Few Hydraulic system questions

[wkheathjr]

1) I read that if you keep pump and tank very close, it will help keep fluid temperature down and prolong the life of system. I am curious if having a very long hose will cause temperature to rise? If so, would it help to have a little bigger tank for that? Or what is best solution?

2) How do you determine the size of tank and GPM based on what you are using. Suppose you have two gear pumps and four cylinder in your system, how do you determine the result to know what type of PSI your system need at RPM, and how much HP is required from your gas motor for the system?

3) Suppose you want to use a gear pump to move your vehicle at say 10-15MPH, can it be done (belt-driven system similar as kart)? And how do you know how much RPM is needed to get that speed?

Thanks!

-Ken

 

[J_J]

You have to start from somewhere. It takes a certain amount of HP to drive a pump or pumps, in order to pump fluid. The tank size has slowly been reduced down to one gal in the tank for each gal pumped. Theoretically, it should be about 3 to 5 gal tank for each gal pumped, in order to give off some of the heat, and maybe let bubbles dissolve, etc. The pressure is determined by the manufacture of the pump, but is not developed until the fluid sees some restriction in the flow path, such as cylinders, motors, relief valves. If you are using a hydraulic motor, and pulley/belt combination, you have to figure out the torque and rpm available to turn a wheel and how fast, and that will depend on the size of the wheel, and how much weight is involved, and so on and so on. We can give you some do's and don'ts, but you will have to build it your self, or buy it off the shelf when you figure out what all the parts will cost you.

Or you can start backward from how fast do you want the machine to run, and back things from there. There is a lot of engineering know how involved to make things work in a logical manner. A lot of people are always modifying things, and sometimes they succeed, and a good many fail. So, if you do your homework, you might be one of those that succeed.

Maintaining the correct temperature, is just one of the factors you will have to figure, like should I add a hyd cooler, use larger hose, etc

 

[wkheathjr]

Hmm.. well, let me rephrase my question.

What I mean is that suppose I know I am planning on using four 3" bore x 16" stroke cylinder, one 4" bore x 24" stroke cylinder, and one high pressure gear pump with .517 disp cu in. using 4.0 GPM @ 1800/8.0 GPM @ 3600 RPM.

With given information, how do I know what oil capacity will I need for given system and GPM of stage 2 pump will be needed? Then I will be able to locate the HP motor needs to be based on required GPM of stage 2 pump.

Hope this is more clear??

I did ask someone before and his short answer was "2 stage pump will do" but problem is that what GPM of pump? What size of oil reservior and how much gallon of fluid is needed? I want to know how did you find the answer so if I add or deduct the design then I can do it on my own without having to ask and ask.

Many thanks!
-Ken

 

[Mace Canute]

A pump rated 10 GPM at 3600 RPM and 2500 PSI, requires about 17.5 hp to drive it IIRC but please correct me if I am mistaken!
A quick Google for hydraulic calculators and a little perusing of the results should give you all the info you need.
Reservoir size traditionally has been at least 3 times the pump capacity and should contain additional space equal to at least 10% of its fluid capacity, so for an 8 GMP pump that means at least a 26.4 gallon capacity tank filled with 24 gallons of fluid. It all really depends on the usage however and if you are planning on light duty, you could try a smaller tank and less oil. Remember though, you need adequate volume to allow the fluid to rest between work cycles for heat dissipation, contaminant settling, and deaeration.

 

[J_J]

wkheathjr ,

In order to do anything, you need a final goal as to what you expect to achieve. For instance, I want to carry XXXX load at 10 MPH. From this point, you will have to decide on hydraulic drive, gear transmission, belt and pulley, etc. For more instance, how large a tire do I need?What rpm does it have to turn to give me 10 MPH. How much weight will I have to move to achieve this speed, including driver. Will the machine be doing other things other than just driving around. Is this a work machine? What work. How many functions? You need to fill out a work sheet on all aspects of your project. You will have to follow a logical order.

Anybody can throw things together and maybe it will work to some degree, but logical thinking will usually provide good results.

There are a lot of ifs, and what ifs you are asking. We can probably start you off in a general direction, and you can ask questions along the way. There are a lot of smart people on here, but unfortunately I am not one of them.

Just curious, are you trying to make a hydraulic go cart?

 

[wkheathjr]

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 really don't know if this would work but I am trying to do homework first and trying to understand hydraulic system.

 

[wkheathjr]

Mace,

How did you get the answer of 10GPM @ 3600RPM with 2,500 PSI?? That is what I was asking. A guy can tell me what I need but it doesn't help me because it doesn't tell me how you found the answer. In the future if I want to design something new then I will end up coming back to ask and ask. Better to know how to find an answer now so I don't have to ask again in the future.

 

[J_J]

Follow this link.

https://www.surpluscenter.com/hydraulic.asp?UID=2009081811133609&catname=hydraulic

select Tech help
select calculators/ select pump disp & HP
enter the data, and it will give you the results.

You can also punch in figures and work backwards by estimating, like what if.

 

[wkheathjr]

JJ,

Yeah I found the link on Fri but this is what I have: surpluscenter hydraulic

I think the issue I am having is that when there are few motors and few cylinders all together in one system, I am more worried about whether I am having correct GPM stage pump and oil reservoir tank than if I have right motor or cylinder for the job. The calculator is good but where does it give result when you input all the motors and cylinders then get the right GPM pump result?

That is where I am afraid that I might end up buying wrong stage pump and wrong size of tank then see my system fail because of heat from having too much or not having enough power to meet the demand that its working slowly.

Or was I supposed to know the exactly result from each motor/cylinder and then do the add-up and use the result to determine what stage pump I need and how much fluid?

 

[J_J]

The hydraulic pressure will determine the force in lbs/tons. The GPM will determine how fast the cylinders will extend or retract. If you have enough engine force to turn a pump, then you will develop potential force, because with no lever activated, the fluid is going through a loop from pump to tank, with no or very little pressure. It doesn't take a large pump to move cylinders. A 2 GPM pump at 1500 psi will work those cylinders, and the hyd calculators will help you to figure all that out, in force generated, and speed of operation. A Larger pump in psi and GPM, will operate larger cylinders and motors. With all that , you need the correct valve, filters, and reservoir.

Why not use the hydrostatic transmission from, or modify the garden tractor with a large enough motor to run the transmission, and any aux pump for a log splitter, etc. The tractor motor will have two belts , one to drive the hydro, and the other pulley cold drive the aux pump. Using the tractor, you don't have to engineer a lot of stuff.

 

[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.