In today’s complex and frequently rugged process plant environments, liquid pumps are often over-worked and under-protected from adverse operating conditions. Many pumps run nearly non-stop 24-hours a day over multiple shifts. Poor operating conditions can reduce pump performance, require extra maintenance, shorten their lives and increase costs.
Unexpectedly losing a pump is often an expensive or even a dangerous problem in a chemical plant. The results of a pump failure potentially range from the loss of product in sensitive pharmaceutical batch control applications to damage to other nearby equipment from pressure build-up of material that isn’t moving, or even to safety hazards when a pump fails to shut down and literally burns up in the presence of combustible materials. It really pays to protect and care properly for pumps.
Adverse pump operating conditions
Two of the more common problems that can negatively affect pumps are wet/dry conditions and flow disturbances – both of which are preventable.
Nothing damages a liquid pump faster than the heat built up from dry running conditions, which occurs when liquid stops flowing into the line or the pump. When the liquid isn’t there to provide cooling, the heat can destroy a pump’s bearings. If repair is even possible, it is going to be an expensive proposition. For proper and efficient operation, pumps require a stable upstream flow profile in the pipeline before liquid enters the pump. When elbows, valves or other equipment are installed too close to a pump, these other devices can create swirl and velocity profile distortion in the pipeline. These disturbances can result in excess noise and cavitation, resulting in reduced bearing life.
Wet/dry conditions
Installing a point flow/level switch in a pump’s process loop eliminates the damage caused by a pump running dry. Point flow/level switches are capable of detecting not only a low flow situation, but also detecting a dry running condition. This capability allows the control system or operator to take corrective measures before the bearings of the pumps are overheated and fail. Among the many types of point flow/level switches available is FCI’s FlexSwitch FLT Series, which offers dual alarm capability.
Alarm 1 will detect a low-flow situation, which can be regarded as a pre-warning signal for the control system or operator. The system or operator can then decide to keep the pump running or to shut it down.
Alarm 2 occurs if the feed line to the pump is running dry, which would be an emergency signal to shut down the pump because the bearings now see gas instead of a liquid as a heat transfer medium. In this case, the temperature of the bearings may rise very fast. The flow switch prevents permanent damage to the pump’s bearings.
This flow switch is a dual-function instrument that indicates both flow and temperature, or level and temperature sensing in a single device. Available in either insertion or in-line styles for both pipe and tube installation, a single switch measures and monitors flow or level and temperature simultaneously with excellent accuracy and reliability. Dual 6 A relay outputs are standard and are assignable to flow, level or temperature.
The switch operates over a wide flow range, making it suitable for liquid pump protection. Switch point accuracy of 2% and measurement repeatability of 0,5% of reading ensures accurate, reliable operation. The standard configuration withstands operating temperatures up to 175°C, with optional versions available up to 455°C.
Conclusion
If liquid pumps are an important part of a process, then make the investment to protect them from dry running conditions and flow disturbances. You’ll not only ensure that your pump lasts longer, but you just might improve the efficiency of the process, reduce unnecessary maintenance costs and prevent accidents.
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