The hydraulic blast furnaces may have provided a new and efficient solution but many problems are bound to turn up if the problem of flow control is not properly addresses. The stretching of the fluid, especially over long hydraulic lines, must be tested and calculated under stimulated conditions similar to those in the actual furnace. After this, corresponding adjustments can be made in the calibration of whichever flow control systems that you are already using thereby cutting down costs that would have been invested on new systems.
In order to reduce the hydraulic spring (and as you have clearly pointed this out as one of the main problems that comes with long hydraulic lines) we should focus on the factors that contribute to this. For instance, there is the hose contribution which, though normally insignificant, forms an important consideration when it comes to long hydraulic lines.
This is an interesting posting, and quite educational in that I had not been aware of any precision being needed in the loading of blast furnaces. That area is quite far away from the systems that I have designed. So the posting is educational indeed.
But one point, lamenting the springyness of hydraulic systems, I can challenge, since I got much of the spring out of a system in order to make it meet the accuracy requirements. The fact is that hydraulic fluid does not actually compress enough to cause problems. Very small air and gas bubbles do compress, and so it is important to prevent them from being circulated in the system. That is one thing that reduces the system spring. Also, hydraulic lines do stretch, some of them a lot more than others. All hoses are major stretch sources, but using a hose rated for a higher, or even MUCH higher, pressure range reduces the hose contribution to stretch. Likewise, the steel tubing aslo stretches, not very much, but it does stretch a bit. Using tubing with a higher pressure rating and thicker walls will reduce that stretch as well. The result of including all of these choices and selections in a system assembly will often be that the resonant frequency is raised beyond the response ability, resulting in a much more stable system that does not look any different from the outside. That offered us a real competitive advantage for quite a while.
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