Introduction to Vane Operated Flow Switches

What Are They?
A vane operated flow switch is a device which utilizes the force exerted on a vane inserted in a flowing fluid to actuate an electric switch at a predetermined rate of flow. The electric switch may be used to start or stop pumps, open or close valves, actuate a warning lamp, sound an alarm, etc. W.E. Anderson and Dwyer flow switches are suitable for applications with a variety of process fluids. The flow switches are available with a wide range of flow actuation points for all standard pipe sizes. Most W.E. Anderson switches are explosion-proof and UL, CSA, CENELEC approved.

How Do They Work?
When fluid moving in the indicated direction of flow impinges upon the flow switch vane, the vane swings on the pivot point until the vane stop hits the switch body. This moves the magnet keeper away from the magnet on the inside of the switch body. Without the magnetic attraction provided by the keeper, the switch actuation lever swings by the force of gravity, thus actuating the snap switch. With the cessation or a decrease in flow below the deactuation point, gravity allows the vane to return to a vertical position. The magnet is again attracted to the keeper moving the switch actuation lever and deactuating the snap switch. The switch is therefore deactuated in the no flow condition. The actuation/deactuation points are functions of the area of the vane exposed to liquid flow, the pipe diameter and characteristics of the fluid.

What is the Dead Band?
When the flow switch is actuated by movement of the vane, some of the force required to actuate the switch must be removed before the switch will deactuate. The dead band is the amount of flow that must be removed before the switch deactuates. For a given vane size and/or liquid, the dead band is essentially a function of the mechanical movement of the vane and the switch actuation mechanism.

Considerations in Selecting a Flow Switch
Model Selection - For the higher flows encountered in pipe sizes of 1-1/2" or larger, the V4 Flow Switch provides the least resistance to flow (pressure drop) with a wide selection of actuation points. For pipe sizes from 1/2" to 1-1/4", the smaller V6 Flow Switch can be utilized assuming that the specified actuation and deactuation flow rates are satisfactory. For very low flows, the V6 Low Flow Switch with a field adjustable actuation point is recommended. The V6 Low Flow Switch differs slightly in its operation as increasing flow displaces a piston against a return spring and this movement is magnetically coupled to the switch actuating lever. The operating piston does result in a higher pressure drop than for the standard V6 or V4.

Actuation/Deactuation Point - The V6 and V6 Low Flow Switch actuation/deactuation points are fixed to those values given in the specifications. However, the V4 can be supplied for a wide range of actuation and deactuation points for various fluids and pipe diameters. For a given V4 vane area, the deactuation flow is approximately 55% of the actuation flow and the actuation flow rate increases with an increase in pipe diameter or a decrease in specific gravity of the fluid. If the actuation/deactuation points offered in the standard V4-2-U multi layer vane flow switch do not meet your requirements, include the following information with your order: 1. Desired actuation and/or deactuation flow rate. 2. Pipe diameter and schedule. 3. Type of fluid and its specific gravity. Preferably, request an Application Data Sheet, return it to us, and we will fabricate the proper V4 vane for your application.

Maximum PSI Rating - W.E. Anderson flow switches are rated for maximum operating pressures from 150 psig (Series V8) to 2000 psig (Series V4 and V6). See Specifications.

Installation - Install both V4 and V6 Flow Switches with the index arrow on the switch body pointing in the direction of flow. V4 models only, must be vertical. The V4 is installed in a 1-1/2" threadolet welded to the pipe. The shape of the vane will vary, the length being limited by the pipe diameter and the width being limited by the opening of the mounting provided in the pipe. Some V4 vane configurations may require a threadolet up to 2-1/2" in size. The V6 Flow Switches are supplied with installation tees for plumbing directly in line.