two compressors in tandem

[herbet99]

I'm currently using a 6hp compressor putting out about 10-15cfm. I'd like to upgrade to a little bit more flow (15-20cfm). I was looking at larger machines but what would be the downside of running a second compressor in tandem? My current one works great and a new one that puts out another 5cfm would be a lot cheaper. Not to mention that I don't have to upgrade my electrical box if the second compressor is a 120v/15amp type.

Thoughts?

 

[rhandwor]

If you only occasionally would need two compressors it would be satisfactory. A 220V machine with a bigger tank would be more efficient.

 

[Charles (in GA)]

If you do that, you need to use check valves on the tank outlets to prevent backflow from the other compressor. This way the two pressure switches will operate properly for each compressor. If you don't, the one that comes on first will will end up filling the other compressor's tank and that compressor will never come on.

Charles

 

[herbet99]

Yes, this would be for home use and only occasionally.

 

[herbet99]

If you do that, you need to use check valves on the tank outlets to prevent backflow from the other compressor. This way the two pressure switches will operate properly for each compressor. If you don't, the one that comes on first will will end up filling the other compressor's tank and that compressor will never come on.

Charles

good point, except that if the second compressor never turns on, that means the first compressor is able to handle the volume demand. Which isn't the case and is the reason for my wanting to add a second compressor. Right?

 

[wineslob]

I'm currently using a 6hp compressor putting out about 10-15cfm. I'd like to upgrade to a little bit more flow (15-20cfm). I was looking at larger machines but what would be the downside of running a second compressor in tandem? My current one works great and a new one that puts out another 5cfm would be a lot cheaper. Not to mention that I don't have to upgrade my electrical box if the second compressor is a 120v/15amp type.

Thoughts?

It's not 6 hp , more like 3. I think a good "average" cfm per hp is around 3- 3.5. If you get a "real" 5 hp unit you should be in the 17-18 cfm @ 90 psi range.
The tandem idea does work, but both units need to have the same cut-out/cut-in pressure setting.

 

[herbet99]

Thanks for the help

 

[NAYLOR]

Yes, this would be for home use and only occasionally.

The only time it is worth the cost is in industrial applications where you have one compressor providing a constant pressure. The second, usually a variable speed is used during peak times of the day. This setup (adding a variable speed) is only used to reduce energy cost.

Obviously this is not the same situation as you are facing. For home use, and as someone posted above, just get a bigger compressor.

 

[Lhorn]

I painted a car once running two smallish compressors together. One was a 26 gallon, the other a 33 gallon. Worked pretty well. The air from both was plumbed into a manifold (basically a galvanized pipe) that ran into a filter etc. I didn't have it set up perfectly so when you weren't using a lot of air, one compressor did the majority of the work, but when you really started to use a lot of air, they both kicked in.

 

[herbet99]

The only time it is worth the cost is in industrial applications where you have one compressor providing a constant pressure. The second, usually a variable speed is used during peak times of the day. This setup (adding a variable speed) is only used to reduce energy cost.

Obviously this is not the same situation as you are facing. For home use, and as someone posted above, just get a bigger compressor.

I'm not sure I understand your point. It's the cost that I'm trying to save. If I buy a smaller second compressor as suppose to "just get a bigger compressor"... then am I not saving the cost of a bigger compressor?

 

[herbet99]

I painted a car once running two smallish compressors together. One was a 26 gallon, the other a 33 gallon. Worked pretty well. The air from both was plumbed into a manifold (basically a galvanized pipe) that ran into a filter etc. I didn't have it set up perfectly so when you weren't using a lot of air, one compressor did the majority of the work, but when you really started to use a lot of air, they both kicked in.

This sounds like what I'm trying to accomplish.. thanks.

 

[Tim Cowan]

Since it is just for home/hobby use, if you have the space just add a 60-80 gal. storage tank in the corner or attic space and you have a lot more volumn for your tools without the need of #2 compressor. Be sure to use a regulator/dryer to not waste air and keep water out of line.

 

[gearbuilder]

I run two 5 hp compressors with the starting pressure for one set about 5 lbs lower than the other. The second one normally doesn’t start except when sandblasting or running an air grinder. Another point, starting two 5 hp motors at the same time would challenge my wiring.

Jamie

 

[alex71]

Short answer-- yes it will work. Downside for you--the noise of running two small oil free compressors at the same time is unimaginable.

You don't need any special plumbing or check vales. Just plumb them to a manifold or using tees and turn them on.

If you need lots of airflow and you don't have three phase power, this is really the onlyway to do it, as you can't buy single phase compressors over 7.5 hp, at least not tht I've seen.

 

[Thedroid]

You'll want to set the pressure switches different from one another that way one does most of the work, and the other one won't start until needed. As for the check valves there is some merit to that idea. I worked on some big Gardner Denver reciprocating compressors the other day that were burning up the motors and also the starters. These were 25 hp 480V compressors with a shieve/flywheel that weighs a few hundred lbs. At one point they were separate systems with the capability to be tied together. They were recently tied together to meet the demand, and when one of them stopped, the other compressor would cause the pressure switch to chatter, and the system was damaged. I fixed it by separating the set points, and installing snubbers on the switches. Check valves would have worked also, just didn't think about them.

 

[herbet99]

You'll want to set the pressure switches different from one another that way one does most of the work, and the other one won't start until needed. As for the check valves there is some merit to that idea. I worked on some big Gardner Denver reciprocating compressors the other day that were burning up the motors and also the starters. These were 25 hp 480V compressors with a shieve/flywheel that weighs a few hundred lbs. At one point they were separate systems with the capability to be tied together. They were recently tied together to meet the demand, and when one of them stopped, the other compressor would cause the pressure switch to chatter, and the system was damaged. I fixed it by separating the set points, and installing snubbers on the switches. Check valves would have worked also, just didn't think about them.

Interesting.. what's a snubber?

 

[herbet99]

I picked up a porter cable 3.5/1.6hp compressor that has two air outlets. My plan is to hook up this compressor in series from my other compressor by using both air outlets (I guess one will be in inlet). Next time I use a lot of air. I'll report on how it works out.

Thanks all for the input.

 

[alex71]

I picked up a porter cable 3.5/1.6hp compressor that has two air outlets. My plan is to hook up this compressor in series from my other compressor by using both air outlets (I guess one will be in inlet). Next time I use a lot of air. I'll report on how it works out.

Thanks all for the input.

unless i'm misunderstanding, you want to set it up so one compressor flows into another, and then to your air plumbing? that doesn't sound like it will work.

 

[herbet99]

I'm not sure how it's different. Unless there is a check valve in the outlets. Although, I guess the entire volume of air will flow "through" the second tank. That may not be a good idea if for no other reason than it might pick up more moisture. Well, a t-connection won't be that difficult.

 

[herbet99]

Short answer-- yes it will work. Downside for you--the noise of running two small oil free compressors at the same time is unimaginable.

2500 hours in a C130 has desensitized my ears somewhat.. but I'm also a big proponent of ear protection.

 

[FNFS2000]

Done this a couple times with little pancake compressors when I needed a little more volume, I made a manifold that went onto a portable tank that was fed by 2 small carpenter type compressors. It was sort of comical, but sometimes you gotta do what you gotta do. It ran an air hammer quite well....

 

[930dreamer]

Hello, I have an 1983 ish IR with two 3hp /3phase motors. I'm told each pump output is 11cfm. I built a rotary phase converter to power it , works great on 240 v single phase with 50 amp circuit. I need to move it to a shed outside. 930

 

[benjamming]

Interesting.. what's a snubber?

http://www.mcmaster.com/#pressure-gauge-snubbers/=4uv144

 

[herbet99]

http://www.mcmaster.com/#pressure-gauge-snubbers/=4uv144

ok.. thanks.

 

[Thedroid]

ok.. thanks.

Sorry for not responding sooner, been away from the computer. A snubber keeps the pressure pulsations to a minimum is usually used to keep gauges from being damaged, but also smoothes out the response of pressure switches and instrumentation. If you've ever seen a gauge with the needle bouncing, you've seen an excellent candidate for a snubber.

 

[orange02ss]

I have run 2 compressors at my shop for years with no problems. Both of them are 5HP 2 stage. No special pluming or anything, I just hooked up both compressors to the shop supply lines. I do have a bunch of line to feed two buildings though.