Please review my hydraulic design

[TMGT]

I agree with most everything others have said above.

Since you are building this from scratch you might consider using a closed system instead. This would give you better control of more than one function at a time. Being able to swing and control the boom at the same time comes to mind. You can use an open system but it is not as nice as a closed system can be. Just something to consider before you build this.

I'll agree that a closed system would be ideal, but when I looked into it the cost went up quite a bit, that's why I suggested the split open center system. I just wish I had figured it out before I built mine.

OP, what size are you planning to build this? Cylinder size and desired speed will determine pump size.

 

[muddstopper]

No the flow divider wouldn't benefit him as the valves are setup in the diagram.
I was suggesting dividing up the BH controls between the two valves so simultaneous operation of 2 functions could be achieved, this would place 2 stabilizers on one valve and 2 on the other. Since you're already using 2 control valves it would be a minor investment for a good increase in functionality.

If I was to build another BH I would do this, also it is nice somtimes to have float position on the main boom if possible, but definitely not a requirement.

It took me a minute and a reread of your other post to realize what you where suggesting. I agree, as long as the OP can live with the reduced flow. His 2.5in bore cyl are not going to provide a lot of force and I dont know how important speed is going to be. I would probably swap the speed reduction for improved functionality and a the flow divider would provide this.


To the OP.
1. Relief valve one way or both ways, does it matter, what kind?
I suggest before investing in a separate relief valve, you take a look at your control valve. Chances are your control valve already has a relief built in and no other purchase is necessary. You should always have a relief between the pump and the control valve. Your control valves should have the relief built in. Your question about one way or both ways doesnt really apply here and a second relief isnt necessary
2. Could I get away with an 8 horse gas engine?
Hp is in direct relation to pump flow and pressure. At what pressure so you intend to run this system. With standard gear pump, chances are you will not be able to run the 8gpm, or even the 6gpm at any decent pressure with just a 8hp engine.
3. Would I be better off with a 6 gpm pump at 2k RPM?
Many ways to mess with pump flows, rpms being one of them. If you idle down the engine to achieve desired flows, you will also reduce hp generated by the engine. Best to match required flows and pressure requirements with adequate eng. hp
4. Should the tank be a little higher than the pump for good flow or does it matter?
Maintaining fluid levels higher than the pump intake is always better. Oil levels lower than intake levels can cause the suction line to drain of oil when not pumping. Dry suction lines can damage the pump at startup. This doesnt mean the whole tank should be higher than the pump, just that the oil levels in the tank should be above the pump.

 

[bdw9862]

I'll agree that a closed system would be ideal, but when I looked into it the cost went up quite a bit, that's why I suggested the split open center system. I just wish I had figured it out before I built mine.

OP, what size are you planning to build this? Cylinder size and desired speed will determine pump size.

Is the attached design (design 2) what you are talking about?

All cylinders are 2 1/2 bore and about 18 to 20 inches for a stroke. Desired speed is above a crawl.

 

[bdw9862]

It took me a minute and a reread of your other post to realize what you where suggesting. I agree, as long as the OP can live with the reduced flow. His 2.5in bore cyl are not going to provide a lot of force and I dont know how important speed is going to be. I would probably swap the speed reduction for improved functionality and a the flow divider would provide this.


To the OP.
1. Relief valve one way or both ways, does it matter, what kind?
I suggest before investing in a separate relief valve, you take a look at your control valve. Chances are your control valve already has a relief built in and no other purchase is necessary. You should always have a relief between the pump and the control valve. Your control valves should have the relief built in. Your question about one way or both ways doesnt really apply here and a second relief isnt necessary
2. Could I get away with an 8 horse gas engine?
Hp is in direct relation to pump flow and pressure. At what pressure so you intend to run this system. With standard gear pump, chances are you will not be able to run the 8gpm, or even the 6gpm at any decent pressure with just a 8hp engine.
3. Would I be better off with a 6 gpm pump at 2k RPM?
Many ways to mess with pump flows, rpms being one of them. If you idle down the engine to achieve desired flows, you will also reduce hp generated by the engine. Best to match required flows and pressure requirements with adequate eng. hp
4. Should the tank be a little higher than the pump for good flow or does it matter?
Maintaining fluid levels higher than the pump intake is always better. Oil levels lower than intake levels can cause the suction line to drain of oil when not pumping. Dry suction lines can damage the pump at startup. This doesnt mean the whole tank should be higher than the pump, just that the oil levels in the tank should be above the pump.

I want to operate at probably around 2000 to 2500 psi with enough umph to operate a small towable backhoe to dig and pick up relatively heavy stuff.... I have not purchased cylinders yet and could go up to 3 inch if necessary.

 

[muddstopper]

I want to operate at probably around 2000 to 2500 psi with enough umph to operate a small towable backhoe to dig and pick up relatively heavy stuff.... I have not purchased cylinders yet and could go up to 3 inch if necessary.

You have not provided anywhere near enough information to let anybody comeup for a workable approach. Changeing cyl size for more power is always good, but can be worthless if the machine is so lite the boom just drags the machine around instead of pulling out dirt. How long will your booms be, dipper and root boom, what size bucket. How deep do you want to dig. do you plan on adding weight to the rear of the backhoe to hold it down with the bucket reaching out and picking up dirt. towable backhoes are not known for haveing a lot of breakout force for digging. Big buckets, big power needs a lot of weight make everything work. When working with booms, you have a lot of factors as to what you can lift. While a cyll of a certain size might easily lift a big load as long as that load is in line with the cyl. with the cyl hooked to a boom, the lift angle is always changing and the lift capacity changes as the angle and distance fro center line increases.

I would suggest you come up with a design for the boom factoring in how far you need to reach and how much weight you want to pick up and then match your cyl's to meet those demands. Just building and guessing certain parts should be good enough, might become a expensive experience in frustration and aggravation. If it was my build, I would go look at similar machines to what you want to build and take a few measurements from a proven design and use that as a starting point for your build.

I went to a farm auction the other day and there where several 3pt bachoe attachments that sold really cheap. You might consider finding a auction and seeing whats for sale. Take a tape and writing pad to do some measureing with. Even if you dont buy anything, at least you will have a good ideal on how to build what you want.

I just looked at your revised file. It wont work as drawn up. You can not just use a tee to separate flow for the two separate valves. You could use a divider valve in the place of the tee to split flows. You have added a relief after the pump, as I have said, both your CV's should already have a relief built in and purchaseing a addition relief isnt necessary. Spend the money on a divider valve instead. This one 4/3 GPM PRINCE PRIORITY FLOW DIVIDER W/RELIEF will give you 4gpm priority flow for one valve with the remaining fluid diverted to the other valve, and it also has a built in relief.

 

[jenkinsph]

If you go with the two sections approach it may be cheaper to use a two section pump if you have relief valves on both of your control valves. Here is one with 4gpm on each of two sections cheap. �.48/�.48 CU IN DYNAMIC GP-F2�-�8-�8-S9-C HYDRAULIC DOUBLE PUMP

This way you won't need a flow divider'

If you drive the pump with a 2 to 1 chain drive you can run the engine at 3600 and the pump at 1800. That would help a lot with maximum power. All of this needs to be properly sized and calculated as mentioned above. Very important.

 

[jenkinsph]

Another thing you might consider is a good used lawn mower engine. The pumps do not care whether you set them up verical or horizontal shaft. Lots of 20plus hp lawn tractor engines with plenty of life left in them for cheap. Most of them have transmission failures long before the engine has appreciable wear.

 

[bdw9862]

Thank you all for the information. I will try to provide some additional information:

1. The lower boom is six foot in a straight line pivot to pivot on a 30 degree angle.
2. The upper boom is five foot from pivot to bucket pivot straight.
3. I intend to leave attached to my pickup when possible and counter weight when not.
4. I understand the hoe will have significant limitations over the real deal. I am building it to see if I can not because I can't find a used tractor attachment etc....
5. I will try the flow divider.
6. Yes both sets of spools have reliefs built in.
7 Both the boom and the frame are about 50-75% complete, used 3" x 1/4" square tubing. Starting on the boom pivot using 1" x 3" plate steel.

 

[bdw9862]

That double pump is a great idea.

 

[bdw9862]

Ok, next dumb question, can you tee the supply line into the double pump or does it actually require two smaller tanks?