Wedge Wire Screen Flow Directions: Understanding FOTI vs. FITO

When specifying a wedge wire screen tube, one of the most critical decisions is determining the Flow Direction. This choice dictates which side the smooth surface of the V-wire is on and how the fluid interacts with the filter media.

At Johnsonslot, we categorize these configurations into two primary types: FOTI and FITO. Choosing the wrong one can lead to premature clogging and inefficient backwashing.

1. FOTI (Flow Out to In) – Standard Flow

FOTI is the most common configuration for well screens and industrial filters. In this setup, the fluid travels from the outside of the tube toward the inside.

Design: The smooth, flat surface of the V-wire is on the outside of the screen. The support rods are on the inside.
Best For: Water well completions, intake screens, and standard vessel internals.
Advantage: External particles are stopped at the outer surface, where they can be easily removed by mechanical scrapers or external pressure.

2. FITO (Flow In to Out) – Internal Flow / Reverse Flow

In a FITO configuration, the fluid enters the inside of the screen tube and travels outward.

Design: The smooth surface of the V-wire is on the inside of the tube. The support rods are on the outside. This is often called "Reverse Wire."
Best For: Diverter valves, internal pipe filtration, and systems where solids are collected inside the basket for removal.
Advantage: It allows for seamless internal cleaning and is ideal for centrifugal separators.

FOTI vs. FITO: Comparison Table

Feature	FOTI (Standard)	FITO (Reverse)
Smooth Surface	Outside	Inside
Fluid Path	Outside → Inside	Inside → Outside
Primary Use	Well Screens / Intake	Basket Filters / Trommels
Cleaning Method	External Scrapers / Backwash	Internal Brushes / Backflush

Radial vs. Axial Configurations

Beyond the flow direction, you must also consider the wire orientation:

Radial: The profile wire wraps around the tube (Standard for most applications).
Axial: The profile wires run parallel to the axis of the tube (Ideal for vertical screw presses).

Why Direction Matters for Backwashing

The "V" shape of the wedge wire screen is designed to create an inwardly enlarging slot. In a FOTI system, backwashing from the inside forces particles out of the widening gap. If you use a FOTI screen for a FITO application, particles will get "wedged" into the narrowing gap, making the screen impossible to clean.

Are you unsure which flow direction is right for your filtration system? Our engineering team at Johnsonslot can provide a detailed drawing and hydraulic analysis for your specific needs.