Please review my hydraulic design

[bdw9862]

Would you kind and learned gentlemen please review my hydraulic design for my homemade backhoe and provide constructive feedback?

Thank you kindly.

 

[Rich B1]

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.

 

[RickB]

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.

Agreed. The engine throttle control can be used as a whole system flow control as well.

 

[jabelding]

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]

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.

 

[TMGT]

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.

 

[muddstopper]

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.

 

[bdw9862]

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.

 

[TMGT]

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.

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]

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.