FPS - Insertion Paddle-Bellows Flow Switch for Liquids

The KOBOLD FPS is an insertion paddle flow switch for liquids, designed for reliable control of minimum or maximum flow in pipes from 1" to 8" in diameter. Switching points are externally adjustable across ranges from 0.9–4.4 GPM up to 375–760 GPM for water, and brass and stainless steel versions are available, each with a 1" NPT male process connection.

How the FPS Paddle Flow Switch Works

The FPS operates on the proven paddle bellows principle. Flowing media acts on a paddle, and the force of the flow actuates a micro switch at the set point. A bellows hermetically separates the electrical switching cavity from the process fluid, so the switching elements never contact the media.

The switching point can be freely adjusted with the range screw located within the housing, and the replaceable paddle mates the device to different nominal pipe sizes. Stacking the paddle segments together extends the available switching values in larger pipes, and for service in 4" to 6" pipes the longest paddle is shortened to fit.

Models and Switching Ranges

The FPS line consists of two series in two materials. The standard FPS-5000 series covers switching ranges from 2.6–8.8 GPM in 1" pipe up to 374.7–759.5 GPM in 8" pipe, while the FPS-6000 series is specially designed to accommodate lower switching values, beginning at 0.9–4.4 GPM.

Four model numbers define the offering: FPS-5100P (brass, standard ranges), FPS-5200P (stainless steel, standard ranges), FPS-6100P (brass, low ranges), and FPS-6200P (stainless steel, low ranges). Each pipe size from 1" to 8" has separate de-actuating and actuating switching values for water, along with a maximum flow rate from 15.8 GPM to 1056 GPM. A set of spare paddles is available under model number FPS-PPDSS.

Materials, Pressure, and Temperature Ratings

Brass versions use an MS 58 bronze bellows and carry a maximum allowed pressure of 160 PSIG. Stainless steel versions use a stainless steel 321 bellows and are rated to 435 PSIG. Both designs use four 316L stainless steel paddles and handle media temperatures from -40 °F to 250 °F (-40 °C to 121 °C).

Permissible ambient temperatures span -30 °F to 150 °F (-34 °C to 66 °C). Pressure loss across the switch is approximately 0.15 to 0.44 PSIG. The enclosure combines an ABS base with a transparent polycarbonate cover and carries an IP 65 protection rating.

Electrical Ratings and Wiring

Switching is handled by a high-capacity SPDT mechanical contact rated for a maximum of 15 A on resistive loads or 8 A on inductive loads, at switching voltages up to 250 VAC. The changeover contact can be wired as either a normally open or normally closed circuit, and wiring enters through a cable gland.

The red-white connection opens when flow drops to the set value, while the red-blue connection closes at the same moment and can be used as a signal contact. Units ship factory-set at the minimum switch-off value; rotating the range screw clockwise raises the setting.

Installation Requirements

The FPS can be installed in any mounting position, although horizontal flow orientation is preferred. In a vertical pipe, the weight of the paddle and lever is compensated with the range screw, which produces some variation in the switching values. The arrow on the housing must point in the direction of flow.

Select the paddle to suit the internal pipe diameter, keep the shorter paddle in place for stability, and verify that the paddle moves freely without sticking to the pipe wall. The switch threads into a T-piece with a 1" outlet, sealed with sealing tape, and a straight run of five times the nominal pipe diameter should be observed at both inlet and outlet.

Applications and Media Suitability

Typical applications include monitoring cooling or lubricant circuits, dry-run protection for pumps, and prevention of low water levels. The FPS is suitable for water and compatible low-viscosity liquids, and because the bellows separates internal components from the process media, it is also designed to handle dirty media applications.

Monitor only media that do not affect the wetted materials. The FPS must not be used in hazardous areas or with flammable liquids, and for soiled media, especially fibrous soiling, a suitable filter must be connected upstream. With uncontaminated media the FPS typically remains maintenance-free; where dirt is present in the medium, checking the instrument at regular intervals is recommended.

Common Questions about FPS - Insertion Paddle-Bellows Flow Switch for Liquids