The use of flow measuring orifice plates for gas and steam has been a common practice. The orifice plates are efficient and are used in particular for measuring gas and vapor flows, but can also be used with liquids. There is a wide variety of models of orifice plates (see following illustration), all of which are described in the standard rules for their application.
The field of application ranges from models with angular step takes single or double (a, b) to take between devices and between pipe flanges (c, f), very common in the U.S., or compact sections measuring (d). Other designs have evolved to meet specific needs. Among these we may mention devices with quarter-circle geometries segmental, eccentric plaque and other special geometries. Some of these designs are less sensitive to viscosity, others allow wider turndown, and some are designed for fluids with particles or "dirty process."
The pressure is detected in tubes or annular grooves upstream and downstream of the diaphragm. This variety of designs corresponding to the variety of installation options, materials and application areas.
Advantages:
■ Simple and robust design
■ Standard global standard for over 60 years, according to ISO 5167-1 / A1, AGA, ASME (LH Spink)
■ Wide variety of materials (steel, PVDF, Teflon, etc.). For very different
■ Nominal standards available from DN 10 to 1,000 (1 / 2 to 40 ")
■ Low initial investment (depending on model)
Disadvantages:
■ Increased pressure drop in the nozzles and Venturi tubes.
■ wear comparatively easy, and therefore distortion of measurement if the abrasion or deposition affect the g eometría the diaphragm.
■ The installation and maintenance costs will increase if you include the installation of capillaries and associated valves (except for compact counters as "Deltatop" E + H).
Orifice models most important are briefly described below (Fig. below):
Model making ground in one piece (to DIN 19205 Part I):
The pressure is detected with jacks placed immediately before and after the disk diaphragm. This model is designed to be installed between two flanges. The standard describes standard models for nominal diameters from DN 50 to 2,000 (2 to 80 ") and nominal pressures between PN 1 and 400 (14-5800 psi).
Model making ground in two pieces (DIN 19205 Part I):
The pressure is detected in annular grooves upstream and downstream of the diaphragm disc ¬ day. This setting ensures a more accurate average of the differential pressure across the pipe cross section.
Model shots flange (ISO 5167):
The advantage of this design is that the straight input and output are integrated into a single mechanical unit and all components are already assembled in a precision setting. This "compact measuring section" is mainly used for nominal diameters DN 10 to 50 (1 / 2 to 2 ").
Figure: Sample plate hole:
a = plate hole (DIN 19205 Part 1)
b = plate hole (DIN 19205 Part 1)
c = Model outlet flange (ISO 5167)
d = measured section shots compact flange (ISO 5167)
e = insertion hole plate between two flanges (ISO 5167)
f = Model with outlets in remote D & D pipe / 2 (ISO 5167)
Model takes into flange (ISO 5167)
This model uses adjacent pipe flanges upstream and downstream of the diaphragm. According to ISO 5167, the outlets are located 25 mm (1 ") upstream of the disk and 25 mm (1") downstream in the respective cross sections. This model facilitates the replacement of the orifice, which allows easily inserting orifice plates of different diameters (d) and thus increase the field of flow measurement values.
Replacing the diaphragm disk (ISO 5167):
This type of diaphragm disk is installed between two flanges. The outer diameter is of adequate size to ensure that the screws hold the disk perfectly centered. The operator to drill the holes for the pressure taps in accordance with the standard used. This defines three different possible locations for the pressure taps:
■ Take flush
■ Take Flange
■ Tomas distance D and D / 2: The shots are at a definite distance before and after the diaphragm. The operator to drill the holes for pressure taps, these must be perpendicular to the axis of the pipe and be free of burrs.
