Dwyer TFM-LP - Manual (Page 6)

F-20-TF-L, pg. 6 of 30
To calculate the pressure drop at a certain flow rate use the formula
PD = (YourFlow / MaxFlow) 2
x PD
max
PD = Pressure drop at YourFlow.
YourFLow = flow rate (ml/min or l/min)
MaxFlow = 100% rated flow for the sensor (in same units as YourFlow)
PD
max
= Pressure drop at 100% rated flow (see chart above)
If the pressure available for the flow sensor is BELOW the pressure drop at
the required flow then flow through the unit will not be possible.
For example: You have a sensor with a 50-500ml/min flow range and want
to know the pressure drop (or minimum differential pressure required) at
300ml/min. According to the chart above, the pressure drop at 100% of
flow is approx 10psi. Using the formula above:
PD = (300 / 500)
2
x 10 = 3.6 psid
Therefore, at 300ml/min the minimum required differential pressure for this
unit is 3.6 psid. This means that if the available pressure is below 3.6psid
then flow through the unit may not be possible.
Pressure drop through a system is cumulative. If the total pressure drop
across all the components in a system exceeds the minimum pressure
available then flow will not be possible.
For example: A system has a pressure of 30-40psi. There are several
components and the sum of their pressure drops at the required flow rate is
32psid. If the system is operating at 30psi flow would not be possible as the
total of the pressure drops would be greater than the pressure available.
The system will only operate if the system pressure is above 32psi.
If there is any possibility that there may be bubbles or entrapped gas in the
system then the outlet tubing should be elevated above the inlet port. This
will enable any gas that may become entrapped in the unit to escape (see
section C2 for details of how to remove entrapped air or gas).
2. Mounting the Flow Sensor or Flow Meter.
The TF Series of Flow Sensors and Flow Meters have no particular
installation requirements so may be mounted in any convenient position.
It is recommended that units be fixed to a suitable substrate with #4 screws
using the two mounting holes provided.