Two small or one big air compressor (opinions)

[Chrisc75]

Looking to relocated my transmission shop and I've always had issues with my air compressor not pushing enough volume (older unit that belongs to the building I was leasing).

Now I'm currently in a 5 bay shop and moving into a 8 bay. I need to buy a compressor but still unsure of what I wanna get and how I wanna set it up. Currently I'm thinking two 7.5hp two stage 80 tank units and splitting it between the shop (4bays each compressor)

My thought process is if one ever goes down I always have another one to keep working with or even if I'm not using the whole shop I can shut one down. Or should I go practical and get one large unit?

Any input would help its gonna be my first compressor purchase and rather do it right the first time

 

[larry_g]

Nothing wrong with two compressors. Me personally I would put both online with appropriate valving to isolate them if need be. This gives you a built in spare, if one goes down then you still have air from the other. There are a couple of thought on how to control two compressors. One is to have circuitry to alternate which one comes on first. One is to have both run simultaneously, i.e one pressure switch turns both on. One is a cascading control where the primary turns on first and if the pressure continues to drop then the secondary kicks on to help handle the load. Me I've favor the cascading control.

Either way I would suggest that you visit your local compressor store and have someone work with you to design a system that will handle the work your shop will be doing. Design in a port so that you can quickly connect a replacement compressor if one of the primary's fails and you need to rent a spare to bring online.

lg
no neat sig line

 

[Cyberbear]

I agree with Larry Q and his well thought out explanation and preference. The down side of one large compressor is that it always pulls big electrical power, but smaller a/c can be moderated as needed. I use several units from 80 gal., 7.5 hp, two stage down to a 3 hp portable unit as my needs require. Having a back up source of air can often make a big difference.

 

[sberry]

I use 2, a smaller one as the main and a larger one for peak demand. With the extra tanks on the smaller keeps up, I am done before it needs it.
But, how big was the old unit? A trans shop wont have the demand of a paint shop. A newer building with more modern equipment may help, did the old have air hoist etc? Another thing to consider is the number of bays may not change anything, its normally based on men.
An example is a house, can have several bathrooms but the occupancy is based on bedrooms. A real 7.5 makes a lot of wind for a mechanic shop. Smaller motors make for better starts, for larger units make sure the service can handle it. You may start out with 1 unit and add.

 

[sberry]

My thought process is if one ever goes down I always have another one to keep working with or even if I'm not using the whole shop I can shut one down.

There is no reason to split the bays, the air doesn't know any of this, In theory it is shut down if you are not using it. Buy a 7.5 and go from there, really need it get another one when the time comes.

 

[stonesfan68]

Since your customers and livelihood depend on compressed air then I strongly suggest that you get two compressors. I cannot tell you the number of times I have received phone calls from people who call up needing a part to keep their single compressor shop up and running and get really upset that I don't have it on the shelf. Get a back-up, the money spent now will be money saved later.

I would look at getting what is called a duplex unit. It is equipped with two compressors and two motors mounted on a common tank. It is also equipped with an alternator panel that will operate one or both compressors as needed to maintain air pressure.

Spend a little bit of extra money and install a header loop that will keep the pressure even throughout the shop.

Contact your local distributor for assistance in selecting the compressor and installing the air piping. Please don't go cheap and buy stuff on-line and then expect the local distributor to drop everything to help you out when the compressor fails- and it will fail eventually.

 

[Chrisc75]

I should of meantioned we are more then a transmission shop. We also do standard automotive repair. Currently I have 4 techs. After reading a lot about people running dual compressors. I feel as if everyone complained of high electric cost.

I also was looking at the ingersollrand 2545 which seems like it would be capable of what I'm needing in a single compressor. 10 hp 120 gallons pushing 35cfm @175

Best part is I can find it anywhere for the average price of $2600 shipped to my door.

I'm still open to the offer of running two compressors but not sure how I would install them to run them as you guys mentioned above

 

[sberry]

The install really isn't any different but since you have the overhead to run it get the 10 and call it a day. With common mechanical work, trans or wrenches doesn't matter much this should be well sufficient for 4 techs running wrenches. I have a bud with half a dozen men in a tractor dealer type shop, he uses a 10.

 

[sberry]

As a sole operator I can squeak by on 3 with big tanks, a 5 will run 2 men, would be short on auto body for some peak but in mechanical it would handle 4 without sitting on your finger waiting. You didn't mention what the old one was.
While the extra tank doesn't make more it does stretch the duty cycle a lot. By managing the down time I can get on a rhythm and sand near continuous from 3 with large tanks. I actually have the breaker to my 5 off.

 

[sberry]

After reading a lot about people running dual compressors. I feel as if everyone complained of high electric cost.

cost the same either way.

 

[Chrisc75]

Haven't been able to find any specs but the compressor we've been using which belong to the landlord at the current shop is a Wabco (Westinghouse) 2avc

 

[sberry]

Most of the dual setups to allow for no down are for sensitive operations. While you do rely on air its not life at stake critical and for a few hundred and a hose at a box store operation could be resumed in short order if it couldn't be fixed. Most shops I know including a couple busy tire outfits have a single comp.
I was well in to 20 yrs before my first repair which was partly my own fault. I added my second which I scored free and repaired as I was painting and had added men, did a little sandblasting. Demand dropped and a smaller unit serves all of us in regular mechanical. The spare came inhandy a while back as mine needed a 40 yr motor service, I am out in the sticks and was busy, I simply turned on the other unit. If I was bound up would have ran to store for a couple bearings and a cap and returned it to service immediately.

 

[Chrisc75]

Exactly I think I rather have the big unit right now for the price their going for. Wish I could compare it to the model I have now but I can't find any info on it wabco 2avc

 

[James-W]

If it were me, I would buy a larger compressor and keep the one you have to use as a "back-up" compressor just in case it should become necessary.

 

[Chrisc75]

The compressor I currently have now is not mine it belongs to the building I was leasing

 

[78scotts]

You might want to look into a rotary screw compressor. I bought one at work about 5 years ago and it hasn't let us down yet. Plus you can be in the same room as it because it is nice and quiet. The oil change cost a little more but it is well worth it. We do still have our old compressor for a back up but it just sits in the corner collecting dust.

 

[James-W]

The compressor I currently have now is not mine it belongs to the building I was leasing

Sorry, I missed that in post number 11.

 

[stonesfan68]

I should of meantioned we are more then a transmission shop. We also do standard automotive repair. Currently I have 4 techs. After reading a lot about people running dual compressors. I feel as if everyone complained of high electric cost.

I also was looking at the Ingersoll-Rand 2545 which seems like it would be capable of what I'm needing in a single compressor. 10 hp 120 gallons pushing 35cfm @175

Best part is I can find it anywhere for the average price of $2600 shipped to my door.

I'm still open to the offer of running two compressors but not sure how I would install them to run them as you guys mentioned above

$2,600 shipped to your door is an internet price for the 2545E10-V. I'd recommend getting the 2545E10-VP package that includes the starter, automatic drain valve and an air-cooled after-cooler. The "VP" doesn't cost a whole lot more money for a lot more options.

The argument of too much power cost is pretty silly: If you need both compressors to run in order to maintain pressure then you'll be running two 10HP compressors, or doubling the run time of the single 10HP. The math is the same.

To set the two machines up to operate in lead/lag either purchase an alternator for ~$1,100 or adjust the compressors' pressure switches to operate in lead-lag. The standard pressure switches on the 2545E10V compressors have a fixed differential, but they can be adjusted enough to make the system operate correctly.

 

[cashishift]

Big rotary screw, with a piston driven backup?

 

[bad_idea]

Another big aspect of your air supply is the air piping system. Our shop is much larger (machine shop, fab shop, pipe shop, electrical shop, all told 5-25 people working at a time, walk in sand blast conex, etc). We have a large rotary screw compressor, huge, and it has trouble keeping up at times due to the pressure drop through a poorly setup distribution piping setup.

I would suggest you contact a compressor company and get their input.