GPM, PSI, auxiliary flow — the hydraulic specs that determine which attachments your machine can actually run. Get this wrong and you'll either burn out an expensive attachment or pay for high-flow capability you'll never use.
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Ask a dealer in Ontario or BC what GPM your machine produces and most can answer immediately. Ask the same question to a private seller on Kijiji and you'll get a shrug. That's the problem — the hydraulic flow spec is one of the most important numbers on your machine for attachment compatibility, and it's invisible unless you know to look for it.
This guide explains what the numbers actually mean and how they affect what you can run.
GPM stands for gallons per minute — the volume of hydraulic fluid your machine's pump delivers to the auxiliary circuit each minute. More GPM means more hydraulic power available to drive attachment motors and cylinders.
But GPM alone doesn't tell the whole story. Hydraulic attachments require flow and pressure to function properly. Pressure is measured in PSI (pounds per square inch). Think of it this way: GPM is how much fluid is moving, PSI is how hard it's being pushed. An attachment motor needs both adequate flow volume and adequate pressure to develop its rated power output.
Most skid steer attachment specs list a flow range — something like "requires 18-24 GPM at 3,000-3,500 PSI." Both numbers matter. Your machine's operating relief pressure needs to meet or exceed the attachment's minimum. If the pressure is low, the motor runs weak regardless of flow. If flow is insufficient, the motor runs slow and hot.
Standard flow is what the majority of skid steers in Canada deliver from the factory. The range across major manufacturers runs roughly 17–25 GPM, though specific numbers vary by model and engine configuration.
A Bobcat S550 delivers about 20.4 GPM standard. The S590 does 22.6 GPM. A Case SR200 runs around 18 GPM. A Cat 259D3 standard auxiliary flow is approximately 22.5 GPM. These aren't identical, and the differences matter when an attachment specifies a minimum of 22 GPM — some standard-flow machines make the cut, others don't.
Standard flow handles an enormous range of attachments: all pallet forks and grapples, standard bucket work, landscape rakes, snow pushers and blowers (at standard output), sweepers, most tillers, and standard-flow auger drives. If your work is general construction, landscaping, snow removal, or basic farm tasks, standard flow is everything you need. Don't pay for high-flow you won't use.
High-flow systems are an option on many machines, either factory-installed or retrofitted on machines designed to accept it. They deliver significantly more hydraulic fluid per minute — typically 30–45 GPM depending on the machine — and require a secondary pump or a higher-output primary pump.
High flow doesn't just mean more speed on the same motor. It enables attachments with larger hydraulic motors that develop substantially more output power. A high-flow mulcher running at 40 GPM and 3,200 PSI is producing roughly twice the hydraulic power of a standard-flow unit at 20 GPM and 3,000 PSI. That's why these attachments exist in a high-flow-only configuration — standard flow simply can't run them effectively.
The high-flow option on a new machine typically costs $3,000–$6,000 CAD at purchase. That's not nothing. Know what you'll actually run before you spec it.
| Attachment | Flow Required | Notes |
|---|---|---|
| Pallet forks | Standard | No hydraulic motor — pure mechanical. Standard tilt cylinders only. |
| GP bucket, rock bucket | Standard | Hydraulic tilt cylinder only. No motor. Standard flow handles all bucket types. |
| Grapple (root grapple, demolition grapple) | Standard | Operates on the auxiliary circuit but flow demand is low — opening/closing cylinders, not a continuous motor. |
| Auger drive (standard, up to 12" bit) | Standard | Standard planetary drives rated 15–22 GPM work fine. Don't buy high-flow drive for standard machine. |
| Auger drive (large diameter 18"+ bits) | Either | Large diameter in hard soil demands more torque and flow. Check drive manufacturer specs. |
| Snow blower (standard output) | Standard | Most residential and light commercial blowers operate at 16–22 GPM. |
| Snow blower (high-throw, commercial) | High Flow | High-output commercial blowers designed for 28+ GPM for maximum throw distance. |
| Brush cutter / mulcher (up to 60") | High Flow | Mulching heads need 25–40+ GPM to run at rated capacity without overheating. |
| Cold planer / asphalt milling | High Flow | Cold planers almost universally require high flow. Standard-flow machines simply can't drive these motors. |
| Landscape rake / power rake | Standard | Standard flow is fine for all but the largest-diameter powered rakes. |
| Tiller / rotary tiller | Either | Depends on tiller width and design. 72"+ tillers often want high flow; 60" and under typically run on standard. |
| Trencher | High Flow | High-output trenchers need 30+ GPM. Some narrow chain trenchers can operate on standard flow at reduced speed. |
| Hydraulic breaker | Standard | Most hydraulic hammers operate comfortably on standard flow. Match to breaker spec sheet. |
There are two ways this goes wrong. Both cost money.
This is the more dangerous mistake. A mulching head designed for 35 GPM running on a machine that delivers 20 GPM operates severely underpowered. The motor starves for fluid, heat builds up, and the attachment either performs terribly or causes seal failures and motor damage over time. Mulchers, cold planers, and high-output trenchers will all behave this way when underflowed.
Some rental equipment in Canada has had this problem — a contractor rents a machine assuming it has high flow because the machine model line offers it, but the specific unit was spec'd without the option. Always verify the actual machine spec, not the model family spec.
The reverse mistake is less damaging to equipment but more damaging to your wallet. If your work is forks, buckets, grapples, and auger holes — all standard flow territory — paying $4,000+ for the high-flow option at purchase, then adding high-flow compatible attachments throughout, is money you'll never recover. The attachments that genuinely require high flow are specialized. Most operators never need them.
A few reliable methods:
Operator's manual: The clearest source. Look for "auxiliary hydraulics" or "high-flow option" specs. The manual will list standard flow and, if equipped, high-flow output.
Manufacturer spec sheet by model and year: Bobcat, Cat, Case, Deere, and Kubota all publish spec sheets. Search "[brand] [model] specifications" and find the auxiliary hydraulic row. Note that the same model year can be spec'd differently depending on options ordered.
The orange coupler check (Bobcat-specific): Bobcat machines with the high-flow option have an orange auxiliary hydraulic coupler instead of the standard grey coupler. Not a substitute for checking the spec, but a quick field indicator.
Call the dealer with your serial number: Dealers can pull the factory build spec for any machine by serial number. This is definitive. If you're buying used and the seller doesn't know the flow spec — call the nearest dealer and give them the serial. Takes two minutes and removes all guesswork.
Most major Canadian equipment dealers — Brandt, Cervus, Nortrax, RDO Equipment — stock and spec machines differently depending on the region's primary use cases. In Ontario and BC where land clearing, landscaping, and utility work dominate, high-flow machines are more common in dealer inventory because brush cutters and trenchers are steady sellers. On the prairies where the primary use is farm work (forks, augers, grapples, snow), standard-flow machines dominate and dealers will tell you honestly that high flow is rarely justified for that application.
This matters because dealer inventory shapes what gets recommended. Ask specifically whether the job you're describing actually requires high flow, or whether you're being steered toward a more expensive machine than the work demands. A good dealer will level with you.
See which attachments match your machine's hydraulic flow. Browse the skid steer attachment catalog for product specs on high-flow and standard-flow models sold through Canadian dealers.
