FST-221-R Flow Switch With Compact Relay Controller

Supported Applications

The Omega FST200R Series is a flow switch with an integrated compact relay controller designed for liquid and gas applications. It provides reliable low-flow or no-flow detection in relatively clean, non-coating media. The series offers complete solutions for switching valves, pumps, or blowers rated up to ½ hp in pipes or ducting ranging from ¾" to 12" (0.3 m). Common uses include low-flow pump protection and process monitoring.

Application variables supported by the liquid configuration include clean media, slurry, non-coating fluids, low viscosity, medium viscosity, low temperature, and low velocity conditions. Gas configurations support low temperature, non-coating gases, and low to high velocities depending on specific model selection.

Operating Conditions & Performance

The FST200R Series operates with an ambient temperature range of -40° to 70°C (-40° to 158°F) and a process temperature limit of up to 60°C (140°F). The pressure rating is 150 psi @ 25°C, derated at 1.7 psi/°C above 25°C.

Measurement ranges vary by configuration:

• Liquid flow: 0.04 to 3 ft/s
• Gas flow: 1 to 90 fps (per family manual)
• With FT-51 fitting: 0.05 to 1.53 GPM
• With FT-52 fitting: 0.10 to 6.53 GPM

The series features an accuracy of ±5% of setpoint at constant temperature and flow rate, with a response time of approximately 10 seconds. A selectable 0 to 60-second time delay is available to dampen relay chatter.

Configuration Options

The series supports multiple configurations across liquid (FST-2xx-R) and gas (FST-3xx-R) models, with options for different pipe sizes and materials. Key configurable dimensions include:

• Housing Material: Polypropylene (PP), PVDF
• Wetted Materials: PP/PPS or PVDF depending on model number suffix
• Pipe Size Compatibility: ¾" to 1½", and 2" to 12" for long sensor variants
<small>Fittings:</small> FT-51 (0.05–1.53 GPM, PP) or FT-52 (0.10–6.53 GPM, PVDF)

The controller includes a ½ NPT electrical connection and an enclosure rating of NEMA 4X (IP66). Power is supplied via 120/240 Vac at 50/60 Hz. The relay output is SPDT with selectable NO or NC operation, rated for loads up to ½ hp.

Key Product Differences

The FST-2xx-R models are designated as liquid flow switches, while the FST-3xx-R models serve gas applications. Within each family:

• FST-21x/31x: Short sensor for ¾" to 1½" pipe
• FST-22x/32x: Long sensor for 2" to 12" pipe
• Models ending in -R include the compact relay controller; non-R variants (e.g., FST-211) are sensors only.

Material variations distinguish between PP/PVDF combinations: models with suffixes 1 or 3 typically use PP/PPS, while those ending in 2 or 4 utilize PVDF. The series is CE and RoHS compliant.