Quick Overview: What Are Flow Dividers?
What is a hydraulic flow divider?
A hydraulic flow divider is a component that splits a single pump’s output into two or more proportional flow streams, allowing one pump to power multiple circuits simultaneously. It can also operate in reverse — combining multiple flows into one output — which is why it is often called a flow divider/combiner. The two main types are spool-type and gear-type (rotary) dividers.
Main types of hydraulic flow dividers:
- Spool-type divider – splits input flow into two fixed proportional outputs (e.g. 50/50 or 60/40); compact, low internal leakage, high accuracy, but generates heat under load
- Gear-type (rotary) divider – uses interlocking gear sections to split flow into two or more streams; handles more outlets (up to 6–8), more tolerant of contamination, near 98% efficiency
- Flow combiner function – both types can merge multiple return flows into one outlet; gear-type is better suited for reverse operation
- Pressure-compensated output – output flows remain proportional to input regardless of varying circuit loads or pressure differences between outlets
Example
In a telescopic crane, a gear-type flow divider splits the pump output so the primary flow powers the steering circuit while the second flow enables two-speed lifting — all from a single pump, eliminating the need for multiple pumps and reducing system cost and complexity.
Summary
A hydraulic flow divider allows one pump to power multiple independent circuits simultaneously by splitting flow proportionally, making it essential in construction, agricultural, and mining equipment where synchronized multi-actuator operation is required.
What is a flow divider?
A flow divider is a hydraulic mechanism that splits an input flow into at least two outputs allowing a single pump to power multiple circuits simultaneously. They can also combine multiple flows into a single output, which is why they are often referred to as ‘flow dividers/combiners.’ There are two proportional flow dividers: the spool type and the gear or rotary design.
Flow divider types and structures
There are two distinguished types:
Sliding spool (or split-type) dividers
Rotary dividers (they are usually gear dividers)
All flow dividers feature heavy-duty casings made of hardened steel or aluminum. They must withstand very high pressure. Sliding spool dividers have two outlets, and rotary ones usually have 6 to 8 outlets.
Both types differ in mechanical parameters, accuracy, range of flow, and precision. In general, rotary dividers are more rugged, resistant to contamination, and perform better, making them more efficient.
Spool Type
Spool dividers proportionally divide the input flow into two output streams. Typical output ratios include 50/50, 60/40, and 66.6/33.3, although any ratio is theoretically possible.
A spool divider’s primary components are a housing with an inlet port, two outlet ports, and an internal moveable spool. The spool contains cross-drilled holes at its midpoint, intersected by a central flow passage that extends along its length.
The spool can freely slide back and forth within the housing. Flow enters through the center passage of the spool, divides, and moves toward each end. It exits both ends via narrow gaps between the spool’s outer diameter and the housing, then through the ports.
When pressure rises on one side, the spool responds to the pressure difference and moves toward the opposite port. One outlet opens slightly more than the other, but the flow to both remains constant. Thus, both output flows are pressure compensated, and the flow division remains constant despite varying circuit loads and stresses. If the input flow varies, the output flows will vary proportionally. And if one side is blocked, the other will also be blocked.
Gear Type
The gear-type divider can split the flow into multiple paths. It comprises a housing, two or more interlocking internal gears, and barriers that separate these sections. A standard shaft connects the gear sections. Flow enters one housing end and routes through a channel to each gear section. Fluid dynamics exert force on the gear teeth, making them rotate in reverse directions. The fluid between the gear teeth and housing circulates to the other side of the gear segment. When the teeth engage, fluid is expelled from each outlet port.
Since all gear sections are interlinked, they rotate uniformly at the same speed. The gear sections’ positive displacements produce a constant flow division. The inlet flow is divided proportionally between each section. Regardless of pressure variations in the output circuits, the output flows remain proportional to the input. Should the input flow vary, output flows will likewise differ proportionally. If one output is blocked, all the others are blocked as well. A relief valve prevents pressure intensification.
Also, gear-type dividers are capable of combining return flow within circuits. Typically, spool dividers are not built to allow reverse flow.
Rotary-gear dividers exhibit a minimal pressure drop across their sections, with many achieving efficiencies near 98%. In contrast, spool-type dividers generally need a significant pressure drop for proper operation. This generates heat, and engineers must consider the inherent inefficiency when sizing them for an application. Gear-type flow dividers demonstrate greater tolerance to contamination. In contrast, spool-type dividers exhibit minimal internal leakage and offer high accuracy, yet they are generally more expensive than similar rotary-gear dividers.
How does a flow divider work?
The principle of operation of flow dividers is straightforward: Fluid from a source is pumped through a valve into the flow divider, which splits the flow into two or more proportional sub-flows routed through multiple outlets.
Sliding spool dividers typically divide the flow into two fixed, proportional sub-flows (e.g., 50/50). The flow division is predetermined by design and cannot be independently adjusted.
Rotary dividers use gear mechanisms to split the flow into two or more proportional streams based on the design of the gear sections. While these streams are proportional, additional controls may be required for independent regulation.
Hydraulic flow dividers can also operate in reverse, combining two or more inlet flows into a single outlet flow.
Applications of a flow divider
Hydraulic flow dividers are widely used in agricultural, construction, and industrial hydraulic systems. Rotary flow dividers are particularly useful when two or more identical hydraulic cylinders or devices, powered by a single pump, must operate in synchronization. For example, when moving unevenly loaded lorries, the flow divider ensures that all lorries move at the same speed, even if their loads differ, by distributing flow evenly between the systems.
Flow dividers also allow for the creation of multiple independent hydraulic circuits powered by a single pump. This can reduce energy consumption and costs in appropriately designed systems, as it eliminates the need for multiple pumps.
Concrete Pump
Flow dividers are critical in managing pressure and flow distribution in a concrete circuit pump. A two-section flow divider operates in pressure intensification and speed control modes to handle intermittent high-pressure demands and variable speeds. A four-section flow divider also distributes the flow to various machine services, ensuring efficient operation.
Drill Rig
Flow dividers are integral to drill rig operations, enabling precise flow allocation and variable speed control. Two primary flows are directed to the drill motor for operation, while a third flow powers auxiliary services. The fourth flow is further divided to supply additional machine functions, such as drill rod screwing and unscrewing, ensuring seamless multitasking capabilities.
Mining Machine
In a mining machine circuit, flow dividers combined with mid-inlet valves maximize power efficiency while simplifying the hydraulic system. This design eliminates the need for a complex, costly gearbox-driven, multiple-pump setup, reducing maintenance and operational costs.
Container Handler
Flow dividers equipped with priority outlet valves guarantee a steady and separate flow to essential systems on container-side loaders, including steering and remote control circuits. Additional flows are allocated to lifting mechanisms and auxiliary services, optimizing overall machine performance.
Excavator
Excavator circuits leverage flow dividers and mid-inlet sections in valves to deliver intermittent high pressures to essential machine functions. This ensures efficient operation during demanding tasks.
Telescopic Cranes
In telescopic cranes, flow dividers paired with a priority outlet valve ensure reliable power delivery to critical systems. The primary flow powers the steering circuit, while the second flow enables two-speed lifting. A secondary flow from the priority valve is allocated to auxiliary services, enhancing overall functionality.
Flow dividers operate most efficiently with gear sizes of 1″ (2.5 cm) or larger and speeds ranging from 700 to 1300 rpm. When selecting a flow divider, avoid specifying units with all 1/2″ (1.3 cm) or 1/4″ (0.6 cm) gears, as these may reduce performance and reliability.
For optimal operation, position the inlet port closest to the largest gear unit and ensure the largest gear section is centrally located within the unit.
It’s important to note that any flow divider has the potential to intensify pressure. To manage this, adequate relief valve protection must always be installed on the discharge side of the flow divider to keep pressure within safe operating limits.
Benefits of Flow Dividers
Flow dividers offer unique advantages that are often overlooked in hydraulic circuit design. These components “float” in the circuit, operating only when required and to the extent necessary. Unlike variable orifice devices, flow dividers operate on the principle that fluid horsepower input equals fluid horsepower output minus minor efficiency losses.
If the pressure at an outlet is lower than the inlet, the low-pressure section of a rotary flow divider functions as a motor. Instead of wasting energy as heat, this energy is transferred through the interconnecting shaft to perform work in other sections. The total output flow matches the input flow, with each section’s output proportional to its gear width. When used as a flow equalizer, all sections feature equal gear widths.
Automatic and Maintenance-Free Operation
Flow dividers operate automatically, requiring no pilot signals or external devices for activation. They are self-lubricating, require no external drain lines or shafts, and can be mounted in any position using extended studs for convenience.
Economic and Design Advantages
Flow dividers significantly reduce system complexity and cost by replacing expensive multidrive gearboxes, multiple pumps, and extensive plumbing with a single pump and flow divider. Because they operate on a pressure charge, they can be positioned remotely in a convenient location and eliminate common issues associated with feeding multiple pumps.
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