- Machinery and equipment
Elastic Support of Machinery and Equipment
The most common use of Visotech GERB vibration isolation solutions in Australia and New Zealand is with plant and equipment. Eliminating these vibrations is important both for the health and safety of workers near these machines, but also for the machines themselves.
Excessive and long-term vibrations can cause undue wear and misalignment in plant and equipment, requiring expensive repairs or full replacement, as well as shut down time. From small pump and gensets to large coal crushers and printing presses, Visotech can design and supply a GERB vibration isolation system to eliminate up to 99% of vibrations.
Reciprocating compressors have major moving masses (piston, connecting rod, crank shaft), which are in many cases not very well balanced. While balanced multi- cylinder compressors can be installed in most cases directly on springs with only a steel frame as an interface, 1-cylinder machines need a rather big additional mass to limit the dynamic response deflections, which could be a concrete foundation or a steel plate.
Compared to a conventional installation, elastic support with GERB spring elements will provide typically a 90% vibration control effect.Rotating compressors are typically better balanced and run with higher speed. In case of a conventional installation they often cause a high level of structure borne noise. When placing these compressors on GERB spring elements, this noise will be completely suppressed.
Depending on the type of equipment and dynamic loads in vertical and/or horizontal direction, these machines need an additional foundation, which in case of elastic support will reduce and limit the system response amplitudes resulting from shock, random or periodical excitation. This foundation will also increase the overall stiffness and stability of the system.
he most common fans are ID-, FD- and PA-fans of axial as well as centrifugal type. Their imbalances caused by wear and tear during operation result in periodical dynamic forces, which are fully transmitted into the foundation and beyond. Therefore, fan foundation design must consider not only static but also these dynamic loads resulting ultimately in a foundation concept which is practical as well as acceptable in both the technical and economical way. Spring support of fans can conveniently meet these requirements. World-wide acceptance of this concept as a state of the art technology is of course our best evidence.
Conventional fan foundations typically require very massive RCC-blocks but this huge mass alone cannot stop the transmission of vibration into the soil/surrounding at all. It is mainly meant to suppress the detrimental effects of unintentional system resonances, which cannot be ruled out in this case, with very little knowledge of the exact dynamic properties of the soil. Furthermore there is also the risk of settlements, especially uneven settlements due to these vibrations. It is, therefore, common practice to support the conventional foundation at several meters below ground level where the soil bearing capacity is much more than adequate for just the static loads. Such a conventional foundation should therefore be replaced by a better alternative.
The fan foundation can be dynamically fully uncoupled from the sub foundation and soil.
GERB recommends dynamic uncoupling of the fan foundation from the soil by means of spring units equipped with high quality, fatigue free coil springs and non-ageing Viscodampers®. This system provides the following advantages:
Instead of a massive RCC-block, the fan foundation is reduced to a RCC-slab of very limited thickness and the dynamic behaviour of this system can be exactly calculated. System natural frequencies are far away from the speed of the fan ensuring a very smooth running of the fan itself. The fan foundation can be dynamically fully uncoupled from the sub foundation and soil. The vibration isolation efficiency is very high and may reach more than 90%. The substructure below the spring system can be designed for the dead load of the machine and its RCC-deck only. It may be reduced to either walls or frames which will conveniently rest on the soil without settlement problems. Piles, wherever required for a conventional foundation, can be greatly reduced in numbers or even fully eliminated. The highly flexible spring support combined with Viscodampers® will even result in lower stresses in the machine itself i.e. an increase in bearing life, longer maintenance free periods and higher machine availability.
This foundation concept represents, therefore, an economic and timesaving solution providing besides good vibration isolation an excellent protection against settlements and even against earthquakes. The danger of uneven settlements is greatly reduced due to following reasons:
The soil is only statically loaded, while most settlements after commissioning are caused by dynamic loads Up to a certain extent uneven settlements are automatically levelled out due to the flexibility of the springs. If settlements should in spite of all this reach critical dimensions, they can easily be corrected by shimming on spring level in a few hours.
The spring support of a condenser is not for the purpose of vibration control, but to reduce the load reaction caused by its heat expansion in the connected equipment, for example a turbine nozzle. GERB spring elements provide sufficient elasticity to limit such reactions to a permissible level, preventing in this way high cost for analysis and design of the connections or for expensive bellows.
Boiler feed pumps are basic power plant equipment. The driving part (motor or steam turbine) is connected directly or via a gearbox with the pumps.If these pumps are elevated - in earlier days they were generally sitting on ground level - it is very economic instead of giving them separate table foundations to integrate them into the structure of the turbine building. In this way spring elements and Viscodampers® are the interface between the equipment (together with its foundation) and the building.Although the speed resp. speed range of boiler feed pumps is typically high (> 1000 RPM), the springs have still to be very flexible to guarantee an efficient uncoupling of the spring supported system from the substructure. GERB spring elements can easily be adapted to such requirements.
The elastic support system for turbine generator foundations has been widely accepted during the past 30 years by the industry. The GERB system – jointly developed with leading turbine manufacturers - was applied for the first time in the German Nuclear Power Plant STADE in 1968 to support a 660 MW turbo generator. Presently, this system is used world-wide on turbines with capacities up to 1300 MW.
Leading manufacturers of turbines and other power plant equipment using the GERB system, emphasise the following advantages:
The turbo generator foundation is dynamically uncoupled from the substructure, More space below the turbo generator for the arrangement of condensers and piping. Integration of the substructure into the building, which consists of the beams and/or columns, Reduced construction costs for the basemat, Shorter construction time for the foundation By reducing the dynamical loads risk of settlements is reduced, Easy adjustment and realignment in case of settlements. Adjustments can be carried out without interrupting the operation of the machine, Protection of the turbo generator in case of earthquakes.
Big conventional gas turbine foundations are prone to settlements, especially on bad subsoil, which may lead to problems in operation and/or additional stresses in the foundations. Their elastic support on GERB spring elements will prevent that. Subsequent alignment of the system on spring level - without touching the machine - is easy and simple, in many cases even while the gas turbine is running.The GERB spring system can also protect the gas turbine in case of earthquakes, if combined with Viscodampers®.An excellent basic vibration control effect of the spring system is also obvious, which is especially important when the gas turbines are installed on power barges.
Transformers cause vibrations of 50 Hz, 100 Hz and higher frequencies, resulting in structure borne noise, which is mainly disturbing when installed in substations located in residential areas. The elastic support of such transformers on GERB spring elements will provide an excellent vibration and structure borne noise control.A special detail of such elements is the possibility to fix rails directly on their top plate. That allows an easy and simple installation as well as the rolling of the transformer into and out of the substations.
Piping systems in power - or chemical plants are complex dynamic structures. Vibrations are often the reason for failures and damages. They may be generated inside these systems during normal operation by numerous sources, such as, hydrodynamic forces or pressure pulses when valves are opened or closed. Connected machinery, like pumps and turbines, may also transmit vibrations. Excitation may also come through the supporting structure from external sources, for example, in emergency cases such as earthquakes and explosions. In these cases, the results may be excessive displacements and stresses, which can damage the piping system. Even operational vibrations with very small amplitudes may lead to material fatigue and endurance failure.
Based on decades of experience in design and application of VISCODAMPERS® for vibration control of machinery and other industrial equipment, GERB has developed Pipework dampers for the protection of piping systems. These Pipework dampers provide a number of advantages compared to other dynamic restraints:
Reduction of operational as well as shock induced vibrations in all degrees of freedom. Immediate reaction to vibrations without delay or time lag. Velocity proportional characteristics: High forces to counteract shock loads. Low forces in case of low motions, for example, thermal expansion. Simple in design and handling. There are no parts subject to wear and tear. They are maintenance free and have a nearly unlimited lifetime. Normally Pipework dampers accommodate motions of ± 40 mm in vertical and horizontal direction. Dampers for larger displacements are available.
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