To some extent, hydraulic is a neglected technology. Compared to the electronics industry, the research funding to enter the field of fluid power is very small. Part of this is because hydraulics is a mature industry, and I don’t think that’s going to change anytime soon. However, hydraulic technology still has many advantages, so it still has a place in the world.
1. Hydraulic has the highest unsurmountable power density
This means that maximum force and power can be generated with minimal actuators. A medium piston diameter hydraulic cylinder will operate in the 1500psi (approx. 103bar) range. The piston has an effective area of 3.14 square inches with a diameter of 2 inches and can support 1,500 pounds per square inch of 3.14 square inches. A quick estimate gives you more than 4,700 pounds of force on a 2-inch cylinder, which means you can lift your 7-Series BMW with very little effort. To be honest, 1500psi is not a lot of pressure. Most off-highway machinery runs over 4,000 psi, such as excavators or loaders. That same 2-inch cylinder can now lift more than 12,500 pounds, enough to lift a John Deere Series 50D excavator. If you think this is great, consider that in the compact hydraulics industry, they dropped the “pound” and used “ton”. A 2-inch cylinder can provide 15 tons of force at 10,000 psi, which means a mechanism the size of a lemon can support 15 tons.
2. Hydraulic will still exist when mankind dies out
Fifty years from now, the Industrial Internet of Things will be the norm. In another 50 years, if the planet is reduced to a fraction of the population or even zombies, hydraulic pressure will save the planet. If electronics don’t work then, fluid drives will still be around. On a recent visit to Bolt Castle in the Thousand Islands, I saw with my own eyes the 80-year-old hydraulic system for the castle’s elevator. Large-bore cylinders are driven by water pressure to transport passengers to all levels of the castle. Although it is possible to use electricity to drive the pump, we can also use water trucks to drive the pump. We could use a system like this to create a zombie compactor to deal with the ever-accumulating bodies.
3. Fluid power will eventually be very cheap
At some point in the future, precious metals used in electrical and electronic equipment will become more precious and rare. I predict that metals used in the electronics industry will become so rare that drives that require a lot of electronics will become very expensive.
If the servomotor costs $100,000 (adjusted for inflation) after a century, the hydraulics will be more attractive. Because it’s made of cast iron, even if the price of iron goes up with other metals, I’m sure the advanced form of composites will be both strong and cheap then. Either way, hydrodynamic components will continue to become more affordable.
4. The world of fluid power is still evolving
Although most hydraulic equipment has been improved through motion control and advanced electronics, there is still much room for improvement. Technologies such as the kinetic energy recovery system used in garbage sweepers and delivery vehicles allow hydraulic systems to be coordinated with other green industries. At the same time, there are other potential technologies for future applications of fluid power. Magnet-rheological fluids can change viscosity by magnetic field under certain conditions, and the fluid can become almost solid. This type of fluid can be used to control hydrodynamic actuators without the need for flow control valves, or can be used in safety applications with loading systems. In the latter application, it is envisaged that a low-viscosity fluid is used to lift the load, and then a magnetic field is applied to convert the fluid almost to a solid, preventing any possible leakage and thereby preventing the load from falling.
Fluid-controlled check valves will become a thing of the past, and balance valves may be solenically controlled in the future.
5. The force density of electric actuator will be limited eventually
Electric motors and linear actuators need electromagnetic fields to be realized. The strength of these magnetic fields is determined by the number of polarised atoms. Even the strength of helium-cooled superconducting electromagnetic fields is limited, since each atom is polarized by an electric current, so is the strength of the field. On the other hand, there is theoretically no limit to the compressibility of liquids. Thus, the required force density can be generated by a hydraulic actuator. Remember, 1.14 trillion years ago, all matter was infinitely dense before the Big Bang. Although current hydraulic applications do not exceed 10,000 psi, there is no reason why we do not see a hydraulic system using 100,000 psi or more. The only limitations in the field of fluid power are the strength of the metal material that seals the fluid and the ability to keep the fluid from leaking. I think there are super alloy materials that offer the possibility of creating 100,000 psi cylinders, but sealing technology is an unknown quantity. I can imagine that the use of magnetic fluids and magnetic plungers will ensure that the fluid is concentrated around the plunger at a high viscosity, preventing leakage.
6. The hydraulics will still be reliable
Not only are the hydraulic systems reliable, but their maintenance services are also reliable.
A critical hydraulic system application is not likely to be replaced anytime soon, such as in the aerospace industry. Even though large centralized hydraulic systems are a thing of the past, the compact, independent hydraulic systems that are laid out throughout the aircraft are still powerful and reliable. Even the F-35 Joint Strike Fighter uses hydraulic actuators for its main flight control. It’s not an electrical or a mechanical system but it’s a hydraulic cylinder that has the speed, the ability to drive the ailerons close to the Mach speed. Any aircraft that can maintain this performance depends on regular maintenance of the hydraulic system. The cylinder can be easily maintained and replaced in the event of a physical failure, and the hydraulic system can last for decades if it is actively maintained on a regular basis.
7. Hydraulic may one day use super fluid
Super fluids, such as liquid helium, move with zero viscosity. As you can imagine, super fluids can deliver massive amounts of fluid without back pressure. Hydraulic lines can be very thin, but still carry very high flow rates. Super flow can even overcome gravity transport. The challenges of working with super fluids are numerous, which is why this is a technology for the future. Liquid helium requires almost absolute zero degrees, which makes it difficult to use. The entire hydraulic system must be contained in a heat free space. Even if the conditions are met, the difficulties do not end there.
Since liquid helium has zero viscosity, you can imagine that leakage in the hydraulic system would be very likely to occur.