Thermal Dispersion Flow Switch

Ensures Coolant Flow
Thermal Dispersion Flow Switch ensures coolant flow

The SP series thermal dispersion flow switch is a Solidstate flow switch with no moving parts. It can be used for monitoring flow or no-flow conditions of a very wide range of liquids. The SP thermal dispersion flow switch can be provided with Solidstate or relay output. They are relatively compact and can be applied in a range of pipe sizes. Available in a variety of process connection sizes, choices of lengths, and materials of construction to meet a wide range of application requirements. It is also available for general purpose and explosionproof environments.

Thermal dispersion flow switches have many uses. One of their many uses, the thermal flow switch ensures coolant flow to several processes. Technically they operate using thermal dispersion technology. They are solid-state sensors without any moving parts, which is one of their benefits. They detect flow / no-flow conditions for a wide variety of reasons including control.

Large ships and yachts commonly use large diesel engines to propel them through oceans and seas around the world. Usually, they are powered by multiple engines. As with all combustion engines they must be cooled. Ships have the luxury of access to a great coolant, sea water. But like any engine cooling situation the positive flow and continuous flow of engine coolant must be assured and detected. If absent, or if inadequate flow exists, cooling may not be adequate and engine overheating can occur resulting in engine shutdown or damage.

One specific application for the thermal dispersion flow switch is featured in the picture. A diesel engine for marine use with an SP series installed within the seawater cooling inlet.  The flow switch ensures a positive flow of cooling water to allow the engine to operate. To prevent shutdown or damage due to loss of sea water coolant, most ships and yachts use a coolant system that includes a flow switch to indicate a positive flow of sea water coolant. 

Thermal dispersion flow switches operate by detecting loss of thermal energy in one internal sensor due to fluid flow, while a second thermal element is maintained at a constant temperature. These thermal flow switches have no moving parts and this makes them a long term reliable flow sensor.

Thermal dispersion units and paddle type units of flow switches are both used as flow detectors. Wired into the overall coolant or engine system these switches will detect flow and allow their switch contact to close or open to indicate loss of coolant flow.

Principle of operation: The thermal dispersion flow switch is based on the principle of heat transfer. It consists of two temperature sensors. One temperature sensor is the reference and measures the temperature of the fluid where the thermal dispersion flow switch probe is immersed. The second temperature sensor is heated using constant power. This creates a temperature difference between the two temperature sensors. As the flow rate of the fluid increases there is a cooling effect due to the fluid moving past the heated sensor. The more flow, the more the cooling. A reduction in temperature difference between the two temperature sensors indicates that the flow rate exceeds a user adjustable set point. When the flow rate drops, there is less cooling, which causes an increase in the temperature difference. 

Features include:
• No moving parts, Solidstate performance and reliability
• 1~59″ per second (150cm/s) measuring range for water; 1~118″ (300cm/s) range in oil
• 304SS, 316SS, PVDF and polypropylene wetted parts
• Maximum operating pressure up to 1,450psi (100bar)
• Choice of NPN/PNP, N.O. or N.C. relay, or SPDT relay output
• Standard and custom extended insertion lengths
• Standard or high temperature, explosionproof units available
• LED indication of flow status
• Marine certified unit available

Applications and use include:
• Detect positive flow to control downstream process
• Ensure machinery safe operation with detection of coolant flow
• Petrochemical
• Power
• Food processing
• Pharmaceutical
• Many others

For more information on the SP series thermal dispersion flow switch product line, please visit the SP series thermal dispersion flow switch product page or can contact us at (909) 598-2488.