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Hydraulic System

Hydraulic System

Hydraulic System

Hello everyone,

I am currently in the final module of my degree. I have had to design a wheel lift trolley. I am struggling for the following, if anyone can help I would really appreciate it.

How will I go out:

Deciding on the system pressure.
Deciding on what hydraulic pumps to use.
Deciding on the size of hydraulic rams to use.

It seems I need the answers to all of these in the beginning.

Any help would be great.


RE: Hydraulic System

How much force do you need?
How much space do you have?
Larger diameter need less pressure, but more fluid and cost more, until smaller systems reach higher pressures and start to cost more.
Rod length is determined by distance need to actuate your device, but the longer the rod, the greater diameter is required to prevent buckling; see how much force is required.
Force and diameter determine operating pressure.
Velocity of rod required? How fast does the rod need to travel. How fast does the cylinder need to fill? Determine the flow rate.
Velocity and cylinder diameter determine the required flow rate.
That may impact tubing diameter and pressure loss.
All pressure losses in combination with cylinder pressure needed determine pump pressure needed.
Once you know flow rate and pressure needed, look for a pump that can deliver.

RE: Hydraulic System


I am currently in the final module of my degree.
If your degree is in anything mechanical, you slept through about a dozen lectures in previous modules where the principles behind all of these questions were answered.
Go back and check your notes and textbooks.
If your degree is in philosophy, if a tree falls in the forest, will it take more pressure to lift the wheel than if no one hears it?
Seriously, this is where you should be looking through catalogs to see what various components are available at a reasonable price.

Ohm's law
Not just a good idea;
It's the LAW!

RE: Hydraulic System

I think it is quite common for each of the above subjects to be taught separately, consequently students do not get an appreciation of how each is integrated into a useful system that actually does something you want it to do. I learned a lot about hydraulic principles, but little about pipelines and virtually nothing about fluid power. A lot about pressure loss, but nothing about pipe stress. How to analyse a truss and frame, but little about how to design a building. How to combine some organic chemicals, but no idea about what it takes to build a refinery. Those things get integrated on the job when you have to put everything together and deliver something that actually works. More class time needs to be devoted to practical objectives of making something out of all the components.

RE: Hydraulic System

What 1503 said, but add: figure out how to decode the catalogs (figure out the symbology of spool valves and other control elements), learn the lingo -- i.e. what does a 4/3 spool valve with pilot operated check valves do, compared to one with open neutral ports, or what benefit does a variable volume pump give vs. a fixed flow gear pump, etc. etc. A deep dive into the hydraulic catalogs and also finding the relevant ISO or SAE standards for design of circuits and controls is probably in your future.

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