Series-HFO

Supported Applications

The Dwyer Series HFO In-Line Flow Alarms provide continuous monitoring and control of flow rate levels for compatible gases or liquids, including air, water, or caustic fluids. These units are designed to make or break a set of electrical contacts to signal a limit setting. Typical uses include turning on a warning light, sounding a bell or horn, or shutting down a process.

The switches can be configured to open or close a contact for an increasing or decreasing set point. Decreasing flow set points may be located anywhere in the lower 2/3 of the scale while increasing set points may be located anywhere in the upper 2/3 of the scale.

Operating Conditions & Performance

The Series HFO operates with a process temperature limit of 170°F (76°C) and supports fluids up to 500 SSU viscosity. Accuracy is specified as ±2% FS, with repeatability at ±1% of full scale.

Pressure limits vary by body material:

• Aluminum body: 600 psig (41 bar)
• Brass body: 3500 psig (240 bar)
• 304 SS body: 6000 psig (413 bar)

The enclosure is rated NEMA 4X (IP66). Measurement ranges are available in GPM, LPM, SCFM, and SLPS depending on the model configuration.

Configuration Options

The series offers a range of process connections from 1/4" to 1-1/2" female NPT. Body materials include aluminum, brass, or 304 SS. Wetted parts consist of Buna-N or fluoroelastomer seals, PTFE coated Alnico magnets, and other internal parts made of 304 SS.

Electrical output is provided via an SPDT switch rated at:

• 10 A @ 250 VAC
• 0.5 A @ 125 VDC (resistive)
• 1/4 hp @ 250 VAC (inductive) — per manual documentation
• 3A @ 125 VAC "L" lamp load — per manual documentation

The unit features a rugged cast aluminum housing with overall dimensions of 7-1/8 [180.98] height, 4-1/2 [114.3] width, and 2-15/16 [74.61] depth. Electrical connection is made via a 4-pin DIN connector.

Wiring for the dual switch alarm follows this code:

• White: Both Common (Terminal #1 of DIN)
• Black: Decreasing N.O. Contact (Terminal #2 of DIN)
• Red: Increasing N.O. Contact (Terminal #3 of DIN)
• Green: Enclosure Ground (Terminal "G" of DIN)

Key Product Differences

Variants are distinguished by connection size, body material, and flow range.

• HFO-21112: 1/4" female NPT, Aluminum body, Air: 2 to 12 SCFM / 1 to 5.5 SLPS
• HFO-21123: 1/4" female NPT, Aluminum body, Air: 4 to 23 SCFM / 2 to 10 SLPS
• HFO-22205: 1/2" female NPT, Brass body, Water: 0.5 to 5.0 GPM / 2 to 19 LPM
• HFO-22315: 3/4" female NPT, Brass body, Water: 1 to 15 GPM / 5 to 55 LPM
• HFO-22320: 3/4" female NPT, Brass body, Water: 2 to 20 GPM / 10 to 74 LPM
• HFO-22440: 1" female NPT, Brass body, Water: 4 to 40 GPM / 20 to 150 LPM
• HFO-22550: 1-1/2" female NPT, Brass body, Water: 6 to 50 GPM / 20 to 190 LPM
• HFO-23202: 1/2" female NPT, 304 SS body, Water: 2 to 2 GPM / 1 to 8 LPM (dual scale)
• HFO-23210: 1/2" female NPT, 304 SS body, Water: 1 to 10 GPM / 3 to 37.5 LPM

Shipping weights range from 3 lb (1.4 kg) for 1/4" and 1/2" models up to 12 lb (5.4 kg) for the 1-1/2" model.