We get some version of this question a few times a week: “What size unit do I need?”
Sometimes it comes from a contractor who just picked up a new attachment and needs power for it. Sometimes it’s an OEM builder trying to spec a unit into a piece of equipment they’re designing. Sometimes it’s someone who bought the wrong unit somewhere else and is starting over.
The answer is almost always the same — tell us your GPM and PSI requirements and we can point you to the right unit in about five minutes. But if you want to understand the logic behind it before you call, here’s how we think it through.
Start With GPM — That’s Your Flow Rate
GPM stands for gallons per minute. It’s the volume of hydraulic fluid your attachment needs to operate at full capacity. Too little flow and your tool runs slow or won’t function at all. Too much and you’re paying for power you don’t need.
Every hydraulic attachment has a rated flow requirement — check the operator’s manual or the manufacturer’s spec sheet. Here’s a rough sense of where common tools fall:
- Hydraulic breaker (light duty): 4–8 GPM
- Log splitter: 4–11 GPM
- Stump grinder: 8–18 GPM
- Hydraulic auger: 6–15 GPM
- Grapple saw: 20–35 GPM
If you’re running more than one tool off the same unit, add their flow requirements together and start looking at dual-circuit configurations.
Then Match Your Pressure — That’s PSI
PSI is the force behind the flow. Most construction and agricultural attachments run between 1,500 and 3,000 PSI. The majority of HydraTough units are rated at 2,000 PSI, which covers most applications without overbuilding.
If your attachment calls for something outside that range, that’s what custom builds are for. It’s not a complicated change — we do it regularly.
Don’t Overlook Tank Size
The hydraulic reservoir keeps your system cool. Too small and you’ll run hot, especially on longer jobs. A good rule of thumb is a tank that holds at least 1–2x your GPM rating in gallons.
Most standard units come with 5 or 10 gallon tanks. If you’re running a high-flow application or expect to run the unit for extended periods, we’ll factor that into the build.
Single Circuit or Dual Circuit?
A single-circuit unit powers one function at a time — one tool, one attachment, straightforward.
A dual-circuit unit has two independent hydraulic circuits running simultaneously. You’d want this if you’re controlling two separate movements at once — a machine that grips and rotates, for example, or an OEM build with multiple hydraulic functions. It’s also common in rental fleet units that need to handle a wider variety of attachments.
If you’re not sure which one fits your application, single circuit is usually the right starting point. We can always talk through whether dual makes sense for your setup.
When a Standard Model Doesn’t Quite Fit
Most buyers find what they need in the standard lineup. But occasionally a job calls for something specific — a non-standard flow rate, a particular valve configuration, a specialty frame, or engine options outside the standard models.
Custom builds are a normal part of what we do. Lead times are fast and we’ll work from your specs. If you’ve got something specific in mind, tell us what you need — we’ll tell you straight whether a standard unit works or whether a custom build makes more sense.
