For the past thirty years, there has been one constant in hydraulic system design. In this design, the motor spins at 1,800 RPM. Every once in a while, we could get fancy and purchase a 1,200 RPM motor to keep things quiet, but usually we used the 1,800 RPM motor as a system anchor point. Knowing this speed, we designed pumps based on flow at that speed that transported slightly more than needed to overcome vagaries of summer heat and winter cold. Valves were then used to choke down that flow to get the precision and power that makes hydraulics so useful. Even though this system created heat, we had coolers to take care of that; if we didn’t have a cooler on a system, there probably wasn’t enough flow. This loss of continuity can be overcome by the incredible efficiencies that can be gained with new technologies being applied to hydraulic design.
At times, it seems like the world has been turned upside down. Motors spin at whatever speed you need as the use of Variable Frequency Drives in hydraulic applications becomes commonplace. Pumps are moving from basic control applications, such as load sense and horsepower control, to proportional flow and pressure control with swashplate feedback. Valve choices have grown from high-end servo, mid-range proportional and low end bang-bang, to a jumbled mix that offer varying of performance at many different prices. Proportional valves now perform like high-end servos: Pulse Width Modulation coils now offer mid-range performance in traditional manifold valves as well as cartridge bodies. The choices for how to control a system are endless and there is no anchor number, especially when we start to mix and match the new technologies.
This variety reminds me of what it was like when I was a kid and went to the ice cream shop, struggling to decide on which flavor I should choose. Who can choose between chocolate chip, mint chocolate chip, and cookies and cream? This is what it feels like when we try to design a hydraulic system with all the control choices available today.
The truth is, these choices allow us to build hydraulic systems with a focus on system efficiency. In the past, there was little concern for the kilowatts consumed by hydraulic power units, because the energy consumed by these systems was insignificant when looking at an entire plant’s operations. The world is now much more concerned about the efficiency of equipment, especially when using power and water. These new control technologies are the key to bringing the hydraulic system design to the forefront of efficiency. The design options available today allow systems to be designed for the proper level of speed, accuracy and power, which reduces the energy used and heat generated by the system. This, in turn, uses less water for cooling.
Every control option, however, has its own set of capabilities and drawbacks. A PWM coil might allow a cartridge valve to replace a traditional proportional system, but it will not work in a high precision application. A VFD might have the resolution for precision torque control, but the motor and pump might be erratic at low RPM. Every opportunity to design a successful control system is also an opportunity to fail due to the realities of theory in practice. This is why it is so important to work with experienced system designers when it comes to hydraulic systems. They have lived through the failures of applying new technology, learned hard lessons, and used their knowledge to create better systems. By nature, they have a thirst for finding and applying new technology. In fact, it is why they were drawn to this field.
At Kaman, we are proud to have a great team of these designers ready to bring you the best of new technology, armed with the guiding light of experience. Reach out to us today and together we will successfully put theory into action.
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