Under Pressure

02:06AM Jan 07, 2013
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To alleviate compaction, an inflation system allows quick adjustment of tire pressure for the field and the road

In 2011, compaction from tractor and planter tires cost Perry, Iowa, farmer Lowell Garrett more than $100,000 in yield—in just one field. His compaction woes were obvious from the pickup window.

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Using the PTG system, he can inflate his tractor and planter tires for road transport speed and loads.

"Driving down the road at the same interval where the machinery ran, the corn was noticeably stunted," he says. "It was as if I had steamrolled the soil—the compaction was that great."

Garrett admits he is not a huge fan of aftermarket products on his machinery, but he realized something had to be done to alleviate the damage he was causing with his 120' John Deere central-fill planter and 9630 tractor with triple wheels on each axle.

After searching for the right solution and even contemplating fabricating something himself, he tested the PTG central tire inflation system in 2012. Made in Germany by PTG, a familyowned company operated by three brothers, the system has been used in agricultural applications in Europe for almost two decades. In the U.S., Sally Brodbeck markets the system under the name Precision Inflation LLC in Des Moines, Iowa.

"Generally, farmers are seeing the effects of the weight they are carrying through the fields as they move to larger equipment and use GPS. They are running over the same ground again and again, creating highways in their fields where the tire tracks repeatedly run," Brodbeck explains.

A deliberate focus on tire technology and proper tire operation has been building since tractor and tire manufacturers began to tackle the issue of "power hop."

"The technical issue of power hop brought proper tire pressure to the front of a lot of farmers’ minds," says Jack Wiley, a retired John Deere engineer who now does technical consulting work. "A key part of the recipe to correct power hop is to lower tire pressures in radial tires. But this change in habit takes a lot of psychology and technology."

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The high-capacity air compressor for the PTG system, mounted on the rear of the tractor, provides quick inflation or deflation time—about 10 minutes.

Root of the issue. Wiley explains that the pressure where the rubber meets the soil is 1 to 2 lb. per square inch (psi) greater, on average, than the pressure in the tire. Thus, tire pressures need to be lower in the field to decrease the compaction caused by machinery, yet higher for over-the-road transport to keep the tires from overheating.

"The concept has become that farmers need to be able to easily run two pressures: one on the road and one in the field," Wiley says.

On-demand inflation and deflation systems are used in forestry and military applications and are common on agricultural tractors in Europe.

"In Europe, they use tractors like weuse trucks—for over-the-road transport," Brodbeck says. "For them, it is important to be able to quickly inflate or deflate tires many times a day."

The PTG system includes a dedicated air compressor, a dual-line air system, specialty valves and control boxes in the cab. Brodbeck says that what makes this system different than others on the market is that the dual-air lines are under pressure only while the tire pressure is being raised or lowered. The design prevents air leaks and tires from losing pressure.

How it works. As Wiley explains: "When you decide to inflate, the smaller valve opens the line and the larger valve is used to quickly fill the tire. When the proper pressure in the tire is achieved, the valves are closed and the pressure is released in both lines. No air line is under pressure while the machinery is working."

The compressor is mounted on a platform at the rear of the tractor, near the hydraulic outlets, and the system requires a high-capacity hydraulically powered air compressor (40 cu. ft. per minute). In all, Garrett estimates, his system cost around $20,000.

"This system comprises a lot of little pieces and parts that, when assembled, produce outstanding results." Wiley says. "Especially if you have compaction issues to begin with, you can pay for this system very quickly."

Garrett reports that it takes only 8 to 10 minutes to inflate or deflate all of his tires. To shave off a little extra time, he starts to re-inflate his tires as he heads to the gate when a field is completely planted.

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In-cab controls allow the operator to adjust
tire inflation pressure from the seat.

With the PTG system, his tire pressures in the field have changed drastically. Garrett’s over-the-road tire pressures are 25 psi on the tractor and 90 psi on the planter. In the field, his tractor tires run at 7 psi, and the planter tires are set to 30 psi. These are the correct inflation pressures for the loads carried and the transport speeds, according to the tables established by the tire companies.

Without the system, Brodbeck reports, some farmers see as much as a 100-bu. difference on the yield monitor between the wheel tracks and the ground around them. Garrett estimates that he was giving up an average 40 bu. per acre in corn yield.

"We don’t see the streaks from compaction in our yield maps anymore," he says. "My sprayer is 120', so I used to be able to find my route by looking for the stunted corn. Now when I get out there, I can’t see the tractor tracks anymore."

Although the system is primarily being adopted by those running larger and heavier machines, Brodbeck encourages farmers to rethink the compaction they are causing.

"It’s not so much the weight that is damaging as it is the pressure," she explains. "Because today’s tires are designed to carry the weight, it’s up to farmers to decide how to distribute it in their machinery footprint by lowering the pressures at slow speeds."

Garrett says his farm crew uses the same tractor to pull the fall tillage machine, and they use the PTG system to adjust the tractor tires for power hop control.

"When we’re pulling hard, we use the system to adjust for field conditions and eliminate power hop," he says. "I want this on my field cultivator tires too."

You can e-mail Margy Fischer at [email protected]l.com.