Few Hydraulic system questions

[MikesTractor]

J_J gave you a lot of good advice. Another thing to think about, too, is that you will seldom use more than 1 or 2 functions at the same time. It doesn't matter if you have 1 function or 10. If you only use 1 or 2 at a time, you can get by with a smaller pump and engine than you could if you operated all of them at the same time.

Your backhoe would be the exception. You could possibly be using up to 4 functions at the same time when feathering the controls (swing, boom up/down, boom out/in, and bucket curl).

Compare the requirements of the backhoe, and the requirements of the of the "cart" and use the highest one to size the system. That should be enough to handle whatever you need.

Ok, I'm rambling....but maybe you get the idea. Ask Questions....I don't think there is anybody on here that would mind answering your questions.

Mike

 

[wkheathjr]

Mike,

Thanks for answering and I think you got the point there.

I signed up at Hydraulic Innovantions forum. The guy over there built few cool things such as diesel engine using hydrostatic system for motorcycle, remote control 42" mower using camera so you could control mower with radio controller from indoor with favorite beverage by your side(cool isn't it!) and so on. I might learn a thing or two from them as well. Don't worry, I wont be shy to come back in here!

-Ken

 

[jinman]

Ken, I'm sure you can find a calculator to help with your planning, but I'd say you should not overlook the obvious as well. What I mean is that my tractor has a 9.8 gpm @2500 psi spec for its main hydraulic pump. It also has an HST transmission. Both of these pull fluid from a 10 gallon sump. The HST uses a cooler in front of the radiator, but the main hydraulic pump has no cooling other than the heatsink of the running gear and transmission case.

I guess my fluid could be heated up if I used all three of my remote hydraulics to drive motors instead of positional cylinders. For your use in building a UTV, perhaps a look at what Kubota uses on the RTV might be informative. I think because the UTV will have its hydraulic demand be mostly under light loads and used only intermittently, it will not require the high volume reservoir of an application where a motor is driven against a constant heavy load like a cement mixer or other industrial application. I think I'd look at your peak gpm flow and go no higher with the volume in the reservoir. If your peak flow is 8 gpm, I'd expect an 8 gal reservoir would be plenty. Actually, with a cooler, you might be able to use 4 gallons or less.

 

[J_J]

I am thinking that reservoirs should be larger. Those that use small reservoirs are not giving the fluid time to let particles settle out, or heat to escape, or air bubbles to break out of suspension. We, the Power-Tracs have a 20 gal tank, and radiator, and fan, and the fluid still gets hot. So in my opinion, bigger is better. People are now looking at slim and trim, and nobody wants a fat hyd tank hanging around, but to each, his own. That one gal tank for each gal pumped is really stretching design imagination. What every one should know is, that reducing heat is the main factor in extending the hydraulic fluid usability. Burnt ,worn out, water impregnated hyd fluid has no place in a hydraulic operating system. So, go small if you want to, you are the engineer on this project.

 

[jinman]

Sort of. I was thinking of making a utility vehicle similar as gator or mule using hydraulic system that would use gear pump to move it and add a dumping bed that probably can hold 600-1000lbs capacity depending on what it can do. And possible a reconnect hydraulic coupling that you can connect a towable backhoe or towable log splitter to it. Anytime I am ready to use small backhoe or log splitter, I can hook the trailer to it and connect the hydraulic system then open that line to it. The towable backhoe would be from ubuilditplans.com

I am thinking that reservoirs should be larger. Those that use small reservoirs are not giving the fluid time to let particles settle out, or heat to escape, or air bubbles to break out of suspension. We, the Power-Tracs have a 20 gal tank, and radiator, and fan, and the fluid still gets hot...

...That one gal tank for each gal pumped is really stretching design imagination. What every one should know is, that reducing heat is the main factor in extending the hydraulic fluid usability. Burnt ,worn out, water impregnated hyd fluid has no place in a hydraulic operating system. So, go small if you want to, you are the engineer on this project.

J_J, I see wkheatjr's design as something that doesn't compare with your PowerTrac nor my New Holland or somebody else's Kubota, Deere, Kioti, etc.. He is designing a UTV that will pull itself with up to 1000 lb and/or run a log splitter or backhoe, both of which are run by cylinders rather than hydraulic motors. He needs a way to power a motor that will only run fullspeed when he is cruising at high speed, probably around 25 mph. I don't think he will be towing a log splitter or backhoe at that speed. Probably, he won't even be running that speed when he has a 1000 lb load in the bed of the UTV. A HST transmission could provide power to the wheels, but he seems to want to use hydraulic motors. I'm not sure how he intends to build his powertrain, but I don't recall that he said he would use a motor on each wheel. That would surely be a challenge to design from the ground up, even for the most skilled amongst us.

I agree with you completely that you cannot overheat the hydraulic fluid. You must keep it below 200 degrees, clean it with filtration, cool it with a forced air radiator, return fluid to the radiator away from the feed line to allow for turbulence and air to escape before the fluid is recycled in the system. My feeling is most of our CUTs do just that with their hydraulic fluid. We do not see people cooking off their fluid or suffering from contamination when the system is maintained properly. A UTV that doesn't pull a plow or shove a loader bucket into the earth should not generate high temperature in its hydraulic oil under the most demanding circumstances. I believe a 4 to 5 gallon reservoir on a UTV would be huge. If there was a way to reduce that by cooling and filtering while maintaining flow with large lines, that would be my choice. I'd compare what the reservoir sizes are on standalone splitters and towable backhoes that are self-powered. Those would be the types of numbers I'd use rather than an arbitrary number based on constant flow in an industrial situation. Remember, when the backhoe and/or splitter is in use, the motors driving the UTV's wheels will be inactive. All the flow can be redirected to the attachments.

This is not a simple problem. The OP has some major hurdles before he can come up with a final design.

 

[J_J]

I certainly agree.

 

[wkheathjr]

If there is no harm in having a bigger tank to help minimize the heat then I say why not!? I was, at first, under the impression that having bigger tank could cause problem but I am glad that I am incorrect.

As for size of hose, it doesn't matter if the hose needs to be thin or fat as long as the system is running properly without any trouble then that is all I can ask.

Speaking of hydrostatic tranny, I realized that this is better if you want to have UTV running at the speed you set your foot pedal. I was told that using a hydrostatic tranny will allow you to adjust your speed just like you can adjust the dimmer of your light. I suppose the question I now have is that what of the cylinder and others? Is that where the aux pump comes in? Is that what J J is trying to tell me??

When I was telling my friends about this ideal project, one of them said he has a 14.5HP motor with hydrostatic pump he could sell to me cheap and I told him to hold on to it until I find out from you guys if it is worth the investment or if I needed something more powerful. Actually I would be satisfied with 15MPH as max speed but 25HP is decent! Someone was correct that I don't intend to move fast with that payload capacity of 1,000lbs on it and I will not haul the log using it if I build a small log trailer. I would just unhook the trailer and coupling then change the towing vehicle to tractor or truck capable of pulling it.

The backhoe from ubuilditplans.com calls for 6GPM pump so it seems that 14.5HP might be good to have??

Thanks for being helpful and pointing few things out.. and looking forward to your opinion and suggestion/feedback after this post.

 

[J_J]

wkheathjr,

Depends on the number of cylinders you have and the size. cylinder sped is based on volume, and the lifting force depends on pressure. It does not take a large pump to do cylinder work. I have a 3 GPM pump running off the fan belt, and it supplies fluid to the steering cylinder, and to the lift and curl cylinders. Placement of the cylinders on the lift arm dictates the weight you can lift. Another thing you will have to consider is the lifting force balanced against the weight of the vehicle, otherwise a safety factor. If you don't figure the geometry of the cylinders correctly, you will have to much force, and tip the machine. You may have to do trial and error to determine the safe lifting weight, and be able to move and steer the machine fully loaded.