The primary use of a skid-steer loader is as a power source," says Kelly Moore, skid steer and track loader product manager, Gehl Co. Versatility to run a wide array of attachments means performance can be measured using several different criteria.
"Compare all of the specifications before making a decision," says Moore. This includes the specifications of larger and smaller models from the same manufacturer, as well as competitive units. Compare dump heights, bucket rollback angles, hydraulic pressures, hydraulic flows, engine power, breakout force, etc.
The optimum loader for your fleet is based on several operating parameters. "The loader's weight, horsepower, hydraulic flow and hydraulic pressure will play a role in how well the attachment performs," says Mike Fitzgerald, Bobcat product loader specialist.
Match hydraulic flows and pressures
Hydraulically powered attachments require a specific level of performance from the carrier's hydraulic system. "An attachment usually has a range of flows and pressures," says Moore. Suitable carriers must be able to provide flow and pressure that fall within that range.
Hydraulic horsepower can also be a useful comparison measure to determine the capability of a given unit. It is calculated by multiplying the pressure (psi) times the flow (gpm), then dividing by 1,714. "If hydraulic horsepower is not adequate, performance will be poor, as well as detrimental to the skid-steer loader," says Jim Hughes, product marketing manager, Case Construction Equipment.
In addition to losing attachment productivity, using a skid steer that can't provide the optimum hydraulic system requirements places greater stress on the unit. "Operating a loader at the maximum flow and pressure for long periods of time can result in excessive heat," says Moore.
Hydraulic systems are designed with relief valves to protect them from such abuse. However, Hughes, notes, "If you are constantly going over relief, you will be creating heat, which will ultimately damage the hydraulic system and the power train."
Gregg Zupancic, product marketing manager, John Deere Construction adds, "If the machine has more flow and the attachment does not have the proper flow bypass, heat could be created and potentially cause motor and seal failures. If the machine has less flow than the attachment requires, then the attachment may not run at optimal performance and it can potentially cause unnecessary failures to mechanical or structural parts of the skid steer and attachment. A good example would be a cold planer. If the drum is not spinning at optimal speed, instead of planing the asphalt, it would tend to chuck the surface and cause unnecessary machine bounce or attachment vibration."
Jorge DeHoyos, brand marketing manager for New Holland Construction, adds, "Attachments typically list minimum and maximum flows and pressures. Using the wrong attachment can cause physical damage and premature wear on both the skid steer and attachment. Using a cold planer with a lower than required flow capacity, for example, will lead to premature breakage and wear on the cutting tips. Using an auger that requires more flow than provided will overheat both the attachment and skid steer, since the oil runs through both."
But there are measures other than flow and pressure that can affect hydraulic performance. "Another critical item to check is back pressure of the skid-steer loader," says Hughes. "High back pressure robs performance because the machine is working harder to return the oil to the tank."
The role of rated operating capacity
While hydraulic power plays an important role, lifting capacity must also be considered when determining attachment compatibility. "For example, a backhoe attachment can have a considerable amount of weight, but does not require a large amount of hydraulic flow," says Zupancic. "In addition to making sure that the skid steer is compatible with the attachment flow, the customer also needs to be able to safely carry the attachment around the jobsite on all four wheels."