A tandem hydraulic pump efficiently integrates two independent hydraulic pumps into a single unit, driven by a common input shaft, to provide multiple hydraulic circuits or increased flow capacity from a compact design.
Understanding Tandem Hydraulic Pumps
A tandem hydraulic pump is essentially two separate hydraulic pumps coupled together on a single shaft, sharing a common housing or center section. This configuration allows a single prime mover (like an electric motor or an internal combustion engine) to power two distinct hydraulic circuits simultaneously, optimizing space and efficiency.
Core Principle: Two Pumps, One Drive
At its heart, a tandem pump operates by utilizing a single rotational input to drive two separate pumping elements. Each pumping element draws fluid from a common source and expels it into its dedicated outlet port, creating independent hydraulic flows.
Independent Operation and Shared Suction
Hydraulically, the two pumps operate independently of one another, but they share a common suction port in the pump's centre section. This means both pumps draw hydraulic fluid from the same reservoir through a single inlet, simplifying plumbing. Despite sharing the suction, their outlet flows are completely separate, allowing them to power different functions or stages of a single function without interference.
Placement of Pumps
The physical arrangement within the tandem unit is typically optimized for performance and durability. The larger pump of the combination is situated at the shaft end (the drive side). This placement helps manage the higher torque and load associated with the larger displacement pump more effectively, as it's closer to the power input. Similarly, with equal frame sizes, the pump with the larger displacement is situated at the drive side for the same reasons of structural integrity and power transmission.
How Each Pump Section Works (General Mechanism)
While the exact mechanism depends on the type of pump (e.g., gear, piston, vane), the fundamental principle remains the same for each section:
- Suction: As the pump's internal components rotate (gears mesh, pistons reciprocate, vanes slide), they create a partial vacuum, drawing hydraulic fluid from the shared suction port into the pump's inlet chamber.
- Transfer: The fluid is then trapped within the pumping elements and carried from the inlet side to the outlet side.
- Pressurization: As the pumping elements continue to move, they force the trapped fluid into the pump's outlet port, building pressure against the resistance of the hydraulic system. This pressurized fluid then travels through hoses and valves to actuate cylinders or motors.
Why Choose a Tandem Pump?
Tandem pumps offer several significant advantages over using two separate single pumps:
- Space Saving: Consolidating two pumps into one unit requires less mounting space and a single mounting flange, which is crucial in compact machinery.
- Cost Efficiency: Often, a single tandem pump is more economical to purchase and install than two separate pumps, along with their individual mounting hardware and separate drive couplings.
- Simplified Plumbing: A common suction port reduces the amount of inlet plumbing, hoses, and fittings required, leading to a cleaner and potentially less leak-prone system.
- Enhanced Performance: Allows for independent control of two hydraulic functions from a single power source, enabling complex sequences or simultaneous operations with precise flow allocation.
- Power Optimization: By using one prime mover, the overall power transmission is more efficient.
Common Types and Configurations
Tandem pumps can be constructed using various pump types for each section, depending on the application's specific requirements for pressure, flow, and efficiency.
- Tandem Gear Pumps: These are very common due to their robustness, simplicity, and cost-effectiveness. Each section consists of two meshing gears that create flow.
- Tandem Piston Pumps: Often used in high-pressure, high-efficiency applications. They can be axial or radial piston designs.
- Tandem Vane Pumps: Known for their quiet operation and ability to handle varying pressures.
- Mixed Tandem Pumps: It's also possible to combine different types of pumps (e.g., a gear pump as the first stage and a piston pump as the second) in a tandem configuration to meet diverse system demands.
| Feature | Single Hydraulic Pump | Tandem Hydraulic Pump |
|---|---|---|
| Number of Pumps | One | Two (or more) |
| Drive Shafts | One | One (shared) |
| Suction Ports | One | One (shared in the center section) |
| Outlet Ports | One | Two (or more, one for each pump section) |
| Space Required | Moderate | Less for equivalent flow capacity/number of circuits |
| Complexity | Simpler for a single function | More complex internally, simpler system integration |
| Applications | Basic hydraulic systems, single function operations | Multi-function machinery, power steering + auxiliary functions |
Applications of Tandem Pumps
Tandem hydraulic pumps are widely used across various industries where multiple hydraulic functions are required from a compact power unit.
- Construction Machinery:
- Excavators (boom and bucket functions)
- Loaders (lift and tilt functions)
- Backhoes (main digging functions and stabilizers)
- Agricultural Equipment:
- Tractors (power steering and implement lift)
- Harvesters (various hydraulic functions for cutting, conveying, and steering)
- Material Handling:
- Forklifts (lift and tilt functions)
- Telehandlers
- Industrial Machinery:
- Machine tools (clamping, feeding, and tool changing)
- Hydraulic presses
- Automotive:
- Power steering and brake boost systems
Practical Insights
When selecting a tandem pump, engineers consider the flow requirements (liters per minute or gallons per minute) and pressure ratings (PSI or bar) for each individual pump section. The combined power requirement will dictate the size of the prime mover. For instance, in an agricultural tractor, one section of a tandem pump might be dedicated to the power steering system, which requires a relatively constant, low-flow output, while the other section might power the implement lift or auxiliary functions, demanding higher flow and pressure on demand. This separation ensures that essential functions like steering maintain priority and consistent performance.
