How Do I Know My Skid Steer’s Hydraulic Flow?
If you are shopping for a hydraulic skid steer attachment, one of the most important specifications you need to know is your machine’s auxiliary hydraulic flow rate.
You will usually see it listed in GPM, or gallons per minute.
Brush cutters, augers, mulchers, trenchers, concrete mixers and many other powered attachments use the skid steer’s auxiliary hydraulic system to operate. Matching the attachment to the available hydraulic flow is critical to getting the performance you expect and avoiding an attachment that is poorly matched to your machine.
The good news is that finding your skid steer’s hydraulic flow usually is not difficult once you know where to look.
What Does GPM Mean on a Skid Steer?
GPM tells you how many gallons of hydraulic fluid the machine can supply per minute through its auxiliary hydraulic circuit.
Think of hydraulic flow as one part of the equation that determines how quickly a hydraulic motor can operate.
An attachment designed for 15 to 20 GPM is intended to operate within a very different hydraulic environment than an attachment designed for 30 to 40 GPM.
This is why you should never assume that a hydraulic attachment will work properly simply because it has the correct skid steer mounting plate and hydraulic couplers.
Physical compatibility and hydraulic compatibility are two different things.
Where Can I Find My Skid Steer’s Hydraulic Flow?
There are several places to find the auxiliary hydraulic flow specification for your machine.
1. Check the Operator’s Manual
Your skid steer or compact track loader operator’s manual is one of the best places to start.
Look in the hydraulic system or specifications section for terms such as auxiliary hydraulic flow, standard auxiliary flow, high flow, hydraulic flow rate or auxiliary GPM.
Be careful not to confuse the machine’s total hydraulic pump capacity with the auxiliary hydraulic flow available to an attachment. The number you need is the flow available through the auxiliary hydraulic circuit.
2. Check the Manufacturer’s Specifications
If you do not have the operator’s manual, search for the specifications for your exact machine model.
Make sure you are looking at the correct model and, when applicable, the correct model year or generation. Manufacturers sometimes change hydraulic specifications between generations of the same machine.
3. Check the Machine for a High Flow Option
Many larger skid steers and compact track loaders can be equipped with optional high flow hydraulics.
That means two machines with the exact same model number may not necessarily have the same hydraulic capabilities. One may have standard flow only, while another may have an optional high flow package.
Look for high flow markings, additional hydraulic connections, machine option information or settings in the operator display. If you are uncertain, the machine serial number can often help a dealer determine how the machine was originally equipped.
Standard Flow vs. High Flow
You will frequently see attachments advertised as either standard flow or high flow.
Those terms are useful, but the actual GPM numbers are more important.
There is no reason to guess whether your machine and attachment are compatible when both manufacturers provide hydraulic specifications.
For example, CID offers Tree Reaper Brush Cutters in several hydraulic configurations, with models designed around specific flow ranges depending on the configuration.
That is why JST Attachment Sales asks about the machine before recommending a powered attachment. The words “standard flow” alone do not tell the entire story.
What Happens If My Skid Steer Has Too Little Hydraulic Flow?
If an attachment requires more flow than your machine can provide, performance can suffer.
A hydraulic motor may not reach its intended operating speed, which can reduce the effectiveness of the attachment.
On a brush cutter, that may mean reduced blade speed and poorer recovery when the cutter encounters heavy vegetation. On an auger, the hydraulic system affects how the drive performs under load.
Do not buy a hydraulic attachment that requires more flow than your machine is designed to provide.
What If My Skid Steer Has More GPM Than the Attachment Requires?
More available hydraulic flow does not automatically make an attachment perform better.
The hydraulic motor and components on the attachment are designed around a specific operating range. Sending more flow through a system than it is designed to accept can create problems.
This is another reason to look at the manufacturer’s specified minimum and maximum flow, rather than simply trying to buy the attachment with the highest numbers.
Some machines allow the operator to adjust auxiliary flow. When that is possible, the machine may be capable of operating an attachment that requires less than the machine’s maximum available flow. The key is ensuring the attachment itself is operated within the manufacturer’s specified range.
GPM Is Not the Same as PSI
GPM and PSI are related to hydraulic performance, but they are not interchangeable.
GPM is hydraulic flow.
PSI is hydraulic pressure.
A machine might provide the appropriate GPM for an attachment but still need to meet the attachment manufacturer’s pressure requirements.
For that reason, when evaluating compatibility, you should look at both hydraulic flow and hydraulic pressure.
We will cover hydraulic pressure in more detail in a future Attachment Resources article.
Why Hydraulic Flow Matters So Much With Brush Cutters
Brush cutters are a great example because different cutters can have very different hydraulic requirements.
The attachment’s hydraulic motor is selected to operate within a certain flow range. Matching that motor to the machine helps the cutter reach the blade speed and performance for which it was designed.
Your current JST catalog includes the 72 Inch CID X-Treme Tree Reaper Brush Cutter, with CID configurations designed around specific hydraulic ranges rather than one universal motor for every machine.
JST also offers the 78 Inch CID Tree Reaper Brush Cutter.
CID’s catalog is a good illustration of why knowing GPM matters. Across its powered cutting equipment, hydraulic requirements vary significantly by attachment and configuration.
Hydraulic Flow Matters With More Than Brush Cutters
The same principle applies to other hydraulic attachments.
Auger drives are a good example. An auger drive does not simply have one universal hydraulic requirement. Different drive models are designed for different flow ranges.
Belltec’s LC Series demonstrates this clearly. The LC-150 operates from 6 to 15 GPM, the LC-200 from 10 to 20 GPM, and the LC-300 from 15 to 30 GPM.
That allows the drive to be matched much more closely to the machine.
The same concept applies whether you are shopping for an auger, brush cutter, mower or another hydraulically powered attachment.
Does Engine Horsepower Tell Me My Hydraulic Flow?
No.
Engine horsepower can help indicate the general size and capability of the machine, but it does not tell you the auxiliary hydraulic flow rate.
Two machines with similar horsepower can have different auxiliary hydraulic systems. Likewise, two versions of the same skid steer may have different hydraulic capabilities if one has an optional high flow package.
When buying a powered attachment, use the actual hydraulic specifications rather than estimating GPM from engine horsepower.
What Information Should I Have Before Buying a Hydraulic Attachment?
Before contacting JST Attachment Sales about a powered attachment, it helps to have your machine manufacturer, machine model, model year if known, auxiliary hydraulic flow in GPM, hydraulic pressure in PSI if available, standard flow or high flow configuration, and the type of work you plan to perform.
If you do not know all of those numbers, that is okay.
In many cases, your machine make and model give us a good starting point for determining what information we still need.
Do I Need a Case Drain?
Some hydraulic attachments require a separate case drain line, while others do not.
This is another specification that should be checked before purchasing an attachment.
Never assume that the two primary hydraulic hoses are the only connections an attachment requires. If an attachment requires a case drain, your machine needs to be properly equipped for it.
The Bottom Line
Before buying a hydraulic skid steer attachment, know your machine’s auxiliary GPM.
Then compare that number to the attachment manufacturer’s specified hydraulic flow range.
Do not choose an attachment based solely on machine horsepower, physical mounting compatibility or whether someone calls it “standard flow.”
For the best match, consider hydraulic flow, hydraulic pressure, attachment flow range, case drain requirements, machine size and the work you actually intend to perform.
Getting those details right before purchasing can save you from buying an attachment that your machine cannot properly operate.
Not Sure What Your Skid Steer Flows?
Send JST Attachment Sales your machine make, model and year, along with the attachment you are considering.
We can help you determine what specifications you need to check and match you with an attachment suited to your machine.