CHAPTER 2 Laboratory Rig and Experimental Procedure for
2.2 Laboratory Rig and Experimentation
2.2.3 Faults Considered on the CP
Figure 2.4: Accelerometers mounting position
Figure 2.5: Current probes measuring motor line current
be many reasons why hydraulic CP faults may arise. However, some of those causes are considered in the present work.
I. Suction blockage
The low pressure side or the piping carrying the fluid to the CP from the sump is called as the
‘suction side’ of the CP. The suction pressure is generally low so as to draw fluid to the CP.
Whenever the suction side is clogged (or blocked or flow is restricted), the pressure further drops at the eye of the impeller to overcome the resistance. In addition, the fluid entry angle at the inlet changes, resulting in the flow recirculation. This type of flow recirculation results in low pressure pulsations and thus leads to the bubble formation, formation of it inside a CP is dangerous as it results in a cavitation like damage and head loss resulting from the energy expended in compressing the air bubbles.
To simulate the suction blockage (SB) condition, a mechanical modulating valve which can be seen in Figure 2.6(a) is placed on the inlet hose pipe connecting the CP. As the restriction to the flow increases the associated recirculation and bubble formation also increases. This valve is calibrated so as to give six different levels of flow restrictions between 0% blockage and 100% blockage. The line diagram of the calibration is shown in Figure 2.. The different flow restrictions are depicted by SBk. where, ‘k’ stands for k/6th suction blockage restriction.
Though six different blockages may be administered on the CP using the modulating valve, only SB1, SB2, SB3 and SB4 are considered to be the suction blockage conditions.
Figure 2.6: (a) Mechanical modulating valve with markings; (b) cracks on the impeller; (c) pitted cover plate
Inlet Outlet
No Flow
B5 B4 C0 B3
B2 B1 B0
Rotatable knob
Figure 2.7: Line diagram showing different blockage levels II. Discharge blockage
The second type of fluid-flow abnormality is induced by clogging the ‘discharge side’ of the CP. Discharge side basically refers to the high pressure side or outlet of the CP. Whenever the CP outlet is restricted, the discharge flow rate drops and thus the load on the impeller vanes increases. This again results in a suction recirculation and bubble formation.
To obstruct the flow on the discharge side, a mechanical modulating valve placed on the discharge pipe is used. A calibration similar to that of the suction blockage modulating valve as shown in Figure 2.6(a) and Figure 2. is used. The discharge blockage fault is given by the
abbreviation DB. Here, DBk. signifies k/6th discharge blockage restriction. DB1 to DB5 levels of discharge blockages are considered in this work.
III. Dry run faults
The absence of priming fluid in the CP results in a ‘dry run’ condition. To simulate this condition on the CP, the flow is restricted on the suction side of the CP. It is observed that when SB5 restriction has been given on the suction side, the CP falls short of fluid. Hence, SB5 condition has been considered as a dry run condition.
2.2.3.3 Mechanical CP faults
Mechanical faults refer to the damages on the stationary or rotating mechanical components of the CP. The different possible mechanical faults in the CP are described in details in Chapter 1. In this work two mechanical CP faults have been considered. They are: impeller defects and pitted cover plate faults.
I. Impeller defects
The impeller is the heart of the CP. The faults in the impeller could be due to manufacturing defects, handling corrosive fluids, erosion of the impeller material due to abrasives present in the fluid, and cavitation damages. Whenever there is damage on the impeller, there is a rotating unbalance that is created and also the head developed by the CP gets affected. Hence, impeller damage is considered as one of the mechanical faults in this work. The impeller faults (IF) have been artificially created by cutting through-through notches on the CP vanes. Two notches have been cut on each vane. The location and orientation of these notches have been kept arbitrary. The IF can be seen in Figure 2.6 (b).
II. Pitted cover faults
The mechanical faults in the CP can also be stationary faults. To account to this, a pitted cover plate fault (PC) is considered. Any deviation in the geometric configuration of the CP from its standard design may result in fluid flow abnormalities and thus affecting the performance of the CP. The PC fault is shown in Figure 2.6 (c). This is also an artificially created fault. On the cover plate, pits of arbitrary depth have been made at random locations. Approximately, 70 pits which are protruding into the CP have been made on the flat surface of cover plate having an outer diameter of 92 mm and inner diameter of 49.98 mm.
2.2.3.4 Combination of CP faults
In this work, apart from considering the independent existence of the hydraulic faults or the mechanical CP faults, the co-existence of them has also been considered. Three configurations of CPs are used for this purpose whose details are shown in Table 2.3. On each of these CP configurations, the suction and discharge blockages are given externally using a mechanical modulating valve at the inlet and outlet of the CP, respectively. The different fault combinations considered in this work are given in Table 2.4.
2.2.3.5 CP faults nomenclature and description
A total of 33 faults are considered on the CP. The nomenclature, description and characteristics of various faults the CP are given in Table 2.5. The faults considered are:
(i) healthy pump (HP),
(ii) suction blockage faults (SB1, SB2, SB3, SB4),
(iii) discharge blockage faults (DB1, DB2, DB3, DB4, DB5), (iv) impeller defects (IF),
(v) impeller defects in addition to suction blockages (IFSB1, IFSB2, IFSB3, IFSB4),
(vi) impeller defects in addition to discharge blockages (IFDB1, IFDB2, IFDB3, IFDB4, IFDB5),
(vii) pitted cover plate faults (PC),
(viii) pitted cover plate faults in addition to suction blockages (PCSB1, PCSB2, PCSB3, PCSB4),
(ix) pitted cover plate faults in addition to discharge blockages (PCDB1, PCDB2, PCDB3, PCDB4, PCDB5) and
(x) dry run faults for all the CP configurations (SB5, IFSB5, PCSB5).
Table 2.3: Three CP configurations used in the current research Configuration
number CP Type Good
impeller
Good cover plate
I Healthy CP Present Present
II CP with impeller faults Absent Present
III CP with pitted cover plate faults Present Absent
Table 2.4: Fault combinations considered in the proposed work Fault combination SB DB IF PC
Healthy CP Absent Absent Absent Absent Only SB Present Absent Absent Absent Only DB Absent Present Absent Absent Only IF Absent Absent Present Absent Only PC Absent Absent Absent Present Both IF and SB Present Absent Present Absent Both IF and DB Absent Present Present Absent Both PC and SB Present Absent Absent Present Both PC and DB Absent Present Absent Present
Dry run Present Absent A Absent
Dry run with IF Present Absent Present Absent Dry run with PC Present Absent Absent Present