If you're asking what stepper motor do I need? or you're about to order from the HYDAC cartridge valve catalog, put the part number aside for a minute. Not because part numbers don't matter, but because they only matter after you've verified the specifications behind them.
The most expensive part in any machine is the one that's almost right. A NEMA 23 stepper motor with the right faceplate but the wrong winding will overheat before it burns out. A cartridge valve with the right threads but the wrong pressure range can turn a 300-bar circuit into a leak manifold. These failures rarely show up during testing. They show up after installation, when you've already paid for the crane, the wiring, and the production delay.
Verification is cheaper than correction. Five minutes of checking before purchase saves five days of rework after installation.
I'm a quality and brand compliance manager at an industrial fluid power and automation distributor. I review every product data sheet, marking, and sample lot before it enters our inventory—roughly 200 unique items each month. In 2024, I rejected 11% of first deliveries for documentation or tolerance issues. This isn't a theoretical preference. It's the difference between a shipment that goes out on time and one that needs an expensive replacement.
Here's a recent example. In Q3 of last year, we received 240 NEMA 23 stepper motors that had the correct manufacturer label but didn't match the approved electrical sample. Inductance was 5.4 mH instead of the specified 3.7 mH. On paper, that looked minor. In practice, it meant the torque curve flattened exactly where the customer's new linear actuator spent most of its cycle. If we hadn't caught it, the customer would have blamed the actuator for being weak. We rejected the lot before it got any further. That cost two weeks of lead time. Installing 240 wrong motors would have cost more.
The Question What Stepper Motor? Hides a Frame Size Problem
Let's start with the electric side. A stepper motor is a synchronous motor that rotates in discrete steps—usually 1.8 degrees per pulse, or 200 steps per revolution. That makes it useful for position control without an encoder.
But the phrase stepper motor isn't specific enough. The question what stepper motor gets interesting only after you discuss frame size, current, torque, and lead-screw options.
NEMA 23 defines a frame size, not performance. It means the faceplate is 2.3 inches per side. A NEMA 17 faceplate is 1.7 inches per side, and a NEMA 34 is 3.4 inches per side. The mounting pattern is standardized; the electrical characteristics are not.
A NEMA 23 stepper motor can be rated for holding torque below 100 oz-in or close to 300 oz-in, depending on motor length and winding. Don't hold me to the exact numbers for every manufacturer—ranges vary—but that's the scale. The torque available at a given speed also depends on the driver voltage and current. So if you order NEMA 23 without verifying current and inductance, you might get something that fits the bracket but can't do the job.
When you need straight-line motion, a linear stepper motor is a common alternative. Inside a linear stepper, the motor rotor is threaded and engages with a screw. Each step moves the screw (or shaft) forward or backward by an amount determined by the screw lead. It removes the need for a separate mechanical conversion, but it doesn't remove the need for spec checking.
A NEMA 23 linear stepper motor can be configured with different screw leads, thrust ratings, and travel lengths. The outside body can look identical. Compare the linear force and the travel per step, not just the frame size.
Personally, I go back and forth between a rotary stepper motor with a lead screw and a linear stepper motor every time a customer asks about a new positioning axis. The rotary version is often cheaper to source; the linear version removes the alignment headache. I make the final call only after checking the force at the actual speed. The frame size alone doesn't settle it.
The HYDAC Cartridge Valve Catalog Is Not a Menu
Now the hydraulic side. It's tempting to treat a cartridge valve as a generic insert—if it fits in the cavity, it will work. Not quite.
Cartridge valves are threaded, insert-style valves installed in manifold blocks. They can be check valves, pressure relief valves, flow controls, or directional poppet valves. The same outside dimensions can hide different internal behavior. In the HYDAC cartridge valve catalog, each model code corresponds to a data sheet with rated flow, maximum pressure, seal material, and performance curves. Those details are easy to skip if you already think you know which valve you need.
I remember a supplier telling me their valve was the HYDAC equivalent to the one on our BOM. The cavity dimensions matched, and the HYDAC logo was stamped on the side. But when I checked the model number against the HYDAC cartridge valve catalog, the cracking pressure was off by 15 bar. In that customer's machine, a 15 bar difference could have changed the sequence and caused tooling damage. The catalog data caught it.
The HYDAC logo tells you who built the component. It's a good sign of manufacturing quality. It does not tell you whether that specific part is right for your flow, pressure, fluid, and duty cycle. That's what the part number and catalog data are for.
Four Checks to Add Before You Send the PO
You don't need a full quality management system to avoid these problems. Just answer four questions:
- Do I have the exact model code? Don't order a standard NEMA 23 or the same valve as last time. Use the complete code and confirm it against the official datasheet or catalog.
- Is the interface spec confirmed? For a stepper motor, that includes shaft diameter, mounting dimensions, lead wire count, and connector type. For a cartridge valve, it includes cavity type and seal package.
- Are the operating limits verified? Check current, voltage, inductance, holding torque, and temperature for motors. Check pressure, flow, cracking pressure, and fluid compatibility for valves.
- Does the printed code on the delivered item match the approved sample? It sounds basic, but item-level marking is where quality escapes happen. Don't accept a part because the package has the HYDAC logo on it—read the nameplate, record the code, and compare.
I once rejected 8,000 motors because the factory changed the winding configuration without notifying us. It was a significant order, and I didn't enjoy making that phone call. But those 8,000 motors would have behaved differently at the customer's duty cycle. The rejection cost us some schedule pain; acceptance would have cost us the account.
When This Level of Checking Is Overkill
If you're replacing a component on a machine that has worked for years and the old part number is legible, order the exact same number and move on. You probably don't need to re-validate the entire spec. Same thing if you're ordering an exact spare for a stepper motor with a driver you've already tuned.
But be careful not to limit this discipline to big purchases. The wrong part often doesn't fail immediately. It fails after the warranty period, when the machine is down and everyone's forgotten what was ordered. The component may cost $40; the downtime can cost thousands.
So, yes: if you're choosing a NEMA 23 stepper motor, compare the winding data with your driver settings. If you're looking at a linear stepper motor, calculate the force and travel per step. And if you're browsing the HYDAC cartridge valve catalog, read the specs that come with the model code—not just the photo.
Ten minutes of checking now is cheaper than ten days of correction later.