When fluids are transported through a process system, a number of problems can arise. Products must be free or air for centrifugal pumps to work properly. If fluid levels in the suction side of a pump get to low, cavitation can occur. To ensure constant, uniform flow, suction head must be kept constant. Previous posts have focused on issues like pump suction and cavitation. Today we’ll build upon this and discuss balance tanks and their application in metering and dispensing processes.
A balance tank is a vessel that keeps product at a constant level above a pump inlet. The primary purpose of a balance tank is to keep the pump NPSHA constant. A balance tank will generally have a level sensor to help maintain tank volume. Often times this can be a simple float, but Holland does offer several other products for continuous balance tank level measurement, including the HB, LD, and LN continuous level transmitters by Anderson.
As the pump draws more fluid from the tank, the tank level drops and the level device allows the flow of additional fluid into the tank. Balance tank inlets are often located at the bottom of the tank so that liquid enters below the surface, eliminating splashing and product aeration. Additionally, air already present in the product will try to rise in the tank. Some deaeration will actually take place, which favorably affects pump performance.
Balance Tank on an STHT System
Balance tanks are a staple of a dairy’s pasteurization and other beverage STHT loops. At Holland, however, as we’ve begun developing in house metering skids and systems, we’ve identified the balance tank as a critical process component in any application we’re we are trying to deliver a constant, uniform amount of product. Many times we will use Waukesha sanitary PD pumps as a type of metering pump due to their high efficiencies and low slip. Testing has shown, however, that if we can’t ensure we get constant and consistent levels of fluid to the pump, not only do we risk damaging the pump, but metering is not consistent.
While our metering systems do employ flow meters to measure the actual amount of product dispensed, inconsistent discharge can wreak havoc on meter accuracy. Empty tube conditions on a mag meter or air entrainment in a mass meter can greatly impact meter accuracy and precision.
Additionally, many of our metering systems will use complex piping arrangements between the pump discharge and meter to “condition” the flow and create smooth, laminar flow heading into the meter. Creating laminar flow, critical to mag and turbine meter performance, becomes exceedingly difficult with inconsistent pump head.
Other applications where maintaining fluid head and constant flow is critical range from counter pressure beer filling systems to pharmaceutical aseptic filling systems. While most counter pressure beer fillers will have a fill bowl of some type, maintaining level and delivery to the bowl is critical to ensure consistent fill. Holland has worked with several OEM’s to minimize product aeration and agitation, as well as monitor level in beer fill bowls (the LN is great in fill bowl applications where level measurement often needs to be top mount).
To conclude, if consistent, precise product dispense is required, maintaining consistent pump suction head is critical. This means more than just having a tank upstream feeding the pump. In applications like these, monitoring balance tank level, temperature, and pressure are all critical to ensure consistent process performance. Contact Holland today with any questions you have about your metering application.