bdw9862
Bronze Member
Would you kind and learned gentlemen please review my hydraulic design for my homemade backhoe and provide constructive feedback?
Thank you kindly.
Thank you kindly.
Please review my hydraulic design
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Rich B1
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The one thing that is odd to me is the needle valve after the pump. I wouldn't put it there without a relief valve before the needle valve.
If you are concerned about controlling function speed, it should be done on the individual functions. Yes that is more pieces, but that is the right way to get your function speeds where you want them with basic control valves.
If you are concerned about controlling function speed, it should be done on the individual functions. Yes that is more pieces, but that is the right way to get your function speeds where you want them with basic control valves.
RickB
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Agreed. The engine throttle control can be used as a whole system flow control as well.
jabelding
Gold Member
As others have said you never want to control the flow on a open center system with flow control it is just wasted power and energy. The best way to control the flow is with the engine speed, pump size or with feathering the control valves. You want to make sure that you have a system relief in your valves or if they don't an overall system relief just after the pump before the valves. With 13hp and 8gpm you will need to set your relief at around 2000psi any more and you risk staling the engine.
Fallon
Super Member
Make sure you put a relief valve close to the pump unless you want a hand grenade when you make a mistake. Others already covered the needle valve.
Nice flow chart diagram, makes communicating designs easier.
Nice flow chart diagram, makes communicating designs easier.
TMGT
Elite Member
Since you're going to have 2 valve sets have you considered using a flow divider and seperating functions? I wish I had separated the main boom from the swing on mine.
Could put bucket and swing on 1 and main boom and crowd on the other. Not sure on the size of your bh but 4gpm goes a long way on a small bh.
Could put bucket and swing on 1 and main boom and crowd on the other. Not sure on the size of your bh but 4gpm goes a long way on a small bh.
muddstopper
Veteran Member
Like others, I cant see the reason for the needle valve next to the pump. Pump should always be protected with a relief valve before any functions. Only possible reason I can see for the needle valve would be if it is in a tee in the pressure line to provide a port for your pressure gauge, but the needle valve should in no way restrict flow from the pump.
Also, it seems you are using a 8gpm pump, but have a filter rated for 7gpm. Restricting flow back to tank will cause back pressure in your return. to much back pressure and it could blow the filter off. I would look for at least a 10gpm filter.
Reliefs are most likely already on your 4 spool CV. The first control valve relief will set max pressure for the entire system. The relief on the second control valve can be used to adjust for lower pressure setting below the max setting of the first control valve relief. It will work but, I am not familar with small backhoes, larger ones usually have individual reliefs for each spool to allow for different PSI setting for individual functions. Of course, CV with reliefs for each spool are more expensive than a single relief CV.
Using the CV with PB will also result in single function operation. Whenever the first spool in the line of spools is activated, it will rob any available oil to any other spool further down the line. In other words, you wont be able to, as an ex, lift the boom and swing it at the same time. You will either lift then swing or swing then lift, just depending on which function is first in the line of spools. Feathering the levers will allow some functional ability of multiple spools at the same time
I see no reason to separate the two controls valves by using a flow divider as suggested. The second control valve seems to be dedicated to the 4 outrigger cyl's. Since the outriggers would only be extended/retracted while setting up the machine to dig and then not being used at the same time while digging. If this was a closed system, (I assume you are building a open system), and you where using a variable displacement pump, you could tie/tee, the control valves into the pressure line and have pressure to both valves and be able to do more than one function at the same time.
Also, it seems you are using a 8gpm pump, but have a filter rated for 7gpm. Restricting flow back to tank will cause back pressure in your return. to much back pressure and it could blow the filter off. I would look for at least a 10gpm filter.
Reliefs are most likely already on your 4 spool CV. The first control valve relief will set max pressure for the entire system. The relief on the second control valve can be used to adjust for lower pressure setting below the max setting of the first control valve relief. It will work but, I am not familar with small backhoes, larger ones usually have individual reliefs for each spool to allow for different PSI setting for individual functions. Of course, CV with reliefs for each spool are more expensive than a single relief CV.
Using the CV with PB will also result in single function operation. Whenever the first spool in the line of spools is activated, it will rob any available oil to any other spool further down the line. In other words, you wont be able to, as an ex, lift the boom and swing it at the same time. You will either lift then swing or swing then lift, just depending on which function is first in the line of spools. Feathering the levers will allow some functional ability of multiple spools at the same time
I see no reason to separate the two controls valves by using a flow divider as suggested. The second control valve seems to be dedicated to the 4 outrigger cyl's. Since the outriggers would only be extended/retracted while setting up the machine to dig and then not being used at the same time while digging. If this was a closed system, (I assume you are building a open system), and you where using a variable displacement pump, you could tie/tee, the control valves into the pressure line and have pressure to both valves and be able to do more than one function at the same time.
Thank you very much gentlemen. Here are the changes I propose to the system:
1. Remove the needle valve and put in a relief valve.
2. Adjust pump flow with RPMs on the engine.
3. Bigger return filter.. at least as big as the pump at max flow (I assume you can find one to fit the 3/8 fitting I will be buying).
Questions:
1. Relief valve one way or both ways, does it matter, what kind?
2. Could I get away with an 8 horse gas engine?
3. Would I be better off with a 6 gpm pump at 2k RPM?
4. Should the tank be a little higher than the pump for good flow or does it matter?
Thank you for you kind assistance.
1. Remove the needle valve and put in a relief valve.
2. Adjust pump flow with RPMs on the engine.
3. Bigger return filter.. at least as big as the pump at max flow (I assume you can find one to fit the 3/8 fitting I will be buying).
Questions:
1. Relief valve one way or both ways, does it matter, what kind?
2. Could I get away with an 8 horse gas engine?
3. Would I be better off with a 6 gpm pump at 2k RPM?
4. Should the tank be a little higher than the pump for good flow or does it matter?
Thank you for you kind assistance.
TMGT
Elite Member
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.
jenkinsph
Super Star Member
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.
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.
TMGT
Elite Member
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
Veteran Member
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.
muddstopper
Veteran Member
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.
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jenkinsph
Super Star Member
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.
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
Super Star Member
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.
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.
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.
