What happens if the lift lever enters the "continuous pumping" sector?
If the lever passes the detent and stays in the pumping zone the relief valve stays open; the oil heats, the spring slackens, the engine is loaded for nothing.
If the position lever is left beyond the detent of the quadrant, in the continuous pumping sector, the pump goes on delivering, the pressure leans on the relief valve setting and the valve dumps continuously. Nothing breaks at that moment; the problem is the lever staying there. For as long as that lasts the hydraulic oil heats up quickly, the spring in the mechanism loses its tension and the pump power is spent without turning into work. The right thing is to leave the lever in the transport position, without going past the detent of the quadrant.
The two sectors of the quadrant
On quadrant systems the travel of the position lever divides into two sectors. The part near the detent is the transport position: the linkage is up, the system settles into balance and the load on the pump comes off. The sector beyond the detent is the continuous pumping zone. Here the pump goes on delivering, the pressure leans on the setting of the relief valve and the valve stays open, dumping the flow to the tank. The lever entering that sector is not a use outside the design; what was not allowed for is its staying there.
What happens when it is kept up
| Effect | Reason | Symptom in the field |
|---|---|---|
| The oil temperature rises | All the flow passing through the relief valve turns into heat | The tank and the hoses become too hot to hold |
| Oil and seal life shortens | High temperature speeds up the degradation of the oil | The oil darkens, weeping is seen around the seals |
| The setting drifts | The spring stays under high tension continuously | At the same lever position the linkage stops at a different height |
| The engine is loaded for nothing | The pump power is dumped without doing work | A change in the note at idle, needless fuel consumption |
If you want to see in detail where the heat comes from, the entry on hydraulic oil heating describes the mechanism. Since the oil thins as it heats, the response of the lever changes through the day as well; a linkage that behaves differently in the morning and in the afternoon is usually a complaint for this reason.
Is that zone entered with the kit fitted
It is, and the most frequent cause is the cable adjustment. The retrofit kit pulls the lever by the cable; if the cable has been attached shorter than it should be, the lever turns further on every command and goes past the detent. The LFT20 pulls the cable 60 mm and the LFT54 50 mm. Those figures were chosen to move the lever through a particular range of angle, not to force the mechanism to its end stop; settle what the pull distance means before installation. When setting the cable length, make sure the lever rests in the transport position and confirm by eye that the lever returns to the same point when you give a command and release it. A frequent mistake is to set the cable so that the lever comes up against its stop when the kit is at full stroke; a setting like that pushes the lever beyond the detent on every command.
Where this warning does not apply
The behaviour described is peculiar to the quadrant, cable-controlled Lift-O-Matik arrangement. On hydraulic arrangements where this relation between lever position and pump load is not set up, the same result does not follow. Not every case of heating comes from the lever position either: a low oil level, a blocked filter or a leaking valve heat the oil as well. If the system still heats up with the lever in the transport position, look for the cause elsewhere.
What to do in practice
When you start work, mark the transport position of the lever once; let that be your reference for the rest of the day. After lifting the linkage, do not leave the lever forgotten beyond the detent, but bring it back to the transport position. On long transport runs, check the tank temperature by hand from time to time; if there is more heating than normal, look at the lever position first and the oil level second.
The full topic: Converting a tractor hydraulic lever to electronic control