Hydrodynamic Coupling

Fluid couplings (hydrodynamic couplings) are designed to transmit torque from an electric motor to driven machinery and to provide smooth speed control for driven equipment. In pumping units, fluid couplings allow varying the pump speed, thereby regulating its flow rate and head according to the actual operating parameters of the process system.

A fluid coupling is installed between the driving electric motor and the pump. Power transmission occurs hydrodynamically via the circulation of working fluid between the impeller (pump wheel) and the runner (turbine wheel). Due to the absence of a rigid mechanical connection between the driving and driven elements, the fluid coupling provides smooth torque transmission and helps reduce dynamic loads on the equipment.

Industrial pumping units utilize fluid couplings of various structural designs: single-circuit and double-circuit, with or without gear transmission, step-up gear (speed increaser) designs, and right-hand or left-hand rotation options. Adjustable industrial fluid couplings of the MG (МГ) and MGL (МГЛ) series feature scoop tube regulation.

Purpose of Fluid Couplings

The primary purpose of a fluid coupling is to transmit power between an electric motor and a pump while enabling speed regulation of the output shaft.

The use of fluid couplings allows:

• Regulating the capacity/flow rate of the pumping unit;
• Varying the pump head according to system head characteristics;
• Ensuring smooth equipment startup;
• Reducing shock and dynamic loads on the drive;
• Decreasing motor load during startup modes;
• Ensuring stable operation of pumping equipment under variable operating conditions;
• Implementing manual or remote speed control;
• Increasing the operational reliability of the pumping unit.

The application of variable-speed fluid couplings is especially relevant for high-power centrifugal pumping units where equipment performance needs to be adjusted based on current system demand.

Operating Principle of a Fluid Coupling

Unlike rigid mechanical shaft couplings, a fluid coupling transmits energy via a working fluid.

The main working elements are the impeller and the runner (turbine wheel). The driving impeller receives rotation from the electric motor and accelerates the working fluid. The fluid stream transfers kinetic energy to the turbine runner, which is connected to the driven shaft of the equipment.

Thus, torque is transmitted without direct mechanical contact between the driving and driven rotors.

By changing the amount of working fluid in the working circuit of a variable-speed fluid coupling, the speed of the driven shaft can be adjusted. In designs with scoop tube regulation, this process can be performed manually or automatically.

Advantages of Fluid Couplings

Integrating a fluid coupling into a pumping unit or other industrial equipment provides a range of operational benefits:

Smooth Speed Control

The fluid coupling allows varying the speed of the driven machinery without stopping the unit.

Reduced Starting Loads

Acceleration of driven equipment occurs more smoothly, reducing mechanical stress on the motor, shaft, coupling elements, and driven mechanism.

Equipment Overload Protection

The hydrodynamic power transmission principle mitigates the impact of transient shock loads on the drive.

Pump Performance Regulation

Changing the centrifugal pump speed enables control over its capacity and head according to current process requirements.

Automation Capability

Fluid coupling speed control can be integrated into the automated control system of the pumping unit.

Operation of High-Power Pumping Units

Fluid couplings are utilized in high-power installations, including power generation plants and industrial pumping stations.

Design Configurations of Fluid Couplings

Depending on design, industrial fluid couplings vary by the number of working circuits, direction of rotation, and presence of an integrated gear transmission.

Key configurations include:

• Single-circuit fluid couplings;
• Double-circuit fluid couplings;
• Gearless fluid couplings;
• Geared fluid couplings;
• Fluid couplings with integrated step-up gear (speed increaser);
• Right-hand rotation fluid couplings;
• Left-hand rotation fluid couplings.

For the MG and MGL series, known variants include single-circuit gearless models MG-600 and MG-670, geared model MGL-M-710, as well as double-circuit models MG2-600 and MG2L-650.

Fluid Coupling Models

Depending on drive power, required speed regulation range, operating speed, and pumping unit design, different sizes of fluid couplings can be applied.

Note: For MG-600, power transmission is rated up to 2,000 kW; for MG-670 and MG2-600 — up to 5,000 kW; and for MGL-M-710 and MG2L-650 — up to 7,000 kW. Specific operating parameters must be clarified based on the requested model variant and operating conditions.

Applications of Fluid Couplings

Variable-speed fluid couplings are mainly applied in high-power equipment designed for continuous duty.

Primary applications:

• Thermal power generation;
• Nuclear power generation;
• Industrial pumping stations;
• Industrial water supply systems;
• Oil and petrochemical industries;
• Process pumping systems;
• Boiler feed pumping units;
• High-pressure centrifugal pumps;
• Other industrial rotating machinery.

Fluid couplings are particularly effective in systems where equipment performance needs to be adjusted dynamically during operation.

Ordering a Fluid Coupling

SNT Slovakia s.r.o. selects and supplies components for industrial pumping and rotating equipment, including various coupling types.

To select a fluid coupling, providing specialists with the following data is recommended:

• Model of the existing fluid coupling;
• Pump model;
• Electric motor model and rated power;
• Motor speed;
• Required pump speed;
• Direction of rotation;
• Equipment nameplate data;
• Drawings or mounting dimensions (if available);
• Operating condition details.

Based on this information, the appropriate fluid coupling model can be selected, replacement feasibility evaluated, and required delivery scope confirmed.