Insane Hydraulics

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Tackling Torque Limiting Pump Controls - Part Two

So - I went back to the app that I built last week, and made some changes:

1) I changed the scale of the power axis, and now the ideal curve can be bumped all the way up to 30 kW.

2) I added an interactive schematic of a double spring feedback system for better visualization of the two-spring concept. Note that the travel is actually greatly exaggerated - in real life, the relational displacement of the springs is actually pretty small - at least for the parallel spring systems. There is also the springs-in-series solution - but it is so nice that I decided to leave it for a separate (future) post.

3) I added the displacement slider to animate the spring feedback drawing. It looks very cool!

My goal was to show how double-spring feedback torque-limiting pump controls function - and I believe that the interactive graphic at the bottom of this page does a good job doing that.

First and foremost - it visually shows the physical limitations of such systems, and the most important one to note is the fact that the effective torque-limiting range (or power liming range, if you will, for constant speed scenarios) is defined by the physical stiffness of the springs. So you can't set these pumps "infinitely".

An example to illustrate this point:

Setting the graphic to the following parameters

will result in a nice-looking approximation to 20 kW.

Now - try using the same springs (don't change the Spring constants) to set this control to 10 kW (use the ideal curve for the reference). Of course, you will achieve something, which, I guess, is better than nothing, but still the approximation will be very ugly.

I truly hope that this graphic breaks the myth that a pump equipped with a torque-limiting regulator can be used with any motor. I am sorry, gentlemen, but it can't. Not without replacing the damned feedback springs. And, unfortunately, while most catalogs and parts lists will readily provide you with information on the common rotatory group parts, I dare you to get a list for torque limiter feedback springs from your supplier! The best you can hope for is a generic mentioning in the catalog that you should "clearly state" the power of your prime mover when ordering a new unit with such control. What? Your pump parts dealer has it? Congratulations - you've got a stellar supplier then!

There also was a slider to move the outer adjustment piece, but I didn't have time to finish the code and eventually decided to remove it (for now). It's actually a bit complicated to simulate, because, when you unlock "the large" lock-nut, and move the external setting screw - you are shifting two things at the same time - you are changing the preset pressure of the first spring (defined by the spring's constant), and you are also shifting the displacement point at which the second spring comes into play. Now - this would be great to depict on the graphs, but a couple of hours I managed to find today to put together this piece of code weren't enough for me... Amateur coder here... Sorry... I'll find a way to get it done next week.

Anyhow - once again, do take the graph for a spin and try out different power and spring settings out. And do share!