Power to your bucket
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J_J
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- Power-Trac 1445, KUBOTA B-9200HST
The hydraulic pump has the potential to produce pressure and GPM. The power is the same once the pump is running. The force produced by the pump is pressure, which is developed by some restriction to the flow of hyd fluid, a cyl, a motor, etc. Your pump is rated for so many GPM's at a certain rpm. The faster the engine runs, the more GPM's the pump produces. The rpm essentially dictates how fast the hydraulic driven components will operate. If you are not doing any hydraulic work, then you only need enough engine rpm to make the tractor move itself.
With a hydrostatic tractor, you can run the engine at a high rpm, and use the hydro pedal to drive the tractor at any speed from 0 up to max.
With a hydrostatic tractor, you can run the engine at a high rpm, and use the hydro pedal to drive the tractor at any speed from 0 up to max.
OP
First one
Gold Member
J.J
So your telling me that the faster the engine is running the more power I'll have using my FEL and be faster right? So if I ran in the 2700 rpm range I'll be able to lift more ? I just didn't want to beat on it if reving it up so high wouldn't make the diff.
So your telling me that the faster the engine is running the more power I'll have using my FEL and be faster right? So if I ran in the 2700 rpm range I'll be able to lift more ? I just didn't want to beat on it if reving it up so high wouldn't make the diff.
jinman
Rest in Peace
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No, you won't be able to lift more, but you might be able to lift it faster. I believe our tractor's hydraulic systems are designed to be very efficient at 1800-2000 rpm. At that rpm, you will have less speed in the hydraulics than at 2700 rpm, but the hydraulics should be able to lift just as much.
The maximum lift of a FEL is set by the hydraulic system relief valve setting. It will open at the set pressure (which equates to maximum lift) and dump all the fluid from the hydraulic pump to the reservoir. It's common when doing heavy work to open the relief valve, but you don't want to leave the valve in relief or the fluid will heat up.
Remember, 2700 rpm is PTO rpm and not associated with the maximum lift pressure of the hydraulics. If you are running a hydraulic motor, running your engine up to 2700 rpm or greater will make the hydraulic motor run faster as long as the back-pressure does not exceed system relief pressure.
J_J
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- Power-Trac 1445, KUBOTA B-9200HST
No, not exactly. Your hyd pump has a potential of, say 2500 psi. That is the available force as soon as the pump is running. As soon as you activate a cylinder, the pump starts building up pressure to the cylinder, and can be any pressure between zero to the pumps designed pressure. Some loads in your bucket will not take much pressure. If you raise an empty bucket, it might only take 800 psi to get the job done. If you scoop up and lift max load, the pressure might build up to say 2500 psi. If you should try and lift a load above your limit, the relief valve will relieve and protect the valve or cylinder. Just running the tractor at a faster rpm only increases the ability of the cylinders to work faster. You have the same force through out the tractor rpm range.
I would recommend installing a pressure gage at the input to the FEL valve, or making up a hyd test set including a 3000 psi gage, hose and fittings. You could also make it using Quick Disconnects, so you could just plug it in and read the pressure throughout the system.
I would recommend installing a pressure gage at the input to the FEL valve, or making up a hyd test set including a 3000 psi gage, hose and fittings. You could also make it using Quick Disconnects, so you could just plug it in and read the pressure throughout the system.
tatra805
Silver Member
JJ, can you agree with my findings...
I agree with your point of equal pressure over the rev range with a variable flow rate. However i noticed when using my logsplitter which i operate at say 1000rpm that if the cylinder stalls i have a stable reading of 225 bar when i keep the valve open. (so relief set at 225bar)
Now, when i open the throttle and go over pto speed > 2750 rpm, the pressure rises up to 270 bar with the valve still open.
That would lead me to conclude that the relief valve does open at the set 225 bar but is not able to let the full flow through at higher rpms. This resulting in a "power boost"for the hydraulics.
I use this a quite often with the pallet forks on my bucket in order to curl a heavy loaded pallet upwards.
Must add that i have no idea on my tractor if the relief valves of the FEL and remote valves are set at 225 bar and the main relief at the pump is set higher or not.
Just my input on a phenomen i noticed too.
I agree with your point of equal pressure over the rev range with a variable flow rate. However i noticed when using my logsplitter which i operate at say 1000rpm that if the cylinder stalls i have a stable reading of 225 bar when i keep the valve open. (so relief set at 225bar)
Now, when i open the throttle and go over pto speed > 2750 rpm, the pressure rises up to 270 bar with the valve still open.
That would lead me to conclude that the relief valve does open at the set 225 bar but is not able to let the full flow through at higher rpms. This resulting in a "power boost"for the hydraulics.
I use this a quite often with the pallet forks on my bucket in order to curl a heavy loaded pallet upwards.
Must add that i have no idea on my tractor if the relief valves of the FEL and remote valves are set at 225 bar and the main relief at the pump is set higher or not.
Just my input on a phenomen i noticed too.
J_J
Super Star Member
- Joined
- Sep 6, 2003
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- 18,952
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- JACKSONVILLE, FL
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- Power-Trac 1445, KUBOTA B-9200HST
Do you know the hyd pump designed pressure? The pump will build up pressure until the pressure is used by a cyl, or a motor, or the relief valve goes off. There is a cracking pressure that starts the relief valve to open, and when the relief valve is fully open, there is the relief pressure that you set to protect your system. Depending on the design of the pump, the pressure could rise above the pump safety pressure, and the pump could burst, fitting split open, or hose blow out, etc. The pressure in the hydraulic system is going to be variable depending the work you are doing. Easy work, low pressure, hard work/ max load, high pressure. If you put a gage in your system, you can watch the pressure at any given time. You can experiment with different loads to see what pressure is required, and watch for spikes in the system when you work the system and drop a load suddenly and catch it. You can see pressure above pump pressure. The pressure provides the force, and the GPM provides the speed of the components.
If the pressure will change by 500 psi, then the force will change about 1500 lbs
If the pressure will change by 500 psi, then the force will change about 1500 lbs
Stonehaller
Platinum Member
JJ, can you agree with my findings...
I agree with your point of equal pressure over the rev range with a variable flow rate. However i noticed when using my logsplitter which i operate at say 1000rpm that if the cylinder stalls i have a stable reading of 225 bar when i keep the valve open. (so relief set at 225bar)
Now, when i open the throttle and go over pto speed > 2750 rpm, the pressure rises up to 270 bar with the valve still open.
That would lead me to conclude that the relief valve does open at the set 225 bar but is not able to let the full flow through at higher rpms. This resulting in a "power boost"for the hydraulics.
I use this a quite often with the pallet forks on my bucket in order to curl a heavy loaded pallet upwards.
Must add that i have no idea on my tractor if the relief valves of the FEL and remote valves are set at 225 bar and the main relief at the pump is set higher or not.
Just my input on a phenomen i noticed too.
Most relief valves have some sensitivity to flow. In its simplest form, the relief valve is a valve held closed by a spring. At low RPM, and thus low flow, the valve does not have to open much to let enough oil through to reduce the pressure. At high RPM, and thus high flow, the valve has to open farther to let enough oil out through to relieve the pressure. Opening the valve farther compresses the spring more which takes more force resulting in a higher pressure. This is why manufacturers specify to adjust the relief valve setting at max operating RPM. There are piloted valves and other designs that minimize this flow sensitivity, but I suspect most tractors use a low cost design as some nonlinearity will not affect tractor operation. This does mean that you get the most power (highest pressure) at high RPM.
