In the area of hydraulics, Ross also points out when using an attachment such as a hydraulic hammer, its best performance will be achieved with one-way hydraulic flow.
"Most machines will come standard with two-way flow to use with attachments such as hydraulic thumbs so you can open and close them," he says. "But a hammer builds up pressure until it fires, then it repeats the process. The best way to utilize this type of attachment is with one-way flow so the pressure line fires the hammer, and the other line takes the oil straight back to the tank instead of going through the valve bank. While you can run it in two-way flow, it creates a lot more heat in the oil, and these hammers create a lot of heat anyway because they're building pressure and firing several hundred times a minute."
Optimizing hydraulic flow
A compact excavator is a hydraulically driven machine, as compared to a backhoe-loader, which is horsepower driven. But you will still want to ensure that the engine in your machine has enough horsepower to adequately power the hydraulic pump.
In some cases, manufacturers have introduced new models with smaller engines than the models they replace, although Gearhart emphasizes the smaller engines shouldn't necessarily be of concern. "We work to match the lowest horsepower possible to the hydraulic system," he states. "The pump will only have so much capacity for volume and pressure. Putting in a larger engine than is needed only makes more noise and burns a lot more fuel. We work to size the engine horsepower and the hydraulic system for each other."
According to Connor, it's important to consider the correlation between hydraulic flow and pressure when determining if an engine is of adequate size. "It's difficult to know exactly what you get out of a system," he says. "The key is to know how well flow is maintained under load. You can create hydraulic flow with very little horsepower. But when you start to run attachments that have resistance, like augers and breakers and even buckets for digging, the function begins to slow down if you can't maintain that flow."
For this reason, Connor maintains that Bobcat compact excavators traditionally have higher horsepower engines to maintain flow at higher pressures. He offers the following example of two pickups pulling a trailer down the road. "The difference between the two shows up when you load the trailer," he says. "You need more horsepower to pull more weight. The same theory applies to pushing oil out to the cylinders for digging when using an attachment. A torque limiting system comes into play for anything you do with an excavator. It actually destrokes the pump so the flow declines before you load the engine or before you pull the engine down.
"In a nutshell," he summarizes, "the more engine horsepower you have, the higher auxiliary flow loads you should be able to carry."
Ensure adequate stability
While you may be tempted to oversize an attachment to speed productivity, in the end this could not only increase wear, but it might also compromise stability.
In the case of a bucket, Conley notes that upsizing too dramatically can warp the dipper arm and cause the machine to become unstable, especially when working off to the side. "It may work now, but down the road you could have problems," he says. "The long-term consequences could be sacrificed wear."
Stability tends to be a greater concern on these compact machines because some of them have especially narrow tracks - less than 3 ft. wide in some cases - for maneuvering in confined areas. "On our smallest machine, width is less than 3 ft. so it can go through a doorway or narrow passage," says Gearhart. "Once to the jobsite, you can expand them for stability."
Ross indicates that a dozer blade, which is standard on most manufacturers' compact sizes, adds stability by acting as an outrigger. "We find that when contractors are craning heavy material, they can keep the blade in front of them and dig it into the ground, which is the best load lifting position for this type of machine," he says. "It allows them to crane more weight."