An attachment is only as strong as the host machine that provides its hydraulic power," notes Kelly Guthrie, marketing, Coneqtec/Universal. Consequently, cold planer attachments and skid-steer loaders must be properly matched to ensure optimum performance.
It's important not to underestimate the hydraulic demands that will be placed on the carrier. "Case does not recommend using a planer that is oversized for the base unit," says Bill Harris, attachments engineer, CNH. "Some skid-steer manufacturers tend to be optimistic regarding the maximum hydraulic output, and some planer manufacturers tend to be optimistic regarding minimum requirements. If the loader just makes the planer's recommended requirements, the user will likely be disappointed with performance."
Also consider engine speed. "Available horsepower is critical to production," Harris states. "There needs to be enough engine horsepower left for traction."
According to Justin Odegaard, attachment product specialist, Bobcat, "The machine needs to be run at high idle, or throttle open completely, in order to achieve maximum horsepower. Some contractors will run at three-quarters of maximum to save fuel." Yet, this can prove counterproductive. "The engine actually has to work harder to achieve the performance required for the planer attachment."
He adds, "Planers are one attachment where it's hard to have too much power. More power will typically make production increase."
As planers go up in size, they usually require a carrier with both higher engine and hydraulic horsepower. "The requirement for machine size/power will be related directly to the job at hand," Odegaard points out. "The wider a planer gets and the deeper it goes, the [higher horsepower] it needs to plane effectively."
"The general rule of thumb is 2 hydraulic horsepower (hhp) for every 1-in. width of drum," says Guthrie. "For example, for a 24-in. planer to be productive, it will require around 48 hhp. Otherwise, there will not be enough power delivered to the attachment for it to run effectively when milling more than 1/2 in."
Gallons per minute (gpm) taken alone can be misleading, he cautions. "The power needed to effectively run a particular attachment is determined by the hydraulic horsepower," he states. This is calculated by multiplying the gpm by the psi, then dividing by 1,714. To account for system inefficiencies, 10% is then subtracted to estimate net hhp.
For example, a loader rated at 40 gpm at 3,000 psi would have 70 gross hhp. Subtract the 10% for system inefficiencies and you have 63 net hhp. A second loader rated at 34 gpm at 4,500 psi would have 89 gross hhp. Minus 10% leaves you with 80.1 net hhp. "That's a lot more power with less gpm," Guthrie comments.
Of course there are going to be slight differences in hydraulic system efficiencies between the various units on the market. "Hydraulic systems are set up in many different ways for loaders and planers," says Odegaard. Some systems are able to better put the power to the ground."
Using math to calculate hydraulic horsepower produces a theoretical number. "As the hydraulic fluid moves through hoses and valves in the system, it loses efficiency," says Odegaard. "Bobcat has found in its M-Series loaders that significant actual gains can be achieved with a more efficient system. M-Series loaders with less 'theoretical' hydraulic horsepower will actually outperform other models that have more theoretical hydraulic horsepower."
Balance is important when it comes to hydraulic components. "The planer also needs to have hydraulic components that match the carrier's flow and pressure," says Odegaard. "Planers need to have a balance between speed and torque. A planer that is set up for a high flow, lower pressure will perform better on a machine that has those specifications. Putting the same planer on a machine with higher pressure and lower flow may see decreased performance."