Air compressor doubling w/ a tee?

[CraigStu]

So my 36 yr old Craftsman is a small one but it has an output of 7.7 scfm@ 90. I have been looking around and there are a ton of compressors that go to 4-5@90 for $350-400. A couple of them are quiet versions. It seems that now a days one needs to be happy w/ 4-5 or jump up to 11+ w/ a large price bump. I know that in the past my die grinder wouldn't quite stay going w/ the existing compressor but I am doing less metal work than I used to and it is all just a hobby. So I am wondering could I buy the $400 quiet one now

26 Gallon 175 PSI Ultra Quiet Vertical Shop/Auto Air Compressor

Amazing deals on this 26Gal 1.7Hp 175Psi Oil-Free Compressor at Harbor Freight. Quality tools & low prices.

www.harborfreight.com

and if I ever run into a problem just buy another one and and Tee their out put hoses together. Would two compressors at 4.5@90 be equal to one at 9@90?

 

[atch]

... Would two compressors at 4.5@90 be equal to one at 9@90?

They might or might not actually put out 9@90; I don't know. What I do know is that it's not terribly uncommon for large shops to have more than one compressor piped into the same system. That is essentially what you would have. It works for them so I bet it would work for you.

 

[larry_g]

I used to have three small compressors. At times I would have them all tied together. So if your old one is still working keep it and tie it into the new quiet one when the new one can't keep up.

lg
no neat sig line

 

[CraigStu]

Thanks guys, that is what I was thinking but I was afraid there was something I was missing. Atch, now that you mention it, I remember working in a shop that had double compressors. Larry, that is an excellent idea. I was wondering what to do w/ the old one anyway. It still works but I figure it is on it's last legs so been researching so I'd have some idea what to do if it suddenly dies.

 

[nadogail]

I have two compressors, one small and the other smaller, and when I need a lot of volume, like when spray painting, I tee them together.

 

[bradpac]

Just have them piped together with a valve so you're not filling the tank on the second compressor when you just need the one going. Then when you need a bigger cfm fire them both up and open the valve.

 

[HoosierBuddy]

I like what bradpac is saying. A way to insure this would be to install one or more inline check valves at the outlet of compressor(s). Still a valve as he suggests, but this would work automatically.

Here's a 1/2" one for instance:

Amazon.com

 

[TractorJeff]

I wouldn't go thru the expense of check valves, let one compressor fill both tanks, if you feel the recovery time is too long, then fire up the 2nd compressor assuming you are going to tie them permanently?
I very often run the hose from my engine drive into the shop and plug it in to the air system when I feel the need for more volume or faster recovery.

 

[PoorUB]

I would not worry about check vales either. I don't see the point. If you leave the compressors hooked up together all the time the one that turns on first will have to fill both tanks, so what?

I have connected multiple compressors often over the years. I always set one to come on slightly before the other so one did the bulk of the work and the other turned on when the demand was high. For years I ran a little 3/4 HP unit connected to a 2 HP unit. The 3/4 HP would turn on a fill both tanks and the 2 HP would rarely run until the demand was high.

 

[brianh]

I tied two compressors together this winter after putting up with my screaming craftsman oiless for 20 years, I bought a harbor freight compressor pump and made a nice quiet compressor, lucked out on a 60 gallon double wall stainless co2 tank for it for scrap cost . I set up the craftsman to kick on at a few pounds less than my new one so unless I am using a lot of air it is just another air tank. Works great.

 

[CraigStu]

I hadn't thought of connecting them semi permanently. Having the quiet one fill both it's and the old tank would certainly help if I need quicker recovery. I could just leave the old one's electrical switch off and only turn it on when needed. After my initial post I was leaning toward a 60gal that provides 11.5@90# for $549 at Rural King. It is the best deal I have found but it would probably be overkill for my needs and of coarse it is an old style and I bet it is noisy. Thanks guys.

 

[The Cobbler]

your plan is doable, but note that many of the regulators have a bleed feature, where they bleed off air pressure to the setpoint. so in other words, if 1 regulator is 1 lb higher than the other lower set reg, the lower set reg will bleed off air . you never really get them set to the exact same pressure so one will always bleed some air
to get away from that, tie in before the regulators

 

[theoldwizard1]

My nephew needed to do some serious sandblasting. The two compressors he had access to were not adequate. Combined, they did the job. Probably not the best long term solution.

 

[dogdog]

I have Tee them to a broken 15 or 17 gallon craftsman compressor as a surge tank (tank is still good). works fine.

I just adjust both compressor to output like 100psi and put them on a different circuit because one is at 150PSI max cutout pressure, the other is 125PSI max cut out pressure, it won't be good just connecting them.

When I had only 1 compressor " craftsman 33 gallon oil-less" I adjust the cut-in pressure to be higher so the compressor kicks in faster and regulate the output to 100psi then pipe it to a surge tank (my 17 gal craftsman), it works some what for spraying but it's PITA... so YMMV I guess.

 

[Citation]

Nothing wrong with a T setup. I would suggest putting the T before the regulator (with a ball valve). I have T'ed two small compressors together. When I set the regulators to full I had no issues with air leaving the regulators.

For safety reasons you need to verify that the operational pressure of each compressor is lower than the rated tank pressure/blow off valve pressure of each unit. You don't want one compressor with a 175 psi cut out pressure and the other with a 150 psi blow off valve.

I would guess the old Sears compressor might be a 20A model. I think almost all 120V compressors these days are 15A max, not 20A. For example this 30 gallon model is 15A

Husky 30 Gal. 175 PSI Oil Lubed Belt Drive Portable Vertical Electric Air Compressor C304H - The Home Depot

Finish your sanding and painting work easily with the selection of this Husky 2-Oil Lubed Belt Drive Portable Vertical Electric Air Compressor.

www.homedepot.com

Some of the older Sears models were 20A and had the plug with the horizontal tab. The extra 1/3rd more power is likely why those older compressors had better numbers.

 

[CraigStu]

Citation that is a very good point. Many of the current ones are advertised to do 150-175# and my old one only runs at 125 so I was thinking that the extra pressure would be nice but I don't know if I would want 175# in the old one.

 

[Don R]

I piped five Ingersol Rand screw compressors into a 10" welded air main, we welded in an 8" loop around the plastics dept with 4 inch "ladder rungs" between the loop and 2" drops to each machine. It could have fed the entire factory. They had multiple compressors rooms in different areas and we welded in valved connections to feed other buildings as needed. I'd guess at times the new ones fed most of the plant.
I added an 80-gallon tank to my small Quincy twin cylinder, but it's in the back shop. What it all boils down to is the cfm of the compressors. The one set higher will run all the time, the other one may cycle. I piped 3/4 copper air line in the walls and keep air in the lines all the time. The bleeders only bleed down the pipe between the pump and check valve.

 

[matt_i]

I would take a look at your local electric. If you intended to put both compressors on the same circuit due to physical proximity, the inrush and or the steady load may be enough to trip your circuit protection.

 

[andyvh1959]

Piping two 4.5cfpm compressors together do not produce 9.0cfmp. Piped together they are basically plumbed in parallel, especially just teed together. The max output of either compressor is the max of the pair. You do gain the tank volume of both compressors when teed together. So if each tank is 60 gallons then you're air load draws from a total 120 gallons, but the output is still only 4.5cfpm.

 

[CraigStu]

To close this out, I finally got this.

https://www.lowes.com/pd/CRAFTSMAN-30-Gallon-175-Oil-Lubricated-Portable-Air-Compressor/5000042449

It runs on 120V and I put in a new 20A circuit for it. It isn't exactly quiet but is definitely quieter than my old one. One side benefit of it running on 120V is I put one of these in line to the new outlet.

https://www.amazon.com/dp/B01LVTGKBR/?tag=atomicindus08-20

This may be the best thing I have done to make my shop/garage better. Yep sometimes I go out there and have zero pressure because my distribution has a small seep and I forgot to close the valve at the compressor outlet. But I never have to worry about the compressor coming on when I am not there. BTW that is a link to amazon but I actually got it at Lowes or HD.

 

[Citation]

Piping two 4.5cfpm compressors together do not produce 9.0cfmp. Piped together they are basically plumbed in parallel, especially just teed together. The max output of either compressor is the max of the pair. You do gain the tank volume of both compressors when teed together. So if each tank is 60 gallons then you're air load draws from a total 120 gallons, but the output is still only 4.5cfpm.

I'm not following. If you put two 4.5 cfm pumps in parallel you should get about 9 cfm. You are right if you are thinking of the max output from the the tank is basically the same but that number is much higher than the pump CFM in most cases.

 

[nadogail]

4.5 plus 4.5 adds up to 9, two 4.5 CFM compressors will probably not be as efficient as a 9 CFM compressor, but only one small compressor should be able to maintain pressure in your air system during periods of low demand.

Compressor controls could be adjusted so that one compressor is your primary source of air and the other compressor runs only when the primary compressor is not maintaining system pressure.

 

[andyvh1959]

Opps, I stand corrected. If each compressor puts out 4.5cfm into one outlet then the total delivered cfm would be 9.0cfm. Wonder how much the length and plumbing of each output have to be exactly equal, or one output would tend to charge the other line. Maybe have something like a balance "reservoir", each compressor outputs into a large chamber from which one output line exits.

 

[PoorUB]

What good would a balance reservoir do? Both compressors would see the same system pressure unless you were running a large amount of CFM and one compressor had a slight restriction leaving the tank. A restriction that flows CFM than the compressor delivers.

 

[Don R]

The air will continue to equalize until one compressor is satisfied and turns off or the load is great enough that they both stay on. An experienced flow technician once explained it to me in an eloquent way. Liquids don't compress but air don't care.

 

[andyvh1959]

I was assuming a timing delay of one compressor lagging behind the other. Yes if both compressors are running a constant duty cycle then no balance reservoir would make any difference.

 

[PoorUB]

I was assuming a timing delay of one compressor lagging behind the other. Yes if both compressors are running a constant duty cycle then no balance reservoir would make any difference.

Still no difference. Just tee the lines together and don't worry about it. If the air demand is low the first compressor will run and fill both tanks. If the demand is more than one compressor can handle, the other one will run. Air will flow where it needs too.

It ain't rocket science!

 

[BarrelRoll]

Opps, I stand corrected. If each compressor puts out 4.5cfm into one outlet then the total delivered cfm would be 9.0cfm. Wonder how much the length and plumbing of each output have to be exactly equal, or one output would tend to charge the other line. Maybe have something like a balance "reservoir", each compressor outputs into a large chamber from which one output line exits.

You might be way over complicating this. Having multiple compressors feeding a plant is very common. Usually they are set up in a lead lag scenario with pressure switches. When both compressors are running they will equalize output pressures. Usually I set pressure switches up with a minimum 5 psi difference Lead would be 125/100, lag 120/95. The minimum 5 psi is to keep needlessly running 2 compressors at the same time and give the lead a chance to keep up before calling for a lag and make up for pressure transducer differences on PLC controlled machines. Pressure switch settings really depends on the air demand and what you are trying to accomplish. With the 2 small compressors running a die grinder you might have your main compressor set at 150/125 and you lag set at 100/90 so it doesn't fire up except when you have a big air demand.