Help me understand hydraulic systems

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NoPaint

Feeling the Heat
Jan 2, 2009
269
USA
So if I want to use my garden tractor to run a belt driven ball bearing pump I will run its lines to the back of the tractor. Hanging off the back I want a vertical splitting apparatus. I would like to leave the belt on the pump all the time so its always spinning even when I am just cutting grass. How does the oil system work then? Is it always pumping into a tank or can I have the tank removable with the rear splitter (has to come off when I am bagging)? I guess I just don't understand what happens if there are quick disconnect hoses on the rear of the tractor what direction does the oil go? Or is there a valve or something at recirculates the little bit of oil in there when the tank is off? Basically help me understand how these systems work. Lots of tractors have quick disconnects on the front when the plow blade is off but then what happens to the fluid?
 
You need the tank always to handle both expansion and cooling.
 
a typical fixed dispalcement pump will be moving oil whever it is turning. You will need the tank always.

There are many more issue here beyond a quick BB post.

FWIW, Bud Trinkle's books on hydraulic systems are available free on the internet at Hydr Pneum magazine. Good stuff, foundational, but may scare off many readers who want a quick answer rather than working through to understanding.



Bud's book, Fluid Power Basics is available for free viewing on our website, http://www.hydraulicspneumatics.com/200/ebooks/




kcj
 
Just pull the belt off of the pump when not "pumping". Chances are, you will be using the mower far more hours as a mower, than you would as a splitter. I would want to reduce the wear and tear on a pump that is not in use. They are mechanical, and its not "if" they will fail, but "when".

Then think of the extra burden on the engine. Always turning an unused pump. I realize that it would be in a low pressure environment, but it will still drag on the engine (and consume more fuel).

Just drop the belt when not in use.
 
Jags said:
Just pull the belt off of the pump when not "pumping". Chances are, you will be using the mower far more hours as a mower, than you would as a splitter. I would want to reduce the wear and tear on a pump that is not in use. They are mechanical, and its not "if" they will fail, but "when".

Then think of the extra burden on the engine. Always turning an unused pump. I realize that it would be in a low pressure environment, but it will still drag on the engine (and consume more fuel).

Just drop the belt when not in use.

Jags right, as usual. If you want more info go to TractorByNet.com > General Forums
Hydraulics Hydraulics
Ed
 
Cool,

So when the pump belt is on the tank will be on and if the belt if off the tank will be off. I want to run my splitter off my riding mower for a couple reasons. 1. Only 1 engine to maintain and rebuild because I have tons of equipment and would like to keep it down. 2. I don't want a trailer hanging around my yard. 3. If I had a trailer one I would still have to move it with the tractor so why not just make the splitter maneuverable!
 
NoPaint said:
Cool,

So when the pump belt is on the tank will be on and if the belt if off the tank will be off. I want to run my splitter off my riding mower for a couple reasons. 1. Only 1 engine to maintain and rebuild because I have tons of equipment and would like to keep it down. 2. I don't want a trailer hanging around my yard. 3. If I had a trailer one I would still have to move it with the tractor so why not just make the splitter maneuverable!

I think you would be better off with a splitter run off a 5.5 Honda motor . I like to use synthetic oil made for small motors . Am soil is good stuff and they make a special mix . A larger motor burns way more fuel and will cost you in the long run .
I have a skidsteer with a splitter and i use it for splitting larg rounds . I just line them up and split them .
 
The standard splitter hydraulic circuit has a suction line from the bottom of the tank, often one size larger than the rest of the lines, going to the pump intake. It is VERY important that you not add any obstructions or restrictions to this line, as doing so can cause the pump to cavitate as it pulls a vacuum, and rapidly self destruct.

From the pump there will be a high pressure line to the valve - if you put a guage on the system, this is where it should be. Note that while this line is billed as high pressure, the actual pressure on it will vary with the splitter load, and will actually only get "high" while you are splitting. However this line MUST be made with a high pressure hose, and all fittings on it should be high pressure rated hydraulic fittings - DO NOT use "schedule 40" plumbing parts, they will not take the pressure.

From the valve you will have a high pressure line going to each side of the cylinder, and a low pressure line going back to the tank. You should put a good hydraulic fluid filter in this return line.

When the valve is in the neutral the pump will circulate oil from the tank, through the valve and back to the tank.

When the valve is in either the extend or retract positions, it will send the fluid from the pump through the high pressure cylinder line to ONE side of the cylinder causing it to move. The moving piston will push the fluid out of the other side of the cylinder into the return line, and back to the tank.

If you hit a gnarly round, or run the cylinder to it's travel limit, the pressure in the high pressure lines, valve, etc. will build until the pop-off relief valve in the operating valve opens and diverts the excess flow into the return line back to the tank - note that this will cause the fluid to heat rapidly, and is generally hard on the equipment, it is best avoided as much as possible.

I would totally agree with the other posters on disconnecting the belt from the pump when not using it for splitting (or other hydraulic applications) but I would go even further and say that it would be best if you can keep the pump attached to the splitter parts and avoid the quick disconnects. Even the best QD fittings add a certain amount of flow restriction, and while this is tolerable on the high pressure and return lines (not ideal, but OK, best to go up at least one size on the QD fittings, though that gets expensive) IMHO it's problematic at best on the suction line. If you did have to leave the pump on the tractor, I'd keep the tank on it as well, even though it's a good bit of extra weight) so that the suction line would be unrestricted. I'd put the same size, matching QD fittings on the pressure and return lines so that when I detached the splitter, I could plug the two lines back into each other, both to keep the crap out and make sure that if the pump does turn at all, at least the fluid will be able to circulate.

Gooserider
 
A couple of other thoughts in addition to the other replies:

If you think you may have to use the splitter for any reason in the cold of winter, make the pump inlet line from the tank as large and short as possible. This will be critical to prevent cavitaion at the pump during cold weather operation. Not using a QD in the suction line goes double for cold operation.

If you have QDs between the pump and the splitter valve (where the system pressure relief valve is commonly located) you need an additional pressure relief valve someplace on the high pressure line between the pump and the QD. If you ever accidently ran the pump with the QDs uncoupled, or one of the QDs was accidently uncoupled with the pump running, you might find the weakest point in the hydraulic plumbing the hard way.

One final thought related to QDs: The return line filter should be located near the tank on the tractor side of the QDs, NOT on the removable portion of the splitter. If the return QD is ever disconnected with the pump turning (and the high presssure QD is still attched), the entire circuit on the removable side of the hydraulics will be pressureized to the relief valve setting (assuming a relief valve is present on the tractor side of the system). If the filter is located on the removable side of the system it will rupture. The entire hydraulic ciruit on the removable side of the log splitter, including any parts on the return path, should be sized to withstand full system pressure.
 
Thanks for the amazing tips gentlemen. Sounds like I should just build this with a separate engine as a trailer the tractor pulls then. I won't ever take the splitter off my property so it can be lowwww lowww lowww to the ground and just be fixed horizontal but I can have a little ramp to get the huge logs into it. How does that sound?
 
Sounds fine... I'm a fan of vertical mode, but that's not as big of an issue. More important is that, much as I like the idea of reducing the number of engines to take care of, it would probably be simpler to do the separate engine approach.

Gooserider
 
I have a horizontal unit I use on the 3 point hich on one of my old tractors. It was built so I could lower the splitter beam all the way to the ground for splitting the large pieces. It works well for the large chunks that are hard to lift, but when I am splitting the smaller stuff it's hard on the back if the splitter is on the ground. I don't know if there is a simple way to solve this problem on a horizontal with a fixed beam height unless you build in a log lift of some sort. For me it's no big deal, i just raise the splitter to a comfortable working height when I'm splitting rounds that I can lift and only run it on the ground to downsize the really big stuff. If all you are splitting is big rounds a low beam may be the way to go. If most of what you split is "liftable" you may want to consider building it with the beam at a more comfortable height and find an alternate means to cut/split/whatever the big rounds to liftable size. I ran mine with the beam on the ground almost exclusively for the 5 years I had my OWB and did not need to split into small pieces. It was hard on the back but I was not spending enough time spliting nto make it painful. Now that I spend more time splitting into smaller pieces for my gassifier I really like the comfort of being able to stand at the splitter instead of bending over the splitter.

FWIW, I think using the tractor engine to power the splitter is a good idea. The only difficulty is finding a place to locate the hydraulic tank and pump so that it is either removable or out of the way.
 
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