Every piece of heavy equipment has a heartbeat, and on a Bobcat skid-steer loader, that heartbeat is hydraulic. The network of hoses, valves, fittings, and pumps running through your machine is what gives it the power to lift, tilt, dig, and push with precision. Without a properly functioning hydraulic system, even the toughest Bobcat sits idle.
The Bobcat 751 G-Series is one of those machines that earned its reputation on job sites everywhere — compact, reliable, and surprisingly powerful for its size. Its hydraulic circuitry, especially the configuration equipped with a bucket positioning valve, is a well-engineered system that balances performance with serviceability. Understanding how each part fits into that system can save you hours of troubleshooting, hundreds of dollars in repair bills, and a whole lot of frustration.
Whether you’re a fleet mechanic keeping a rental yard running, an owner-operator maintaining your own rig, or someone who picked up a used 751 and wants to learn it inside out, this breakdown is for you. Let’s walk through the hydraulic circuitry system piece by piece so you know exactly what you’re looking at under that cab.
Bobcat Parts Diagram & Details
The diagram shown here is pulled directly from the Bobcat Model 751 G-Series Loader Parts catalog, specifically page 48, which covers the Hydraulic Circuitry (W/Bucket Positioning Valve). It presents an exploded schematic view of the entire hydraulic circuit — from the pump assembly at the lower right, through the control and positioning valves, up through the network of hoses and fittings that deliver pressurized fluid to the lift arms and bucket. Each component is individually numbered (ranging from 1 through 51 and beyond), with leader lines pointing to exact locations within the assembly. You’ll notice that the hoses follow long, sweeping paths across the diagram, reflecting how they’re actually routed through the machine’s frame and over the engine compartment.
What makes this particular diagram useful is that it shows relationships between components — how one hose connects to a specific port on the valve body, where each O-ring sits, which fittings thread into which adapters. It’s a map, essentially, of your machine’s circulatory system.
Each numbered part plays a specific role in keeping hydraulic fluid flowing at the right pressure, to the right place, at the right time. Here’s a detailed look at what each major component does and why it matters to your machine’s performance.
1. Hydraulic Pump Assembly
Sitting at the lower right of the diagram (marked near the circled reference points A and B), the hydraulic pump is the engine-driven heart of the entire system. It draws hydraulic fluid from the reservoir and pressurizes it, sending it through the circuit to power every movement your Bobcat makes.
On the 751 G-Series, this is a gear-type pump — durable, relatively simple in design, and well-suited for the demands of a compact loader. It generates consistent flow rates that match the machine’s operating specs. When this pump starts to wear, you’ll feel it first in sluggish arm movement and delayed bucket response.
Keeping the pump healthy comes down to clean fluid and proper filtration. Contaminated oil is the number one killer of hydraulic pumps, so staying on top of filter changes and fluid condition checks is one of the best investments you can make in your machine’s longevity.
2. Control Valve Body
The control valve body sits centrally in the hydraulic circuit and acts as the traffic controller for all fluid movement. When you push your joystick forward to lower the arms or pull back to curl the bucket, it’s the control valve that opens and closes internal passages to direct flow where it needs to go.
This component houses multiple spools — each one corresponding to a different function (lift, tilt, auxiliary). As you operate the controls, the spools shift within the valve body, channeling pressurized fluid to the correct cylinder while simultaneously allowing return fluid to flow back to the tank. It’s a precise ballet happening inside a cast-iron housing, and it all needs to work smoothly for the machine to respond accurately.
3. Bucket Positioning Valve
This is the part that gives the diagram its subtitle, and it’s a feature that many operators appreciate once they’ve used it. The bucket positioning valve allows you to preset the bucket’s return-to-dig angle. Basically, after you dump a load, the bucket automatically returns to the angle you set — no need to eyeball it or feather the controls every single cycle.
Mounted inline with the tilt circuit, this valve uses a mechanical detent to “remember” a position. It’s a time-saver on repetitive grading and loading tasks, reducing operator fatigue and increasing consistency. If your bucket seems to stop at random angles instead of returning to the same spot, the positioning valve’s detent mechanism may be worn or the valve itself may need adjustment.
Over time, internal seals within the positioning valve can degrade, leading to slow drift or failure to hold position. Replacing the seals is a straightforward job if you catch it early, but ignoring it can lead to erratic bucket behavior that slows your whole operation down.
4. Lift Cylinder Hoses
The long, sweeping hoses visible on the left and upper portions of the diagram (items like 26, 28, and 33) are the lift cylinder hoses. These high-pressure lines carry fluid from the control valve to the lift cylinders mounted on the loader arms, and they’re some of the hardest-working hoses on the machine.
Every time you raise a full bucket of dirt or gravel, these hoses are handling serious pressure — often exceeding 3,000 PSI. They’re built with reinforced rubber and braided steel layers to handle that load, but they’re still subject to wear. Rubbing against the frame, exposure to heat from the engine bay, and constant flexing as the arms move all take a toll over thousands of operating hours.
Inspecting these hoses regularly is something that takes two minutes and can prevent a catastrophic blowout on the job. Look for surface cracking, bulges, wet spots, or areas where the outer cover has worn through to the braid. If you see any of those signs, replace the hose before it fails under load.
5. Tilt Cylinder Hoses
Running a parallel but distinct path through the circuit, the tilt cylinder hoses deliver fluid specifically to the bucket tilt cylinders. These are the hoses responsible for curling the bucket in (to scoop) and rolling it out (to dump).
Because the tilt function operates at high frequency during loading cycles — you’re constantly curling and dumping — these hoses endure repeated pressure spikes. They tend to age in a pattern that mirrors your most common work tasks. If you do a lot of grading, where tilt adjustments are small and constant, the wear profile differs from heavy bucket loading where full tilt range is used every cycle.
6. O-Rings and Seals
Scattered throughout the diagram — you can see them clearly at items like 43 near the top left, and at various fitting junctions — the O-rings and seals are small parts with an outsized impact. Every threaded connection, every hose fitting, every valve port relies on these rubber or synthetic rings to maintain a pressure-tight seal.
A single failed O-ring can cause anything from a slow, annoying drip to a full loss of hydraulic function on one circuit. The tricky part is that O-rings can look fine from the outside while being cracked or flattened on the sealing surface. That’s why experienced mechanics replace O-rings as a matter of course whenever they open a fitting, rather than trying to reuse them.
When sourcing replacement O-rings, sizing and material matter. The 751 G-Series uses specific durometer ratings and compound types (often Buna-N or Viton, depending on the location and temperature exposure) to match operating conditions. Using a generic hardware-store O-ring might hold for a day, but it won’t last under sustained pressure and heat.
7. Hydraulic Fittings and Adapters
You’ll notice dozens of small components at every hose junction in the diagram — items numbered throughout the schematic like 5, 11, 14, and 24. These are the hydraulic fittings and adapters that physically connect hoses to valve ports, cylinders, and other components.
Most fittings on the 751 use O-ring face seal (ORFS) or JIC 37-degree flare connections. Each type has its strengths: ORFS fittings offer excellent leak resistance and are common at valve ports, while JIC fittings are widely available and easy to field-repair. Knowing which type is used at each connection point on your machine saves you from buying the wrong replacement and making a second trip to the parts counter.
Proper torque is critical with hydraulic fittings. Over-tightening can crack the fitting or damage the sealing surface, while under-tightening leaves you with a leak. A hydraulic fitting torque chart specific to the fitting size and type should be your go-to reference during any reassembly.
8. Hose Clamps and Routing Brackets
Less glamorous but absolutely necessary, the clamps and routing brackets (visible at various anchor points across the diagram, including items like 12 and 19) secure the hydraulic hoses to the machine’s frame and keep them from shifting, rubbing, or sagging into moving parts.
Without proper clamping, a high-pressure hose can vibrate against a sharp frame edge and wear through in a matter of weeks. The resulting failure usually comes at the worst possible time — under full load, in the middle of a job. Replacing a hose that failed due to chafing also means tracking down and fixing the clamp that let it happen, or you’ll be right back in the same spot a month later.
9. Quick-Disconnect Couplers
Located at the front of the hydraulic circuit where auxiliary hydraulic lines connect to attachments, the quick-disconnect couplers (often near item references in the upper-right portion of the diagram) allow operators to swap between attachments — a hydraulic breaker, an auger, a grapple — without tools.
These couplers contain a spring-loaded poppet valve that seals the line when disconnected, preventing fluid loss and air ingestion. Over time, the poppet springs weaken and the sealing surfaces wear, which leads to slow leaks or difficulty connecting under residual pressure. Cleaning the coupler faces before each connection and storing dust caps on unused ports goes a long way toward extending their service life.
If you’ve ever struggled to connect an attachment and had hydraulic fluid dribble down your arm, worn couplers are likely the culprit. Replacement sets are relatively inexpensive compared to the frustration and fluid waste of running damaged ones.
10. Hydraulic Fluid Reservoir and Return Lines
The return side of the circuit — hoses carrying low-pressure fluid back to the reservoir — traces a path through the lower portion of the diagram. The reservoir itself serves as both a storage tank and a cooling/settling chamber where air bubbles separate from the fluid and contaminants settle out before the fluid is recirculated.
Maintaining proper fluid level in the reservoir is one of those basic checks that’s easy to overlook and expensive to ignore. Running low on hydraulic fluid introduces air into the system, which causes cavitation at the pump (a grinding, whining noise that means internal damage is happening in real time). It also reduces the system’s ability to dissipate heat, which accelerates seal degradation across every component in the circuit.
The return lines themselves operate at much lower pressure than the supply side, but they still need to be in good condition. A cracked return hose might not spray fluid dramatically, but it will allow air into the system and slowly drain your reservoir — both problems that create bigger issues down the line.
11. Elbow Connectors and Swivel Joints
Throughout the hydraulic circuit, especially where hoses need to change direction sharply — around the engine compartment, near the valve body, and at cylinder ports — you’ll find elbow connectors and swivel joints (referenced in several numbered positions across the diagram, including items like 9, 13, and 21).
These components reduce stress on hoses by allowing the hose to connect at an angle rather than being forced into a tight bend. A hydraulic hose that’s bent past its minimum bend radius is a hose that’s being weakened at that point every single operating hour. Proper elbow fittings eliminate that stress and extend hose life significantly.
Swivel joints add another layer of flexibility, allowing rotation at the connection point so the hose can move naturally with the machine’s articulation. They’re especially useful at lift cylinder connections, where the hose path changes as the arms raise and lower. When a swivel joint seizes due to corrosion or lack of lubrication, it forces all the movement stress onto the hose itself — and a failure usually follows within a few hundred hours.
12. Pressure Relief Valve
Built into the control valve body but sometimes visible as a separate cartridge component in the diagram, the pressure relief valve is the hydraulic system’s safety net. It sets the maximum operating pressure for the circuit and opens to redirect fluid back to the reservoir if pressure exceeds that threshold.
This matters because hydraulic systems generate enormous force. On the 751, maximum system pressure typically runs around 2,900 to 3,100 PSI, depending on configuration. If something causes pressure to spike beyond that — a stuck cylinder, an overloaded bucket, a sudden impact — the relief valve opens to prevent damage to hoses, seals, the pump, and the valve body itself.
A relief valve that’s set too low will limit your machine’s lifting and digging power. One that’s set too high (or stuck closed) puts every component in the circuit at risk of pressure-related failure. Testing relief valve settings with a calibrated gauge should be part of your annual maintenance routine, or anytime you notice a change in machine performance.
