S - All-Metal Flow Switch for Liquids or Gases

The KOBOLD S is an all-metal, variable-area (float-type) flow switch that monitors liquids or gases and triggers a reed-contact output at user-adjustable flow setpoints. It uses a cylindrical control tube with a conical groove in place of the conventional open conical tube, to create the variable area needed for flow sensing in a compact design. A permanent magnet in the float actuates a reed switch mounted on the outside of the housing, so the electrical switch is hermetically separated from the medium. The S provides ±5% of full-scale accuracy and is offered in brass or 304 stainless steel for service pressures up to 5,000 PSIG.

How the KOBOLD S flow switch works

The S works on the variable-area principle but replaces the typical open conical measuring tube with a cylindrical control tube that has a conical groove machined along its axis. As flow increases, the magnetic float rises within the tube, and a reed contact on the exterior housing changes state when the float reaches the position that corresponds to the set flow value. It is a switch rather than a meter: it signals that the flow is at or above the setpoint instead of continuously measuring the flow rate.

Flow ranges, media, and connections

The S covers water switching ranges from 0.075–0.25 GPM up to 1–14 GPM, and air ranges from 0.2–1.1 SCFM up to 3–70 SCFM, depending on model. Standard process connections are ¼" or ¾" NPT, with a ½" NPT connection available as an option for the ¼” standard models. Individual models are scaled either for water or for air service.

Wetted-material options let you match the switch to the process fluid:

• Housing and slotted nozzle: brass (nickel-plated) or 304 stainless steel
• Float: brass, 304 stainless steel, polypropylene (PP), or PVDF
• Seals: NBR on brass housing units, FKM on stainless-steel housing units

Pressure, temperature, and accuracy

The all-metal build is designed for high-pressure service: up to 3,600 PSIG with a brass body and brass float and 5,000 PSIG with a stainless-steel body and stainless steel float. Units fitted with a PP or PVDF float are rated to 230 PSIG. Maximum medium temperature is 240°F, or 160°F with a PP or PVDF float. Accuracy is ±5% of full scale with repeatability of ≤±1% of full scale.

Switch output and setpoints

The S provides a reed-contact output, normally open (N/O) as standard, with an SPDT changeover contact available as an option. Single-contact (S-3…) and dual-contact (S-4…) models are offered, and the switch can be factory-fitted with up to three reed contacts to monitor up to three setpoints. Each setpoint is user-adjustable to any flow value within the instrument’s range by sliding the contact along its rail on the housing.