Flow Measurement Instruments

Flow Switches

Name: Rheotherm Thermal Flow Switches
Brand: Rheotherm
Availability: InStock

Rheotherm flow switches provide reliable switch protection in all types of liquid or gas service. From critical monitoring of extremely low flow process additives to loss of flow protection in large water or air lines, we can handle most flow switch applications. With no moving parts in these devices, their long-term reliability is assured. Options for hazardous sites (explosion-proof, intrinsically safe) are available as well. These devices, like all Rheotherm flow instruments, are protected by an ISO-9001:2015 certified Quality Assurance program.

Overview of Flow Switches

Flow switches play an important role in regulating the flow rate of fluids through a system. They perform this function by sending a trip signal to another system element (often a pump) that responds by modifying the fluid flow rate as needed. Flow switches are also used for indication of certain process conditions such as flow/no-flow to alert operating personnel by connecting them to indicator lights or audible alarms.

Every flow switch has a set point, which is a maximum or minimum flow rate. The set point is typically user-adjustable. When the flow of media reaches the existing set point, the switch prompts the pump (or other mechanism) to turn on or off. The switch can be set to trigger in either low-to-high (e.g., trigger when flow goes from 0 to any flow) or high-to-low (e.g., trigger when flow goes to 0 from any flow value) to match the process requirements. This sequence of events results in the increase or decrease of the flow rate, depending on the requirements of the application.

What Applications can Rheotherm Flow Switches Monitor?

Rheotherm thermal flow switches are used to monitor flow in a wide range of liquids, gases, and specialty process fluids and can be configured for hundreds of liquid and gas services. Proven applications include:

Industrial gases: Argon, Helium, Oxygen, Carbon Dioxide, Methane, Natural Gas, Propane, and Ethylene
Chemical process streams: Ammonia, Ferric Chloride, Hydrofluorosilicic Acid, Liquid Chlorine, and Sulfur Dioxide
Fuel and hydrocarbon services: Flare Gas, Fuel Gas, Coal Gas, Coke Gas, and Hydrocarbon Vapors
Specialty applications: Digester Gas, Flue Gas, Diesel Exhaust, Tungsten Hexafluoride, and Antifoam Systems

Don’t see your fluid listed? Contact us to discuss your application or review our Applications section for a more comprehensive list of the various fluids where our flow switches have been used.

Rheotherm Flow Switches can be found in a broad range of applications, from HVAC systems to water treatment facilities. Some of the industries that currently use our air, liquid, and gas flow switches include:

Aerospace
Chemical and Petrochemical
Natural Gas
Oil and Gas Production
Wastewater Treatment
Pulp and Paper

The Industries section has more information on the industries and applications where our low flow switches have been used. Contact us with any questions about your specific application.

How Are They Installed?
Rheotherm Insertion thermal mass flow switch Our in-line flow switches for monitoring flows in small lines are usually installed with standard tube fittings, but are optionally available with flanges, NPT, sanitary fittings, etc. Insertion probe flow switches for monitoring large (1” or larger) pipe flows are typically installed with 1” NPT or flange fittings. They can be used in vertical or horizontal lines. For most common applications, the sensor and electronics form an integral unit.

How Do They Work?

Rheotherm flow switches and monitors come with highly advanced thermal flow-sensing technology to ensure optimal performance. Our in-line flow sensors use a straight-through flow tube with a heated and an unheated RTD (Resistance Temperature Detector) attached to the outside of the tube. The insertion probe flow sensors include one tip with a heated RTD and another tip with an unheated RTD. With both sensor styles, the temperature differential between these two RTDs produces the primary flow signal. At high flow rates, flow removes more heat, resulting in a lower differential. At low flow rates, the flow removes less heat, so the differential is higher.

With our inline industrial flow sensors, nothing touches the fluid but the metal sensor wall, and there are no mechanical parts that are susceptible to wearing, sticking, or breaking. We use unstressed components to enable years of low-maintenance operation. The sensor will not be damaged when the process flow stops or when the line empties.

Trip points are field adjustable, so you are always able to adapt quickly to changes in system conditions. Trip response times generally range from 2 to 25 seconds and can optionally be extended with a time delay. Our flow switches can operate in environments in the range of 0–120°F (-18–50°C); optional customizations can extend this range to -20–400°F (-29–200°C). Standard wetted parts are Grade 316 stainless steel, with other materials optionally available. More on Method of Operation (PDF)

Inline Sensor

Insertion Sensor

What Models Are Available?

We currently offer the following flow switch models:

Model 100CS – Lowest cost industrial option. Integral sensor/electronics with one SPDT relay, which is rated 10 A @ 120 Vac or 5 A @ 24Vdc. CE mark is available. Can be ordered with in-line or insertion probe sensor.

Model 100FS – Separate sensor and electronics with one SPDT relay. Option for second relay for high and low set points. Can be ordered with in-line or insertion probe sensor. This model is also available with an intrinsically isolated sensor for use in hazardous locations. Refer to the Instruments for Hazardous Locations page for more information.

Model 400 – Integral insertion probe sensor and electronics; has two SPDT relays or single relay w/ non-linear analog flow output signal. Calibrated signal optional.

Please contact us if you’re uncertain about which model would work best in your application.

How Do I Get One?

Contact our flow measurement application specialists to discuss your process requirements and receive expert guidance on selecting a Rheotherm flow meter for your application. Our team will review your information and help configure a solution tailored to your specific flow measurement needs, including challenging or low-flow applications.

To get started, please submit the form on this page with details about your application, including process conditions and performance requirements. A specialist will follow up promptly to assist with your Rheotherm flow meter selection and application review.

You can also download and complete the Flow Application Data Sheet and email it to us at sales-flow@bionetics.com.
For other questions and ways to reach us, visit our Contact Us page for telephone, fax and email information.

FEATURES
SPECIFICATIONS
FLOW RANGES
DOCUMENTATION

No moving parts
Exclusive inline TU sensor
Advanced signal processing electronics
Field adjustable switch point
Maintenance-free
Easy installation
Choice of wetted materials
Long-term reliability

	Standard	Options
Temperature	Process: 0 – 140°F (-18 – 60°C) Environment: 0 – 120°F (-18 – 50°C)	Inline: -20 – 350°F (-30 – 175°C) Probe: -20 – 400 °F (-30 – 200 °C)
Pressure	0 – 1,000 PSI	Up to 30,000 PSI
Calibration Accuracy	± 1% of reading typical
Response Time	1 sec. ; 3 – 5 sec. typ. (63% of range);	Time constant/delay option
Repeatability	± 0.5% of reading
	Standard	Options
Line Sizes	Inline sensor (flow range dependent): – Capillary; – 1/16”; 1/8”; 3/16”; 1/4” – 3/8”; 1/2”; 5/8”; 3/4”; 1” Probe sensor: Pipe/Duct from 1.5” – 72” (round, square, rectangular)	Other sizes via fittings/adapters
Process Connection	Inline sensor: Plain tube stubs suitable for compression fittings Probe sensor: 1″ MNPT	– MNPT; – Tri-Clover (Sanitary); – SS Flange (1/2” – 2”); Most other fittings available
Wetted Material	316 SS	– Hastelloy C-276®; – Monel®; – Alloy 20; – Titanium; – Tantalum; – Inconel
	Standard	Options
Enclosure	Sensor: – Inline – PVC – Probe – NEMA 4X (junction box) Electronics: – Integrated – NEMA 4X Cast Aluminum – Remote – NEMA 4	Inline sensor: Stainless steel Remote electronics: – Stainless steel – NEMA 7 Explosion-proof
Hazardous Environment		Remote electronics with 100FS only FM Approved for: – Class I, Div. 1, Groups A,B,C,D – Class I, Zone 1, IIB+H2 (US) – Class II, Div. 1, Groups E, F, G – Class III, Div. 1
Outputs	Single SPDT Form C relay (10A, 125 VAC)	Remote electronics with 100FS only – Second independent SPDT relay – DPDT relay – Time delay on switch
Input Power	110/230 VAC ±10V	24 VDC ±4V (200 mA)

Inline Sensor Flow Capacities for Liquids

	TUBE SIZE
FLOW RATE LIMITS	C	¹/₁₆	¹/₈	³/₁₆	¹/₄	³/₈	¹/₂	⁵/₈*	³/₄*	1*
Extended Maximum	2	60	500	0.4	1	2.5	4.6	8	10	20
Normal Maximum	1	30	250	0.25	0.5	1	2	3.5	4.5	8
Normal Minimum	0.03	0.8	6	0.008	0.01	0.03	0.05	0.2	0.3	0.5
Extended Minimum	0.007	0.05	3	0.002	0.006	0.01	0.02	0.07	0.1	0.2
	cc/min			GPM

*Limited applications. Consult Factory

Inline Sensor Flow Capacities for Gases

	TUBE SIZE
FLOW RATE LIMITS	C	¹/₁₆	¹/₈	³/₁₆	¹/₄	³/₈	¹/₂	⁵/₈	³/₄	1
Extended Maximum	0.027	1.25	5	11	20	45	80	125	180	320
Normal Maximum	0.017	0.75	3	7	15	34	70	109	160	280
Normal Minimum	0.0017	0.02	0.1	0.2	0.4	0.9	1.6	2.5	3.6	6.4
Extended Minimum	0.0009	0.0017	0.05	0.1	0.2	0.5	0.8	1.2	2	3.2
	SCFM