Backwash Rates & Water Temperature

Backwash expansion schematic

Water temperature plays a critical role in properly installing a water treatment system. Water temperature affects flow rates, backwash rates, and even systems capacities. The most critical of these is the backwash rate. Colder water is more dense and requires considerably less water to properly backwash a system. Hot water requires much more. The chart below shows standard cation water softening resin backwash expansion at varying temperatures. A 50% bed expansion is achieved with only 2.5 gpm/ft² at 40°F. At 86°F, it requires 7 gpm/ft² or nearly three times more water to achieve the same bed expansion. Common backwash rate charts assume a water temperature of 68°F. It is important to consult with each media manufacturers temperature charts to ensure your system is properly applied.

Variable Pressure Flow Controllers
Theory of Operation and Service
Flow controls are commonly used in water treatment to regulate the backwash required to expand and agitate the media in a tank
(DLFC), control the amount of water going into the brine tank (BLFC) or to regulate the maximum flow going through a UV chamber. The variable pressure flow control principle is accurate among a wide range of pressures unlike a fixed orifice flow control. The specified rate of flow will be very close to the design parameters regardless of inlet pressure variations. This is accomplished by the changing orifice size of the flow washer as inlet pressure varies as shown in the drawing below.

work of flow control or flow restrictor

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