp i can prime one fender and start the other but the compressors kicks on and wont keep up. i am wanting to paint my car.

 

It will be fine. Especially if you plug them in on separate circuits. You don't need any special wiring or pressure switch. You don't really need an extra tank either, but it will give you extra reserve for painting or sandblasting.

What you are talking about is a makeshift but plenty good enough for a home shop.

 

What kind of spray gun do you have? I use one of the cheap gravity feed jobs and it doesn't take much air at all. I use a pressure regulator on the gun and cut the air down as low as possible. It makes painting a little slower but does not make a lot of overspray.

 

Where you are using high volumes of air for extended periods of time, you need enough compressor to supply that and extra receiver volume won't help that. But, I think your 2hp +2 1/2 HP setup with lots of reciever volume would be enough to paint cars. Some compressors are quite a bit more efficient than others, so that's a factor too.

 

Anyone ever experieance a rusty tank explosion??? If so, how old of a tank? Really concerned of the youngest too ever? Personally, I havent in my 39years

 

I painted my OT car with this little compressor and a Harbor Freight gun.
Sure, I had to stop now and then for it to catch up, but overall it worked.

 

Not saying it couldn't happen, but all the rusty tank failures I know of didn't explode, they just leaked. The one tank explosion I know of was from welding on a pressurized tank that was thought to be empty. Fortunately there was no serious injury, but windows were blown out of the building.

 

We had a compressor tank fail at a marina I once worked at and all it did was blow out a chunk of the bottom about the size of a dime and the air all leaked out. I can't see one rupturing so bad that it would "explode", but I guess anything is possible.

I have heard of PVC lines blowing though and it isn't pretty when they go.

Don

 

More is better......... PVC lines bursting, has a way of commanding one's attention..... To be assured re; the tanks,..you can have them hydro tested by a local testing company.

4TTRUK

 

You can reduce the chance of a tank rusting out by draining off the condensation regularly. They rust at the bottom where the condensation lays, eventually they rust thru. When they do, they lose all pressure immediately making it impossible for them to explode.

I don't know how long it takes to rust out an air compressor tank, have never seen one fail and I have seen some old compressors. Have seen water pressure tank failure in a well pump or hot water heating situation, but only on tanks 40 years old or older. I saw one pressure tank in an old apartment house with 17 stoppers screwed into it to plug leaks. Hot water systems run about 20 PSI, well pumps around 40. These were tanks that had water in them at all times.

 

What's the life expectancy of sch 40 and 80 plastic 3/4" PVC? I have some outside, in the Central Calif heat: around 98* to 106* summer..

 

if you try and run two compressors into one tank while still running two pressure switches then only one compressor will ever start, i have done this with two 10HP compressors, we had one pressure switch running both motors with the second motor on a time delay, two start both at the same time you need to know what the amp draw of both motors is at start up and have a breaker and pressure switch big enough.

 

they do explode.

 

I worked with a guy who had 2 small compressors neither one capable of much. had them both going at once and when one got slow he "unchucked" his air tool and chucked it on the other hose.

 

By re-pulleying, you can speed up a pump and decrease the operating pressure so you get more air at a lower pressure, same hp. You don't need 150 psi to paint a car. You have to know the max operating speed of your pump and monitor motor temp until your confident you have not overloaded it.

Bill

 

thanks guys. started looking on craiglist and found some good ones cheap. 1/3price of new. think i will go this route. afford at least a 5 hp. 220 unit.

 

The other side of that equation is that compressor efficiency goes down as speed increases. How much that happens varies quite a bit from one compressor to the next.

 

There is no reason to run both pumps if you don't need them. If the system pressure never falls low enough for one of the compressors to start that means the one running is making enough air on it's own. If both pressure switches were adjusted exactly the same then both machines would start simultaneously. As you pointed out, that could be too much current draw for some electrical services.