In some ways, hydraulics is an ignored technology. The research dollars going into fluid power is miniscule compared to electronics, and although it’s partly because hydraulics is a mature industry, I don’t foresee this changing any time soon. Regardless, the benefits of hydraulics are high, so it will always have a place in our world, and I feel strongly enough about this to share my list of 7 reasons hydraulics will still be around in 2116.
1. Hydraulics have the highest power density of any mechanical transmission system in existence. This means the most force and power can be created from the smallest possible actuator. A medium-duty hydraulic cylinder with a 2-in. diameter piston will operate in the range of 1500 psi. A 2-in. diameter piston has an effective area of 3.14 in.², and every one of those 1500 pounds per square inch will work upon every one of those 3.14 square inches on the piston. Quick math results in that little 2-in. cylinder being able to push more than 4700 pounds of force, which could lift your 7-series BMW without breaking a sweat.
To be honest, 1500 psi is not a lot of pressure. Most off-highway machinery runs over 4000 psi, such as in excavators or loaders. This same 2-in. bore cylinder could now lift over 12,500 lbs, which is enough to elevate a John Deere 50D excavator itself. If you think that’s awesome, consider the cylinders used in the compact hydraulic tools industry, where they drop “pounds” altogether and start talking in “tons.” A single, 2-in. bore cylinder operating at 10,000 psi can create force to the tune of 15 tons; that’s 15 tons from something the diameter of a lemon.
2. Hydraulics will exist after the zombie apocalypse. In fifty years, when the Internet of Industrial Things is the norm, and then in a further fifty years hence when we are left with a fraction of our population non-dead from the undead, hydraulics will save the day. If and when electronics cannot operate, liquids will certainly exist for us to push through tubes and move things at the other end.
In a recent visit to Boldt Castle in the Thousand Islands, I witnessed an eighty-year-old hydraulic system which previously operated the castle’s elevator. A large bore cylinder was powered with pressurized river water, lifting passengers up the multiple levels of the castle. Although electricity was available and used for the pump, the same kind of system can be created with only water-mill driven pumps. A similar system can be used to create a zombie compactor, when the bodies start piling up.
3. Fluid power will eventually be very inexpensive. At some point in the future, the precious metals used in electrical and electronic equipment will be become even more precious and rare. I predict the metals used in electronics will become so rare that huge electrical components required for very large actuators will become extremely expensive.
If in a century, a servo motor costs $100,000 (inflation adjusted), then hydraulics is suddenly more attractive, what with its cast iron construction. Even if iron prices rise in tune with other metals, I’m sure advanced forms of composite materials will be both strong and inexpensive by then. Either way, fluid power components will continue to become more affordable.
4. Advancements are still happening in the fluid power world. Although most hydraulic advancements have been through motion control and advanced electronics, there are still cool things happening. Technologies such as kinetic energy recovery systems used in garbage trucks and delivery vehicles are ensuring hydraulics are in step with other green industries. As well, there are exotic technologies with potential for future application in fluid power.
Magnetorheological fluid changes viscosity with exposure to a magnetic field, and in some cases, the fluid can go nearly solid. This type of fluid could be used to control fluid power actuators without the use of flow control valves, or could be used in load-holding applications for safety. In the case of the latter example, imagine lifting a load with low-viscosity fluid, and then turning on a magnetic field to turn the fluid nearly solid, preventing any possible leakage which would allow the load to drop. Pilot operated check valves could be a thing of the past, and the operation of a counterbalance valve could be achieved magnetically.
5. Electrical actuators will eventually be maxed-out in force density. Electric motors and linear actuators require electromagnetic fields to operate. The strength of these magnetic fields is dictated by the number of atoms polarized to create that field. Even helium-cooled, superconducting electromagnets are limited, because when every atom is polarized by ridiculous levels of electrical current, your magnetic field is maxed out.
On the other hand, there is literally no limit to the compressibility of a liquid, and therefore, the force density which can be created by a hydraulic actuator. Remember that at one point 14 billion years ago, all the not-yet-matter in the universe was infinitely dense at the start of the big bang. Although current hydraulic applications don’t go much higher than 10,000 psi, there is no reason we can’t see 100,000 psi in a hydraulic system, or perhaps even more.
The only limitations in fluid power pressure is with the strength of the material containing the fluid, and the capacity of the sealing technology keeping the fluid captured. I imagine some hyper-strong synthetic material of reasonable mass already exists to create a 100,000 psi cylinder, but sealing technology is an unknown. I can picture in my head a magnetorheological hydraulic fluid used, and a magnetic piston that keeps the fluid near the piston high-viscosity, preventing leakage—please send royalty cheques care of Fluid Power World.
6. Hydraulics will still be reliable. Not only is hydraulics reliable, they’re easy to service to maintain that reliability. A key application not likely to replace hydraulics anytime soon is in the aerospace industry. Although the large, centralized hydraulic systems are a thing of the past, compact, self-contained circuits placed throughout an aircraft are powerful, fast and reliable.
Even the F-35 Joint Strike Fighter uses hydraulic actuators for its primary flight controls. Neither electrical nor mechanical systems have the speed and power capability of a hydraulic cylinder, which is able to move an aileron while the jet is travelling at near mach speed. Any aircraft is able to maintain this performance with regular servicing of the hydraulic systems. With the exception of physical damage, a cylinder can be serviced and replaced many times, and if done proactively, allows the hydraulic systems to last decades.
7. Hydraulics may one day harness the superfluid. A superfluid, such as liquid helium, moves with zero viscosity. As you can imagine, a superfluid can be pumped at massive volumes with no backpressure. Fluid lines could be miniscule, but still pump at a high rate. A superfluid will even travel against gravity under its own volition; nobody said quantum physics made sense.
The challenges with a superfluid are numerous, which is why this is a technology for the future. Liquid helium requires pretty much absolute zero to be a superfluid, which makes it difficult to take advantage of. The entire hydraulic system would have to be self-contained in a space with no thermal energy. Even if the conditions were prime for superfluidity, the difficulties don’t stop there.
Because liquid helium has zero viscosity, you can imagine how prone to leakage a hydraulic system would be. Not only would a helium pump spin freely as if it was pumping in a vacuum, any actuator would not be able to take advantage of the moving liquid helium. This superfluid would enter a hydraulic cylinder and proceed to move past the piston seals as if there was no piston even in the cylinder.
Challenges aside, superfluidity is a fantastic concept, with too many benefits to ignore in Future World.
For those 7 reasons, I’m certain hydraulics will be a large part of machinery for the next century. I’m also certain this list could be longer, because it’s difficult to predict the technologies that will surface as we advance exponentially forward. For example, absolutely nobody predicted the Internet in 1950, but I’m still waiting for my flying car. I only hope I’m around for another fifty years to see how this list changes halfway through this next century.