1. Home
  2. D. Mechanical installation
  3. D1. Select the right installation point

D1. Select the right installation point

Reading Time: 3 minutes - Video Time:

1. Introduction

In this chapter we will cover:

  • How to select the right installation point for your flow meter: what to take into account and what to avoid.
The installation point is crucial for correct measurements! To ensure the highest possible measurement accuracy: follow this chapter carefully!
These devices are for use with Air, Nitrogen, Argon, Helium, Carbon Dioxide and other non-hazardous and non-corrosive gases.

2. Take into account 

2.1 Instrument specifications

Stay within the specification of the specific flow meter (Chapter J). These include, but are not limited to:

  1. The type of gas
  2. Range of the flow, pressure and/or temperature

Note that the basic specifications can be found on the sticker on your flow meter. For all specifications, check the product datasheet

2.2. Accessibility

  • For wiring.
  • For maintenance: at least once a year be able to handle the device either directly or e.g. by use of scaffolding.

2.3 VPFlowScope technology and locations

The key to the proper installation of your VPFlowScope is selecting the right location for the installation. Always check the measurement principle of your flow meter and the associated air conditions.

VPFlowScope Supply and Demand diagram

Type Description and location
VPFlowScope DPDifferential pressure technology. Meant for installation before the dryer in saturated, hot air conditions with relatively high flows.
M / Probe / In-line
Thermal mass flow sensor. Install in clean, dry air only. Installation after the dryer. The sensor will damage when being installed in wet air conditions.

2.4 VPFlowScope DP location

The VPFlowScope DP is a compressed air flow meter, not a water meter. A location that could hold water, should be avoided in all cases!

Number Description
1Water might build up at the lowest point. Your VPFlowScope DP will be flooded with water and eventually stop functioning.Icon - Thumbs down
2 / 4Never install in a vertical pipe as water will stay in the negative pressure hole and it will flood your VPFlowScope DP.Icon - Thumbs down
3The meter is installed at the highest point. Good! Water will flow to a lower point.Icon - Thumbs up
5The meter is installed at a high point above possible water, after the wet receiver. Excellent! The drain in the receiver will drain most of the water, so you will expose the flow meter mainly to mist.Icon - Thumbs up
During the installation of VPFlowScopes the up- and downstream lengths have to respected by the pipeline table, which can be found in the following chapter: D1.2.5 Stable gas flow profile.

2.5 Stable gas flow profile

Any obstacle in the pipeline like an elbow or diameter change will result in non-stable flow and thus incorrect measurements.

An example is a double elbow and gas profile. In this case, stable at a length: 30 * pipe diameter.

Gas profile


Please follow the piping table as a practical guideline. These are minimum industry recommended lengths. If you have more length available, please use it, this will always lead to better results. Also be aware that any upstream or downstream objects, for example, other insertion probes may affect the measurement results.

D = inner pipe diameter

 PictureDescriptionEffectMinimum upstream lengthMinimum downstream length
 Piping single elbow iconSingle elbowDistorted flow profile30 * D 10 * D
 Complex feed-in situation (header)Distorted flow profile 40 * D10 * D
 Double elbow piping iconDouble elbow, multiple elbows following each otherDistorted flow profile + swirl40 * D10 * D
 Diameter change in piping iconPipe diameter change.

Small –> large

Gradual or instant

Jet shaped flow40 * D5 * D
Diameter change piping 2 iconPipe diameter change.

Large –> small

Gradual: 5° to 7°

Flattened flow profile10 * D5 * D
TIP iconPractical situations can have multiple sources of distortion. The guidelines are practical, not science. VPInstruments does not take any responsibility for the correctness.

3. Avoid the following 

1. Mechanical stress on the flow meter: this might damage the entire flow meter.
2. Excessive heat. This can damage the sensor. Check temperature specifications.
3. Corrosive atmosphere. This can damage the sensor’s housing over time.
4. Electrical problems: high voltage / high power.
5. Mechanical Vibrations. These can lead to damage over a longer period of time.
6. The danger for damage e.g. walking bridges of forklift trucks passing by.
7. Water exposure VPFlowscopes are rated IP65, they are only splash prove. Potential water damage on the outside, avoid areas of high humidity and avoid dripping.
8. Any environmental source that can cause a potential error.

4. Next Step

Now that you know what to take into account when positioning the VPFlowScope it is important to know how to do it with the right specification of your insertion flow meter.

Next Step: D2. Insertion point for insertion flow meters and how to hot tap one. 

Updated on July 16, 2020

Was this article helpful?