Scissors Rings - Teledyne 4250 Installation And Operation Manual

4250 Flow Meter
Section 3 Installation

3.8.2 Scissors Rings

3-18
Make sure the sensor cable is securely fastened along the
back (downstream) edge of the ring. Otherwise, the sensor
may provide inaccurate level readings under conditions of
high velocity.
Do not overtighten the plastic cable ties; they should be tight-
ened just enough to secure the cable in place, without greatly
indenting the cable. Overtightening the plastic ties may col-
lapse the reference tube in the cable, blocking it.
The spring ring may need anchoring. Under conditions of high
velocity (greater than 5 feet per second or 1.5 meters per second),
the ring may not have sufficient outward spring force to
maintain a tight fit inside the pipe. The ring may start to lift off
the bottom of the pipe in a waving fashion, or may even be
carried downstream.
This problem is more prevalent in the larger diameter pipes (10",
12", and 15", and in pipes with smooth inside surfaces, such as
plastic pipes). If any of these conditions are present, or if
movement of the mounting ring is detected or suspected, you
must anchor the ring in place. You can do this by setting screws
through the ring into the pipe, or by other appropriate means. If
there is a problem with the smaller diameter rings, it may be suf-
ficient to simply increase the outward spring force of the ring by
bending it into a less round configuration.
For pipes larger than 15" in diameter, Teledyne Isco offers the
adjustable Scissors Ring (also known as the Universal Mounting
Ring). This device consists of two or more metal strips that lock
together with tabs to form a single assembly. There is a base
section where the sensors are mounted, one or more extension
sections (usually), and a scissors section at the top that expands
the entire assembly and tightens it inside the pipe. The scissors
mechanism includes a long screw that increases the width as it is
tightened.
The assembled rings fit pipe diameters from 16" to 80". Secure
the unit in place by tightening the scissors mechanism with a
socket wrench or other suitable tool. Ring sections are .040" thick
half-hard 301 stainless steel sheet. All other parts are also
stainless steel, except for the plastic cable ties in the hardware
kit.
Each extension, 1, 2, 3, and 4, adds 9.0", 21.5", 31.5", or 41.5",
respectively, to the circumference of the ring. Used alone, the
base section fits pipe that is approximately 16" to 18" in
diameter. The 9.0" (the smallest) extension exists so that in
larger pipe sizes, where large variations in circumference can
occur, you can use one or two of these extensions to take up or
remove slack, to bring the scissors mechanism into a position
where it can be effectively tightened.
CAUTION
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