Hydraulics 101 for my Mini Backhoe Build

[NormL]

Norm
No to P.O. check on boom cylinders

I will check the boom cylinder first. I hope to do this by raising the boom and supporting it while removing the hoses and plugging the ports with screw-in plugs. Then remove support and see if it still extends as before. The stabilizers I'll test in a similar way and see if they return like they have. Can't do this today as everything is closed for Canadian Thanksgiving. Tomorrow!!
Thanks for the help guys

 

[oldnslo]

Backhoes don’t have those.

I will have to look but fairly sure bigger commercial back hoe loaders do have load holding valves. I can’t think of another piece of equipment that doesn’t have load holding PO check on a stabilizer.

suspect these small back hoes do not due to cost

 

[ptsg]

I will have to look but fairly sure bigger commercial back hoe loaders do have load holding valves. I can’t think of another piece of equipment that doesn’t have load holding PO check on a stabilizer.

suspect these small back hoes do not due to cost

Yes they do. Specially on stabilizers of any piece of equipment.

I also think that have pilot operated check valves on the boom and stick as well, however, those have pressure applied externally to keep the check valves open. Then when the machine shuts down, it locks the check valves. At least, that's my understanding from seeing the check valves mounted on these two cylinders but I haven't searched for more info about that yet though.

 

[NormL]

Yes they do. Specially on stabilizers of any piece of equipment.

I also think that have pilot operated check valves on the boom and stick as well, however, those have pressure applied externally to keep the check valves open. Then when the machine shuts down, it locks the check valves. At least, that's my understanding from seeing the check valves mounted on these two cylinders but I haven't searched for more info about that yet though.

I checked the catalogue from Princess Auto and discovered that the POC valve I could use costs 55 bucks plus taxes and I might need four or more of them. Also, if the cylinders have leaking seals, the check valves would be useless until that was remedied first. So, first things first, I say!!

 

[4570Man]

I will have to look but fairly sure bigger commercial back hoe loaders do have load holding valves. I can’t think of another piece of equipment that doesn’t have load holding PO check on a stabilizer.

suspect these small back hoes do not due to cost

My fairly new 310 didn’t. I’ve never seen a backhoe that did.

 

[oldnslo]

My fairly new 310 didn’t. I’ve never seen a backhoe that did.

Do you have a hydraulic schematic for your 310? I am just curious to see if there is a mechanically operated check in the directional control valve vs something at the cylinder.
I have operated older Deere 510 and Ford back hoe loaders and the out riggers would stay locked in position. A typical spool valve is not going to prevent drift unless they are specifically manufactured with very low leakage. Note: I have seen a hydraulic schematic on any of these.

 

[4570Man]

Do you have a hydraulic schematic for your 310? I am just curious to see if there is a mechanically operated check in the directional control valve vs something at the cylinder.
I have operated older Deere 510 and Ford back hoe loaders and the out riggers would stay locked in position. A typical spool valve is not going to prevent drift unless they are specifically manufactured with very low leakage. Note: I have seen a hydraulic schematic on any of these.

I don’t have a schematic but there definitely wasn’t a check valve on the cylinder.

 

[NormL]

I retracted the boom, supported it, removed the hoses and installed plugs. It has been holding position for almost two hours with no drift. That one at least points to the scroll valve. I'm not looking forward to that job! But before I tackle the boom valve I'll check out the stabilizers. There I expect to see at least one cylinder drifting. There may also be leak-down through the valve(s).

 

[NormL]

I retracted the boom, supported it, removed the hoses and installed plugs. It has been holding position for almost two hours with no drift. That one at least points to the scroll valve. I'm not looking forward to that job! But before I tackle the boom valve I'll check out the stabilizers. There I expect to see at least one cylinder drifting. There may also be leak-down through the valve(s).

Here's an update regarding the "sleuthing" I've done. The cylinders are not the problem.... So over to the next suspect - the spool valves. I tried to open the valve that operates the boom to see if there was evidence of any kind of junk making trouble. I followed the instructions in the manual that came with the BLB BM 20 and got as far as removing the Positioner Cap, the positioner, and the Handle Cap. At that point It instructed me to move the spool just enough to expose an "o-ring" groove but not too far, and remove the o-ring. I could see the groove but I could not push the spool far enough to see an o-ring. The internal resistance is presumably another 0-ring at the opposite end of the spool and forcing it is not recommended. I wound up putting it all together for now till I get some wise council as to what to do next.

 

[NormL]

Here's an update regarding the "sleuthing" I've done. The cylinders are not the problem.... So over to the next suspect - the spool valves. I tried to open the valve that operates the boom to see if there was evidence of any kind of junk making trouble. I followed the instructions in the manual that came with the BLB BM 20 and got as far as removing the Positioner Cap, the positioner, and the Handle Cap. At that point It instructed me to move the spool just enough to expose an "o-ring" groove but not too far, and remove the o-ring. I could see the groove but I could not push the spool far enough to see an o-ring. The internal resistance is presumably another 0-ring at the opposite end of the spool and forcing it is not recommended. I wound up putting it all together for now till I get some wise council as to what to do next.

I've done some more reading up on the topic of spool valve leakage and as mentioned by one of the commenters on this thread, it can be quite a common occurrence. The solution suggested is a check valve and to fully solve the issues I'm having I'll need four of them at a cost of $55.00 each. I'm going to experiment with a different try first. For nine bucks each I can buy brass shut off valves with NPTF fittings and 600 PSI rating. I'm sure that to simply hold the cylinder fluid from seeping back through the spool, I don't need 3000 PSI rating. I'll try it out on the stabilizers first as they never get to the digging pressure the boom, dipper and bucket need. As a reminder to open the valves before operating the spools, I will drop a wedge between the valve handles and the valve block to prevent accidental attempt to operate the valve before it has an open path. You guys probably think I'm a crazy Canuck, but hey, I'm OK with that!!