Among the many decisions you can make to secure the lowest pump operations cost, the most important one still remains to be choosing the right control for your application.
The easiest way to choose the right one is to carry out a short cost-benefit analysis of the prospective control methods, starting with the head capacity curve interactions and anticipated operating flow needs, the preliminary cost of the drives and any other necessary equipment. Eventually, you can calculate the return on investment for all of the promising control methods.
Few of the commonly used pump control techniques include:
- Variable speed operation
- Control vale operation
- Start-stop level control operation
- Bypass valve operation
Variable Speed Operation
Variable Frequency Drivers that can match the motor speed to the load are typically the perfect option where efficiency in flow and operation is a top priority.
These control systems work perfectly, particularly under conditions that involve high operating hours and significant load variations. At the same time, these controls also cut down the need for starters and throttle valves.
The most important reason to implement VFDs is its ability to considerably cut down energy costs. This happens due to the speed reduction. The larger the reduction, the more the savings. At the same time, they also offer a number of other benefits like:
- Increased life of the pump by maintaining low speed
- Soft starting reduces the effect on the motor, pump and supply network (they cut down inrush current on startup)
- Also offer diagnostics and fault protection
Start-Stop Level Control Operation
When it comes to sewage lift pumps, this is the most commonly used method for flow control. Depending upon the application, this method can be the most efficient option as the pump can operate without any bypass valves.
The pump turns off when the pressure reaches the designated low point and starts when it reaches the designated high point, which is done with the help of sensors.
Multiple parallel pumps can further increase the efficiency when combined with start-stop level control operation.
However, depending on the application, a start-stop level control operation may come with some complications:
- This method may put additional stress on pump motors. Particularly heavier duty motors might wear out sooner as they are unable to start-stop frequently
- This may lead to damage at lower sump levels as it also requires changing the NPSH available to the pump
Control Valve Operation
A control valve operation is typically a low cost pump flow controlling method, but it is rarely as efficient as other control methods. They work by boosting the pressure drop and compelling the pump to operate back on the H-Q curve. The problem is that the drop in pressure and the energy consumption for this method can be significant.
For lower specific speed pumps, a discharge control valve may be the best option on flat H-Q curves where the flow doesn’t change as much and the pump doesn’t need to be operated as often.
Bypass Valve Operation
Bypass valves are often used to stop the pump from functioning at minimal flow rates to safeguard the pump from potential wear. They are rarely used to control the flow. This control method may be best for high-specific speed pumps on flat H-Q systems where the rate of the flow doesn’t change as much.
If you are looking for efficiency, it is a good idea to use bypass flow instead of a valve in the discharge line on high-specific speed pumps.
These are some pump control methods that are commonly used across different centrifugal pump applications. Other types include hybrid control, parallel operation of multiple motors and multiple speed motors that we’ll highlight in the next blog post.
Looking for high head centrifugal pumps or still unsure which control method to use for your centrifugal pump application? Feel free to email us at firstname.lastname@example.org