# Fault Investigation of Circulation Pumps to Detect Impeller Clogging
## 2 Materials and Methods
### Experimental Setup  
To find out whether the above-mentioned faults can be detected, a test bench is required. This test bench must fulfill two different requirements. The first requirement is that the test bench has to provide all relevant data. This includes an accurate acquisition of the motor currents with a high sampling rate and the acquisition of static variables such as current, voltage, flow and head. Due to the background of testing circulation pumps, the second requirement is that it should be possible to carry out life-accelerated tests. In order to record the wear process of a pump during a life accelerated test, the test bench must allow automatic data acquisition. The design and measuring the concept of the built test bench is explained in the following. Two hydraulic circuits were combined into one test bench (see Figure 2). Each hydraulic circuit consists of five parallel vertical pipes. The larger circuit (see 1 in Figure 2) had a nominal diameter of DN 100 and the smaller one 2 had a nominal diameter of DN 80. Pumps can be installed in the three middle pipes. The medium flows through the outer pipes back to the suction port of the pumps. Additional radiators 3 were mounted on the back of both hydraulic circuits, which can be switched on if the medium temperature is too high. Shut-off valves 4 were installed in each of the central pipes on the suction side and the pressure side. They allow a complete separation of the single pipes, but also the change of the hydraulic resistance and thus the load of the pump in a pipe strand. In addition, pressure sensors 5 (IFM PU5415) were installed in each pipe strand on the pressure and suction side of the pump. They measure the differential pressure provided by the pump. The measuring signal of the pressure sensors is transmitted to the data acquisition system (NI USB-6363) via an 0-10 V signal. Figure 2: Test bench for condition monitoring and life accelerated tests of circulation pumps. Sophisticated safety technology is particularly necessary for life-accelerated tests. For this reason, an electronic pressure switch (r) (WIKA PSD-30) and an electronic temperature switch (r) (WIKA TSD-30) were used in both circuits. Both were integrated into the enabling logic of the energy supply to the pumps. The pressure switch enables an absolute pressure of 1 bar or more, which ensures that no pressure loss of the test bench, e.g., due to leakage, occurs. It closed from a pressure of 5.5 bar. The temperature switch enabled temperatures of up to 50 \({}^{\circ}\)C. As a safety switchgear a Siemens 3 TK2825-1 BB40 is used. An electronic time relay (3 RP1555-1 AP3O) is additionally integrated into the enabling logic. This makes it possible for the supply to the pump to be automatically switched on and off for certain periods of time. The electronics and safety technology are designed for pumps with a one-phase connection. Pumps with a three-phase connection can be tested on the test bench, but cannot be integrated into the safety engineering. The electrical components are located in a control cabinet (r). Additional mechanical protection was provided by a pressure relief valve, which is triggered at a pressure of 6 bar (r). A circulation pump (r) with a maximum power consumption of 1.1 kW and a nominal pipe size DN 50 was used as a test item. The functional principle is based on a wet-rotor pump driven by an 8-pole PMSM. The motor was fed by an integrated converter with the option to set the speed to any value between 1000 and 3000 rpm. The impeller was designed as a radial impeller with seven blades. The pump data can be transferred via a Modbus interface. The pump supplies important parameters such as flow and head. The typical accuracy of flow estimation of that kind of circulation pump is 5% of the final value [8]. The measurement of electrical values is designed in such a way that only one pump can be measured at a single time. With the help of the power analyzer Yokogawa PX8000 (r) the one-phase input values (U, I, power factor) of the pump are measured.