Laminar Flow Element (Lfe) Configuration - Teledyne 200 Series Instruction Manual

200/202 Series Flowmeters and Controllers Instruction Manual
higher pressures), applying a diluted soap solution to the flow connections, and monitoring the
connections for bubbles of escaping gas.
2.4.5.

Laminar Flow Element (LFE) Configuration

200 Series flowmeters can also be mounted in parallel with a larger laminar flow element. The
installation of a Laminar Flow Element (LFE) in a flow circuit requires sufficient conductance before
entering and after exiting the LFE sensor taps to allow the flow to fully develop and promote accurate
flow sampling with a minimum of turbulence. To ensure the proper conductance around the flow
instrument with LFE, a rule of thumb is employed when choosing the lengths of pipe or tubing upstream
and downstream of LFEs:
Example: Suppose a 4-inch LFE is selected. The length of 4-inch inner diameter tubing or pipe,
upstream of the sensor inlet tap, will be a minimum of 20 inches. The minimum length of 4-inch tubing
or pipe downstream from the sensor outlet tap will be at least 4 inches. The length of additional 4-inch
inlet tubing required for the 4-inch LFE is (20 – 2.5 = 17.5) inches. The additional length of 4-inch
tubing required for the outlet side of the 4-inch LFE is (4 – 2.5 = 1.5) inches. This brings the overall
length of the assembly to (17.5 + 1.5 + 10 = 29 inches).
Tubular configurations upstream or downstream that
involve conical shapes or optimized expansion nozzles
will reduce the length of tubing required for flow
straightening, but the actual length necessary will be
a function of that geometrical shape. Testing of that
configuration will be necessary for each application.
The same is true for screen meshes or flow
straighteners. A brief listing of the ranges associated
with LFEs of different sizes is given on the right.
EAR99 Technology Subject to Restrictions Contained on the Cover Page
1) The upstream flow tube length must be at least 5 times the inner diameter of
the selected LFE before the sensor inlet tap.
2) The downstream tube length must be at least the diameter of the selected LFE
after the sensor outlet tap.
To properly apply the rule of thumb we also need to know the distance between
the LFE edges and the sensor taps:
LFE ID
< 3 inches
≥ 3 inches
Edge to Sensor Tap LFE length
1.5 inches 8 inches
2.5 inches 10 inches
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