Hydraulics 101 for my Mini Backhoe Build

[NormL]

I recently resumed work on the Mini Backhoe I began building nearly ten years ago. To quote what has been said on these pages a number of times, "Life got in the way" and I had to set it aside for a while. Now that I have the time, I'm back at it and the hydraulic aspect of it is what's on the agenda. My knowledge of the rules and precautions related to getting this right without risk to life and limb is elementary at best so I'm here for the wise counsel I'm confident is available on this forum.

I have drawn up a crude diagram of two sets of spool valves, one is a BM40 - four spool and the other a BM30 - three spool. The BM40 will be the first after the pump followed by the BM30 via power beyond. I'll try attaching the diagram and my apologies in advance for the poor quality of the drawing and photography!! Please advise if I am making mistakes.

 

[NormL]

I'm sorry folks, that picture did not work. I'm going to have to work on getting a better one.

Try clicking on the one on the right.

 

[NormL]

View attachment backhoe hydraulics.jpg Hmm.... still trying to figure out how to navigate the recent upgrade of TBN.

I'll try my best to explain the drawing: The hydraulic fluid is sent from the pump to P1of the BM40 and P2 has a plug. From there the A and B ports are plumbed to the indicated cylinders. At T1 the fluid return is plumbed to the T1 port of the BM30. T2 has a Power Beyond adaptor installed and is plumbed to P1 of the BM30. T2 of the BM30 is plumbed as the tank return and in "theory" will also carry The return fluid of the BM40.

If anyone sees issues here, please advise because as I said earlier, I'm not well educated where hydraulic protocols are concerned. I am preparing to acquire the hoses for the various hookups so I need to know if I'm getting it right.

 

[ptsg]

I was checking some info on that valve to get a little bit familiar with it. I have similar valves on my homemade backhoe.

So I think you have it figured out. You're kinda saving some hoses and a T fitting by using both T ports of the BM30 as a T fitting.

 

[NormL]

I was checking some info on that valve to get a little bit familiar with it. I have similar valves on my homemade backhoe.

So I think you have it figured out. You're kinda saving some hoses and a T fitting by using both T ports of the BM30 as a T fitting.

Thanks ptsg, I was hoping I could get this right. The BM30 and BM 40 are manufactured in Italy so they could be more common in your market than here. I'm a S&PC (scrounger and proud cheapskate) so saving on hoses and fittings works for me!!

 

[ptsg]

We're on the same boat regarding the saving everywhere we can. Hydraulics can get expensive really fast.

My Badestnost valves look just like yours pretty much.

 

[Rich B1]

I would simply use a T at your 3 spool valve, with sufficient size hose to reduce back pressure. If I am reading your schematic correctly, you are using the valve as a T. IMO, that will create some back pressure on your primary valve (4 spool).

 

[NormL]

I would simply use a T at your 3 spool valve, with sufficient size hose to reduce back pressure. If I am reading your schematic correctly, you are using the valve as a T. IMO, that will create some back pressure on your primary valve (4 spool).

I wondered about that too but I'll try it first and if that is a problem I can make that change without much hassle because that area is easily accessible. Thanks for the heads-up.

 

[dfkrug]

Do you have written plans for the machine? I see you have a spool for a blade. Will the unit stand alone and be self-propelled?

Since you ask about the hydraulic valves, I do not see any particular issues, but you may consider a flow divider if you are set on using 2 different valve banks that are on the same pump circuit. Usually a single valve stack is used, with as many as 8 spools. A flow divider will make it easier to operate 2 valves at once.

 

[Rich B1]

He has the secondary functions on the 2nd valve (3 spool), primary functions on his primary 4 spool valve. A flow divider would just rob from his primary functions.

 

[ptsg]

I agree with Rich.

NormL has this thing pretty well figure out.

 

[NormL]

I must apologize for not providing more information. This backhoe build is documented on the Build it yourself forum here: It's time; either get started or.....

But to answer the question, the backhoe is built on the back of a Craftsman/Sears GT18 garden tractor. so it is self propelled. The dozer blade is adapted from an attachment from another similar garden tractor and serves where a FEL would otherwise be needed. The BM30 bank of valves is only in operation during set up and set down. In addition, the dozer will be useful for refill after digging is done. Thanks Rich and ptsg for your helpful comments. I appreciate and give serious consideration to all the advice I have received on this thread as well as on the above mentioned thread. It has been immensely useful, let me assure you. Cheers!

 

[NormL]

Since I last posted to this thread, I have installed and tested the hoses to all the cylinders. There were a few leaks which I have taken care of. One of the potential problems I was concerned about was whether the hydraulic pump would still be functional as it was a salvage item from an old bale loader. As it turns out that pump is more than I need for this machine. It delivers a volume in excess of the amount required and as a result I'm not able to easily control the movements of any of the cylinders. I'm running the engine as slowly as I can without stalling it when I move a valve. I already slowed the pump as much as I can without adding another set of pulleys and a belt. I would have to do all of that underneath the tractor - not a pleasant prospect! I have looked for restrictor fittings but have come up blank. There must be a source for them because I have seen some. I'm open to ideas here....

 

[lennyzx11]

Since I last posted to this thread, I have installed and tested the hoses to all the cylinders. There were a few leaks which I have taken care of. One of the potential problems I was concerned about was whether the hydraulic pump would still be functional as it was a salvage item from an old bale loader. As it turns out that pump is more than I need for this machine. It delivers a volume in excess of the amount required and as a result I'm not able to easily control the movements of any of the cylinders. I'm running the engine as slowly as I can without stalling it when I move a valve. I already slowed the pump as much as I can without adding another set of pulleys and a belt. I would have to do all of that underneath the tractor - not a pleasant prospect! I have looked for restrictor fittings but have come up blank. There must be a source for them because I have seen some. I'm open to ideas here....

You can make restrictor fittings by welding/brazing them shut then drilling a smaller hole in center. You only need one in each circuit to slow the fluid.

I would only do this on the individual circuit lines though. If on the main supply or return lines then the constant flow may cause fluid to heat.

Your valves/controls really should match your pump in flow per minute also.
Example
A 10 gpm(gallon per minute) pump .
With a valve that flows 10 gpm the halfway open flows 5gpm in theory.
But a valve rated at 20 gpm halfway open will flow 10gpm .harder to make delicate adjustments as each bit of handle movement makes a larger adjustment in the flow volume.
And a valve rated at 5 gpm (too small) though slower at halfway (2.5 gpm) is restricting the constant flow causing heat from friction AND the pump to be working harder constantly just
to move the fluid in the system.

Slowing the pump though slowing the flow also lowers the pressure produced.

 

[ptsg]

You can also use a Pressure Compensated Flow Control valve and adjust the flow to your needs and dump the excess to tank. Or just get a smaller pump now that you have an idea how the system works.

Link to an example of a flow control valve: https://www.princessauto.com/en/pre...w-controls/product/PA1000000773?skuId=8252785

 

[NormL]

Thank you to lennyzx11 and ptsg for your helpful advice!! I was considering the flow control valve concept and I also realized it would never do to restrict the flow of the pump without a release provision as lennzx11 cautioned me. As for mating the flow rates and valve capacities, I'll have to work with what I have as best I can for now. The idea of fashioning restrictors is the solution I'll try first if my search for suppliers continues to hit the wall. I have some galvanized street elbows to practice on as I'm taking seriously the warning to not use those for hydraulics. If I succeed in modifying them, I'll go on and make up a batch of restrictors for the seven cylinders that need slowing down. The ones I practice on can be drilled back out and used as normally.

PS: Yes, I also realize how careful I need to be inhaling fumes while welding galvanized material. I have read horror stories about that!!

 

[NormL]

I've revisited the possibility of slowing the pump some more and I think it can be done. I've posed the same issues on my build site (see post#12) as I have done here and it was suggested I use a similar setup to the one I slowed down one of my drillpresses. I'll give that a try as well as the restrictors. I've done a couple to see how brazing works and I think it will work. I'm starting with 1/16" openings as that is what I see on some fittings I have but are the wrong size. I can drill them bigger if need be.

 

[Xfaxman]

--------------------------
Slowing the pump though slowing the flow also lowers the pressure produced.

Can you explain how?

My machines will generate maximum pressure at idle and same pressure at max RPM.

 

[NormL]

I would simply use a T at your 3 spool valve, with sufficient size hose to reduce back pressure. If I am reading your schematic correctly, you are using the valve as a T. IMO, that will create some back pressure on your primary valve (4 spool).

I am having a problem that I originally suspected to be a worn out pump scavenged from an old bale loader/stacker. Thinking it over and remembering this comment about possible backpressure and the issue I am having with the movement of the boom as well as the dipper and bucket to a lesser degree, I will investigate this possibility further before changing out the pump. Thanks in advance, especially if this proves to be what is happening here. Cheers, NormL

 

[NormL]

You can also use a Pressure Compensated Flow Control valve and adjust the flow to your needs and dump the excess to tank. Or just get a smaller pump now that you have an idea how the system works.

Link to an example of a flow control valve: https://www.princessauto.com/en/pre...w-controls/product/PA1000000773?skuId=8252785

I have isolated the difficulties I'm having with the hydraulics and it is that the pump is delivering a much higher GPM than I need and when I try to dig, the engine stalls. It's an 18 HP Briggs and Stratton and it should be more than enough engine for the task. I picked up a flow control valve much like the one you suggested but by the time I add in the hose and fittings I'll need for it, I can almost buy a new pump that matches the job. Does "pressure compensated" mean that the pump will continue to deliver the same pressure to the cylinders while dumping excess volume of fluid back to the tank?