HYDAC Gear Pumps, Cartridge Valves, and Motor Questions: A Purchasing FAQ

When I took over purchasing for our manufacturing plant in 2020, I figured a HYDAC order was like any other MRO buy: find the part number, check the price, submit the PO. I was wrong. I manage roughly $250,000 a year in maintenance and repair purchasing across eight vendors, and I learned the hard way that HYDAC components have their own rules. After a few restocking fees and one embarrassing conversation with a maintenance engineer about “5th gear motors,” I started keeping notes. Here are the questions my engineers actually ask, and the answers that took me too long to find.

A quick note before the list: these are the questions that come from my maintenance team, not a replacement for the HYDAC catalog. For specific application details, the catalog and an authorized distributor are the final word.

Frequently Asked Questions

1. Where should I start when ordering HYDAC gear pumps?

Start with the HYDAC gear pump section in the current catalog. I used to call a distributor and describe what I needed. That's how I ended up with the wrong displacement... twice. Now I pull the spec sheet and check the pump series, mounting flange, shaft type, and port orientation before asking for a quote. The online HYDAC catalog—the February 2025 edition—is the reference we use for every gear pump PO. It takes ten minutes, and it saves a lot of headaches (and restocking fees). One more thing: if the pump is already on your machine, read the model tag. That little engraved plate answers half the questions before you even open the catalog. If you can't find the pump series, take a photo and send it to an authorized distributor. Most of them have application engineers who can match it. Every distributor I've used has a different way of quoting, so I ask them to include the model code from the HYDAC catalog in the confirmation. That way, I can compare apples to apples.

2. Can I use any gear pump with a HYDAC motor?

Not without checking. I once assumed all hydraulic pumps and motors used the same mounting pattern because a senior guy said “they're all SAE.” That's an oversimplification. A HYDAC gear pump and a HYDAC motor have to match on flange size, shaft diameter, and spline engagement. For pump displacement, you're looking at flow requirements; for the motor, it's torque. Honestly, I'm not the engineer—I just make sure the part numbers line up. When in doubt, we send the old pump to the distributor and ask them to confirm. It feels basic, but it's cheaper than ordering the wrong rotation. The catalog's technical drawing shows exactly what to measure. Use it. And if you're building a new system, ask the designer whether you need a through-shaft pump—that changes the coupling completely. One more thing: if the old motor is burnt out, don't rely on the part number alone. The nameplate may have a code that includes winding type or thermal protection. That changes the replacement.

3. What's actually in the HYDAC cartridge valve catalog?

The HYDAC cartridge valve catalog is basically a technical reference. It covers poppet-type and spool-type cartridge valves, with dimensions, flow ratings, pressure ratings, and cavity details. What most people don't realize is that the cavity drawing matters as much as the valve itself. Get the tolerance wrong and the valve can leak or bind. The catalog also lists recommended seals and pilot options. I'll be honest: I used to order cartridges like light bulbs, just by model number. That's not enough. For pilot-operated valves, you also need coil voltage. Oh, and check the catalog's pressure limits—they vary by size. If the valve has a position sensor, you have to include the connector type too. That's a detail I forgot once; the valve arrived with no way to hook up the signal. Our maintenance supervisor now reviews every cartridge valve line item before I place the order. It slows things down by a day, but it beats a return. It also helps to know whether the valve is normally open or normally closed—that's not something you can guess from the shape.

4. What do people mean by “5th gear motors”?

That phrase confused me too. When an engineer emailed me about “5th gear motors,” I thought he was asking for automotive transmission parts. Turns out he meant the fifth gear motor on a packaging line—a gearmotor with an electric motor and a speed reducer. If you're searching that term, you're probably looking for a gearmotor, not a manual transmission gear. In the industrial drive side of the catalog, that usually maps to an AC motor with a reducer, a servo gearmotor, or even a hydraulic gear motor if it's driven by a hydraulic power unit. But don't write “5th gear motors” on a PO—use the part number from the catalog. That's the lesson I keep learning. I should add: my go-to move now is to ask for the motor nameplate before I search anything. The nameplate gives you voltage, frame size, and output speed, which is worth more than any description someone writes in an email. Honestly, enough misspelled part numbers have crossed my desk that I double-check everything. There's no shame in asking.

5. Wait—what's the difference between a linear induction motor and a HYDAC linear actuator?

A linear induction motor uses electromagnetic force to create linear motion—think maglev trains or certain high-speed doors. A HYDAC linear actuator is typically a hydraulic or electro-mechanical cylinder designed to push, pull, or hold a load. Both produce straight-line motion, but they're not interchangeable. The linear induction motor needs an inverter and precise air-gap control. A linear actuator is usually simpler to install and more familiar to maintenance teams. If an engineer asks for a “linear induction motor,” they're asking for a specific electric machine. The HYDAC catalog has linear actuators, not linear induction motors. I know this because I once put the wrong phrase in a purchase requisition and got back a very polite email from applications engineering asking if I meant a rod-style actuator. Details matter. If the application involves high-speed, long-stroke motion with low load, a linear induction motor might be the right topic. But in a standard factory setting, a linear actuator does the heavy lifting. If I'm unsure, I put the phrase in quotes and send the engineer a screenshot of the search results before ordering. Openly clarifying has saved us a lot of wrong orders.

6. Which gear is most likely to use a spur gear?

If you mean in a manual transmission, the answer is reverse gear. Most forward gears use helical gears for quieter operation and better load capacity. Reverse gear is more likely to use a spur gear because it's simpler, cheaper, and easier to slide into mesh. In gearmotor applications, spur gears also show up in compact inline reducers where noise is less of a concern. But for automotive gearboxes, reverse is the classic answer. Our senior maintenance tech explained this to me after I mixed up transmission gears and gearmotor pinions. So if someone asks “which gear is most likely to use a spur gear?”—reverse is the answer that'll get you a nod from the mechanics. If they mean in a gearmotor, look at the reducer type: parallel shaft and planetary designs often use spur gears, while right-angle designs tend to use bevel or worm gears. That nuance matters when you're shopping for replacement motors. When in doubt, ask which gear stage they're talking about. That single question has saved me from ordering the wrong part more than once.

7. How can I tell if I'm getting genuine HYDAC parts?

Check part numbers against the official HYDAC catalog, buy from an authorized distributor, and inspect the packaging. I learned this the hard way. A non-genuine filter insert collapsed after about 20 hours, and the resulting contamination cost us a hydraulic pump rebuild—around $3,800 in parts plus downtime. The genuine insert was not wildly more expensive. Now we use three trusted vendors and one rule: no substitutions without written approval from maintenance. Also, if the price on a HYDAC part is way below the market, that's a red flag. It's not a bargain; it's a future problem. Watch the packaging too—HYDAC parts come with proper labels and batch codes. If a supplier hesitates when you ask for a certificate of conformance, do not proceed. That check alone has kept us out of a few gray-market situations. The best procedure I've found is simple: catalog part number → phone quote → written confirmation → visual inspection at delivery. It's boring, but it catches mistakes before they become downtime.