Orifice plate flowmeters are widely used in industrial flow measurement due to their simple structure, high reliability, and cost-effectiveness.
Their working principle is based on the differential pressure method, which determines fluid flow rate by measuring the pressure drop across the orifice plate.
Proper installation is crucial for ensuring accurate readings and long-term stable operation. This document outlines key installation guidelines, common mistakes, and best practices to ensure a successful installation.
Selection of Installation Location
Straight Pipe Requirements
To ensure stable flow conditions and minimise disturbances, the orifice plate flowmeter should be installed in straight pipe sections with sufficient upstream and downstream lengths:
The upstream straight pipe length should be at least 10 times the pipe diameter (D).
The downstream straight pipe length should be at least 5 times the pipe diameter (D).
If there are flow-disrupting components upstream (e.g., elbows, valves, reducers), the straight pipe length should be increased accordingly to reduce turbulence.
Avoid Unfavourable Locations
Avoid installing the flowmeter at the highest or lowest point of the pipe to prevent gas or liquid accumulation, which can affect accuracy.
For gas flow measurement, the pressure measuring point should be located at the upper part of the pipe.
For liquid flow measurement, the pressure gauge should be placed at the bottom of the pipe.
For steam flow measurement, the pressure gauge should be placed on the side of the pipe to prevent condensation from affecting the reading.
Orifice Plate Installation
Alignment and Positioning
The centerline of the orifice plate must be precisely aligned with the centerline of the pipe.
The upstream face of the orifice plate should be perpendicular to the pipe axis, with a deviation not exceeding 1°.
Orifice Plate Orientation
The sharp edge (upstream side) of the orifice plate must face the direction of incoming flow.
A common mistake is reversing the orientation, which leads to inaccurate measurements and increased pressure loss.
Sealing Precautions
Use appropriate gaskets to ensure a good seal and prevent leaks.
Gaskets must not extend into the pipe; otherwise, they will change the flow pattern and introduce measurement errors.
Pressure Tapping and Pulse Piping Installation
Selection of Pressure Tapping Method
Common pressure tapping methods include:
Angle taps (suitable for smaller pipes)
Flange taps (commonly used in industrial applications)
DD/2 connectors (for large piping systems)
The choice depends on the system design and accuracy requirements.
Pulse Piping Installation Guidelines
Use short, straight pulse lines to minimise response time and pressure drop.
The inner diameter of the pulse line should be at least 6 mm.
For horizontal lines, maintain a slope (not less than 1:10) to facilitate drainage and prevent blockage.
For gas flow measurement, the pulse line should be arranged upwards from the pressure measuring point to prevent liquid accumulation.
For liquid flow measurement, the pulse line should be arranged downwards to avoid air bubble formation.
If necessary, the pulse line can be insulated and heated to prevent condensation, freezing, or vaporisation.
Differential Pressure Transmitter Installation
The transmitter should be installed as close to the orifice plate as possible to minimise pressure signal loss.
Maintain the same elevation as the pressure measuring point to avoid errors caused by height differences. If height differences are unavoidable, a correction factor must be applied to the measurement system to account for these differences.
Ensure easy access for transmitter maintenance and calibration.