vibration Acceptance Limit for fan /compressor/blower shop test & selecting proper balancing grade for a rotary machine.

1.
VIBRATION ACCEPTANCE LIMIT
FOR FAN /COMPRESSOR/BLOWER
SHOP TEST & SELECTING PROPER
BALANCING GRADE FOR A ROTARY
MACHINE.
Prepared by
Ashik Ahmed
Section Manager
Technical Services
Tel.: +880 31 618972~4; Ext.: 2237 (Office)
Email: ashik.rofy@gmail.com, ashik_rofy@yahoo.com,ahmed.ashik@kafcobd.com
Mobile: +880 1730059920

2.
PART-I
Tuesday, September 17, 2013
VIBRATION ISSUE ON SHOP TEST CONDITION
First of all, we have to go Fan for general purpose Part 7; Specifications for
balancing & vibration (ISO 14694:2003).
On page# 09, Balance & vibration application category (BV) is described.
For Kafco case, the fan application category, BV is BV-3.So, the balance quality
grade is G6,3.

3.
The most important for our case is on 8.3, Page:15, ISO 14694; Fan vibration
limits for tests in manufacturer's work-shop.
Here is the confusion came for rigidly mounted vs flexibly mounted vibration limit.
The flexibly mounted Fan has slightly higher vibration limit. From your pic of site,
we understand that the test bench Fan is on flexible mounted condition. As you
found vibration 3.5mm/s for thrust end and 3 mm/s for fixed end; the value
is well comply with the vibration range.

4.
Again from Balance and vibration application categories (BV categories) ;table
01,we can find that for BV-3, you have to see ISO 10816-3 also.
From ISO 10816 you can find that 2-K-611 & 2-K-613 are in class III
condition having the satisfactory vibration velocity 4.5 mm/s. Both the fans
got speed less than 2000 rpm
CLASSIII
2-K-611
2-K-613
RPM 1486 90 KW
RPM 1480 200 KW
Cause they both have flexible Mounting on the Test shop & flexible Drive ( Flexible
Coupling).
For KAFCO case all are Flexible Coupling.
If you considered 2-K-614 which is in class IV condition having the
satisfactory vibration velocity 4.5~7.1 mm/s.

5.
CLASS IV2-K-614
FAN RPM 4241
MOTOR RPM 1486 310 KWAs the speed is over 2000 RPM so ,it is in Class
IV.Flexible Drive means the Coupling.For KAFCO case 2-K-614 has Flexible
Coupling. The Table is given below for your better understanding.

6.
PART-II
Thursday, September 19, 2013
Dear
Thank you for your valuable response regarding the FAN BV category.
First of all you consider balance & vibration application category BV-4.
On ISO14694:2003), page# 09 the BV value is given.
BV-4 came from balance & vibration chart considering the process gas/hazardous gas,
balance quality grade G 2.3 & driver power > 37 KW.

7.
Again from opposite site;
Fan for general purpose
Part 7; Specifications for
balancing & vibration (ISO
14694:2003), on page# 10,
Table: 02, Balance quality
grade is described. Then, if
you consider the fan
application category, BV is
BV-4; the balance quality
grade is G2.5.
Considering BV-4 from
ISO 14694 on Table 8.3,
Page: 15,; Fan vibration
limits for tests in
manufacturer's workshop. The vibration limit is
r.m.s 2.8mm/s for flexibly
mounted Fan.
Although the peak value is
3.8 mm/s.
So, if you consider
BV-4; the shop test
value (3.5 mm/s) is

8.
found higher than the nominal criteria.
Actually now we are in condition where it is hard to say which will be actual process.
If you go through the ISO 1940 table-1 Page #11; Fans are in balance quality grade G 6.3.
For balance quality G 2.5; the following equipment's are considered:•
Compressors
•
Computer drives
•
Electric motors and generators (of at least 80 mm shaft height), of maximum rated
•
speeds above 950 r/min
•
Gas turbines and steam turbines
•
Machine-tool drives
•
Textile machines

9.
So, if you want to proceed with ISO 1940, Fans are in Balance quality grade G 6.3.
But the problem is Form our existing 2-K-601 & 2-K-603 test run balancing report which
shows the grade is G 2.5.The UIPL specification sheet filled by FSV do also indicate that
the grade is G 2.5.

10.
The balancing report shows that the maximum vibration on test run was 2.1 mm/s with
flexible mounting condition .FSV also did mention on that time (26.05.1993) max vibration
is 4.5 mm/s.
But the reference is not found. (Compatible ISO Standard)
That means the residual permissible specific unbalance is 16~17 g.mm/Kg for 1500
RPM.But if we consider Balance quality grade G 6.3 the residual permissible specific
unbalance is more 40 g.mm/Kg.So,the tolerance is higher in case of Balance quality
grade G 6.3.

11.
CONCLUSION
So, If we consider G 2.5; we prefer that rotor balancing should be done from the
Fan vendor site as it is a new machine. Although we are well capable & has
completed successful mass balancing for Fan (2-K-601) we don’t prefer field
balancing during the installation to push the vibration level lower.
If you want to proceed with ISO 1940, Fans are in Balance quality grade G 6.3.
And considering balance quality grade G 6.3 the vibration value 3.5 mm/s is
acceptable from our side.
But as we required balance grade G 2.5 on our Data Sheet (Although it is a over
demand for a Fan perspective);we can’t accept the test value vibration of 3.5mm/s.