Selecting the proper Flow Switch
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- Published: Sunday, 27 September 2015 04:12
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The typical application for an industrial flow switch or flow indicator is to ensure that adequate flow is occurring in the process system, and to provide a flow alarm should the flow rate drop below acceptable levels.
Typical applications are:
- Chillers
- Furnace Cooling Systems
- Irrigation Systems
- Pump Protection
- Lubricating Oil flow
- Heat Exchangers
- Boilers
- Semiconductor Manufacturing
- Waste Water Treatment
- Dosing of Chemicals
- Marine applications
- Flow if Air in Ducts
- Compressed Air flow monitoring
The selection of the proper flow switch for the application requires careful consideration of a variety of parameters, any of which could render the sensor or flow switch useless in your particular application.
Here are some Key Parameters to consider when making your decision and the type of flow switch you should consider as a result.
Calorimetric Flow Switches
These are ideal for flow switch applications where dirt or particulate matter is in the flow media that could foul mechanical flow switch devices. They have no moving parts and operate on the principle of thermal conductivity of the media. They can be used in oil applications, water/glycol, chemicals, DI water, and a variety of other process media. They are not harmed by overflow conditions and can monitor very low flow rates with better that 1% repeatability.
Cautions:
Typically the media temperature for calorimetric flow switches must not exceed 80C. Pressures are typically in the 100 Bar max range, and the possibility of coating of the sensing surfaces (depending on the flow media properties) can result in reading errors.
Media with Bio Wastes should not be monitored with Calorimetric Flow Switches.
Price range:
$300 - $2,000
Paddle Flow Switches
Paddle Flow Switches are the most commonly used simple flow monitors for flow or no flow conditions. They are simple mechanical devices that close a reed contact when flow occurs and require no internal power to operate. These flow switches are fine for clean media, with no particulate matter that could foul or cause the paddle or moving components to stick. They are typically good for media temp up to 230F or higher and for pressures up to 3500 PSI or higher.
Cautions:
Since these flow switches have moving parts, they may stick during use, and reliability needs to be considered. They can be damaged by overflow (typical overflow limits are 5X the increasing trip point range.) They also are not as capable for setting very low trip points. If very low trip points are required, the Calorimetric Flow Switch is preferred.
Price Range:
$70.00 – $250.00
Variable Area Flow Monitors (Variable Area Flowmeter)
Variable Area Flow Meters and Flow Switches provide a relatively inexpensive means for monitoring flow rates (including quantitative flow readout measurement) and a wide adjustment of flow switch trip points. They also allow very low flow rate measurement and a variety of process connection sizes from 1/8” NPT up to 2” NPT or higher. They can also be supplied in Viscosity Compensating types so that accurate measurement of oil flow under varying temperature conditions can be accomplished. These flow meters and flow switches also do not require internal power to operate and can be used with intrinsic barriers for hazardous locations. Ranges as low as .02 Gallons per HOUR are available and are commonly used in dosing applications.
Cautions:
Be sure that the meter selected will accommodate your maximum flow range as overflow can damage internal parts. These units also use moving parts and orifices can be somewhat narrow so that particulate matter in the flow media can cause sticking of the float mechanism.
Price Range:
$70.00 – $2,500.00
