To overcome the limitations of tractor spool valves when using implements with numerous hydraulic functions, tractor makers can extend performance with power beyond. But what is it and what can it do?
Geoff Ashcroft reports...
Tractor hydraulic systems were once simple, straightforward systems.
And depending on the make of tractor you bought, you were presented with either an open centre, or a closed centre hydraulic system.
Open centre, as its name suggests, saw, and still does depending on specification, a constantly circulating supply of oil through the spool valve block when all valves are in their neutral position.
This puts oil in the valve block ready to divert through spool valves to offer a control function.
However, it is a system that wastes energy by pumping oil using a fixed displacement gear pump – even when spools are not being operated. This creates heat, soaks up power and reduces fuel efficiency.
Open centre is also a system that relies on engine revs for flow – more revs means higher flow rates, and this prompts the need to hit the throttle when tipping silage trailers, for example.
Closed centre hydraulic systems differ by using a variable displacement pump, which charges the hydraulic system, essentially trapping oil under full pressure, ready for use.
If there is no demand, the pump does not circulate oil, which means lower heat build-up, reduced fuel consumption and reduced power use.
A closed centre system supplies oil in response to a pressure drop anywhere in the system, and when a spool valve is opened the pump steps up to deliver flow.
A development of this has led to load sensing, using a line that returns to the pump. Its purpose is to trigger the pump’s swash angle to increase flow in response to a valve being operated. Flow sharing is a big benefit, as oil is supplied on demand.
While it offers considerable advantages in terms of fuel efficiency, it can be a little more complicated to set up implements correctly using spool valve flow and timings, to make the most of a tractor’s hydraulic capability.
To combat this, power beyond is an extension of this functionality, and delivers oil to an implement without having to use the tractor’s spool valves.
WHAT IS POWER BEYOND?
MARTIN Hamer, Fendt’s national sales manager, says: “If you are running a potato harvester with eight hydraulic functions and your tractor only has five spools, how do you operate the additional three functions? The answer is, you do it with power beyond.”
Power beyond sees implement makers integrate a hydraulic valve block on the machine, which allows the machine to be configured to precisely optimise all flow and pressure settings to make the most of implement performance. This can then be managed directly from the tractor’s load-sensing capability.
At this point, spool valves become redundant, and operating such an implement then requires a tractor with power beyond capability. This uses a small-bore, load-sensing trigger line, plus a high-flow oil supply line and a free-flow return.
Its sole function is to offer extended hydraulic performance to run complex implements, instead of relying on tractor spool valves, and is viewed as a plug-and-play, hydraulic system.
“Power beyond simply moves the oil flow to the implement, instead of relying on the tractor having enough spool valves to control hydraulic functions,” says Mr Hamer.
“Implement control can then be through a dedicated machine control box, or through an IsoBus universal terminal.”
MR Hamer says: “Importantly, power beyond takes away the need for constant pumping by using a spool valve to push oil around an implement.
“It also eliminates the need to dial-in spool valve flow and pressure settings too, and this contributes to greater fuel efficiency.”
Pottinger’s UK sales manager Shaun Groom agrees. He says: “With increasingly sophisticated implements, such as forage wagons or combi-balers, there is a huge requirement for hydraulic services.
“The tractor is unlikely to have enough spools to run a machine efficiently, and power beyond is the solution.
“Yes, it adds cost to the implement, but it also delivers greater efficiency and improves productivity without putting more of a burden on the operator,” he says.
“Using load sensing hydraulics on an implement is simply a logical move that eliminates the need for an operator to spend time fine-tuning flow and time-based settings with spool vavles.”
He points out that a non-load sensing system can have its oil flow influenced by other spools.
“A hydraulic fan drive on a seed drill is a good example of how insufficient oil flow can impact on performance,” he says.
“Lifting the drill at the headland and pulling the marker arms can cause the fan speed to slow – and on a wide drill, with 72 outlets, you need a lot of airflow. The last thing you want is a slow-down on the fan.
“Load sensing cures this, and power beyond makes more oil available exactly where it is needed, without causing the oil to overheat or the pump to cavitate trying to keep up.
“And Pottinger, like many others, includes the ability to run its implements on non-power beyond tractors,” he says.
“It needs a spool to be put into constant pumping, and is less efficient, but it still allows the implement to be used.”
ONE possible downside of choosing power beyond is that it does add cost to a new tractor.
While there will be models that are already equipped with it as part of the standard specification, many offer the functionality as an option, along with different pump capacities too.
Though the amount of oil flow you should choose is open to discussion, and some dealers advise on not scrimping on hydraulic pump capacity.
Dan Sharood, Valtra specialist with Lister Wilder, says: “Power beyond is an option on any Valtra Active, Versu or Direct tractors, and pump capacities can be 115, 160 or 200 litres.
“It can be retro-fitted, but is far more cost effective to include as a factory-fit item.”
He advises potential buyers faced with seeking power beyond to choose the 160-litre pump option.
“This future-proofs the purchase, and gives plenty of flow for more complex implements. The 200-litre option is forestry-oriented, to meet the needs of timber cranes and forwarding trailers.”
TIM Baker, of the Kverneland Group, says tractor buyers should not just consider how much oil flow an implement needs, but they should also consider having enough oil flow in reserve.
“Primary tractor functions, such as brakes and steering, always take priority, and while these functions are adequately met, when brakes and steering are used simultaneously, this can sometimes cause a dip in oil flow for additional hydraulic services,” he says.
“As a result, you might find that an implement’s functions can momentarily slow.
“There does not seem to be an industry standard from tractor makers when it comes to loadsensing pressures to make pumps react quickly enough,” he says.
“So it is worth making sure the tractor you buy is more than up to the task of running an implement through power beyond.”
Deutz-Fahr has been fitting power beyond as part of the standard specification to all its tractors over 180hp for almost 10 years. SDF’s tractor specialist
David Jefferson says: “Implement firms could not rely on tractor manufacturers to provide a consistent oil supply from spool valves, so they took the initiative to control hydraulic power, beyond the tractor.
“And it is an easy system to retro-fit to older Deutz-Fahr tractors.”