When selecting a submersible pump for your plant, you want the pump that is going to best handle the liquids and waste you deal with on a daily basis. But, choosing the right pump is step one. You need to make sure that you’re maximizing pump performance to the optimal level. Not only will this ensure you prolong the life of your submersible pump, it will minimize downtime and save maintenance and repair costs.
In general, it’s best to factor in the concepts below during the selection process. A high-quality manufacturer or distributor will help you capture the information they need to make the right recommendation and to install it to perform optimally. But, even if you’re looking to improve an already installed pump, these tips apply.
Operate at the Best Efficiency Point
Best efficiency point (BEP) is defined as the flow at which the pump operates at its optimum efficiency for its impeller diameter. At BEP, you reduce the radial and axial loading on the bearings to the lowest possible value for that pump. For shredder pumps, this is the best balance point between passing solids through and having enough time to shred them sufficiently. If the flow is insufficient, the velocity will be too low to move the solids through the system. Solids in the fluid will likely drop out and settle out in the piping system, potentially leading to clogs. If there is too much velocity, the flow moves too fast through the pump and solids may not get shredded enough and cause clogs.
Either scenario causes inefficiencies as the radial loading increases. Continuous failures, such as seal failure due to shaft deflection or repeated bearing failures, are signs that you are too far away from your BEP. An orifice plate or throttling valve can help to increase total dynamic head, or a bypass line back into the wet well can allow more flow through. This bypass line will also provide the benefit of mixing the wet well and breaking up large clumps of solids.
Minimize the Number of Pump Cycles per Hour
Balancing the influent rate and discharge rate minimizes the number of pump starts. The influent rate is the water coming into the sump, while the discharge rate is the amount of flow the pump is producing. If you have a wet well that’s too small, you’ll have to fill it up and drain it down repeatedly. You may end up short-cycling the pump every minute or two until the motor overheats and fails. Fewer cycles keeps the motor cooler and the pump running more smoothly.
There are a number of ways to minimize the cycles, including:
- Change the pump size to better meet the influent rate. Closely matching the influent rate and discharge rate keeps the water level in the pit fairly constant. A higher influent rate fills the pit faster than the pump can discharge the water. A higher discharge rate draws the liquid down very quickly and increases cycling.
- Increase the basin size. This is much easier to do when installing a pump. For existing installations, Increasing the size of the basin can be an expensive option.
- Use a variable frequency drive (VFD) to keep the wet well level at a constant level. VFDs control the motor by taking power going to the pump and shifting the frequencies to fluctuate the pump speed. This is recommended for all submersible pumps, except shredder pumps. It’s the most efficient way to minimize starts, but on shredder pumps it reduces the torque available for shredding and could result in clogging.
Match Pipe Size to Pump Size to Increase Velocity
A velocity between 2-4 feet per second used to be enough to minimize the wear of the piping system. With flushable wipes and more solids in wastewater systems, you now need to aim for seven feet per second to avoid solids settling out in the line and plugging the system.
For slurries and heavier solids, you may need even more velocity. It depends on the specific gravity and concentration of the solids in your liquid. If you don’t have enough velocity in the vertical leg, the solids will sit and swirl. When the pump stops, they flow back into the pump and cause clogging.
The pump size should match the pipe size. For example, you should use a 3-inch pump if you have 3-inch piping. Velocity is heavily affected by the pipe size. It’s critical that pipes are not oversized or undersized. Oversized piping requires higher velocity to keep the solids from falling out of the flow and clogging the system. Undersized piping increases the head to the system. This leads to more friction and less flow.
Additional Optimization Tips for Installed Pumps
As mentioned above, these recommendations are best handled during pump selection and installation. But, for those with installed pumps, these additional tips will also help minimize your repair costs:
- Install a lift system for pulling the pump. Don’t pull it by the power cord.
- Install a seal fail circuit (BJM offers Seal Minder® for most pumps). This is an inexpensive addition (if not included) and alerts you of leaks so you can change the seals before the water gets into the motor and causes damage. If you already have a seal fail circuit, be sure to hook it up!
- Conduct preventive maintenance every 6 months. Pull your pump to check oil, seals, the impeller, etc. A little preventive maintenance can save much bigger repair costs down the road.
- Before putting the pump into the sump for the first time, check the rotation to ensure it is not running backward. It’s not a common issue, but it does happen from time to time.
Since 1983, BJM Pumps and our highly-qualified distributors have partnered with our customers to recommend reliable, long-lasting submersible pumps for their specific applications. We have the expertise to help you maximize your pump’s performance. Customers receive unparalleled service from specification through installation and continued support throughout the life of the pump. Contact us or call us at 860-399-5937 for more information.