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- 17 December 2007 -

Pump monitoring and communications

Improving the utilization of plant assets involves careful monitoring and control of plant and equipment so that action can be taken to prevent any unplanned outages and to ensure that optimum efficiency is attained. This means more and better-automated monitoring and communication of data in a form easy for engineers and managers to assimilate at any location. Bryan Orchard looks at a cross-section of product and equipment offerings coming onto the market.

Monitoring does not require ultra-advanced technology to detect parameters such as temperature, vibration and loss of lubricant in a simple condition monitoring scenario. Many pump manufacturers are in fact now including their own condition monitoring modules and automatic control devices either as standard or as an option. Clearly, much more advanced techniques and systems, particularly for vibration detection, are available where justified but these are not cost effective on the vast majority of simple rotating devices.

Data transmission

"Transmitting the data collected from the device itself to a central computerized analysis facility presents a challenge, for it is generally the last 20-50 m that is the most difficult to overcome cost effectively," comments Mike Knights of Southampton, UK-based telemetry experts Pacscom. "Low-power wireless, of which there are now many technologies, solves this specific problem. Collecting and transmitting condition data (temperatures, vibration alarm signals, oil loss alarm data) from the actual plant housing or control box to a collection point within the wireless range is well within the performance characteristics of many current wireless technologies," he continues. A number of competing solutions at 868 MHz and 2.4 GHz exist, although in the environment of a pump hall 868 MHz is likely to be the more robust and by using mesh network techniques will be able to avoid any shadowing or radio frequency (RF) dead spots. "Prior to these wireless options, the cost of adding signal cabling to all rotating assets was prohibitive, particularly retrospectively," Knights explains.

Once off the pump set and received into a hub station or similar device, a link onto the site-wide LAN or an additional wireless link back to a central office is, according to Pacscom, simple to implement with modern systems such as their OpenNET 6000. In fact, with the growth of GPRS (general packet radio service)-based private networks, it is also feasible to put the data straight into an offsite location and have it reported immediately in a maintenance facility many miles away and on demand on a portable laptop browser display.

Temporary bypass systems

Although some manufacturers are sceptical about the level of demand from end-users for sophisticated control, monitoring and remote communications devices as integral components, others have clearly been stimulated by the requirements of specific applications. Controlling temporary bypass pumping systems (Figure 1) is one area that has been exploited by Godwin Pumps.

Michael Ramos, Godwin Pumps' chief engineer, says that a measuring device that can transmit a variable signal - like a pressure or level transducer or a flow meter with an analogue signal output - can be used to relay process variable data to the diesel engine control or the variable-frequency drive (VFD) for varying pump and driver speed. "A process variable is a measurable condition that is directly affected by the speed of the pump and changing system conditions, such as discharge pressure on the outlet of the pump, liquid level in a wet well, inlet pressure on the pump in a booster application, or flow rate at the inlet or outlet of the pump," comments Ramos. The engine control and VFD take that variable signal and compare it to a desired pressure, level or flow rate, then adjust pump and driver speed to maintain the necessary set point. "Operators can make adjustments to control how fast the driver reacts to changes (Figure 2). This is helpful in applications such as drinking water distribution systems, booster pumps, pumping into sanitary sewer force mains and applications that require the pump to match a pressure level or flow condition," Ramos continues.

Used in combination with a multiplexer, temporary bypass pumps can be controlled in a variety of ways. Multiplexers are also helpful in facilitating timed shutdowns and start-ups so that lead and lag pumps can be exercised throughout a bypass project. To further remote monitoring capabilities, temporary bypass applications can be equipped with a Godwin Pumps Auto Dialer, which monitors the inputs connected to it from the pumping application. If emergency conditions are met, the Auto Dialer initiates a user-defined call list. When an emergency contact is reached, that contact can hear a brief, voice-synthesized description of the problem.

The capabilities of an Auto Dialer are varied. In a standard application, an Auto Dialer is an output device that uses a cellular signal to communicate with either a phone line or a data processing centre. It can also be an input device, depending on the availability of AC power.

Wireless communication equipment other than an Auto Dialer uses high-frequency bandwidth below the FCC (Federal Communications Commission) maximum ceiling limit. These devices can be integrated into Ethernet, LANs or RS232 Modbus to match customer requirements. This type of wireless equipment can be used in an input and output function for both diesel-powered and electric-driven pump sets.

Switching technology

The Delta M Corp ( Tennessee, USA ) has been successful in applying its Versa-Switch dual and single-channel switching technology for pump protection. The company's pump protection solution incorporates patented thermal differential technology that has no moving parts that can wear or become stuck. This, says Delta M, gives reliable and superior performance over technologies such as pressure switches and sensors containing seals and diaphragms that may leak.

The effectiveness of this technology is illustrated by its application with a Moyno progressive cavity pump (Figure 3). By using a dual-channel version of the Versa-Switch, the user is able to monitor the presence of fluid, thereby preventing dry start-up. At the same time, the second channel is used to provide a low flow rate alarm and prevent damage to the pump. This is seen as an inexpensive way of prolonging pump life. Delta M reports that many customers install a time delay relay in parallel with the switching contact to permit them to run the pump for short periods to allow pump priming on start-up.

The single-channel version of the Versa-Switch also provides a cost-effective solution for pump protection applications such as low flow alarm and dry line indication where only a single alarm is required. The dual-channel switch can also be set so that one channel alarms on temperature while the remaining channel monitors either flow or dry line conditions.

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