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Attachments also typically list minimum and maximum flows and pressures. "Attachment manufacturers publish specifications or fit up charts that specify what hydraulic output is required to operate their attachments," says Koch. "The charts will list the attachments with different hydraulic capacities and ranges of hydraulic output required. Some heavy-duty attachments require high-flow options on the loader. Some of these attachments require a third line to relieve back pressure. The loader must be equipped with these options to operate the attachment and prevent damage."

Ron Peters with CEAttachments says instructions must be given to customers at the point of rental to ensure proper sizing. "If a customer is using a mid-range attachment, such as a broom, it could be used on a standard-flow machine; they would need to attach both of the hydraulic hoses. But a high-flow attachment, such as a cold planer or a snow blower, would usually need three hydraulic lines and absolutely need a high-flow machine; there's no way a high-flow attachment could operate on a standard-flow skid steer."

The role of rated operating capacity

While hydraulic power plays an important role, rated operating capacity must also be considered when determining attachment compatibility.

The rated operating capacity is an SAE-designated standard. For skid-steer loaders, rated operating capacity is measured at 50% of the machine's tipping load. The rated operating capacity is the weight a machine, including an attachment, is rated to safely lift and move.

"The tipping load is the weight within the bucket it takes to just bring the back tires off the ground," says Angel with JCB. "This is measured with the bucket at full reach, an operator of 175 pounds, and a full fuel tank. When fitting attachments, an operator needs to look at the weight of the attachment to be sure it does not exceed the rated operating capacity."