Sizing eductor nozzles
Eductor nozzles are positioned under the surface of fluid in a tank in order to keep the liquid in motion. The liquid in the tank is circulated through the eductors so that it is 'turned"' over a period of time to ensure that sedimentation or liquid separation does not occur. Eductors have gaps at the back of the nozzle casing that allows surrounding fluid to be drawn in and moved in addition to fluid being pumped through the nozzle. This means that about 5 times the pumped fluid is actually moved by an educator.
Like all nozzles eductors have a flow rate that is proportional to the pressure drop across the nozzle. So it is a simple matter to consult the flow rate vs pressure charts for eductor nozzles to determine how quickly they will turn the fluid in the tank. One 'turn' is defined as moving the whole volume of fluid contained within the tank. So, given that eductors move 5 times their motive flow rate, eductors should be sized to 'turn' 1/5th of the fluid in the appropriate time.
The 'turn' time will vary greatly depending on the application but typically :
A general circulation of fluid with no solids only 1-3 'turns' per hour will be required.
For mixing fluids to keep solids suspended between 5-10' turns' per hour are required.
For plating and rinsing tanks between 10-25 'turns' per hour are required.
For blending applications anything between 20-120 'turns' per hour
These are general rules of thumb and some variations outside these guides may occur fro specific applications.
It is very common to attach eductors to pipework with adjustable nozzle holders that allow for the eductor to be moved 45 degrees in two dimensions. This means that the final plume directions can be adjusted in the field for optimum coverage.
We offer two ranges of eductors. For metal nozzles the Turbomix eductors offered by SNP are made as standard in 316 stainless, cast iron or brass but in principle can be made in any metal desired. The Uni Eductor from Uni-Spray is made in either glass filled polypropylene or PVDF (Kynar) and form part of the Quik Fit system for pre-treatment spray tunnels. Datasheets on both ranges can be accessed by clicking on the boxes below.