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  3. D3. Insertion point for insertion flow meters and how to hot tap one

D3. Insertion point for insertion flow meters and how to hot tap one

Reading Time: 2 minutes - Video Time: 2:30

1. Introduction

In this chapter we cover:

  • The right specifications for your flow meter insertion point.
  • How to make an installation point for your flowmeter.

2. Insertion point specifications

Use a ball valve for inserting and retracting your flow meter any time under pressurized conditions, to prevent major pressure losses.

Insertion hole width: > 16mm / 0.63 inch.

Smaller holes will give problems like misalignment, no insertion (you measure pressure, but no flow) and even damage to the sensor tip can possibly occur.

2 types of Insertion point possibilities:

1. Via welded tap with ball valve.

  • Welded tap with 1/2″ female thread with
  • 1/2″ Full bore or 3/4″ ball valve.
Welded tap
2. Via hot tap saddle with ball valve.

  • Hot tap saddle: This can be used to drill an installation point under pressurized conditions.
  • Ball valve:
    • 1/2″ Full bore or 3/4″ ball valve.
    • In the case of VPInstruments hot tap drill: drill size is 1″. So use a 1″ ball valve with reducer to 1/2″ full bore.
Hot tap saddle

3. Create welded tap

Ask a certified installation person to create a welded tap. Make sure it complies with the recommendations given above. After welding the tap, the hole can be drilled using a hot tap drill.

4. Insertion point: make it smooth

It is important to create a smooth inner pipe all the way, so that the flow will remain undisturbed. Rules of thumb:

  • Keep the connection smooth
  • Avoid welding rims on the inside
  • Avoid seals (from flanges) to block the flow path
  • Avoid large dead spaces around the probe
Good practice Bad practice 
The pipe is smooth and the hole is relatively small, leaving a small gap around the sensor tip.A standard T-piece is used. This causes turbulence around the sensor. Furthermore, the diameter changes in the measurement section, leading to the unpredicted behavior of the flow meter over the measurement range. Especially in smaller pipes < 3 inches, this is a very unwanted situation.

5. Next Step

You are almost ready to install your flowmeter but the next step will provide you with the knowledge about how to position the flowmeter when inserting it.

Next Step: D4 Correct positioning insertion flow meter

Updated on August 26, 2020

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