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© 2019 VPInstruments | MAN-VP-SPRO-EN | Revision: 1901 | Date: 04-07-2019
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6.1 Piping table
Check the piping table below and match it for your application. The table shows the amount of
upstream and downstream length depending on the installation. If applicable in front of the meter, use
given upstream length. If applicable in behind the meter, use given downstream length. Gas flow in
pipes follows certain rules, which must be observed for optimal measurement results. In some cases
the upstream length needs to be longer, in other cases it can be shorter.
If possible choose a longer upstream length, as these are minimum values. The up- and
downstream lengths are used industry wide as guidelines, but will never be a guarantee
for obtaining the “true value”. So always be careful and try to build up your own
experience from practical measurements
Piping table
The following table provides a guideline for proper distances between upstream or downstream
objects and the VPFlowScope probe. The upstream length is the length between the last non-straight
object and the VPFlowScope probe. If the upstream length is straight, and the distortion is
downstream of the VPFlowScope probe, you can use the column "downstream length" as a
guideline. In very complex situations, with multiple up- and downstream objects, you should consider
another location. This table is a practical guideline and is not exact science. Practical situations can
have multiple sources of distortion, therefore VPInstruments does not take any responsibility for the
correctness.
Picture Description
Upstream
length
2
Downstream
length
2
Effect
Single elbow 30 * D1 10 * D1 Distorted flow profile
Complex feed-in situation
(header) 40 * D1 10 * D1 Flow profile will be
distorted
Double elbow, multiple
elbows following each
other 40 * D1 10 * D1 Distorted p
swirl
Diameter change from
small to large (gradual or
instant) 40 * D1 5 *D1 Jet shaped flow
Diameter change from
large to small (gradual
change, between 7 and
15 degrees) 10 * D1 5 * D1 Flattened flow profile
1 = inner diameter; 2 = minimum length