Older B5200 with 4520A Backhoe Question

[dtomlin]

Can someone tell me what speed to run my PTO when using my backhoe as well as how many RPM's I should be running my engine on my older B5200 and 4520A backhoe? I just picked this up for $5500. Seems to run great, I think that it was a steal. Thanks in advance.

 

[fried1765]

Can someone tell me what speed to run my PTO when using my backhoe as well as how many RPM's I should be running my engine on my older B5200 and 4520A backhoe? I just picked this up for $5500. Seems to run great, I think that it was a steal. Thanks in advance. View attachment 108449

From outward appearance it does appear that you stole it!
Do you feel guilty yet?

 

[torch]

Run the PTO in the low range. Engine speed 2,000 rpm or so -- faster if the movement is too slow, slower if it is too touchy.

 

[cthomas]

Is there an arrow or notch within the tach? Kinda like this

 

[dtomlin]

Run the PTO in the low range. Engine speed 2,000 rpm or so -- faster if the movement is too slow, slower if it is too touchy.

Thank you

 

[dtomlin]

Is there an arrow or notch within the tach? Kinda like this
View attachment 108480

Exactly like that. Is that the "recommended" RPM speed for "most" attachments?

 

[torch]

That is the engine speed where your low range PTO speed will be 540rpm. Usually a tractor is geared so the engine is making max HP at that speed -- great if you are blowing snow, etc. But using a PTO pump powered backhoe, there's little to no increase in digging force and a beginner will likely find the controls too touchy at that speed.

 

[Vigo]

I have a near identical backhoe on a B8200 and i run the pto in the higher range and the engine at lower rpm.

Most of the hydraulic pumps on these backhoes, or tractors this size in general, require no more than 8-10hp to make max pressure at their max flow. If you spin them slower they flow less and require less hp to make max pressure. Basically, they can make peak pressure without stalling the tractor at anything above idle. So, you lose almost no strength (pressure = strength) regardless of what rpm you run at. The minor caveat is that the pumps have less internal leakage when spun faster, so they may make slightly less pressure when spun slowly but if that pressure is still above the relief pressure setting in your valve set, you wont notice anyway.

So, what im saying is your engine rpm basically dictates how fast the hoe moves, but not really how strong it is. So you adjust your rpm to suit your desires. Whatever feels good, go for it! When i get on the backhoe first thing in the morning i run mine just off idle in pto high range. When ive been on it long enough to get impatient im revving the engine like everyone else.

 

[torch]

If you spin them slower they flow less and require less hp to make max pressure. Basically, they can make peak pressure without stalling the tractor at anything above idle. So, you lose almost no strength (pressure = strength) regardless of what rpm you run at. The minor caveat is that the pumps have less internal leakage when spun faster, so they may make slightly less pressure when spun slowly but if that pressure is still above the relief pressure setting in your valve set, you wont notice anyway.

The flip side of that is that hydraulic oil temperature increases with flow rate (rpm). The pressure relief valve will limit the pressure, but it does so by dumping the excess flow back to the reservoir, not by reducing the overall flow rate through the pump. So if you find yourself trying to feather the controls to keep the backhoe speed down then you are not only wasting the fuel, you are heating the hydraulic oil unnecessarily. That's harder on seals, fluid, etc.

Kubota actually specifically says not to use the high PTO range in my backhoe manual ("IMPORTANT: The backhoe has been designed to operate in the 540 PTO-RPM position only. Do not operate in the 750 position or backhoe hydraulic system damage may result."). There is also a warning sticker to that effect on the control pedestal. I'm not certain why, and have asked this question here before.

My hypothesis is that there is an increased likelihood an operator will rev up the engine and overspeed the pump. The flow rate coming out of the overspeed pump could then overwhelm the capacity of the relief valve and that would cause system pressure to rise above the limits of the components.

So, if you choose to ignore the warning and run the PTO in a higher range, you do so at your own risk. IMHO, the tractor will be quieter and use less fuel but it is incumbent on the operator to ensure the PTO speed remains below 540 rpm.

A new operator, such as the OP, might be better off to stick with Kubota's directions at least until they gain proficiency and familiarity with the equipment.

 

[TheOldHokie]

The flip side of that is that hydraulic oil temperature increases with flow rate (rpm). The pressure relief valve will limit the pressure, but it does so by dumping the excess flow back to the reservoir, not by reducing the overall flow rate through the pump. So if you find yourself trying to feather the controls to keep the backhoe speed down then you are not only wasting the fuel, you are heating the hydraulic oil unnecessarily. That's harder on seals, fluid, etc.

Kubota actually specifically says not to use the high PTO range in my backhoe manual ("IMPORTANT: The backhoe has been designed to operate in the 540 PTO-RPM position only. Do not operate in the 750 position or backhoe hydraulic system damage may result."). There is also a warning sticker to that effect on the control pedestal. I'm not certain why, and have asked this question here before.

My hypothesis is that there is an increased likelihood an operator will rev up the engine and0 overspeed the pump. The flow rate coming out of the overspeed pump could then overwhelm the capacity of the relief valve and that would cause system pressure to rise above the limits of the components.

So, if you choose to ignore the warning and run the PTO in a higher range, you do so at your own risk. IMHO, the tractor will be quieter and use less fuel but it is incumbent on the operator to ensure the PTO speed remains below 540 rpm.

A new operator, such as the OP, might be better off to stick with Kubota's directions at least until they gain proficiency and familiarity with the equipment.

No need to hypothesize. If you go shopping for PTO pumps you will find they come in two basic flavors - 540 and 1000 maximum input RPM. The difference is mechanical not hydraulic. Overspeeding a 540 max RPM pump using a higher PTO speed will shorten its life same as it will with a rotary mower, chipper, etc.

Dan

 

[Donystoy]

The backhoe that the o/p has looks like the Woods 650 that I had on my b7200. Kubota used them back in the early days prior to having their own. Mine had a 6 gpm pump at 540 rpm. I always ran mine at around 1800 engine speed with the pto on high speed (825 rpm). I found the 540 rpm just gave too slow of operation. Someone just learning how to operate a b/h might start with the lower pto speed. Once you become comfortable with the controls and do more than one operation at the same time you soon realise that you want more flow.

 

[Vigo]

Torch, i agree with most of your points. I know not everyone is fluent in the concepts of gear ratios but i find it pretty intuitive to ballpark a 'safe max rpm' based on the proportion between 540 and 750 rpm. For example 540 / 750 = 0.72 X (engine rpm for 540 @ pto)= new max engine rpm. Let's say if mine do 540pto at 2400rpm, 2400 X 0.72= 1700rpm. I don't recall if i've ever sped it up past that point while on the high PTO range, but if i have i can at least say i haven't yet killed the pump.

But i can find no fault with your last sentence/suggestion.. run it by the book until you feel the need and the justification (understanding that math, for example) to do otherwise.