Servo disc couplings for pump applications

Pump applications place special demands on the torsionally stiff servo disc couplings. Servo disc couplings transmit the torque in the plate pack via frictional engagement. This prevents micromovements in the connection of the lamella and increases the rigidity of the coupling. In order to offer precisely fitting coupling solutions for the respective requirements, R+W Antriebselemente GmbH has numerous model variants, which can be obtained in many different sizes and option possibilities.

Basically, the R+W servo disc couplings of the LP model series are robust, torsionally stiff and maintenance-free all-steel couplings that are used for torque transmission as well as for the compensation of shaft misalignments. Due to the use of high-strength materials, all model series have a high power density. The compact couplings can be used in a temperature range from -30 to +280 degrees Celsius. Optionally, the couplings are also available for use in explosion protection areas (ATEX).

The heart of the coupling: the disk pack

R+W servo disc couplings are equipped throughout with six-hole plates made of highly elastic spring steel, which can compensate for shaft misalignments in the package. High-strength screws are used to fasten the laminae package. These transmit the torque via frictional locking, which guarantees backlash-free torque transmission in the disk pack. Micro-movements in the connection to the lamella are thus avoided and the overall stiffness is increased. Due to the compensation capability of the disk pack, the couplings can compensate for both angular and axial shaft misalignment. If the coupling is double flex with two disk packs, lateral shaft misalignment can also be compensated. In order to meet the different requirements of the various fields of application, R+W has numerous series which are already suitable for many applications in the respective standard versions.

Models for various connections and inserts

Couplings of the LP1 series have two precisely manufactured coupling hubs, which are connected to the disk pack by means of bushings and high-strength screws. Axial fixing on the shafts is achieved by means of clamping screws fitted over the keyways in the coupling hubs. Axial as well as angular misalignments can also be compensated. Due to its compact and simple cardanic design, the LP1 coupling is often used where very high torsional stiffness is required or only limited installation space is available. Among other things, these are often used in test bench, process pump or agitator applications.

In contrast to the models of the LP1 series, the LP2 has two lamina sets as well as an intermediate tube, which is available in customized lengths on request. Due to their double-cardanic design, these couplings can also compensate for lateral misalignment. They are often used to bridge a greater distance. Since they can be mounted without moving the components to be connected, such as the motor and pump, their use saves time and effort. The areas of application for LP2 couplings are also diverse. For example, they can be used in pump applications that do not require compliance with API standards. The servo disc couplings of the LP1 and LP2 series are available in twelve different sizes, for nominal torques from 350 to 12,000 Nm.

Due to the symmetrical conical clamping hubs, the LP3 (double cardanic) and LP4 (single cardanic) couplings have very high clamping forces. As a result, these products are particularly suitable for reversing drives or for applications with high speeds. Both series are available in different sizes for nominal torques from 500 to 12,000 Nm.

The products of the LPZ series have compact, double-cardanic spacers. According to the modular system, these can be easily combined with the various hub types of the LP model series, such as conical clamping hubs or hubs for keyway connections. This means that requirement-specific coupling solutions can be configured quickly and easily as standard, which transmit the torque with very high torsional stiffness.

Servo disc couplings according to API 610 and 671

A special version in the LP series is the LPA model. The double cardanic couplings have been designed to API 610 standards in the standard version and are available with keyway connection for direct drives. The American Petroleum Institute (API) guidelines provide design standards for pump applications far beyond the U.S. and are used worldwide. LPA couplings thus comply with the general regulations for pump applications in the chemical and petrochemical industries.

API 610 specifies design guidelines, which concern, for example, materials, balancing or catching. However, the implementation may vary. In the couplings of the LPA series, the spacer is radially secured by a component that ensures safety against catching and emergency running in the event of any plate breakage. The radially removable spacer is designed so that it can be disassembled without moving the hubs. Upon delivery, this is always fully assembled.

Servo disc couplings according to API 610 are required in a wide variety of applications. For example, they are used in the onshore and offshore oil industry, refineries or in gas power plants and are often used for the connection between the engine and horizontal or vertical centrifugal pumps.

The Servo disc couplings of the LPA model series are available in six different sizes, for nominal torques from 500 to 12,000 Nm and in metric as well as imperial versions. Their balancing quality corresponds at least to AGMA 9000 Class 9, which is a guideline for balancing couplings. In addition, couplings for special applications according to API 671 are also possible as special designs.

Other options and special designs

The wide range of R+W servo disc couplings is also complemented by numerous options and special solutions. For example, a special design based on the LP2 in Series 10000 was the suitable coupling solution in a recent case.

For the transportation of liquefied gases or petroleum by sea, tankers must be appropriately loaded and unloaded with the safety precautions appropriate to the hazardous material. These pumping operations require large compressors driven by powerful electric motors. In this specific case, a 350 KW engine produces a torque of about 4800 Nm at around 700 rpm. However, jerky shock torques at the beginning of the pumping process can briefly increase the torque to over 9000 Nm. The special version of the LP2/10000 here connects the motor shaft with a solid, rigid shaft approx. 2 m long. This shaft is fed into the compressor compartment via a bulkhead bushing. The end of the shaft is in turn connected to the drive flange of the compressor by means of another coupling. The special requirements for the couplings here included a certain resistance to seawater, the specified balancing quality, and ease of installation. The additional safety factor of the coupling also allows a short-term torque of up to 20,000 Nm in an emergency and thus also meets the requirements for corresponding safety reserves.