Basic Flout Design

Familiarity with the various Flout System components is crucial for the Designer to create the best system plan. This section will lead the Designer through the tasks of applying, sizing, and specifying Flout, Alternator, and Cuebox designs.

Flout Applications:

Flouts are available in pipe sizes from 1" (25mm) through 4" (100mm). Typically, 3 and 4 inch units are used in wastewater applications. One and 2 inch Flouts are popular in hydroponics and aquaponics.  Single Flouts may supply downstream distribution boxes . Multiple "Ganged" Flouts may supply individual distribution lines, eliminating distribution boxes and manifolds all together.  They may supply fractional flows when partially recombined or larger single flows when completely recombined.  

Single and/or Multi-Flouts may be alternated in pairs or sequenced in groups of two or more.

Flouts may replace bell siphons. Retrofitting is simple and the existing dosing chamber can usually be re-used. Flouts are popular for Grass Strip Dairy Waste Disposal. Replacing a trickling  waste flow with a fast flow and complete shut-off eliminates freezing of the grass strip disposal header pipe. (Link under construction)

The Flout is simple to specify. We need to know:

1. How much elevation do we have available

2. How much do we want to dose?

3. How fast?

4. Will it re-float and shut-off at the anticipated inflow rates?

5. Will it fit?


The minimum drawdown (DD) for 3" Flouts is  6". The minimum DD for 4" Standard width Flouts is 11".  The minimum DD for 4"N (narrow) Flouts is 16".  Alternating Flouts need at least 15" DD.  Maximum DD for all Flouts is 50". 

1. Elevation is our best friend. It allows for faster flows and/or lets us use deeper , smaller  footprint tanks.

The Total Drop in elevation between the inlet and outlet (TD) is the sum of the Shut Off depth(SO) plus DrawDown(DD) plus the recommended height of the inlet above the highest liquid level (3" is recommended but it can be less**). The SO is 1" to 2" more than the diameter of the Flout size (pipe diameter). SO for 3" Flouts is 4-5". SO for 4" Flouts is 5-6".

TD = SO+DD+3(recommended*)  > TD,SO,DD Example...

** A dry Flout will flout to a higher level because it has no residual liquid in it from a previous dose.  If the pitch from the septic tank to the Flout chamber is minimal , there is a chance the Flout chamber may back up into the septic tank, causing a much larger dose and possible carrying solids from the septic tank. 

Therefore a 3" Flout with 15" of drawdown needs a total drop of:

(SO=5")+( DD=15")+3"= 23" TD

Shims and drift control: The outlet is normally "on the floor". The Flout must never sink below the outlet. If the outlet is higher than the floor, a suitable shim pad  or built-on shim must be provided for the Flout to land on. The shim pad must be solid, not perforated (such as hollow core blocks - if hollow core blocks are used, lay them on their sides), so the liquid can cushion the Flout when it lands. >Shim examples...... 

Multiple Flouts do not drift. Single Flouts tend to drift.  The shim pad must be wide  enough so the Flout cannot miss it. Guides (driftbars) of small diameter pipe and brackets can be incorporated to control drift. Drift bars are not required for single Flouts with a wide shim, built-on shim, no nearby impediments, or enough room between adjacent Flouts and equipment. The Alternator has a built-on drift bar good to 36" drawdown. >Drift control examples...

2. The amount of dose is the volume of the tank in gallons per inch X DD. The gallons per inch (GPI) is the (length) X width in inches) / 231 cubic inches per gallon).  A 5' (60") square tank with 24" of drawdown is:

(60" x 60")/231= 15.5 GPI x 24"DD =  375 gallon dose. The  minimum TD of this arrangement with a 3" Flout is 32 inches.

3. For maximum, average, and maximun shut-off flow rates, refer to this chart.  The average flow from the above example tank is 92 gallons per minute. With multi Flouts, multiply these figuresby the number of outlet pipes.

 4. Minimum Dimensions: Chamber Width: The  single 3" or 4"Narrow Flout  needs a tank at least 12" wide.  Three inch or 4" Narrow Multi Flouts need 8" per Flout + 4".  Three inch  and 4"N Flout outlets are 8" on center. Four inch standard width Flouts  12" on center. For Alternator Chambers, add up total width of Flouts with the closest pipes  12" on center and clearance . Four inch Alternating Flouts must be the N (narrow) type. Special spacing is available on any Flout. Inquire.

Chamber Length: For non- alternating Flouts, The minimum length of the tank with internal venting is 24"+ DD for 3" Flouts and 30"+ DD for 4" flouts. With external venting, minimum length is 12"+DD for 3" Flouts and 18"+ DD for 4" Flouts. >Learn more about venting...

For Alternating Flouts , multiply DD x 1.2. >Learn more...

For CueBox Flouts, add on an additional 3 inches to DD.> Learn more...

Chamber Height: 

The ceiling height  should be at least 8 inches above maximum liquid height.

Inlet Location: Keep the inflow away from the Flouts in any position. Provide a baffle on the inlet to keep inflow away. >Learn more...

Access: Access is best placed over the Flouts in their maximum position. Access over equipment such as the Alternator and the Cuebox is mandatory. Access for permitted entrance is also recommended. >Learn more...

Alarms: Many designers and regulators require alarm systems to send an alert if the Flout chamber level gets too high. Rissy normally supplies vent pipes 3 inches higher than the starting depth of the Flout. For an alarm to work, the length of the vent and the total drop (TD)must be increased. This will provide necessary working room for the alarm switch to work. If the TD is not available, other monitoring methods are available. Rissy recommends counting doses instead. A regular increase in the count will indicate proper function.

Rissy Plastics, LLC, 350 Cedar Lane, Torrington, CT 06790 USA, 1-877-221-4426
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