Understanding the hydraulic system is critical when choosing work tools and attachments for mobile machines.
George MacIntyre and Ted Polzer, Product Managers, Case Construction Equipment, Racine, Wisconsin
Skid steers and compact track loaders (CTLs) are two of the most useful pieces of mobile equipment, and adding attachments makes them all that much more versatile when tackling jobs from construction and landscaping to brush cutting and snow removal. Rarely does a skid steer or CTL user rely on a bucket alone.
The auxiliary hydraulic systems on these machines are designed to power a wide range of attachments. Having a good understanding of both equipment capabilities and worksite demands helps ensure safe and efficient operation.
CASE CE, like a number of OEMs, offers three core systems. Most-common is the standard-flow auxiliary hydraulics package. Although flow rates differ by model and manufacturer, standard-flow systems typically range from 17 to 24 gpm. They are included in all machines from the factory and operate on the same pressure as the machine’s main hydraulics, approximately 3,000 to 3,500 psi. A standard-flow system powers many of the most common hydraulic attachments on the market, such as 4-in-1 buckets, hydraulic hammers, augers, trenchers and grapples.
Beyond that standard functionality is the high-flow auxiliary hydraulic system, which further increases a machine’s versatility and productivity. As with standard-flow, it operates on the same pressure as the main hydraulic circuit. The flow rate, however, ranges from 30 to 42 gpm. A high-flow system can be a factory-installed option or added later in the field. It powers production-type attachments that require a higher flow rate. Examples include cold planers, many snow blowers, small mulchers and chipper-shredders.
Enhanced high-flow auxiliary hydraulics have flow rates similar to that of a high-flow package, but they operate at a higher pressure. Attachments that use enhanced high-flow systems include large cold planers, rock saws and large mulchers.
Some newer machines offer all three possibilities in one package. For example, the recently introduced CASE TV620B CTL has implements and attachments powered by an axial-piston pump. The base TV620B comes with a high-flow circuit delivering 41.6 gpm at 3,450 psi (at rated engine speed of 2,500 rpm). An in-cab switch lets the operator reduce output to standard flow as needed, delivering 24.2 gpm at 3,450 psi. And an optional enhanced high-flow version boosts pressure to 4,100 psi at 41.6 gpm.
All three take advantage of the same pump and hydraulic system. The CUP (connect-under-pressure) manifold has 0.75-in. couplings in place of typical 0.5- in. couplings to handle the extra flow. Standard default is 41.6 gpm. All hoses and connectors are the same for each version.
In addition, secondary auxiliary hydraulic systems can be added for applications that require multiple hydraulic movements simultaneously. This would include, for example, the side shift function on a cold planer or stump grinder, direction change on a snow blower chute or a tree spade with down riggers.
Relating pressure and flow
When it comes to matching attachments with a machine’s auxiliary hydraulic capacity, understanding the difference between pressure and flow is critical. Let’s start with the fundamentals. Flow equates to the speed of an attachment under no restriction. When an attachment’s specs say it is rated for maximum 30 gpm, that’s usually with no pressure or resistance to flow. But as soon as the device starts to engage and resist flow, pressure begins to build.
Pressure gives an idea of how much work can be done. High-flow and enhanced high-flow attachments might use the same flow, but the added pressure in the latter case is important for demanding attachments like mulching heads. Running at 4,000 psi versus 3,000 psi means overcoming more resistance to the drum turning the mulcher, letting users clear brush and small trees much more efficiently.
So it’s important to understand the maximum constraints on flow and pressure for a given attachment. A common misconception is that it’s best to run an attachment “wide open” and use all of the flow and pressure available. This is incorrect, and many attachments come labeled with recommended parameters for best operation.
Most large attachments are equipped with a pressure gauge to help operators stay well within recommended pressure ratings. Otherwise, maintenance personnel can mount a gauge that’s visible to the operator. In lieu of specific guidelines, a good suggestion is to keep the attachment at 5 to 10% below its maximum pressure to ensure optimum cooling and performance. Exceeding these limits can lead to unnecessary stress and damage to the machine.
Understanding hydraulic horsepower
Hydraulic horsepower (hhp) is important because it is essentially an indication of a machine’s hydraulic capabilities, and what kind of productivity and effectiveness to expect from attachments. Many OEMs and attachment manufacturers publish the rated hydraulic horsepower of their products, and users can quickly calculate it themselves:
Hydraulic hp = P × Q/1714
where P is pressure in psi and Q is flow in gpm.
Because many attachments are rated by their hydraulic horsepower, this is typically a way to assess the fit between attachment and machine. It doesn’t make a lot of sense to go with an attachment that can only accept 40 hhp on a 90 hhp machine, or vice versa.
Or users can lay out the maximum pressure and flow that an attachment will handle. Attachment manufacturers do publish the range of acceptable flow rates for their products. Compare those to the maximum outputs of your machine. That’s a quick and easy way to determine if they match.
And then, of course, make sure that the coupler itself is compatible with the machine and that the type and size of quick disconnects for hydraulic hoses also match.
A common misconception is that a standard-flow system can adequately run high-flow attachments. Powering high-flow attachments with a standard-flow skid steer will lead to inefficient operation. In addition to realizing lower-than-expected results, it can also damage the attachment or skid steer.
Many users also make the mistake of buying a larger-than-necessary attachment with the hopes that they’ll “grow into it.” Well, it will function. However, an attachment built for higher pressures such as enhanced high-flow typically has a different type of internal drive motor, such as an axial-piston motor versus a gerotor motor on a low flow, low pressure type of attachment. While a specific attachment may be able to couple up to other machines, it may not be particularly productive. Always delve into the details and make sure exactly what the attachment can do on your specific machine.
Likewise, be aware that an enhanced high-flow auxiliary hydraulics package is designed for more-extreme situations where operators are truly pushing the limits. The enhanced high-flow package is only available on larger skid steers with the horsepower available to ensure proper operation of the attachment.
Although a number of newer machines let operators adjust flow from inside the cab, there can be some confusion when setting the flow best suited for a specific attachment. Equipment owners, fleet managers and rental companies need to provide specific instructions — even a simple laminated card kept in the cab is fine — to designate flow for a given attachment. This ensures better productivity and reduces the risk of having the wrong attachment, or incorrect flow and pressure, which could lead to failure.
The maintenance requirements for auxiliary hydraulic systems are essentially in line with those of most any hydraulically operated machine. First, it’s important to maintain the proper hydraulic fluid level as specified in the owner’s manual. To ensure safety and accuracy, check the level with loader arms in the down position. Loader arms in the up position will draw fluid from the hydraulic tank, giving the false impression that fluid is low.
Always follow equipment manufacturer’s recommendations regarding hydraulic oil and filter change intervals. Equally critical is the need to minimize the potential for contamination, whether it’s dirt, particulates or water. Check connection points to ensure they’re tight and keep them clean. Contaminated hydraulic fluid decreases the life of the hydraulic pump and system and can lead to more serious issues.
Viscosity is the most important factor when selecting a hydraulic fluid for use in a skid steer. Follow the manufacturer’s recommendations so the viscosity grade meets the machine’s operating requirements and surrounding climate. Doing otherwise will result in poor performance or worse. The wrong oil in a cold climate could lead to sluggish performance and damage hydraulic components, while the wrong oil in a warmer climate may not provide the needed lubricity and lead to heat buildup and excessive wear.
If the climate suggests that the machine needs a specialty oil, such as a cold-weather synthetic oil, as soon as the operator hooks up and engages that attachment, the oil will flow through and mix together. The attachment will see the same benefits as the machine.
While there’s no need to invest in more-expensive high- or enhanced-flow systems if your attachments only call for standard hydraulic flow, one of the most common mistakes that contractors make is buying a skid steer without enough hydraulic power. Having high flow and not needing it is better than not having high flow and being forced to live with underwhelming performance.
Over the last 10 years a lot more customers are looking for machines that have high-flow and enhanced high-flow systems. It is often prudent to spend a bit more up front and be prepared for more-demanding requirements in the future. That avoids the time and expense necessary to install an upgrade kit on a machine after the fact.
And for owners who mainly rent attachments, having a machine equipped with high-flow auxiliaries from the factory makes it easier to get attachments, rather than having to sort through exactly which ones fit. It provides more flexibility.
With literally hundreds of attachments available and more introduced each year, it’s a given that the versatility of skid steers and CTLs will continue to grow. By outfitting them with the right auxiliary hydraulic systems, operators can capitalize on all the machines have to offer, achieve a favorable return on investment and, ultimately, add to the bottom line.
CASE Construction Equipment
A few practical tips
Here’s a bit more advice for equipment users, technicians and engineers faced with matching and troubleshooting auxiliary systems and hydraulic attachments.
What if a new attachment underperforms on a seemingly suitable machine?
If a new attachment matches up on paper with an existing machine — but in reality doesn’t offer the predicted performance — check that the machine is running as intended. On a unit with a lot of operating hours, components can fall out of spec. For example, a main relief valve just a couple hundred psi low can make a big difference. A service technician can run some quick tests to determine if hydraulic output is up to par, or if adjustments are in order. It can result in considerable savings in higher productivity alone.
Are there any concerns with sharing attachments from machine to machine?
Yes, there are some unique considerations. If you share one attachment across multiple machines, and one machine has experienced a hydraulic cleanliness issue, let your dealer know. The specific attachment probably needs to undergo a cleanup process or at least an inspection. Avoid the case where there’s contamination in a system, and then that “dirty” attachment is installed on a known good machine, introducing same problem. Always document and understand exactly which machines have been run with which attachments if at all possible.
What’s the preferred way to store attachments?
When not being used, attachments are typically out in the elements with hoses exposed. Make sure that when storing attachments, you prevent hydraulic couplers for the hose ends from lying on the ground. Keep them covered and protected as much as possible. Some operators prefer to snap them together, which is another option. And prior to coupling up to any machine, make sure that the connection points on the manifold, and the hose connections on the attachment, are extremely clean.
Can I use attachments from various manufacturers?
Absolutely. However, make sure that you are using an OEM-approved attachment. CaseCE engineers work with many different attachment suppliers. But when we do see issues, invariably it’s because a customer bought an attachment from an unknown supplier that didn’t necessarily understand the specs on the machines. Also, take into consideration the type and size of the quick disconnects and electrical connections. The 14-pin electrical connections are standard equipment on almost all CASE skid steers and CTLs. Other manufacturers offer seven- or eight-pin connectors. Companies like Skid Steer Genius sell adapters for mating attachments and machines when the connectors differ.
Filed Under: Engineering Basics, Mobile Hydraulic Tips, Trending