The KOBOLD LSP is a duct air flow switch that controls air flow setpoints in horizontal HVAC ducts. Air flow exerts a force on a paddle, actuating a dust-tight SPDT microswitch, and the switching point can be adjusted continuously within a wide range, making the LSP useful in a wide variety of applications.
Rugged and inexpensive, the LSP mounts on horizontal square or rectangular HVAC ducts with a flat mounting plate and is factory set to switch at 195 FPM.
How the LSP Air Flow Switch Works
The paddle extends into the duct and deflects as air velocity increases. Its movement actuates the microswitch, which indicates whether the air flow is above or below the set switching point. The red and white terminals close with increasing air speed, and the red and blue terminals close with decreasing air speed.
Switching Range and Setpoint Adjustment
The switch-off range spans 195 to 1575 FPM (0.99 to 8.0 m/s), and the switch-on range spans 495 to 1810 FPM (2.51 to 9.2 m/s). The factory setting is 195 FPM, and rotating the range screw clockwise sets a higher switch-off value.
To handle air velocities greater than 920 FPM (4.67 m/s), the paddle is cut at a precalibrated mark. This automatically changes the factory setpoint to 490 FPM (2.49 m/s).
LSP Specifications
The LSP switches electrical loads of up to 15 A resistive or 8 A inductive across a switching voltage range of 24 to 250 VAC. The maximum media and air temperature is 185 °F (85 °C), and the enclosure provides IP65 ingress protection from the outside. Additional construction details include:
- Paddle: 304 stainless steel
- Paddle lever: brass
- Housing: ABS and fiberglass
- Mounting plate: zinc-plated steel
- Flat gasket: Flexoid
- Cable entry: M20 cable gland
- Conformity: EMC Directive 2014/30/EU, Low Voltage Directive 2014/35/EU, RoHS 2011/65/EU, EN 60730-2-15:2010
Installation in HVAC Ducts
The standard installation is vertical, in a horizontal air duct, over a cutout in the duct wall. Installation consists of drilling a 0.79 in (20 mm) hole and a 3.19 in (81 mm) slit, securing the zinc-plated mounting plate with four metal screws, and sealing the joint with the supplied flat gasket.
The arrow on the housing must point in the direction of flow, and straight inlet and outlet sections of five times the duct diameter are required upstream and downstream of the switch. Mounting is position independent; with vertical mounting, the switching point must be adjusted to compensate for the weight of the paddle. For gases containing dust particles, the switch is positioned so that no particles can deposit inside the connection head, for example by mounting on the upper side of the duct.
LSP Air Flow Switch Applications
The LSP monitors minimum or maximum air flow in ducts and air handling equipment. Its continuously adjustable switching point suits it to comfort HVAC systems as well as industrial processes such as pneumatic conveying, filtration, and drying. Typical applications include:
- Air ducts in air conditioning systems
- Air discharge and exhaust gas channels
- Pneumatic conveyors
- Filters
- Cyclones
- Cooling and drying plants
- Ventilator and blower performance monitoring
Common Questions about LSP - Air Flow Switch for HVAC Ducts
The air flow being monitored presses against the paddle, which is mechanically linked to a changeover microswitch. The switch signals whether the minimum or maximum preset air flow exists, and the switching point is adjustable over a wide range of values, so one unit covers many duct velocities.
A higher switch-off value is set by turning the range screw in the clockwise direction. When a switching value above 920 FPM is needed, the paddle must be truncated at the marked position, which changes the factory-set value from 195 FPM to 490 FPM.
The LSP uses a dust-proof SPDT micro switch with a switching voltage of 24 to 250 VAC. The contact handles a maximum of 15 A on resistive loads and 8 A on inductive loads, and the maximum air temperature at the switch is 185 °F (85 °C).
Yes. The contact is a change-over type that may be used as a normally closed or normally open switch depending on connections. After connections are made between the external units and the limit contact, the unit is ready for operation on a 24 to 250 VAC supply.
Mounting requires cutting a hole and a slit into the duct wall and fixing the switch with four 0.14 in (3.5 mm) metal screws; the supplied gasket seals the opening. The paddle can also be fitted after the unit is installed, in which case a 0.79 in (20 mm) diameter hole is sufficient.
The actual flow value must remain within the switching range of the unit, and a minimum straight run of five times the inner duct diameter is required on both sides of the switch. The permitted maximum operating temperature of 185 °F (85 °C) must also not be exceeded.
The LSP is designed for air and for gases that do not attack its wetted materials, and its media category is gas. It must not be used for monitoring flammable or explosive gases, and dust-laden air calls for mounting positions that keep particles out of the connection head.
When the monitored medium is not polluted, the LSP flow monitor is regarded as maintenance-free. In polluted media, large dust particles may lead to jamming of the paddle arm, so a routine check at regular intervals is recommended, with the frequency depending on the degree of pollution.
LSP-1100P is the standard order number, covering a switching-off range of 195 to 1575 FPM and a switching-on range of 495 to 1810 FPM. Each unit ships as an air flow monitor together with a flat gasket for sealing the connection to the duct.
Product Specifications
Switching Range
195...1575 FPM
Wetted Materials
304 SS/Brass/Zinc-Plated Steel
Switch Capacity
15 A Resistive, 8 A Inductive
Max. Temperature
185 °F (85 °C)
Ingress Protection
IP65 (From Outside)
Mounting
Flat Plate for Square/Rectangular HVAC Ducts
Product Features
For Horizontal Square/Rectangular HVAC Ducts
Sample Applications: Air Conditioning Ducts, Air Discharge and Exhaust Gas Channels, Pneumatic Conveyors, Filtration, Cyclones, Cooling and Drying Plants, and Blower Performance Monitoring
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