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The best piping designs provide a bypass line, as shown in the following diagram,
which allows isolation of the flow-meter and associated strainer from the main process
line. The benefits of installing a bypass line are that your system can be purged before
start-up, to remove any foreign particles or air slugs that would cause serious damage
to your meter. Other benefits of this piping design are that maintenance and repairs
on your flow-meter and strainer can be carried out quickly and economically without
interrupting critical processes. Smaller installations, or non-critical processes may not
see a benefit from installing a bypass line.
3.3 Filtration / Straining
All liquid products have the chance of solid particles being present, especially in any new
installations, or in installations where the liquid is open to atmosphere at any point. Solid
particles may come from dust settling on an unsealed storage tank, wear particles from
upstream mechanical devices such as pumps or mixers, or even large metal particles from
cutting or welding on new or modified installations.
It is always advisable to fit the inlet side of any Oval Gear flow-meter directly to a strainer
of appropriate pipe size and mesh size to suit the liquid being measured. The minimum
mesh size as shown in the specifications section of this manual should be adhered to where
ever possible. When metering medium or high viscosity fluids it may be necessary to use a
strainer one pipe size larger than the flow-meter nominal size, in order to limit the pressure
drop across the strainer basket and maintain strainer efficiency.
3.4 Pipe Connections
When installing a flow-meter it is important that no upstream pipe join between the
flow-meter and the strainer are sealed using PTFE sealing tape. Lose pieces of PTFE tape
are common causes of failure in new meter installations due to the tendency to wrap
around the rotating components inside the meter. It is recommended that the sealing of
pipe joins should be done with a sealing paste (such as Loctite® 565 thread sealant paste),
however care must be taken to avoid excess sealant entering the flowmeter when
screwing in fittings.
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