R and R Lift Station Services in Tampa Bay gets this question all the time from its customers. The most common way is to check how efficient your pumps are and have it reviewed for maintenance once problems occur. The longer you wait to have it checked, the higher your electricity bill will be.
Lift stations have gone through technological advances since the 1960s with the liquid rheostat. This device controlled wet well levels to reduce motor starts. A Variable Frequency Drive Level Control was introduced to reduce motor starts. The way it worked was a bubbler system was used to determine the level of a wet well to control a linear motor that would raise and lower to keep the level of water running smoothly.
Variable Frequency Drive Control System
Although the process of the liquid rheostat was efficient, the heat that the device generated did not help with potential energy savings. As a result, the pump would run at low optimal speeds to keep it from stopping leading to low hydraulic efficiency.
One of the benefits of VFD is a perfect level control does not have to be programmed. When inflow goes below the acceptable minimum, the drive stops the pump and restarts it at a later time. When it restarts, it begins at a lower frequency and ramps up to the programmed pump frequency. Level control may not work for every lift station since it is better for stations that have a few starts per day.
In addition to using VFD Level control, a soft start and stop can delay the pump and motor life. This helps with reducing costs by using a smaller wet well requirement. A cost efficient variation on level control is another option to using smaller pumps. For example, variable fixed speed (VFS) control is used vary the speed of a pumps inflow with float switches.
Stay tuned to upcoming R and R Lift Station Services blogs for more topics and advice.