Pumps become intelligent
Intelligent pump condition monitoring reduces LCC

Dipl. Ing. Gerhard Berge, KSB Aktiengesellschaft

Pumps are important parts of processes and plants. Their failure free operation is important for a good process - availability and - quality. The use of electronics can improve their operation and availability. The pumps take care of the transport of liquids in plants and processes. If they stand still, the result can be loss of production or even failure of entire hydraulic systems. The more expensive a pump is or as more valuable a process is, the more important it is to regularly record and control the condition of the pumps. As pumps also react to changes in a plant, they are also indicators of the conditions prevailing there.

In order to achieve real process improvement, it is important to find out the cause of failures and disturbances. With respect to centrifugal pumps, this could be the following:
· defective mechanical seals point to dry-running or partial-/ over-load
· damaged rolling element bearings are the consequence of gas content of the pumped medium
· eroded impellers and casings are the result of cavitation.
This shows that the determination of the pump condition allows for the drawing of conclusions regarding the condition of the process.
In order to increase the availability of plants, this knowledge constitutes an important approach and starting basis for a new, intelligent development in the area of monitoring the condition of centrifugal pumps. The goal was to be achieved with a minimum of sensory devices. An analysis of failure statistics of service units and operators (Fig. 1) showed that 2 to 3 sensors suffice to detect the most important faults of a pump.
· Dry-run recognition
· Bearing temperature
· Vibrations
It is important to the user of such a system to have a simple, clear and easy to understand presentation of the pump condition. This eliminates a solution where the measurement values are connected each to a separate conditioning device (Fig.2) and each value having to be interpreted separately by experts. In this case the user would have to draw his own conclusions from the combination of reports. A first step in the direction of benefit from the knowledge gained resulted in the definition of the threshold value for early warning signals. However, this solution requires a well founded pump knowledge on the part of the user in order to define the appropriate magnitude of the threshold value. If however the goal is preventive maintenance, the solution only has limited significance with respect to the general pump condition. It does not at all allow conclusions regarding plant-induced influences. When identifying impermissible operating conditions, the question also is which pump components could be damaged. Therefore, the analyses may not be limited to a simple, singular recording of threshold values. An intelligent combination of information which each sensor supplies, makes it possible to draw conclusions with regard to pump and plant which clearly exceed the interpretation of individual values. The utilization of micro-processors allows the linking of individual data and signals (Fig. 3). The application of “fault tree analysis” is thus possible in principle. However, it requires high computer capacities in order to generate really predicative information. For this reason a simpler solution was sought. The result was the use of the fault table which is derived from the fault tree. The fault table links/compares several data/signals according to the principle “ if... then” and deduces from this accordingly predicative information. This generated information can be transmitted very easily instead of the original large data quantity.

Data become Information!
For this purpose, a programme was developed which can be stored in a micro-processor and which must be adapted specially to every pump type series. Practice has shown that individual values can be in an “acceptable range”, the combination however may well signalize a critical condition. Example: Bearing temperature warning “yellow” plus vibration warning “yellow” at the same time can cause a “red” traffic light! With the use of this method of fault table (Fig. 4), this can also be recognized. Thus pump components at risk can be localized in time and in part even the cause of the pro­blem can be determined. To assure easy handling despite the existing complexity and large data quantity, a simple traffic light information – green, yellow, red – is made available. If needed, e.g. depending on the condition, further details
can be requested and presented to the pump user such as for example the following messages:
· Dry-running
· Rolling element bearing defect
· Impeller blocked
· Viscosity of pumped medium too high
· Alignment mistake
· Plant not filled
· Medium contains too much air or gas
· Flow cut off
· Cooling of motor bearing bracket disturbed by cooling air of motor
Additional information like operation time counter, start/ stop counter etc. is available to get a general impression of the pump status.
Besides the overall information by the traffic light and the precise diagnosis messages supplied the user retains full access to the data collected from the sensors if requested. Thus the expert on site can use the general pump knowledge at his hand to analyse and improve the individual process. An additional specialty of the system is that it not only creates precise diagnosis messages but also instructions for adaequate actions. Such detailed information can only be generated by the one who best knows the behaviour of the pump and that is the pump manufacturer.
These findings constitute great progress in the improvement of pump availability and even of the entire process. They facilitate service and maintenance and enable the user to take first steps in the direction of preventive maintenance. A digital, bi-directional data transfer, e.g. on Profibus-DP basis, transmits electronically the information calculated out of a multitude of collected data to the control station. Thus details on the pump condition can be requested from a distance. When realizing a product, recourse should be had to less expensive components which nevertheless are flexible in their usage. Furthermore, the components should be introduced on the market in order to assure high reliability and stable functionality as well as a trouble-free acceptance by the users. An explosion protected version for installation in Zone 1 should be relatively simple to realize. The decision, when selecting the electronics, fell to an intelligent entry/exit modular system supplemented by a mini-PLC (programmable logic controller) with different fieldbus-interfaces, e.g. Profibus-DP (Fig. 5). In the mini-PLC, the software of the pump manufacturer is stored which does the evaluation of the data by means of fault table analysis. Thanks to the open structure, different types (Fig. 6) and also other pump makes can be equipped with the new “Pump Expert“. Depending on the pump design, sensors will be mounted to the unit upon delivery and thus delivered in cabled condition. Even already on site mounted pumps can be equipped. With the Profibus, detailed data can be called for when needed and presented (Fig. 7). All components are mounted as a device in an enclosure of class IP 54 on top hat rails (Fig. 8). This robust casing enables the mounting on site at the pump and thus the cabling costs are reduced drastically. As sensors, all standard models on the market can be used, even those already available in the process. For the explosion protected design, intrinsically safe sensors are used, the remaining electronics will then be mounted in a pressure-proof enclosure. With the new concept, combining a minimal number of sensors to an intelligent unit with the aid of a programmable logic controller, the process quality can clearly be improved in an economic manner especially for critical plants and expensive pumps. Installation, commissioning and maintenance costs are reduced because alignment mistakes or dry-running are discovered immediately. With the use of advance alarms, standstill periods can be kept very short or even be completely avoided. Environmental impacts and leaks are prevented by timely recognition. The availability of the plant is thus significantly increased. That means Pump Expert S makes an important contribution to the reduction of life-cycle costs of the pump as well as of the plant.