Guide Explores Hydraulic Motor Efficiency in Industrial Applications

Imagine a precision agricultural machine that needs to drive multiple fans simultaneously for even fertilizer distribution or power sharp blades for efficient vine pruning. Behind these seemingly simple operations lies the ingenious design of series-connected hydraulic motors. Many professionals wonder: can hydraulic motors truly be connected in series? The answer is affirmative. But how can this be achieved safely and efficiently?

Series connection of hydraulic motors involves linking multiple motors sequentially, allowing hydraulic fluid to flow through each motor in turn, driving them to work in coordination. The core principle lies in energy distribution - the hydraulic fluid's energy is divided among the motors in series, with each motor receiving energy inversely proportional to the total number. For instance, two motors in series each receive approximately 50% of the energy; three motors receive about 33% each, and so forth.

This design proves particularly suitable for applications requiring multiple actuators to move synchronously when each actuator demands relatively low torque or speed.

Key Advantages:

• Synchronization: Series-connected motors achieve excellent synchronous movement, ideal for coordinated multi-component operations.
• Cost Efficiency: Using multiple smaller motors in series can prove more economical than employing a single large-capacity motor in certain applications.
• Compact Design: Multiple small motors may integrate more easily into equipment than a single large unit.

While series connection offers significant potential, not all hydraulic motors are suitable. The critical factor is selecting motors equipped with case drain ports and ensuring these ports connect reliably to zero-pressure areas.

1. Pressure Accumulation Risks

In series systems, all motors except the last one operate with outlet pressures above zero. This means the pressure acting on each motor's shaft seal equals its outlet pressure. Without case drain ports, pressure would accumulate beyond the seals' capacity, leading to failure and eventual leakage.

2. Protective Mechanism of Case Drain Ports

Motors with case drain ports connect these ports directly to the seal's backside, routing to zero-pressure areas. This configuration prevents direct outlet pressure from acting on the seals, avoiding damage from excessive pressure. High-quality reinforced shaft seals with support washers can typically withstand up to 6 bar pressure, but using case drain ports remains the prudent choice, especially in high-pressure or frequent start-stop applications.

To further optimize series-connected hydraulic motor systems, various optional accessories are available, including anti-cavitation valves and relief valves, which significantly improve system protection and longevity.

1. Anti-Cavitation Valves: Preventing Shock Damage

Anti-cavitation valves (or replenishing valves) primarily protect against shock damage from sudden stalling. In applications like forestry cutting equipment where blades might abruptly stop when hitting hard objects, these valves allow fluid circulation within the motor, releasing pressure and protecting against inertial shock.

2. Relief Valves: Preventing Pressure Spikes

Relief valves (safety valves) automatically open when system pressure exceeds preset values, diverting fluid directly to the tank and protecting motors from overpressure damage.

3. Combined Protection Systems

For maximum protection, combining anti-cavitation valves with relief valves creates a dual-protection system that guards against both shock damage and pressure spikes, ensuring reliable operation under demanding conditions.

A practical example demonstrates the effectiveness of series-connected hydraulic motors: An agricultural equipment manufacturer implemented this solution in a new seeding machine requiring simultaneous operation of multiple seeding units. Each unit demanded relatively low but precisely synchronized torque. The series configuration achieved perfect synchronization while maintaining operational reliability through proper case drain implementation and anti-cavitation protection.

While series connection offers flexibility, practical limitations exist regarding the number of motors (due to energy distribution efficiency) and compatibility between different models (requiring matched displacement and pressure ratings).

Future advancements may include intelligent control systems using sensors and controllers, energy-efficient designs reducing power losses, and integrated solutions combining series motors with other control systems for more complex functionalities.

Proper maintenance of series-connected systems requires regular inspection of case drain ports, hydraulic fluid quality, seal conditions, and valve functionality to ensure long-term reliable operation.