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Flow Switch - Paddle Type

Flow Switch paddle type Paddle type flow switches are simple economic yet reliable monitoring instruments that can be used for flow switching applications. For example, they are widely used in water cooling system of air conditioning units and oil lubrication system for flow/no-flow detection.

With the possibility to adjust the set point, LKB-01Cb is a universal flow monitoring instrument that has been sold to many world renowned companies, e.g. Carrier, York, Trane, McQuay, Sinko, Haier, Midea. They are among the few paddle flow switch in the world that carry UL and CSA approval (file no. E356174).

Working principle

A paddle fixed to the paddle arm and pivoted on a metallic bellows is deflected by the flowing fluid. The deflection is proportional to the velocity of flow. The movement of the paddle actuates a micro switch against a control spring. The bellows provides total isolation for the switch mechanism from the process fluid.


  • Easy installation with direct installations into existing pipes
  • One unit suitable for a wide range of pipe sizes (diameter 1" - 6")
  • Customer adjustable set point
  • Max service pressure: 16 bar
  • Process connection: R1" or NPT1"
  • Neck height of Tee pipes to be mounted: 25mm in most case
  • Operation temperature: -10°C - 150°C
  • Switch contact capacity: 250Vac, 7.5A
  • Switch type: SPDT
  • Material of wet housing: brass
  • Material of paddles: brass or stainless steel
  • 5 paddles of different size supplied

Pipe size, paddle No. and flow control range


Pipe Size Paddle No. Flow Control Range
Switch Difference (L/min)
on decreasing flow
1" #1 20-48 8
1¼" #1 34-100 10
1½" #1 65-160 14
2" #1 120-280 26
2½" #1 210-550 18
3" #1 380-750 20
2" #2 40-140 18
2½" #2 110-340 15
3" #2 180-470 18
4" #2 350-920 20
3" #3 115-220 20
4" #3 210-590 20
5" #3 380-1200 40
6" #3 550-1800 80
6" #4 550-1800 80
Pipe Neck Height Paddle No. Flow Control Range
Switch Difference (m/s)
on decreasing flow
25mm #4 0.37 - 1.22 0.05
25mm #5 0.26 - 0.86 0.04
50mm #4 0.57 - 1.68 0.08
50mm #5 0.33 - 1.08 0.05



flow switch paddle sizepaddle flow switch installation


UL approved flow switch

The flow switch should be mounted in a horizontal section of the pipe where there is a straight run of at least 5 pipe diameters on both upstream and downstream sides of it. The straight run implies that there should be no bends, restrictions such as valves in the required length. It is suggested that the flow switch be located in the suction side piping where less turbulent flow conditions exist.

Please also ensure that the boss height does not exceed 25mm from the top surface of the pipe line and that the boss is perfectly vertical.

Setpoint Adjustment

setpoint adjustment of flow switch

The flow switch is preset at factory prior to dispatch as specified in the purchase order. In case the order does not specify the actuation point, it is factory set to actuate at the minimum limit on falling flow.

If it is necessary to change the setting of the flow or no-flow conditions at site, please follow the following procedures.

  1. Remove the cover
  2. Allow fluid to flow through the pipe line and monitor the volume following over a period of time. From this arrive at flow rate in liters per minute
  3. Regulate flow to desired limit. For falling flow the flow switch should actuate when rate of flow comes down from above the limit and vice versa for rising flow.
  4. Turn range adjustment screw (position ① in the figure) clockwise to reduce actuating point and anti-clockwise to increase setpoint.
  5. After setting the switch re-confirm by increasing and decreasing flow a few times.
  6. Replace the cover. Now the flow switch is in service.

*Screw ③ is for adjustment of the paddle, which has already been set properly.