Backhoe B26 hydralics bypassing

[woody]

I carried my B26 to the dealer today and had a long talk with him. I cannot be there tomorrow I hate it when work gets in my way, but I did talk with the shop manager for a while. he told me today that they set it at 2440 the last time they worked on it then I told him I checked it and could only get 2200 that he needs to check his gauge or I do one. now that he knows that I knows then maybe it will be fixed.

 

[wdchyd]

I carried my B26 to the dealer today and had a long talk with him. I cannot be there tomorrow I hate it when work gets in my way, but I did talk with the shop manager for a while. he told me today that they set it at 2440 the last time they worked on it then I told him I checked it and could only get 2200 that he needs to check his gauge or I do one. now that he knows that I knows then maybe it will be fixed.

Woody,

Did the dealer say he could do a Flow/Load test on the system?....It'll show flow efficiency at rated pressure.....very important......

Don't forget it takes pressure AND flow......if they are a good dealer then they'll do it......

 

[woody]

Woody,

Did the dealer say he could do a Flow/Load test on the system?....It'll show flow efficiency at rated pressure.....very important......

Don't forget it takes pressure AND flow......if they are a good dealer then they'll do it......

I would hope since the rep knew about this problem in advance he prepared for it, but I did find it funny that the service manager could not tell me the pressures before but now he knows. :confused2:

 

[Skyco]

When you reach out with the backhoe and try to get some dirt it does not dig, does not move the machine, and does not pull the motor down.

Good advice given to you in this thread....re: your statement above I don't think you'll ever see the motor pull down- I know my BX24 doesn't even grunt when digging at recommended RPM, even with a stalled backhoe digger.
Regarding the two readings, yours and the dealers, differing- wouldn't surprise me if low cost gauges are 3% or worse accuracy...so the two of ya'll could differ by several hundred lbs and neither is "wrong".

 

[woody]

Good advice given to you in this thread....re: your statement above I don't think you'll ever see the motor pull down- I know my BX24 doesn't even grunt when digging at recommended RPM, even with a stalled backhoe digger.
Regarding the two readings, yours and the dealers, differing- wouldn't surprise me if low cost gauges are 3% or worse accuracy...so the two of ya'll could differ by several hundred lbs and neither is "wrong".

skyco you made a good point on the gauge being off and I did think of that. I have decided that I am going to fix me up a two gauge tester that way I can compare the readings with out disconnecting it from the tractor.
thanks for your input.

 

[woody]

Well, the Kubota rep. did not show up the dealer has had my B26 since Tuesday and I still don't know what to do. So far I have not had a good experience with Kubota.

 

[woody]

First of all, thanks for letting me vent my problems. now I called the service man today and he said the Kubota rep came down this morning and look at my B26 for about an hour and has declared it done he said it is doing all it will do. When I asked him what he did to it he said absolutely nothing. He checked the pressures and then went out and ran it. The pressure is now reading 2360psi, ok I checked it a week ago and I got 2200psi and the last time it was in the shop they said it was 2440psi sounds funny to me. I will go in the morning and pick it up I hope it is mysteriously fixed. :confused2:

 

[J_J]

You might ask them to leave the gage in the system and show you the results. You might take your gage in and compare the two gages. If you install a permanent gage, you can monitor the pressure at any time.

 

[dfkrug]

If you install a permanent gage, you can monitor the pressure at any time.

That's a good idea, if you can find a convenient location. That is where you
would want to tee into the In or PB_Out on one of the valves. Sometimes
there is a plug on the valve body itself for a guage connection. I
permanently mounted a guage on my CADDigger hoe valve, and it was useful.

I do not have a B26, but my B21 had RVs on the main gearbox, the FEL
valve, the hoe valve, the OEM AUX valve, and the 4-in-1 valve. Whatever
was set lowest determined the effective hyd system pressure. That's a
lot of RVs to set if you wanted to raise the pressure....mine was between
2000 and 2100psi.

I have seen it written that the B26 also has a separate hyd pump for the
hoe swing circuit. That would be an independent system with its own
RV, even if it sucks from and dumps to the same reservoir.

 

[dfkrug]

you can disconnect any hose from BH controls going to a cyl providing it's not one with a work port relief (that pressure will show up lower)......

Lower? I am not saying it is not possible to have a work port RV set lower
than the system pressure, but all the hoe work port RVs I have seen are
set considerably higher than the system RVs. I often see 3000psi settings
in these "shock-relief" valves.

 

[Egon]

Have you got flow/pressure curves for the pump? They may be quite useful:thumbsup:!

 

[wdchyd]

Lower? I am not saying it is not possible to have a work port RV set lower
than the system pressure, but all the hoe work port RVs I have seen are
set considerably higher than the system RVs. I often see 3000psi settings
in these "shock-relief" valves.

A normal WPR Valve is set at a lower pressure rating on a typical control valve than the main relief (at the inlet section ) to protect that circuit from overpressure from the hyd pump ......

When you mention a "Shock-relief" valve set at a higher pressure then you are talking about a "Cushion Valve" protecting the circuit from an induced load.....(pressure exerted from an outside load).....ie: snowplow hitting a snowbank/curb or manhole cover........then it bypasses to protect from overpressure exerted from the external source, not from internal pressure from the hyd pump.....

Snowplow controls do this all the time.......And I've seen it on BH swing circuits because of the overrunning load when swinging at high speed and the control lever is quickly stopped or reversed......

Yes, In that case the cushion relief valve will be set higher than main PRV.....

 

[dfkrug]

A normal WPR Valve is set at a lower pressure rating on a typical control valve than the main relief (at the inlet section ) to protect that circuit from overpressure from the hyd pump ......

Protecting the circuit from overpressure from the hyd pump is what the
RV on the IN port of any valve does. Work port RVs are there to protect
the work circuit when the valve is closed, so you would want it set
higher than the other RVs, not lower.

I suppose you could design a system where you had work port RVs that
were LOWER than the system pressure, but it would be a more efficient
approach to use smaller cylinders, or a different bore-to-rod ratio on the
cyls in the work circuit.

 

[woody]

thanks for all the input, going to pick it up in the morning after working a 12 hour midnight shift. I hope all is well with my hoe.

 

[wdchyd]

Protecting the circuit from overpressure from the hyd pump is what the
RV on the IN port of any valve does. Work port RVs are there to protect
the work circuit when the valve is closed, so you would want it set
higher than the other RVs, not lower.

I suppose you could design a system where you had work port RVs that
were LOWER than the system pressure, but it would be a more efficient
approach to use smaller cylinders, or a different bore-to-rod ratio on the
cyls in the work circuit.

I suppose in tractor hydraulics this makes sense but in construction and logging equipment I see it all the time (WPR set lower).....WR ported valve sections can be different settings on the same spool or plugged to go with the main RV.....full size JD TLB's and skidders do it all the time to limit power to some BH functions......

 

[woody]

Picked my B26 up and tried it out no better than before but he did say they did not do anything but try it out. The rep. said the pressure is 2360psi and that it will pick up the backhoe. I agree if it picks up the BH then I cannot ask for more. I carried it home and tried it out if I put the bucket down a few feet from the tractor it will pick it up, but if you reach out to dig the prv will open and you have to baby it to dig. I loaded it up and carried it to a buddy's shop checked the pressure at the prv and true enough we read 2340psi close enough to the rep reading. I think I'll just have to get use to using an inferior machine than what I was using, they said it is doing all it will do. I admit if this had been my first BH I probably would not have though anything about it but compared to my other BH it sucks.

 

[J_J]

Have you checked for restrictions in the work ports of the BH? .

I am thinking that a pressure gage and flow meter on the work ports will tell you the true story,

 

[dfkrug]

I suppose in tractor hydraulics this makes sense but in construction and logging equipment I see it all the time (WPR set lower).....WR ported valve sections can be different settings on the same spool or plugged to go with the main RV.....full size JD TLB's and skidders do it all the time to limit power to some BH functions......

I imagine that a manufacturer of a hydraulic attachment will have a
certain max hyd pressure he will expect to encounter on the various
tractors that are in his target market. He will have an IN port RV to
protect from those with higher pressures. (That is why I recommend
that you match your attachment to your tractor's hyd pressure
capabilities. If the attachment has a lower RV vs the tractor RV, you are
weakening your other hyd implements, like the FEL.)

OTOH, if the manufacturer is protecting one hyd circuit of a multi-circuit
attachment with a work port RV set below the system pressure, then
he can not use shock RVs (higher pressure RVs) in that circuit. Hoes
often use shock RVs in at least the swing and boom circuits. It would
also be more efficient design to design for the same system pressure
in all circuits. This is exactly the issue you have in designing a hyd
thumb for a hoe.

The OP's BT801 hoe probably has 4 or more shock RVs.

Can you give a specific example of a hyd implement's work port RV that
is lower than the system pressure? Construction or ag implement. It
does not make sense to me.