Can I plumb two 60 gallon compressors together?

[gayler]

I have a 60 gallon compressor in my shop. I need to move the compressor from my late FIL’s garage. Can I plumb the tanks together and adjust the pressure switches to match or run them both on one pressure switch? Or am I better off keeping them completely separate?

 

[Firebrick43]

You absolutely can tie them together via the air output of each. In the industrial world its done all the time. I have seen 4 big scroll compressors (200 hp) and 4 piston (7.5 HP) all manifolded together. The big ones ran the plant air for normal operations, the piston ones were just for back up systems, and could be ran off the generator or when the plant was on shut down but certain processes, such as waste water treatment, still needed to run.

I would suggest not running them on the same switch but two separate switches.

Some like to set the pressure switches of one to come on lower than the other so the Main one will run first as air is consumed and then the other one kicks in say 20 psi lower. This only puts wear on both when the output is needed and it also keeps both from trying to start at the same time causing power fluctuations. You will undoubtedly need to put them on separate breakers.

 

[Jswain]

Just make sure they are rated for same psi, if not set them both to the lower rated unit.

 

[Gmonkee]

We did it in the diesel shop I worked in. Had to run them on different legs of 3 phase (both were 2 phase) or they could dim the lights kicking on. Boss set them so one shut off at 90 psi and the fresher one at 100psi.
It worked, it was hellsh noisy when both were running.

I was kind of in charge of daily draining the water and keeping the oil up in them. They will lose oil into the tank as they wear. Great for impacts, horrible for painting.

 

[DaveAndStuff]

Why do you want to run them both, do you generally not have enough air now?

You can used one pressure switch, but I would use an on-delay relay so that the slave unit starts five seconds after the mater units to avoid the big amp hit.

 

[larry_g]

What I did was build a Tee that had two male QD plugs on it and one QD outlet. When I needed the power of two compressors I would plug the two male plugs into the out put of the two compressors and the load into the out put of the Tee. Each input plug should have a quarter turn valve on it so that you can shut the input when you disconnect it. I did not mess with the pressure switches because they were far enough apart on cut-in pressures they worked fine as is. If you just want more storage then you can leave things connected and shut power off to one of the compressors. You can shut off the quarter turn valve on one and just run one compressor but have the second pressured up and ready to go with the opening of the valve.

lg
no neat sig line

 

[gayler]

Why do you want to run them both, do you generally not have enough air now?

You can used one pressure switch, but I would use an on-delay relay so that the slave unit starts five seconds after the mater units to avoid the big amp hit.

Don’t really need both, but I have two so might as well use them. I do occasionally use a plasma cutter and a sand blaster so I thought it would help with that.

 

[MOwens]

If you don’t need the cfm? I would plumb them so that you could use one as a backup and isolate each of them so that you can service one of them while the other is still in use. That way you have no downtime. I plan to do this in my shop in the near future. Depending on if you have a demand electricity meter or not, running two compressors at the same time could really spike your electricity bill if they both come on at the same time though.

 

[nadogail]

Industrial plants I have worked in had their compressors wired to a Alternator switch so that one compressor would start and recharge the system, and the other was in stand by.

This helped split the Running Hours between the two compressors.

 

[Superbowl]

Just leave one unplugged until you need more cfm's. The one can fill both tanks giving you a good amount of air.

 

[OldCarGuy]

Having two compressors tied into the main air line doubles your air receiver capacity. And is a highly effective way to optimize a compressed air system, especially for high-volume, intermittent tools. This upgrade drastically changes how your system stores and delivers air, altering your compressor's motor duty cycle and run times. It's best to stage the two compressors. The second compressor cuts in when the pressure falls below set point.

The heart of my compressed air system consists of two 80 gallon vertical five HP compressors that are piped together. Devair and Benpack. I run the Devair compressor 24 hours a day year round. Except when I leave town. When the first compressor drops below 110 pounds. The Bendpak compressor kicks in. Delivering twice the CFM output. That only happens when I'm sandblasting or using the 1” air impact wrench. The compressors are located in the large detached garage.

Moisture, oil, and dirt are the enemy in any compressed air system. Each tank has an auto drain valve at the bottom that's timed at 30 minute intervals to drain off any water in the tank. The compressed air first passes through a coalescing filter that removes oil, water, and contaminants. Then enters the refrigerated air dryer that extracts gaseous water vapor to ensure completely dry. Followed through a second particular filter before exiting to the shops in 1" black pipes to each of my seven garages. Braided rubber hose run under ground through 2" PVC pipes to the other buildings. Each of my six garages have 1" main runs that are routed on top of the ceiling joists. Most of the 1/2" steel drops are hidden in the walls, between the siding and drywall. For precaution the paint booth has a Devilbiss Camair filtration system that'll remove any missed contaminants.



One of seven reels


One of a 8 wall mounted air hoses.


Camair filtration system in paint booth.


I installed my system 25 years ago, and happy to say it performed great. Other than replacing the air dryer five years ago...

My home garage complex.. 3,500 ft house and 9,000 garages.

 

[oldtractors]

Just did it. A 7.5 HP and a 5 HP. Both set at 175 psi. The 5HP burned out the pressure switch because of cheap Chinese electrics, so I added a magnetic starter and wired it to the 7.5 HP pressure switch with a timer set at a 5 second delay. The 7.5 HP kicks on, and 5 seconds later the 5 HP comes on. Then both turn off at the same time. Works great. When they both ran independently, sometimes the 5HP would kick on first and barely keep up, so the 7.5 wouldn't kick on and the 5Hp would just run constantly.

 

[amgent57]

Keep the better of the two,
sell the other one.

 

[rsanter]

I guess I have a different though on this.

i think I would connect both compressors to the same tank. Then run a jumper from one tank to the other through a dryer. This would give you a wet and a dry storage tank.

i would also install a ball valve in the cross over so that I can turn it off to just fast fill the wet tank for say a quick tire inflating or something. For this you will either pull from the dryer or just on the post side of the dryer.
you can also use the ball valve to trap compressed air in the dry storage tank for holding

 

[Dagny]

An amp draw would be helpful.

 

[finn]

I’m thinking of installing a check valve between two tanks. Use the larger 175 (set to 165) psi to feed the system. And set the smaller, 120 psi tank to feed if the blast cabinet draws enough that the bigger compressor can’t keep up.

I run the lines at about 120 psi, and regulate that down to about 90 or 100 psi for media blasting..

Comments?

 

[BurtEggley]

I have a 125PSI sytem and a 150 PSI system. Both the tanks are tied together with quick disconnects. Both are set to the lower pressure - acutally about 120 PSI.

 

[DaveAndStuff]

I’m thinking of installing a check valve between two tanks. Use the larger 175 (set to 165) psi to feed the system. And set the smaller, 120 psi tank to feed if the blast cabinet draws enough that the bigger compressor can’t keep up.

I run the lines at about 120 psi, and regulate that down to about 90 or 100 psi for media blasting..

Comments?

What is the purpose of the check valve?

 

[finn]

What is the purpose of the check valve?

Safety check to protect the smaller 125 psi tank in case something goes wrong, like I forget to disconnect it in the event I want higher pressure. That 125 psi tank is the weakest link.

Really, it’s redundancy, which isn’t always bad.

The only time I need more air is for media blasting, so this is an intermittently used setup, and cheaper than buying new 5 or 7.5 hp motoy / bigger pulley, or a new $3500-$4200 compressor.

 

[DaveAndStuff]

Safety check to protect the smaller 125 psi tank in case something goes wrong, like I forget to disconnect it in the event I want higher pressure. That 125 psi tank is the weakest link.

Really, it’s redundancy, which isn’t always bad.

The only time I need more air is for media blasting, so this is an intermittently used setup, and cheaper than buying new 5 or 7.5 hp motoy / bigger pulley, or a new $3500-$4200 compressor.

But you lose the benefit of the additional storage capacity.

You regulate your line pressure to 120psi, yes? Just tie the 125PSI tank in after the regulator.

 

[Hohn]

I’m thinking of installing a check valve between two tanks. Use the larger 175 (set to 165) psi to feed the system. And set the smaller, 120 psi tank to feed if the blast cabinet draws enough that the bigger compressor can’t keep up.

I run the lines at about 120 psi, and regulate that down to about 90 or 100 psi for media blasting..

Comments?

The main use of a check valve here would be preventing the small compressor from running forever trying to fill the big tank if the big compressor somehow goes offline.

The downside to the check valve is that you'd need a second connection to a header/riser if you ever want air to flow both ways. I decided a ball valve at the tank outlet for each tank was a simpler and more versatile control setup.

You'd have a more efficient air plumbing system if you ran the lines at full tank pressure and regulated farther downstream near the point of use.

Unless you need to lower pipe pressure to protect marginal plumbing, there's no advantage to lower pressure in the lines.

 

[Hohn]

Safety check to protect the smaller 125 psi tank in case something goes wrong, like I forget to disconnect it in the event I want higher pressure. That 125 psi tank is the weakest link.

Really, it’s redundancy, which isn’t always bad.

The only time I need more air is for media blasting, so this is an intermittently used setup, and cheaper than buying new 5 or 7.5 hp motoy / bigger pulley, or a new $3500-$4200 compressor.

Is the small tank ASME rated? If so, what's the working pressure rating on it? What does it means when you say it's a "125psi tank"?
If it's not ASME and the 125 is the MAWP, then you really don't want to run anything in the system above that pressure. THere's a good bit of margin in ASME ratings that might make it ok to go higher, but without ASME I think it's rolling the dice a bit.

If I were you, I'd put your check valve on the outlet of the small compressor. THAT would protect the small compressor when it's off and you want to run higher line pressures than the little guy is rated. In the event the small compressor comes on, it should only do so when pressures are low enough to be safe for it. The pressure switch on the small unit can't "See" high line pressure until the check valve opens up when line pressure drops below tank pressure on the small unit.

 

[DaveAndStuff]

Virtually all the air tools we used at the plant were 90psi max. Running the line pressure higher than that made little sense. You would have to regulate every point of use.

 

[Hohn]

I've give this subject a bit of thought recently because I'm knee deep in my own shop air rework in light of getting my 80 gallon Champion commissioned. Watch for a posting on this soon.

In the meantime, I'm using my little 120v compressor with a LOT more tank than it was intended for (it's own 26 gallons, plus the 80 gallon Champ tank, plus a 10 gallon snubber downstream). My little guy is rated 150psi.

My small compressor's tank at 150 isn't ASME rated. Is another 25psi going to hurt it? Probably not. Not unless I was pressure cycling it down to 0 psi with regularity, which it isn't.

Remember, the relevant design factor for air tanks is *pressure fatigue* from cycling. Going 25psi over the MAWP and holding it there or even bouncing from 150-175 isn't what will hurt the tank. What hurts tanks is going 0-175 and back and forth for hundreds to thousands of cycles. THAT is how you get cracking.

A 125psi tank is ok if it's post-regulator. But often times adding tank capacity at lower pressure is counter productive. A 60 gallon tank at 175psi is more air than an 80 gallon tank at 125psi.

The smarter call IMO is never to add tank capacity post-regulator. The corollary being that you always want your tanks rated to handle full line pressure.

Then, regulate only at each point of use. Then you can tailor delivered pressure to the intended use.

 

[Hohn]

Virtually all the air tools we used at the plant were 90psi max. Running the line pressure higher than that made little sense. You would have to regulate every point of use.

Precisely.

But the 90psi rating is running pressure at the tool. If you want to keep dynamic pressure at 90psi at the tool inlet on the end of 50ft of hose, you need significantly higher pressure upstream of your hose reel. Like 105psi upstream of the hose as a minimum with even modest air demand tools.

Add any tool like a die grinder, band file or cutoff tool and you'll want 110-115 upstream of that hose reel to keep 90psi at the tool.
Unless a person is committed to oversizing all the plumbing (1/2 hoses everywhere) and using only V style plugs and couplers, you'll want to avoid regulating far upstream.

 

[finn]

Is the small tank ASME rated? If so, what's the working pressure rating on it? What does it means when you say it's a "125psi tank"?
If it's not ASME and the 125 is the MAWP, then you really don't want to run anything in the system above that pressure. THere's a good bit of margin in ASME ratings that might make it ok to go higher, but without ASME I think it's rolling the dice a bit.

If I were you, I'd put your check valve on the outlet of the small compressor. THAT would protect the small compressor when it's off and you want to run higher line pressures than the little guy is rated. In the event the small compressor comes on, it should only do so when pressures are low enough to be safe for it. The pressure switch on the small unit can't "See" high line pressure until the check valve opens up when line pressure drops below tank pressure on the small unit.

The compressor is an old DeVilbis pump “Sears Best” with a 2 hp 240 v motor that I bought new in about 1980. It’s advertised at 125 psi and around 10 cfm @ 90 psi. I doubt if it’s an ASME tank, though it might be. I’d have to check. It was sold prior to the compressor horsepower inflation nonsense.

The other compressor is an R15 Champion pump and an 80 gallon ASME tank. It’s a nominal 175 psi rating, but I turned it down to 165 psi in deference to its age.

Yes, the intent is to put the check valve at the outlet to the small compressor as a redundant protection.

i have a regulator / water separator on the wall at the outlet to the large permanent mounted compressor. The wall regulator is usually set to 125 psi in the piping anyway, so the check valve idea is a little overkill…. But I’m not infallible.

There’s another regulator at the cabinet. 75 feet away that I typically set to 90 psi for media blasting.

The piping is 3/4” black iron, with the final 30’ a 3/4” RapidAir knockoff.

 

[jblnut]

I have a self regulating system. It’s pretty slick, the compressor turns off when it hits 150psi and back on at 120psi or so. No need for additional fancy regulators lol.

Seriously though, I am mostly a one man band here so I have one regulator on a hose that I use if I need to lower pressure to a tool. Plug it in, plug into it and away it goes.

As to answer the OP’s question. Yes, use them both in whatever way you see fit. More air on hand isn’t a bad thing if you need it. Absolutely stage them so one comes on at a higher psi if you do high air draw things often. If you’re worried about cycling them so they each get used equally you can easily enough wire the pressure switches so they can be flipped to use on the other compressor. Alternate them whenever you think of it and walk by or do some fancy auto switch. Whatever you want to do will likely be overkill in a home shop.

 

[Hohn]

If you don’t need the cfm? I would plumb them so that you could use one as a backup and isolate each of them so that you can service one of them while the other is still in use. That way you have no downtime. I plan to do this in my shop in the near future. Depending on if you have a demand electricity meter or not, running two compressors at the same time could really spike your electricity bill if they both come on at the same time though.

This is what I'd do also-- primary and backup. You want to be able to isolate each compressor electrically and pneumatically. That means ball valves on each outlet and separate electric shutoffs. You also want to be able to depressurize either tank without depressurizing the other. The ball valves with the little condensate port in them are PERFECT for this. Just unscrew the little drain port on the side and let it bleed down slowly and safely without blasting your ears or your garage.

Think of it as the home gamer version of lockout/tagout. You want to be able to isolate a given compressor such that it has no stored energy and is not connected to energy.

Single phase 60 gallon units will have an appreciable amount of inrush. Which means you want to minimize starts and stops. Assuming that both of these 60 gallon units are 100% duty cycle rated and don't have cheap "compressor duty" motors, you would want to stagger the compressor cut ins but have either compressor capable of feeding both tanks.

For most home shop usage, the real win here is having 120 gallons of tank available. Whichever of your 60 gallon compressors has the higher pressure and duty cycle rating is the one you want to make "primary." Set that one cut out at 175psi and in at 140psi or so.
Set the backup compressor to a lower cut in and out-- something like 125 cut in and 145-150 cut out. This way your primary compressor is managing the 120gallons worth of pressure and the backup only kicks in when necessary, which will be very rare with 120 gallons of tank online. IN this setup, you'd want your compressor cut ins and outs to overlap but just barely.

Where it gets dicey is if both of the 60 gallon compressors are box store style units with limited duty cycle. In that case, you need to account for each compressor's different capabilities.

 

[Hohn]

The compressor is an old DeVilbis pump “Sears Best” with a 2 hp 240 v motor that I bought new in about 1980. It’s advertised at 125 psi and around 10 cfm @ 90 psi. I doubt if it’s an ASME tank, though it might be. I’d have to check. It was sold prior to the compressor horsepower inflation nonsense.

The other compressor is an R15 Champion pump and an 80 gallon ASME tank. It’s a nominal 175 psi rating, but I turned it down to 165 psi in deference to its age.

Yes, the intebt is to put the check valve at the outlet to the small compressor as a redundant protection.

i have a regulator / water separator on the wall at the outlet to the large permanent mounted compressor. The wall regulator is usually set to 125 psi in the piping anyway, so the check valve idea is a little overkill…. But I’m not invaluable.

There’s another regulator at the cabinet. 7 tweet away that I typically set to 90 psi for media blasting.

the piping is 3/4” black iron, with the final 30’ a 3/4” RapidAir knockoff.

I think we're of similar minds on this. Sounds like you have it well sorted out. The check valve on the old Sears outlet is the easy option here to protect a marginal tank from the mighty blast of the big R15.

 

[Hohn]

I have a 60 gallon compressor in my shop. I need to move the compressor from my late FIL’s garage. Can I plumb the tanks together and adjust the pressure switches to match or run them both on one pressure switch? Or am I better off keeping them completely separate?

If you can provide details on each unit, we can give you better recommendations.
It's one thing to say you *can* combine two units. It's entirely another to say how that should be done.

 

[Hohn]

Some general thoughts on combining compressors of unequal capability.
-- Put a check valve on the outlet each unit.
-- If the units are of different duty cycle ratings, you want the higher duty cycle rating to be your primary compressor.
-- Put a ball valve on the outlet of each tank. If you have a check valve too, the ball valve goes closest to the tank (check valve after ball valve).

If your higher duty cycle compressor is also lesser in pressure rating (unlikely, but it happens): Set your higher duty cycle compressor to be the primary, regardless of pressure capability.

Plumb a pressure relief into the common header that is no higher than the lowest rated tank in your system. If you have a 125psi tank in the system, use a 125psi relief (actually cracks higher) in your main header.

 

[Hohn]

Having two compressors tied into the main air line doubles your air receiver capacity. And is a highly effective way to optimize a compressed air system, especially for high-volume, intermittent tools. This upgrade drastically changes how your system stores and delivers air, altering your compressor's motor duty cycle and run times. It's best to stage the two compressors. The second compressor cuts in when the pressure falls below set point.

The heart of my compressed air system consists of two 80 gallon vertical five HP compressors that are piped together. Devair and Benpack. I run the Devair compressor 24 hours a day year round. Except when I leave town. When the first compressor drops below 110 pounds. The Bendpak compressor kicks in. Delivering twice the CFM output. That only happens when I'm sandblasting or using the 1” air impact wrench. The compressors are located in the large detached garage.

Moisture, oil, and dirt are the enemy in any compressed air system. Each tank has an auto drain valve at the bottom that's timed at 30 minute intervals to drain off any water in the tank. The compressed air first passes through a coalescing filter that removes oil, water, and contaminants. Then enters the refrigerated air dryer that extracts gaseous water vapor to ensure completely dry. Followed through a second particular filter before exiting to the shops in 1" black pipes to each of my seven garages. Braided rubber hose run under ground through 2" PVC pipes to the other buildings. Each of my six garages have 1" main runs that are routed on top of the ceiling joists. Most of the 1/2" steel drops are hidden in the walls, between the siding and drywall. For precaution the paint booth has a Devilbiss Camair filtration system that'll remove any missed contaminants.

30 minute duty cycles on the moisture drains is excessive. Especially on the lower pressure unit that is rarely used. If you're monitoring it, you'll notice no moisture comes out. The high duty cycle increases the chance of solenoid failure.

A 4 hour drain cycle is quite sufficient for your usage. I'll spare you the math of calculating the actual moisture removal rate, but in round numbers you'll need to run a compressor for two hours straight to produce a pint of water at 68F and 50% humidity.

Which means something like 2000 SCF of actual air usage per pint of water. 30 minute cycles aren't necessary unless your staff of technicians is really hard into air usage.

 

[racecougar]

Unless a person is committed to oversizing all the plumbing (1/2 hoses everywhere) and using only V style plugs and couplers...

That's the way to go, IMO & IME.

 

[Hohn]

That's the way to go, IMO & IME.

I did that as well. But not because I wanted to run lower line pressure. I did it because I want to lowest pressure drop in my system that I can reasonably achieve. High transient performance for short bursts. I'm not optimizing for a blast cabinet. I'm optimizing to make the best possible use of the air I have before cut-in. I have no couplers or plugs until the point of use, everything from the air tanks to the access point is 3/4 black pipe. The runs to the riser are -8 hose with JIC fittings. (cooler air as its out of the tanks, will within limits of push lock hose).

3/4 black pipe from the compressors, vertical riser to act as a knock out pot of sorts, all 3/4 black pipe header and drip leg to my main drop, which feeds the filter/reg/flowmeter/distribution manifold.

My milton 1020-8 at the point of use never has any water in it. It pretty much all condensed in the initial vertical rise of 3/4 pipe. In hindsight, I should have made that one riser 1" black pipe. Not for flow purposes, but for condensation purposes.

That said, I'm seeing no water at my usage point whatsoever, with no aftercooler or other special condensing provisions made. The black pipe alone seems sufficient to that task.

 

[OldCarGuy]

30 minute duty cycles on the moisture drains is excessive. Especially on the lower pressure unit that is rarely used. If you're monitoring it, you'll notice no moisture comes out. The high duty cycle increases the chance of solenoid failure.

A 4 hour drain cycle is quite sufficient for your usage. I'll spare you the math of calculating the actual moisture removal rate, but in round numbers you'll need to run a compressor for two hours straight to produce a pint of water at 68F and 50% humidity.

Which means something like 2000 SCF of actual air usage per pint of water. 30 minute cycles aren't necessary unless your staff of technicians is really hard into air usage.

I concur with your statement that cycling the moisture drains every 30 minutes may be excessive. Seeing that the two tanks are hard-plumbed together. While the secondary compressor runs but once a week. The main compressor's air enters the second tank with each cycle. Hence some moisture could/would enter the secondary tank. That's why I have an auto drain in each tank.

Despite the minor pressure drop from the two tank auto drains, plus the built-in auto drain on the air dryer. The main compressor only cycles once or twice a day, If the shops are idle. Despite the minor pressure drop from the tank drains, and the built-in auto drain on the air dryer. That pretty good, knowing the system has over 1,000 feet of distribution lines and hoses across seven different work areas.

The system has been running trouble free for 25 years now. Only issue was replacing the air drying, few nozzles, and some hose reel o-rings.