I can think of a million ways to use hydraulics. Its legendary power density, easy controllability and flexible application options means it finds its way into everything from underwater robots to injection molding machines. However, just because there are myriad perfect applications for hydraulics, it doesn’t mean it should be used everywhere. Here are my top five applications where you should not use hydraulics.
1. For tiny robots. By “tiny,” I’m not referring to the kind of robots used in the old TV show, Robot Wars. I’m talking about little drones the size of crickets. Even if hydraulics could be made that small, the conveyance of hydraulic fluid gets very difficult with small conductors. Unlike electrical current, hydraulic fluid requires conduits large enough to achieve usable flow rates.
Micro-bore hoses already exist for use with test points and pressure gauges, but they’re not designed for any reasonable flow. Even if flow wasn’t a concern, the method of flow creation (i.e., the power unit) would be extremely challenging in a small package. To create a pump, relief valve, directional valve and actuators to take advantage of less than a cubic centimeter of flow per minute would be nearly impossible, especially when you factor in viscosity.
2. Cars. “But wait,” you exclaim, “hydraulics have been used in cars for years, such as in power steering systems.” This is true, but notice the phrase “have been.” Although a few modern vehicles still have hydraulic power steering, they’re mostly limited to vehicles that cherish mechanical feedback through the steering wheel, such as sports cars. The reality is electric power steering is lighter, less expensive, takes up less space and is more reliable. Sure, it’s not there yet when it comes to feedback and control, but it will be one day, and manufacturers won’t be going backwards.
3. You’re on a budget. To this day I’m still involved with the design of hydraulic systems from a sales function, and you’d be amazed at the number of hydraulic tire-kickers who have no clue how expensive hydraulics can be. Yes, hydraulics can be had for a reasonable price, if you’re looking for cookie cutter applications like the log-splitter.
However, when you get the bright idea for your six-million-ton soda can crusher with four synchronized cylinders costing thirty large each, and the 250-hp power unit running torque limiting pumps and servovalves, how about you check out some Internet forums to first get an idea your system is going to cost a cool half a million, before you go shopping around at your local fluid power distributor? You’ll save everyone a lot of time and headaches.
4. As a soda can crusher. Seriously, you can smash a soda can on your forehead. Why the heck do you need tons of force, as gloriously provided by hydraulics? (disclaimer: if you’ve created a hydraulic soda can crusher, please send me a YouTube video … that’s just badass!)
5. To power your bicycle. Don’t laugh, I’ve had this request. Besides offending Application #3, above, it just doesn’t make sense. Let’s say you mounted a gear pump to your pedal set, and then a gear motor to your rear hub. Inexpensive hydraulics are not known for their efficiency, and gear pumps and motors are likely to top out around 80% efficiency. Because the inefficiencies are factored together, you end up converting the 80% efficiency of your gear pump with the 80% efficiency of your gear motor, and wind up with a less-than-impressive 60% total efficiency.
So now the quarter-horsepower made by your chicken legs is nearly reduced in half. You were better off with the mechanical drive of your chain and 21 speeds, which is 99% efficient and converting your leg power in to forward motion.
Sometimes, hydraulic is just not the best option.