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 application 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 pitot 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 dies 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 ate.
2. Pipe diameter and schedule.
3. Type of fluid and 4.
Its specific gravity. Preferably, request an Application
Data Sheet, return it to us, and we will fabricate the proper
V5 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 o 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.
Typical Flow
Switch Applications
