Episode 47: Making Mixed Compressor Systems Work

Jason Reed

Alright folks, welcome back to The Big Dog Podcast! Today we're rolling up our sleeves on an issue that a lot of bigger plants run into—how do you actually get centrifugal and rotary screw air compressors working together without 'em stepping all over each other? Lisa, this one's kind of wild if you think about it, because we always talk about these compressors like they're from opposite planets.

Lisa Saunders

Yeah, totally! It's funny, you always hear people treat centrifugals and rotary screws as if you gotta pick a side, but the reality—a lot of big sites are using both, and it makes sense when you look at their strengths. I mean, you look at oil-free applications in big facilities—aircraft repair, automotive plants, that sort of thing—centrifugals are super cost-effective at scale, especially when you need oil-free air in big volumes. But rotary screws, especially the oil-free models, they're flexible and efficient at just about any size, right?

Jason Reed

Exactly. Plus, you get into stuff like baseload, trim, backup... Folks forget you don't have to only run one compressor type as your baseload. You can actually have both acting as that steady baseline—just crankin’ full blast. Then your rotary screws kick in when you hit variable demand, trimming off those peaks. The other huge advantage? If you got a rotary screw sitting on standby, you got instant backup that matches your baseload, not some tiny unit that’s just there for show.

Lisa Saunders

That’s a good point. I remember an aircraft plant story we came across—a facility manager started out just with rotary screws, right? And as demand grew and grew, instead of swapping out every compressor, they scaled up by bringing in a centrifugal. Suddenly, they could handle those bigger demands efficiently, but without losing that flexibility from their original rotary screw units. That’s the thing: these two can actually “play nice” when you set ‘em up right.

Jason Reed

Yeah, it’s pretty much the playbook once your compressed air needs go past a certain point. You’re not forced to stick with one type—if you make 'em complement each other, you can hit that sweet spot of efficiency and reliability. I think we covered something like this back in our episode on multi-compressor systems, Lisa, but it’s a different animal when you start combining technologies instead of just stacking more of the same, right?

Lisa Saunders

Right—and it sets up a whole bunch of configuration options: you’ve got your centrifs hammering out high volumes as baseload, rotary screws swinging in for variability as trim compressors, and someone always ready on backup. That’s where it starts getting interesting, with engineered storage and controls. But hang on—I’m jumping ahead. Did you want to add anything about why plants actually end up with both?

Jason Reed

Nah, you nailed it—if you’ve got rapid growth, or if your facility has that variable day-to-day or even shift-based demand, mixing these compressors gives you way more control. And most of the time, oil-free is the name of the game, especially for food, pharma, aerospace—anywhere contamination is a problem. Alright, let’s dig into how those strengths play out in practice, not just on paper.

Lisa Saunders

So this is where things get kinda cool, Jason. Centrifugal compressors? Absolutely kill it at producing high volumes of oil-free air—but they’re only cost-effective once you hit larger sizes, like, usually north of 300 HP. If you're under that threshold, you’re actually better off with rotary screw compressors for efficiency and cost.

Jason Reed

Yeah, exactly. And rotary screws—especially the oil-free ones—can handle a much wider range of demands. You get real flexibility, especially if you throw a variable-speed drive on the unit—then you’re talking smooth adjustments, not all-or-nothing. They’re the Swiss army knife for handling those peaks and valleys in demand. Which, by the way, is super common in plants running uneven shifts.

Lisa Saunders

And this is where engineered storage jumps in—honestly, it gets overlooked all the time. Storage tanks, or receiver tanks, are basically the system’s shock absorber. They let you pull from a reservoir during demand spikes, rather than slamming the compressors with every single uptick. That way, even if you’re running a big centrifugal as your baseload, you can still handle those short-term fluctuations—and not risk running the compressor into blow-off or shutdown.

Jason Reed

I had a plant switchover a while back, and—where was I going with this?—Oh right, we added a couple extra storage tanks. Shift changes used to send demand all over the place—compressors were short-cycling, wasting energy, and alarms firing nonstop. After we sized the tanks to match those surges, it calmed everything down. The centrifugals just coasted, and the screws only had to trim where it really mattered. Simple, but a total game-changer for reliability and savings.

Lisa Saunders

It’s so underrated. People always wanna over-engineer with more compressors, but storage is sometimes all you need. And then, when you pair scrupulous configuration with the right controls—which I know you love talking about—we start solving not just for efficiency, but for actual, real-life problems plants face every single day. System stability, reduced cycling, better performance. That’s worth its weight in… well, compressed air, I guess.

Jason Reed

Ha! I'll take that. And look, if you’re dialing in your mix, it’s always about starting with what your plant really needs day-to-day. Centrifugals for the heavy lifting, rotary screws with variable speed drives as your utility knife, and storage tanks to smooth out all the unpredictable stuff. Set it up right, and you don’t just save some power—you put an end to a lot of those headaches that show up when demand gets bumpy. And, you’re tee’d up perfectly for the last piece—the controls, which is where a lot of people get tripped up.

Lisa Saunders

Yeah, controls seem simple... until you realize, left alone, these compressors will absolutely compete with each other—and waste a ton of energy. It’s not as easy as just setting all the pressure bands and walking away. Like, with basic fixed-speed controls and each machine set to its own pressure, you can actually make them fight for who gets to run. Sound familiar?

Jason Reed

So familiar. I mean, it’s kind of a rookie move but it happens everywhere. Pressure drops, screw compressors jump in with a blast, centrifugal sees it, pulls back or hits blow-off—even if nothing’s changed downstream. Total mess. You gotta have a smarter approach. Best thing? Set up a common pressure sensor downstream, so every compressor references the same actual system pressure. It keeps them in sync, so you’re not working against yourself.

Lisa Saunders

Right, and another move—using schedulers for different shifts. You can run just the rotary screws during, say, the night shift when demand is lower, and let the centrifugal sit out. That way you don’t overrun the big unit just to cover a little blip. It’s not fancy automation, but it solves real problems, you know?

Jason Reed

Yeah—and if you go with variable-speed drives, especially on the rotary screws, all those headaches with load/unload basically disappear. The VSD lets the screw unit ramp up or down as needed, smoothing out pressure and keeping everything running at the most energy-efficient point. It works almost like a centrifugal in that sense, especially in those mixed setups.

Lisa Saunders

I was actually looking at an automotive assembly case recently—they had both types, but it was how they used cascading controls that stood out. The whole thing was coordinated, so as demand rose, rotary screws would carry the early load, then the big centrifugals would kick on once you hit a certain threshold. That way, you weren’t running the high horsepower stuff just for a small increase—not burning energy for no reason. Plus, coordination like that cut their downtime too, because you had more flexibility when something needed service.

Jason Reed

That’s it. A lot of folks overcomplicate this, but it’s about seeing how all the pieces fit together. Whether you use a common pressure reference, smart scheduling, or variable-speed controls—or all three—just getting those controls right lets each type do what it’s best at. Combine that with smart storage sizing and your system is practically running itself.

Lisa Saunders

Alright, so if you’re thinking about mixing compressor types, remember: centrifugals for high-volume, rotary screws for flexibility, storage for balance, and controls for… well, sanity. And honestly, don’t try to do this on your own! This is exactly where your local compressed air expert is worth their weight in gold—they’ll help make sure you get the right system, tailored to your real-world needs, not just a bunch of gear stitched together. Well, that’s a wrap for today! Jason, always good bantering with you.

Jason Reed

Right back at you, Lisa. Thanks for keeping it sharp, as always. And thanks to everyone listening—catch us next time on The Big Dog Podcast, where we’ll dig into more compressed air tech without the fluff. Take care, Lisa.

Lisa Saunders

See ya next time, Jason. Bye everyone!