Schulz builds three families of rotary screw air compressors, all labeled SRP: Compact, Dynamic and Flex. They overlap in horsepower, so choosing between them comes down to how much air you use, how steady that demand is, and how much floor space you have. This guide compares the three lines using the actual models and specs we carry.
Why choose a rotary screw at all?
Piston compressors are built to rest between cycles. Rotary screws are designed for continuous duty: they can run all shift, every shift, while staying cooler and quieter than a piston unit of the same size. If your piston compressor runs most of the day, or you’re adding people, machines or a second shift, it’s time to look at a screw. Our post on when to upgrade from piston to rotary screw lists the warning signs.
The three SRP families at a glance
| Series | Models | Power range | Drive | Best for |
|---|---|---|---|---|
| Compact (SRP 30xx) | 3008, 3015, 3025, 3040 | 7.5β40 HP | Fixed speed | Shops that need screw-compressor durability in a smaller footprint and budget |
| Dynamic (SRP 40xx R) | 4008, 4010, 4015, 4020, 4025, 4030, 4040, 4050 | 7.5β50 HP | Fixed speed | Steady, predictable demand: production lines, body shops, fabrication |
| Flex (SRP 40xx Flex) | 4010 through 4250 | 10β250 HP | Variable speed | Demand that rises and falls during the day; plants focused on energy cost |
SRP Compact: the entry point
The Compact series brings rotary screw reliability to smaller operations. All run at 125 PSI.
- SRP-3008 Compact: 7.5 HP, 27 CFM. Also available as a single-phase version, which is rare for a screw compressor and useful where three-phase power isn’t available.
- SRP 3015 Compact: 15 HP, 59 CFM.
- SRP 3025 Compact: 25 HP, 89 CFM.
- SRP 3040 Compact: 40 HP, 150 CFM.
Choose Compact if you’re moving up from a large piston compressor, have steady demand, and want the most CFM per dollar.
SRP Dynamic: the fixed-speed workhorse
The Dynamic “R” models are fixed-speed screws for steady industrial demand. The 10β40 HP models come mounted on a 120-gallon tank, so you get storage without buying a separate receiver.
| Model | HP | CFM @ 125 PSI |
|---|---|---|
| SRP-4008 R | 7.5 | 25 |
| SRP 4010 | 10 | 40 |
| SRP 4015 R | 15 | 59 |
| SRP 4020 R | 20 | 74 |
| SRP 4025 R | 25 | 92 |
| SRP 4030 R | 30 | 113 |
| SRP 4040 R | 40 | 140+ |
| SRP 4050 R | 50 | 207 |
Choose Dynamic if your compressor runs near full output most of the day. A fixed-speed screw is simple and efficient when it’s working hard.
SRP Flex: variable speed for changing demand
Flex models use a variable-speed drive that speeds the motor up and down to match how much air you’re actually using. When demand drops at lunch, between jobs or on a light shift, a fixed-speed compressor keeps running and unloading; a Flex simply slows down. For plants with uneven demand, that can mean a noticeable drop in the electric bill. Read fixed speed vs. variable speed screw compressors for a deeper comparison.
- Smaller Flex models: SRP 4010E (10 HP), SRP 4015E (15 HP), SRP 4020E (20 HP), SRP 4025E (25 HP), SRP 4030E (30 HP), SRP 4040E (40 HP).
- Industrial Flex models: SRP 4050 Flex (50 HP), SRP 4075 Flex (75 HP), SRP 4100 Flex (100 HP), SRP 4125 Flex (125 HP), SRP 4150E (150 HP), SRP 4200E (200 HP) and SRP 4250 Flex (250 HP).
Choose Flex if your air use swings during the day, you run multiple shifts with different loads, or energy cost is a priority.
How to pick the right size
- Add up your CFM. Total the air use of every tool and machine that runs at the same time, at the pressure they need. Our guide to PSI and CFM for shop tools has typical numbers.
- Add 25β30% for leaks, growth and new equipment.
- Look at how steady the demand is. Steady and near full load β Dynamic or Compact. Up and down β Flex.
- Check your power. Most SRP models need three-phase power; the largest Flex units are 460V only. If you only have single-phase, ask about the single-phase SRP-3008 Compact.
- Plan the air treatment. Pair the screw with a refrigerated dryer sized at or above its CFM, like the Schulz ADS and SACT dryers, plus line filters.
Our article on sizing a rotary screw for continuous use walks through an example.
Maintenance and kits
Rotary screws need regular oil, air filter, oil filter and separator changes. Schulz screws use SG-46 full synthetic oil, and we stock OEM maintenance kits for the SRP Compact, Dynamic and Flex lines. See the rotary screw maintenance schedule for intervals.
Frequently asked questions
What’s the difference between SRP Dynamic and SRP Flex?
Dynamic models run at a fixed speed; Flex models use a variable-speed drive that adjusts motor speed to match demand. Same family, different drive.
Is a variable-speed compressor always better?
No. If your compressor runs at full output all day, a fixed-speed Dynamic is simpler and costs less up front. Variable speed pays off when demand changes.
Do SRP compressors need three-phase power?
Most do. The SRP-3008 Compact is offered in single-phase; the larger Flex models run on 460V three-phase.
Can a rotary screw run 24/7?
Yes. Rotary screws are designed for continuous duty, which is the main reason to choose one over a piston compressor.
Need help choosing? Tell us your tools, hours of operation and electrical service at info@schulzproducts.com or (770) 734-6383 and we’ll recommend the right SRP model. Free shipping to commercial addresses is included. Browse all Schulz rotary screw compressors.
