Installation of Flow-meters.

Installation of Flow meters.

We as a instrumentation Engineers are many times in a situation where we have to mount a new instrument such as flow meters, level indicators etc. This post is regarding the upstream and downstream distances required for mounting of flow meters. A flow meter when mounted incorrectly can lead to erratic reading. A must for all the Instrumentation Engineers.

Vortex flow meter.

These meters work on the phenomenon of vortex shedding that takes place when fluid or gas meets an obstacle downstream termed as bluff body.
These meters can be installed vertically or horizontally.
For liquid measurements the meter must be full at all times.
Vortex flow meters must be often smaller than line size. Installation should keep the meter full at all times. i.e zero flow.
For steam measurements design process piping so that the meter remain full ,with no entrapped air.
The meter can be installed in any orientation without affecting accuracy.

Avoid installation in loops such condition may cause water hammering at start up due to trapped condensation.

Upstream and downstream distance .

Using k factor correction upstream 10d
Downstream 5d
Without k factor ,35d & 5d.
Vortex flow meter doesn’t require the piping arrangement whats more critical is the piping to remain full and that flw profile is completely free of any distortions..
This usually requires a couple of control valves used to reduce pipes and keep the meter full and generous amount of upstream straight run piping.
Between upstream of control valve and the meter 30 d the piping arrangement is required and between meter and downstream valve there should be straight run equaling atleast 5 x the piping diameter..
Pressure transmitter can be mounted at atleast 4x diameter and temperature transmitter at 6x the diameter.

Orifice type Flow meter.

For an orifice plate ,the straight run required depend upon the beta ratio and the type of upstream components in a pipeline.
If using an standard integral orifice plate of 0.4 beta ratio straight run requirement of 20 straight pipe diameters and 10 d downstream.
If using a conditioning orifice plate of beta ratio 0.4 then 2-6 diameters.

If straightening vanes not used:

If collars ,flanges, wide open gates, reducers or bends, elbows or tees which are all in the same plane-10xdiametrs.
Angle turns out in two planes 50x diameters.
Pressure regulator ,control valves or similar apparatus-75 x diameters.

If straightening vane is used:

6 diameters upstream and 5 diameters downstream.

Magnetic flow meter requirements

Always pipe a electromagnetic flowmeter so it is full of liquid.
The pipe configuration should avoid a build up or accumulation of any secondary phase(solid or air).any entrained air should be carried by meter flow.
You can install magmeters in horizontal lines but best practice call for installation in vertical lines with upward flow.
The general rule of thumb for straight piping is 5 diametr upstream and 3 diameters downstream.
Avoid downward flows.
Avoid installing flow meters on top as these give rise to air bubbles.
Always install control valves and shut off valves downstream of flow meters.
Never install flow meters on suction side of pump.

Coriolis type Flow meter.

Coriolis mass flow metrs measure mass directly and offer few installation limitations. These flow meters are insensitive to swirl and velocity profile distortion.
Install flow metrs so they remain full of liquid and air cannot get trapped inside the tubes.The most desirable is the vertical installation but installation in horizontal piping is also acceptable.
Installation wher fluid flows in downward direction is not acceptable.
Good practice call for upstream installation of strainers,filters,air vapor eliminators as necessary to remove all undesirable secondary phases and air bubbles.
Install control valves downstream to increase backpressure on them so as to decrease the probablity of cavitation and flashing.

Turbine flow meter requirements

Typical manufacture specification for turbine flow meters call for straight pipe lengths of 10-15 pipe diameters upstream and 5d downstream .Additional pipe recommendations include 20 pipe diameters for 90 – degree elbow be fitter stainer or thermowell .
25 pipe diameter for a partially open value
50 pipe diameter for two elbows in different planes or if flow is spiraling.
Straightening vanes can reduce the length of straight pipe otherwise required.
Install control valves only on downstream side of meter.

Plusses & minuses.

Moderate cost ,very good at low viscosity fluids,moderate viscosity and stedy flow rate.
Turn down is very good.
Reliable if put in clean fluids especially with lubricity.
Not good for steam.

Thermal Flow Meter.

Upstream obstruction	Minimum straight pipe requirements
Upstream obstruction	Without flow conditioner	With flow conditioner
Single bend preceded by >9 diameters of straight pipe	15d	3
Pipe size reduction in straight pipe run	15d	3
Multiple bends in plane with <9 diametrs of straight pipe between them	20	9
tees	30	10
Multiple bends out of plane	40	5

Plusses and minuses:

Not applicable to abrasive fluids they can damage the sensor.
Fluids that coat the sensorcan alter the relationship between thermal; properties of fluid and the measurement and adversely affect the measurement.extensive coating can render the sensor useless and can increase the maintenance.
Not suitable for applications with fluids that have varying composition and unknown components.
Aerosols and dropletys can cause the meter to read erratic.this is because large amount of thermal energy is used to heat dropletsis interpreted as high flow signal.
Not good for steam.
Dirty fluids should be avoided.
Two phase fluids to be avoided.