Backhoe Rear Hydraulics or Power Beyond Tap for Woods Backhoe on CT230

[DaveK OR]

The pressure relief in the loader valve would open in this case to momentarily protect the pump and the engine will RPM will decrease. This would be no different than going to a dirt pile with the loader, pull back on the lift and nothing happens because you have too much weight in bucket.

I'm not sure this is quite right for the Bobcat tractors. I had thought that that the FEL valving was separate from the rear hydraulic valving, so the relief on the loader valve block would not pop. That having been said, I would be a little surprised if the rear hydraulics (at least with the official Bobcat kit) did not have a relief valve.

Oh, and as far as "nothing happening" when you try to pick up too much in the bucket, unless you have ballast weight on the rear, what actually happens is that the rear wheels lift off the ground! Not a good thing, and an easy way to flip the tractor over.

 

[winston1]

I edited my last post and maybe you didn't see that the auxiliary valve does relieve at something over 2600psi.

My loader will not pick the rear of my tractor off the ground. Relief valve goes off first. Don't know which should be correct. Of course we are talking about no implements hanging on the rear.

 

[DaveK OR]

Thanks for that Winston... I hadn't seen the edit. Of course, I should have remembered that from looking through the tractor specs not too long back. LOL!

What happens when you try to lift too much probably depends on which CT200 model you have, as well as how much power is going to the hydraulic pump. I'll tell you though, the first time you pull those rear wheels off the ground, your pucker-factor goes waaaay up very quickly.

 

[tman1020]

I'm not sure this is quite right for the Bobcat tractors. I had thought that that the FEL valving was separate from the rear hydraulic valving, so the relief on the loader valve block would not pop. That having been said, I would be a little surprised if the rear hydraulics (at least with the official Bobcat kit) did not have a relief valve. Oh, and as far as "nothing happening" when you try to pick up too much in the bucket, unless you have ballast weight on the rear, what actually happens is that the rear wheels lift off the ground! Not a good thing, and an easy way to flip the tractor over.

The rear remotes are protected by the relief valve. I have tested it on a pressure gauge on my 2012 model to check the hydraulic pressure. Not sure on other model years though.

 

[DaveK OR]

The rear remotes are protected by the relief valve. I have tested it on a pressure gauge on my 2012 model to check the hydraulic pressure.

Thanks for confirming that. I'd have been surprised if it was otherwise, but it's good to know for sure.

 

[SSdoxie]

The relief valve for the hydraulic circuit (loader, rear auxiliary, & 3 point) is at the inlet port of the loader valve. Flow of oil goes from pump to loader to rear aux, to 3 pt. so the loader relief does protect the entire circuit.

 

[winston1]

The relief valve for the hydraulic circuit (loader, rear auxiliary, & 3 point) is at the inlet port of the loader valve. Flow of oil goes from pump to loader to rear aux, to 3 pt. so the loader relief does protect the entire circuit.

I respectfully disagree. Manual shows loader valve relief set at 2560psi, 3 point relief valve set at 2845psi, system relief at quick couplings 2611psi.

After further reading I will edit and shut up. Section 20-20-6 (testing main relief valve which is st the loader valve) states pressure at quick coupling at full rpm should be 2560psi. Very hard for me to understand some of these hydraulic schematics.

 

[RickB]

I respectfully disagree. Manual shows loader valve relief set at 2560psi, 3 point relief valve set at 2845psi, system relief at quick couplings 2611psi.

After further reading I will edit and shut up. Section 20-20-6 (testing main relief valve which is st the loader valve) states pressure at quick coupling at full rpm should be 2560psi. Very hard for me to understand some of these hydraulic schematics.

The 3PT relief valve is thee safety relief. This valve is ALWAYS set above system relief and is necessary for when the lift piston is isolated from the pump flow circuit (holding a load in any position other than full down).

 

[DaveK OR]

This is interesting discussion of the reliefs, but the important points are these (I think, correct me if I'm wrong):

1. Either of the rear A-B connectors can provide around 7-8 gpm at full flow, with maximum pressure of about 2500 PSI (not that you would get that pressure at full flow).
2. Either connector will provide "unrestricted flow" when used as the return.
3. If a check valve is used to protect backhoe hydraulics, reverse flow will bring the line to system pressure, but there is a relief valve to protect the deadheaded pump and other upstream hydraulics in that case.

Have I missed anything?

 

[SSdoxie]

This is interesting discussion of the reliefs, but the important points are these (I think, correct me if I'm wrong):

1. Either of the rear A-B connectors can provide around 7-8 gpm at full flow, with maximum pressure of about 2500 PSI (not that you would get that pressure at full flow).
2. Either connector will provide "unrestricted flow" when used as the return.
3. If a check valve is used to protect backhoe hydraulics, reverse flow will bring the line to system pressure, but there is a relief valve to protect the deadheaded pump and other upstream hydraulics in that case.

Have I missed anything?

You have it correct Dave. As an installation precaution, rig up a Tee and pressure gauge so you can check free flowing pressure through the Backhoe valve when the A or B port is activated. Test it at full RPM without moving any BH controls. The is just a check to make sure there is no measureable flow resistance (using 3000 psi gauge) through the Open Center BH valve that would generate extra heat & reduce available work pressure in the cylinder circuits.