Engineering manual - SAB 193-233-283 S A-frame (including ATEX)
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008831 en 2020.10
To check the deflection of the vibration dampers while loaded, measure "A", Fig. 80, while the unit
is still suspended in the crane. After the unit has been installed, measure "A" once more. The dif-
ference (deflection)
must
be between 3 and 5 mm for all vibration dampers.
If this is not the case, insert liner plates under the vibration dampers until the above deflection
has been obtained.
As vibration dampers for marine use should also dampen vibrations coming from the foundation
caused by the main and auxiliary engine, vibration dampers are selected on the basis of an infor-
mation table and the mentioned descriptions. Send the information table, including appendices,
to your local Johnson Controls representative, who will then select the appropriate dampers.
7.24
VSD equipment
Equipment running variable speed (VSD) is more likely to encounter resonance causing critical vi-
brations. During selection, an assessment of equipment feasibility for variable speed must be car-
ried out, based on the risk chart below. The table values are based on reference temperatures of
35°C of condensation pressure and discharge temperatures at 75°C (60°C for HFCs). Every re-
frigerant belongs to either group I, II, III or IV. Which group is determined by the most severe
property, whether this is density or the speed of sound in the refrigerant at operating conditions.
It is also a prerequisite that the compressor is running close to ideal VI as any over- or under-
compression will increase vibrations significantly.
To ensure that vibrations are handled safely, all Sabroe VSD equipment must be checked during
commissioning using our VibraGuard tool and procedure, or equivalent. It is the commissioning
engineer’s responsibility to document the equivalence.
Group
Specific volume
[m3/kg]
Average speed of
sound in gas
[m/s]
Examples of refrigerants
usually in the group
I
< 0.0167
< 175
R507, R404A, R410A
II
< 0.0333
< 300
R134A, R407(A+C+F), R22, CO
2
(R744),
R32, MR gas
Note 1
III
< 0.3333
< 500
(some exceptions)
Ammonia (R717), Propane (R290)
IV
> 0.3333
> 500
Steam (R718)
Note 1: Even though MR gas is typically in group II, be aware that the possibility of performing
hot work (welding) on site may be limited due to flammability. In such case, variable speed appli-
cations must be avoided.
•
Lower speed of sound enables the gas to resonate in smaller volumes
•
Lower specific volume (larger density) increases the amplitude (severity) of the vibration.
Summary of Contents for Sabroe SAB 193 L
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