When a pump fails, the pump manufacturer is typically blamed even though the reason for the failure may be due to external conditions beyond the scope of the pumps design. These conditions include, but are not limited to, frequent dry running, rapid cycling, and incoming voltage problems.
Modern microcontroller-based protection devices will detect these harmful conditions and take the appropriate pump-saving actions. Such devices are both cost-effective and highly reliable. When the cost of replacing a pump is compared to that of installing protection, no pump should be without it.
The basic system
Lets start with a simple automatic water system. This consists of an electric motor coupled to a mechanical pump, a pressure switch, and a pressurized water tank. The pressure switch is used to tell the motor / pump when to run and when to shut off. The water tank supplies pressurized water when the pump is off and provides a reservoir for the pump when its running.
What can go wrong?
In the above system, three major issues can arise: input voltage fluctuations, low-to-no fluid flow, and component failures.
1. Input voltage fluctuations are caused by dynamic loads attached to the public utilitys power distribution network. These loads will cause over voltage and under voltage conditions at the motors input terminals. Such-out of-range input voltages will cause an increase to the motors current draw (current always goes up in a synchronous motor, regardless if voltage goes up or down). This increased current will increase the motors heat load and excessive heart kills motors.
2. Low-to-no fluid flow can be caused by many things, such as sand blocking the input to the pump or a partially closed valve restricting output flow. Regardless of what is causing the reduction in flow, it is important to note that pumps are cooled by the movement of fluid through them at their full rated flow rate. Anytime the flow rate is reduced, the pump will experience less than perfect cooling, and hence, run hotter. This can result in reduced life of its moving parts such as bearings, pump shaft etc.
3. As with any electromechanical system, its the mechanical pieces that have the higher failure rates. If a pressure switch or tank bladder fails, the pump may be subjected to rapid on-off cycles, known as rapid cycling. This constant on-off, on-off will hammer the pump and its internal parts indefinitely (until it breaks or someone notices the problem and intervenes).
What will pump protection do under such conditions?
Modern microcontroller protection circuits monitor input voltage, current, and sometimes power to the motor in an effort to detect any of the previous three conditions described - regardless of their cause- and will take the appropriate actions (usually turning the motor/pump off until the fault has been removed)
Measuring the input voltage for out-of-range conditions is obvious and quite easy to do accurately. The trick comes in knowing what happens to the input current (or power) under other various fault conditions. If the protection device trips too soon, there will be nuisance outages and customer complaints, while tripping too late will generate junk and customer complaints so its fine balance. The better protection devices have proprietary software algorithms for controlling the motor/pump, dependent on the magnitude of the current (or power) over the time span of the anomaly.
So what if something goes wrong?
Well just replace the parts when it does.
This will work, but Its like driving a car without insurance its free until you have an accident, then your out-of-pocket expenses will be very large. The same is true for an unprotected water system requiring service. The minimal cost to roll a service truck for a repair visit is about Rs. 1200 nationwide. Add the cost of parts and any additional labor required to repair the system, and its easy to run up a Rs.2000 invoice for the simplest of service call. When this additional investment is compared to the cost of the service call, its easy to see that the protection is less expensive than the very first service call.
Because distributors and tradesmen enjoy healthy discounts off these prices, its easy enough to sell your clients the added protection. When you point out to them that its not a matter of if something will go wrong, its just a matter of when they ll see the benefits outweigh to additional upfront investment.
By the way, both the service call prices mentioned as well as the product costs are for single phase systems. Three phase systems will have even higher services expenses and replacement costs, while three phase protection devices increase only modestly in price.
So, is pump protection really worth the expense?
Whats your companys reputation worth? How happy would you like your customers to be?
Do you want to return to a job site only a few days to explain to the customer that his equipment needs to be replaced as is not covered under a warranty?
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