The type of application will determine whether a dry or submersible pumping solution should be installed; in some cases a solution combining both dry and submersible pumps can be the best option. This article outlines the benefits of submersible versus dry installed pumping and shares some general rules to bear in mind for both applications.
By Kristoffer Kratz, Product and Application Manager, Xylem
In a dry installation, the hydraulic end and the drive unit are located outside the sump. When using a submersible pump for a dry installation, the slurry pump must always be installed with a cooling system. Consider the design of the sump in order to feed the pump with the slurry. An agitator and side-mounted mixer cannot be used in this installation method. Mixers on guide bars in the sump / tank should be considered in order to keep solids in suspension to avoid settlings in the sump/tank. When investing in a slurry pump, you want to pump slurry, including solids, and not just dirty water. Therefore, it is important to make sure that the pump is doing just that; by using an agitator the pump is fed with solids and will pump slurry.
In a submerged installation, the slurry pump operates directly in the slurry and requires no support structure, meaning it is flexible and easy to install. If possible, the sump should be equipped with sloping walls to allow the sediment to slide down to the area directly under the pump inlet. An agitator should be used when the liquid contains a high volume of solid content and when the density of the particles is high. A stand-alone or a side-mounted (submersible) mixer is an excellent option to re-suspend the solids, especially when the sump is large or lacks sloping walls. A mixer can also help the agitator when pumping very high density particles. In applications where the sump volume is small and / or there is a wish to pump down to lower water levels in the sump, a slurry pump featuring an internal cooling system should be considered in order to avoid the stator overheating (when the water level gets low). A raft installation, which is a type of submersible installation, can be considered when pumping sediments from dams or lagoons. An agitator is recommended, as well as one or more mixers that can be mounted to the raft or to the pump in order to re-suspend particles so that particles can be successfully pumped.
Submersible pumps offer a number of benefits over dry and semi-dry (cantilever) mounted pumps:
• Reduced space requirement - As submersible slurry pumps operate directly in the slurry, they do not require any additional support structures.
• Ease of installation – As the motor and volute are one integrated unit, a submersible pump is relatively easy to install.
• Low noise level - Operating under water results in a low noise level or even silent operation.
• Smaller and more efficient sumps – As the motor is cooled by surrounding liquid, up to 30 starts per hour can be achieved by submersible slurry pumps, resulting in smaller and more efficient sumps.
• Flexible installation – Submersible slurry pumps offer several installation modes, including portable and semi- permanent (also easy to move around since it can hang freely from a chain, or similar, without having to be bolted to the ground/floor etc.).
• Portable and low maintenance - There is no long or exposed mechanical shaft between the motor and the volute which makes submersible pumps much more portable. In addition, since there are no long or exposed mechanical links between the motor and the volute, less maintenance is required, and operating costs are significantly lower.
• Reduced operating costs - Generally, submersible slurry pumps require much lower operating costs than dry installed pumps due to higher efficiency.
If you would like to read more of this article please contact the editor Deirdre Morgan