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Differential pressure instruments for flow (according to ISO 5167)

For DP flow measurement of gases, liquids and steam based on the international standard ISO 5167



Differential pressure instruments according to ISO 5167 are used in almost all industrial sectors. The range of different throttling devices as well as materials that can be used allow the measurement of different fluids. There are also only a few restrictions with regard to possible pressures and temperatures.

Due to their standardization, the expected measurement results are manufacturer independent.

Design features, constraints and error limits are described in detail in the standards, depending on the respective differential pressure flow element. Therefore we limit ourselves here to the presentation of these different elements.

Orifice plates with integral taps

Orifice plates with integral taps are manufactured from a single body and are therefore particularly inexpensive. The pressure tapping takes place at two points. The instruments are easy to handle and offer good accuracy with reasonable inlet and outlet runs.

Orifice plates with annular chambers

Annular chamber orifice plates consist of two rings pressed together, between which the orifice plate is clamped. The pressure is measured upstream and downstream through an annular chamber. The accuracy is comparable to that of the standard orifice even with reduced inlet and outlet runs.

Orifice plates

Orifice plates for the the installation with flange taps consist of the orifice plate with a welded-on marking and grip plate. They plates have no pressure taps and are therefore normally mounted between measuring flanges containing the pressure taps.


Nozzles are divided into two categories of ISA 1932 nozzles and long radius nozzles

 ISA-1932 nozzles are suitable for measuring flow rates of gas, steam and liquid. In the context of ISO 5167 they offer very good accuracy with relatively low permanent pressure losses. Weld-in nozzles are used especially in the environment of power plant applications. The tapping can be carried out as corner taps or annular chamber tapping or also as flange or socket ring tapping.

Long radius nozzles are used in the same application areas as ISA-1932 nozzles and are available in the same design variants as these. They are characterized by very good wear resistance. The disadvantage is the poorer linearity of their individual characteristic.

Venturi nozzles

Standard Venturi nozzles are suitable for measuring flow rates in gases, steam and liquids.In the context of ISO 5167 they offer medium accuracy with significantly lower permanent pressure losses compared to standard nozzles or orifice plates.

They have very good wear resistance, but show reduced linearity compared to other differential pressure elements.

 The tapping can be designed as corner or an annular chamber tapping or also as flange or socket ring tapping.

Venturi tubes

Classical venturi tubes are differential pressure elements which are characterized by particularly low pressure losses and short required straight pipe runs. They show medium to good measuring accuracy in their respective working ranges.

 The taps can be designed as corner or annular chamber taps.

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