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Grasso Compressors

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Introduction

Using the thorough know-how of compressor and welding technology together with the latest three-dimensional CAD design technologies Grasso has developed a new series of reciprocating compressors designated the Grasso 10. The Grasso 10 is the successor of the well-known Grasso RC9 compressor series which has gained an outstanding reputation for more than 30 years. After a thorough R&D and field-testing programme the Grasso 10 has proven itself to be superior to the RC9. A new top quality product with a wider range is now available. A product capable of withstanding today's strict requirements within the world of industrial refrigeration

The unique welded steel compressor body of Grasso reciprocating compressors has given Grasso a special place in the market of compressor manufacturers for many years. The Grasso 10 is manufactured according to this design feature. Due to the very high natural heat dissipation related to this concept the discharge and oil temperatures are kept within limits. This means that additional oil cooling or water cooling systems is not necessary within a large field of application.

The main design criteria in developing the new Grasso 10 series have been:

* Reliability and high efficiency. * Low vibration level. * Long lifetime.

The Grasso 10 Range

The new range of Grasso 10 compressors comprise a total of nine highly reliable open drive reciprocating models. Figure 1 shows the Grasso 10 series containing 5 single stage compressors (145 m3/h to 580 m3/h) and 4 compound compressors (145 m3/h to 435 m3/h). The Grasso 10 runs at a maximum speed of 1500 rpm for ammonia, halocarbon as well as hydrocarbon applications. The minimum compressor speed is 600 rpm.

Reliability and High Efficiency

The reliability and high efficiency of the Grasso 10 compressor are determined by the design of the main compressor components such as oil lubrication and bearing system, capacity control mechanism, piston, cylinder liner and valve design. Figure 2 shows the compressor in detail.

Oil Lubrication and Bearing System

The fully integrated lubrication system prevents oil leakage and ensures effective internal cooling for the shaft seal (1). Also a perfect oil supply to the compressor bearings (2) is realised.

to operate the hydraulic system of the capacity control mechanism, is individually adjustable from the outside with an oil pressure regulator. The oil lubrication pressure as well as the control oil pressure,

The positive displacement gear pump is driven directly from the crankshaft and equipped with a cylindrical roller bearing as well as an angular contact bearing. This enables a maintenance free operation of the oil pump for many years. Changeable oil filter elements with large filtration surfaces and high filtration grades protect the bearings, motion work and shaft seal against early wear and reduces service work to a minimum.

Capacity Control Mechanism

All cylinders are provided with an individually operated capacity control mechanism(3). This feature enables a fully unloaded start as a standard for this type of compressor resulting in a low starting torque and a minimum bearing load during start-up of the compressor. In the case of compound compressors the individually operated cylinders gives the possibility to apply a special "fast pull-down" capacity control regulation. This large freeze capacity is available for shock freezing applications which results in shorter freezing times.

Piston and Cylinder Liner

The material choice and surface finishing of the cylinder liner(4) and piston rings(5) mainly defines the life time expectancy of both compressor components. Grasso uses a special honing profile for the cylinder liners in combination with reverse torsion piston rings ensuring low wear and long life.

Valves

The Grasso 10 valve design is completely new. Composite material valves(6) are applied in combination with a ingenious valve impact velocity reduction system. The selected valve material and the impact velocity with which the valve ring and spring hits the stroke limitor are determining factors for the valve robustness.

* Composite material:

The Grasso 10 valve rings are made out of glass fibre reinforced PEEK material. Compared to steel valve rings, the maximum allowable impact velocity of this valve material is 60% higher.

* Valve impact speed reduction:

Valve impact speed reduction is realised by means of gas damping. The spring behind the suction or discharge valve fits tightly into a recess. Therefore, the spring encloses two chambers filled with refrigerant gas. When the valve opens, the pressure builds up in the chambers due to the trapped gas. This will produce damping and will decrease the valve speed to zero just at the last moment before the valve hits the stroke limitor.

Figure 3 shows the difference in impact speed using a gas damping system compared to a conventional design. Gas damping results in a at least 30% reduction of impact speed. Depending on operation conditions and refrigerant impact speed reductions up to 50% can be realised. Due to this impact fatigue is reduced to the minimum.

Low Vibration Level

To reach a very low vibration level of the compressor special attention is given concerning the compressor cylinder arrangement and the natural frequency of the steel welded compressor housing. For the 4 up to 8 cylinder models a V arrangement of the cylinder is chosen. This ensures an optimum distribution of the gas compression forces. For the smaller models with 2 and 3 cylinders an in-line arrangement is used. To optimise the gas compression force distribution of these models the crankshaft has two cranks.

The natural frequency of the compressor housing is designed on a multiple value of the maximum rotational frequency of the compressor. In simple words this means that the compressor housing is that stiff that it will not vibrate whatever internal movements occur within the compressor.

Long Lifetime

Practice is the only way to prove reliability and long lifetime for a new compressor development. Testing in a laboratory is of course very useful but will not give enough information about how the compressor will perform in actual practice after many operating hours. That is why Grasso decided to perform numerous field tests before they introduced this compressor to the market. Grasso 10 compressors were put into cooling and freezing installations to learn how the new compressor performed under field conditions. The Grasso 10 has proven itself to be a very reliable compressor. Grasso is convinced that the Grasso 10 offers the ultimate in reliability. Good news for those who see reliability, as Grasso does, as top criteria.

Compressors, Evaporators, condensers, Shell & Tube, controls and gauges, Flake Ice makers, Chillers, Pool Heaters, Packages, Electrics, Refrigeration, air conditioning, Grasso Compressors, Gelfred Compressors, Embraco Compressors, Ager, Luve Contardo condensers, Onda, Oref Flake Ice Makers, Teco, VDH controls and gauges, Evco controls and gauges, Geneglace Flake Ice Makers, HL Cooling Chillers, Grasso Chillers, Kali Kolant Pool Heaters, Follet Flake Ice Makers, Grasso Packages, Gelfred Packages, Eidis Packages .

Joondalup Service Providers: 136 Caridean St Heathridge WA 6027 - PO Box 209 Joondalup WA 6919
Telephone: +61 8 9307 8484 - Fax: +61 8 9307 8485 - Email: jsprefr@bigpond.net.au


The unique welded steel compressor body of Grasso reciprocating compressors has given Grasso a special place in the market of compressor manufacturers for many years. The Grasso 10 is manufactured according to this design feature. Due to the very high natural heat dissipation related to this concept the discharge and oil temperatures are kept within limits. This means that additional oil cooling or water cooling systems is not necessary within a large field of application.

The main design criteria in developing the new Grasso 10 series have been:

* Reliability and high efficiency. * Low vibration level. * Long lifetime.




The Grasso 10 Range

The new range of Grasso 10 compressors comprise a total of nine highly reliable open drive reciprocating models. Figure 1 shows the Grasso 10 series containing 5 single stage compressors (145 m3/h to 580 m3/h) and 4 compound compressors (145 m3/h to 435 m3/h). The Grasso 10 runs at a maximum speed of 1500 rpm for ammonia, halocarbon as well as hydrocarbon applications. The minimum compressor speed is 600 rpm.





Reliability and High Efficiency The reliability and high efficiency of the Grasso 10 compressor are determined by the design of the main compressor components such as oil lubrication and bearing system, capacity control mechanism, piston, cylinder liner and valve design. Figure 2 shows the compressor in detail. Oil Lubrication and Bearing System The fully integrated lubrication system prevents oil leakage and ensures effective internal cooling for the shaft seal (1). Also a perfect oil supply to the compressor bearings (2) is realised.
to operate the hydraulic system of the capacity control mechanism, is individually adjustable from the outside with an oil pressure regulator. The oil lubrication pressure as well as the control oil pressure,

The positive displacement gear pump is driven directly from the crankshaft and equipped with a cylindrical roller bearing as well as an angular contact bearing. This enables a maintenance free operation of the oil pump for many years. Changeable oil filter elements with large filtration surfaces and high filtration grades protect the bearings, motion work and shaft seal against early wear and reduces service work to a minimum. Capacity Control Mechanism All cylinders are provided with an individually operated capacity control mechanism(3). This feature enables a fully unloaded start as a standard for this type of compressor resulting in a low starting torque and a minimum bearing load during start-up of the compressor. In the case of compound compressors the individually operated cylinders gives the possibility to apply a special "fast pull-down" capacity control regulation. This large freeze capacity is available for shock freezing applications which results in shorter freezing times. Piston and Cylinder Liner The material choice and surface finishing of the cylinder liner(4) and piston rings(5) mainly defines the life time expectancy of both compressor components. Grasso uses a special honing profile for the cylinder liners in combination with reverse torsion piston rings ensuring low wear and long life. Valves The Grasso 10 valve design is completely new. Composite material valves(6) are applied in combination with a ingenious valve impact velocity reduction system. The selected valve material and the impact velocity with which the valve ring and spring hits the stroke limitor are determining factors for the valve robustness. * Composite material: The Grasso 10 valve rings are made out of glass fibre reinforced PEEK material. Compared to steel valve rings, the maximum allowable impact velocity of this valve material is 60% higher. * Valve impact speed reduction: Valve impact speed reduction is realised by means of gas damping. The spring behind the suction or discharge valve fits tightly into a recess. Therefore, the spring encloses two chambers filled with refrigerant gas. When the valve opens, the pressure builds up in the chambers due to the trapped gas. This will produce damping and will decrease the valve speed to zero just at the last moment before the valve hits the stroke limitor.



Figure 3 shows the difference in impact speed using a gas damping system compared to a conventional design. Gas damping results in a at least 30% reduction of impact speed. Depending on operation conditions and refrigerant impact speed reductions up to 50% can be realised. Due to this impact fatigue is reduced to the minimum.



Low Vibration Level To reach a very low vibration level of the compressor special attention is given concerning the compressor cylinder arrangement and the natural frequency of the steel welded compressor housing. For the 4 up to 8 cylinder models a V arrangement of the cylinder is chosen. This ensures an optimum distribution of the gas compression forces. For the smaller models with 2 and 3 cylinders an in-line arrangement is used. To optimise the gas compression force distribution of these models the crankshaft has two cranks. The natural frequency of the compressor housing is designed on a multiple value of the maximum rotational frequency of the compressor. In simple words this means that the compressor housing is that stiff that it will not vibrate whatever internal movements occur within the compressor. Long Lifetime Practice is the only way to prove reliability and long lifetime for a new compressor development. Testing in a laboratory is of course very useful but will not give enough information about how the compressor will perform in actual practice after many operating hours. That is why Grasso decided to perform numerous field tests before they introduced this compressor to the market. Grasso 10 compressors were put into cooling and freezing installations to learn how the new compressor performed under field conditions. The Grasso 10 has proven itself to be a very reliable compressor. Grasso is convinced that the Grasso 10 offers the ultimate in reliability. Good news for those who see reliability, as Grasso does, as top criteria.