What are typical working pressure and pump flow figures in tractor hydraulics?
On tractors the working pressure is typically 180–220 bar and pump flow 60–90 L/min in the 60–100 HP class. Pressure sets force, flow sets speed.
In tractor hydraulic systems the working pressure is typically in the 180–220 bar range. On tractors in the 60–100 HP class the pump flow is typically of the order of 60–90 L/min. These figures vary with the model, the pump type and the equipment; for an exact number look at the hydraulic table in the operator manual of the tractor and do not decide by guesswork.
What pressure determines, what flow determines
| Quantity | What it determines | Typical range | Symptom if it is inadequate |
|---|---|---|---|
| Pressure (bar) | The force that can be produced | 180–220 bar | The linkage cannot lift heavy equipment at all |
| Flow (L/min) | The speed of the movement | 60–90 L/min (60–100 HP class) | The linkage lifts, but lifts very slowly |
The upper limit of the pressure is drawn by the relief valve setting; the system cannot go above that value and the excess flow returns to the tank. As the flow increases the same cylinder fills in less time, so the linkage lifts faster. The two quantities do not stand in for one another: a high flow does not make up for an inadequate pressure.
Do not forget that the flow depends on engine speed either. The pump is driven from the engine of the tractor; with the engine at idle the flow the pump delivers is lower than at working speed. Trying the linkage at idle and deciding that it lifts slowly is misleading for that reason. Make both the comparison and the measurement at working speed, note the result down and repeat later measurements at the same speed.
Its relation to lifting capacity
The lifting force is roughly the pressure multiplied by the cross-sectional area of the cylinder; the lever geometry and the connection points turn that force into the capacity at the end of the linkage. That is why two tractors with the same pressure can turn out to have different lifting capacities. When you read a catalogue value, note whether the capacity is given at the cylinder or at the ends of the linkage pins; the two are not the same number.
When verifying the figures
- Wait for the oil to reach working temperature before measuring; a reading on cold oil misleads.
- Read the pressure with a gauge of a suitable scale range and from the correct port.
- If the steering and the auxiliary outlets are fed from the same pump, the flow left for the linkage falls; take the measurement with those functions idle.
- Repeat the measurement with the real equipment fitted; an empty linkage does not show the limit of the system.
- Raising the relief valve setting above the manufacturer's value puts the cylinder and the hoses at risk.
For the definition of the term and its symptoms in the field you can look at the entry on working pressure.
A retrofit kit does not change these figures
Electronic retrofit kits never enter the hydraulic circuit. The LFT20 and the LFT54 move the existing control lever of the tractor by way of a cable; the pressure and the flow go on coming from the tractor's own hydraulics. Fitting a kit therefore neither increases nor reduces your lifting capacity, it only changes the way you operate the lever. This limit has to be clear when you make the purchase decision.
The quantities to look at when choosing a kit are different as well: the force needed to move the control lever and the distance the lever travels. Those two are independent of hydraulic pressure and flow and depend on the state of the lever mechanism itself. In other words, the values in the hydraulic table give you no guidance in choosing a kit.
Do not get the order wrong
If your hydraulic performance is inadequate the answer is not in a kit; it is in the pump, the filter, the oil level and the relief valve setting. First decide which side is weak: pressure if it cannot lift, flow if it lifts slowly. Then measure, and change parts last. Even if you have no means of measuring, tell these two cases apart and go to the workshop on that basis; it shortens the diagnosis noticeably.
The full topic: Converting a tractor hydraulic lever to electronic control