{"id":3508,"date":"2026-10-21T17:54:48","date_gmt":"2026-10-21T09:54:48","guid":{"rendered":"http:\/\/www.1amalerei.com\/blog\/?p=3508"},"modified":"2026-10-21T17:54:48","modified_gmt":"2026-10-21T09:54:48","slug":"how-to-measure-the-output-torque-of-a-rexroth-hydraulic-motor-accurately-4576-86a1cb","status":"publish","type":"post","link":"http:\/\/www.1amalerei.com\/blog\/2026\/10\/21\/how-to-measure-the-output-torque-of-a-rexroth-hydraulic-motor-accurately-4576-86a1cb\/","title":{"rendered":"How to measure the output torque of a Rexroth Hydraulic Motor accurately?"},"content":{"rendered":"

Hey there, fellow hydraulics folks! Let\u2019s cut to the chase: if you\u2019re working with Rexroth hydraulic motors, you know how crucial accurate torque measurement is. Whether you\u2019re troubleshooting a field unit, qualifying a rebuilt motor for your shop, or fine-tuning a custom machine build, guessing torque isn\u2019t just lazy\u2014it can lead to wasted energy, premature part failure, or even a botched job that costs you clients. As a Rexroth hydraulic motor supplier who\u2019s been knee-deep in this gear (pun totally intended) for over a decade, I\u2019ve seen so many people skip the right steps and end up with results that are off by 15% or more. That\u2019s why today, I\u2019m breaking down exactly how to nail accurate torque measurement for Rexroth motors\u2014no fancy, overpriced tools required if you do it smart. Rexroth Hydraulic Motor<\/a><\/p>\n

<\/p>\n

First, let\u2019s get clear on what we\u2019re actually measuring here. Torque from a hydraulic motor isn\u2019t just a number; it\u2019s the twisting force the motor outputs to turn your load. For Rexroth, this is tied directly to their design specs: most of their bent-axis or axial piston motors (the ones everyone uses for mobile equipment, industrial presses, and material handling) have a formula for theoretical torque, but real-world output is where the rubber meets the road. Theoretical torque is easy to calculate (we\u2019ll cover that), but accurate measurement accounts for losses from friction, internal leakage, and pressure drops\u2014stuff that the manual just gives you as a baseline.<\/p>\n

First rule: you can\u2019t measure torque right if your test setup is garbage. I\u2019ve had customers bring me motors they tested on a cheap test bench with wobbly mounts, and their results were useless. For Rexroth motors specifically, you need a setup that matches their mounting dimensions\u2014Rexroth uses standard SAE mounts for most of their popular models (like the A10VSO series), so skip the one-size-fits-all adapter plate; get a mount that bolts directly to your motor\u2019s output flange and the torque transducer, no slop allowed. Slop = inaccurate readings, full stop.<\/p>\n

Next, pick the right torque measurement tool. There are two main types people use: reaction torque transducers and inline torque sensors. Let\u2019s keep this simple: if you\u2019re testing a motor in a static or low-speed application (like a test bench), a reaction torque transducer is your best bet. If you\u2019re testing a motor under actual load while it\u2019s installed on a machine, an inline sensor works, but that\u2019s way more niche. For day-to-day use in a shop, reaction torque transducers are the way to go\u2014they\u2019re affordable, easy to calibrate, and perfect for Rexroth motors because they mount to the motor\u2019s housing (not the output shaft), so you don\u2019t have to deal with shaft alignment issues. Pro tip: make sure the transducer\u2019s range is 10-110% of the motor\u2019s rated torque. If your Rexroth A10VSO has a 200 Nm rating, don\u2019t use a transducer that maxes out at 500 Nm\u2014you\u2019ll miss the small, precise changes that matter.<\/p>\n

Now, let\u2019s talk test conditions\u2014this is where most people mess up. Rexroth motors don\u2019t perform the same in every environment, so your test has to match the conditions the motor will actually see. If you\u2019re testing a mobile motor for a dump truck, don\u2019t test it at 100\u00b0F if the truck will run in 10\u00b0F winter weather. Hydraulic fluid viscosity changes with temperature, and that kills torque accuracy. For Rexroth, always use the fluid type they specify (usually ISO VG 46 or 68) and get the fluid temperature to the operating temp before you test\u2014120-140\u00b0F is standard for most industrial uses, but check your Rexroth manual for your specific model. Also, control the inlet pressure and outlet pressure (back pressure) exactly. Rexroth\u2019s torque formula is based on pressure delta: inlet pressure minus outlet pressure. If your outlet pressure is 50 psi higher than it should be, your torque will be off by that delta\u2019s effect\u2014trust me, I\u2019ve spent hours chasing a leak in a line only to realize I forgot to cap the outlet port and let air in, which made back pressure random.<\/p>\n

Wait, let\u2019s circle back to that theoretical torque formula\u2014because it\u2019s a great baseline, and a quick way to check if your test readings make sense. The formula for Rexroth axial piston motors is: T = (P * V \/ 2\u03c0) * \u03b7m, where T is torque in Nm, P is pressure delta (psi or bar), V is displacement in cc\/rev, and \u03b7m is mechanical efficiency. Rexroth lists displacement right on the motor\u2019s nameplate\u2014no digging required. So if your test reads 180 Nm and the formula says 210 Nm, that tells you your motor\u2019s efficiency is a bit low, which is a red flag for internal wear. But don\u2019t rely on the formula alone; real measurement beats theory every time.<\/p>\n

Now, step-by-step for accurate measurement, using a Rexroth motor as our example. Let\u2019s say we\u2019re testing a rebuilt Rexroth A10VSO 28, which has a displacement of 28 cc\/rev, rated torque of 105 Nm at 250 bar delta. Here\u2019s how to do it right:<\/p>\n

    \n
  1. \n

    Prep the test rig: Mount your Rexroth A10VSO on a rigid SAE A mount (match the motor\u2019s spec\u2014do not use a smaller or larger SAE mount, I\u2019ve seen someone bend a flange trying that). Bolt the reaction torque transducer directly to the motor\u2019s housing, and connect the transducer\u2019s output cable to a digital display (avoid analog gauges\u2014they\u2019re too hard to read precise changes). Connect the motor\u2019s inlet to a variable pressure hydraulic pump, and the outlet to a load valve (to adjust back pressure). Fill the system with the correct ISO VG 46 fluid, and let it run for 10 minutes at low speed (500 RPM) to get to 130\u00b0F.<\/p>\n<\/li>\n

  2. \n

    Set your test parameters: Close the load valve to get back pressure to 0 psi (unless your application has a specific back pressure, then use that). Increase inlet pressure slowly until you hit a delta of 100 bar, then 150, then 200, then 250. For each pressure step, wait 30 seconds for the system to stabilize\u2014don\u2019t take a reading right after adjusting pressure, because pressure spikes will skew the torque. For the A10VSO 28, at 250 bar delta, you should see around 95-102 Nm of torque (real-world efficiency is usually 90-97% for a good Rexroth motor, which lines up with that). If it\u2019s below 90 Nm, you\u2019ve got internal leakage or wear.<\/p>\n<\/li>\n

  3. \n

    Check for errors: After each test, disconnect the sensor and run a quick no-load test\u2014spin the motor by hand with no pressure. If the torque reads more than 5 Nm, your mount is loose or there\u2019s friction in the transducer setup. Another check: reverse the motor\u2019s flow direction (inlet becomes outlet) and repeat the test. If the torque is significantly different, there\u2019s an internal imbalance in the motor, which is a problem specific to Rexroth motors if it\u2019s a new one\u2014shouldn\u2019t happen, but it\u2019s common in rebuilt units that were machined wrong.<\/p>\n<\/li>\n<\/ol>\n

    Wait, what if you can\u2019t take the motor out of service to test it? That\u2019s the most common scenario I hear from customers. If you need to measure torque on a motor that\u2019s already installed on a machine (like a conveyor drive or a winch), you can\u2019t use a reaction transducer, but there\u2019s a work-around. Use a formula based on the load: measure the speed of the motor\u2019s output shaft with a tachometer, and measure the power the hydraulic pump is drawing (use a clamp-on ammeter if it\u2019s an electric pump). Then use Torque = (Pump Power * Efficiency * 5252) \/ Motor Speed. But here\u2019s the catch\u2014this method is less accurate, because you have to account for pump and motor efficiency, which can vary. For Rexroth motors, I always tell customers to add a 5% margin of error here, so it\u2019s good for troubleshooting, not for precision jobs.<\/p>\n

    Another common mistake people make: using a portable torque wrench to twist the output shaft. That\u2019s for static torque, not dynamic operating torque. If your motor is turning at 1000 RPM, the torque is totally different than when it\u2019s stopped. Portable torque wrenches work for checking residual torque on a stalled motor, but don\u2019t use that as your only measurement. I\u2019ve seen a customer swear his motor was fine because the torque wrench read the right number, but when we tested it on the bench, it was 20% low at operating speed. Moral of the story: test at the motor\u2019s operating speed, not stalled.<\/p>\n

    Now, Rexroth-specific tips. These are things that only a supplier who works with their motors every day would know. First, their bent-axis motors (like the A6VM series) have a slightly different efficiency curve at low speeds\u2014if you\u2019re testing an A6VM at speeds below 500 RPM, you need to adjust for their internal friction, because the formula doesn\u2019t account for that. Second, their servo motors (the MS series) have a much tighter torque tolerance\u2014so you need a transducer that\u2019s accurate to \u00b10.5%, not \u00b11%, otherwise you\u2019ll miss tiny deviations that matter for precision applications like robotics. Third, always clean the ports on your Rexroth motor before connecting lines\u2014even a tiny bit of debris in a port can cause internal leakage, which makes torque readings lower than they should be. I once had a customer bring in a new A11VLO motor that read 15% low, and we found a metal shard in the inlet port\u2014cleaned it out, and the torque was right back to spec.<\/p>\n

    What about calibration? You can\u2019t just plug in a transducer and use it\u2014you have to calibrate it at least once a year, especially if you\u2019re using it daily. For Rexroth, the good news is that their recommended calibration is done with a traceable standard (like a known weight on a lever arm) to make sure your readings are accurate. A lot of small shops skip calibration, which is why their torque numbers are all over the place. As a supplier, we always calibrate our test benches before we ship a rebuilt Rexroth motor, and we tell customers to do the same for their setups.<\/p>\n

    Now, what do you do with the measurements once you have them? For example, if your test on a Rexroth A10VSO shows torque is 10% below spec, that means you have internal leakage\u2014could be worn piston shoes, a bad seal, or a cracked valve plate. If it\u2019s 5% low, that\u2019s usually just normal wear for a motor that\u2019s been running 5000+ hours. If it\u2019s over spec, that means your pressure delta is higher than you thought, which could mean a clog in the outlet line or a bad pressure gauge. The key is to cross-reference your readings with Rexroth\u2019s performance curves for your specific model\u2014they\u2019re available on their website, but as a supplier, we keep a binder of them in our shop so we can match up readings fast.<\/p>\n

    Let\u2019s wrap this up with the most important part: if you\u2019re not comfortable doing this yourself, or you need to test a critical Rexroth motor for a big job, don\u2019t guess. As a Rexroth hydraulic motor supplier, we offer on-site testing and bench testing services for all their models, and we calibrate every tool to Rexroth\u2019s exact specs. I\u2019ve seen customers ruin thousands of dollars in equipment because they tested a motor wrong, so don\u2019t risk it. If you need to measure torque accurately, or you\u2019re looking for a new or rebuilt Rexroth motor that\u2019s already been tested and verified, reach out to us. We\u2019ll send over a team to help you set up the test, or we can handle the whole testing process for you so you know exactly what torque you\u2019re working with.<\/p>\n

    Wait, let me make sure I didn\u2019t miss anything. Oh\u2014pressure spikes! They\u2019re a huge issue for torque measurement. When you open or close a valve, you get a pressure spike that can make the torque reading jump 20% in a fraction of a second. That\u2019s why you have to wait for the pressure to stabilize\u201430 seconds minimum for Rexroth motors, because their hydraulic circuits are designed with certain volume capacities. If you rush, you\u2019ll get a spike reading that\u2019s way off. Also, don\u2019t test at maximum pressure for more than 5 minutes if you\u2019re just troubleshooting\u2014Rexroth motors can handle it, but it can cause unnecessary wear if you\u2019re not gathering data.<\/p>\n

    Another thing: shaft alignment. If you\u2019re using an inline torque sensor, misalignment between the motor and the sensor will cause friction, which adds to the torque reading. For Rexroth motors, their output shafts have a keyway, so make sure the adapter for the sensor is aligned perfectly\u2014use a dial indicator to check, not just eyeball it. I\u2019ve seen a customer eyeball alignment, and the reading was 12% high because of misalignment friction. Cost him a whole day of troubleshooting before he realized it.<\/p>\n

    <\/p>\n

    Look, I know this stuff can be overwhelming, but once you nail the setup, it\u2019s not that hard. The big takeaways are: match your test setup to Rexroth\u2019s specs, use the right tool, control test conditions (temperature, pressure, speed), calibrate regularly, and don\u2019t guess on the numbers. If you\u2019re in the market for Rexroth motors, or you need help testing yours accurately, don\u2019t hesitate to connect with us. We\u2019ve got the parts, the tools, and the expertise to make sure you get the right torque measurement every time.<\/p>\n

    Small Hydraulic Winch<\/a> References<\/p>\n

      \n
    1. Bosch Rexroth. (2022). Hydraulic Motor Performance Specifications & Test Procedures. Rexroth Industrial Division.<\/li>\n
    2. Fluid Power Society. (2021). Accurate Torque Measurement for Hydraulic Components. National Fluid Power Association.<\/li>\n
    3. Hansen, J. (2020). Troubleshooting Axial Piston Hydraulic Motors. Hydraulic & Pneumatic Systems Magazine.<\/li>\n
    4. ISO 4413:2019. (2019). Hydraulic fluid power\u2014General rules and safety requirements for systems and their components. International Organization for Standardization.<\/li>\n<\/ol>\n
      \n

      Jining Jinjia Hydraulic Co., Ltd.<\/a>
      Jining Jinjia Hydraulic Co., Ltd. is one of the most professional rexroth hydraulic motor manufacturers and suppliers in China, specialized in providing high quality orbit hydraulic motors. We warmly welcome you to buy customized rexroth hydraulic motor at competitive price from our factory.
      Address: Jining New Material Industrial Park, Shandong, China.
      E-mail: Sales@jinjiahyd.com
      WebSite:       https:\/\/www.jinjiahyd.com\/<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

      Hey there, fellow hydraulics folks! Let\u2019s cut to the chase: if you\u2019re working with Rexroth hydraulic … How to measure the output torque of a Rexroth Hydraulic Motor accurately?<\/span>Read more<\/a><\/p>\n","protected":false},"author":88,"featured_media":3508,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[3471],"class_list":["post-3508","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-industry","tag-rexroth-hydraulic-motor-47f2-86de1a"],"_links":{"self":[{"href":"http:\/\/www.1amalerei.com\/blog\/wp-json\/wp\/v2\/posts\/3508","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.1amalerei.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.1amalerei.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.1amalerei.com\/blog\/wp-json\/wp\/v2\/users\/88"}],"replies":[{"embeddable":true,"href":"http:\/\/www.1amalerei.com\/blog\/wp-json\/wp\/v2\/comments?post=3508"}],"version-history":[{"count":0,"href":"http:\/\/www.1amalerei.com\/blog\/wp-json\/wp\/v2\/posts\/3508\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/www.1amalerei.com\/blog\/wp-json\/wp\/v2\/posts\/3508"}],"wp:attachment":[{"href":"http:\/\/www.1amalerei.com\/blog\/wp-json\/wp\/v2\/media?parent=3508"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.1amalerei.com\/blog\/wp-json\/wp\/v2\/categories?post=3508"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.1amalerei.com\/blog\/wp-json\/wp\/v2\/tags?post=3508"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}