DP Flow Meter includes throttling parts (eg. orifice plates), differential pressure transmitters, three-way valves. Used for flow measurement of various liquids, gases and steam.

The Engineers Guide to DP Flow Measurement

What is DP Flow Meter?

The differential pressure flowmeter is an instrument for measuring flow. It uses the principle that there is a certain relationship between the pressure difference and the flow rate generated when the fluid flows through the throttling device. The flow rate is measured by measuring the pressure difference.

The throttling device is a local constriction element installed in the pipeline. The most commonly used are perforated plates, nozzles and venturi tubes.

How is DP flow calculated?

Flow calculation formula 1: The conversion of the relationship between the differential pressure and the flow rate of the differential pressure flowmeter

The differential pressure of a differential pressure flowmeter is proportional to the square of the flow rate. In other words, the flow rate is proportional to the square root of the differential pressure. It is expressed by the following formula:

The scale unit of the flow meter is the flow percentage. The lower limit of the differential pressure is 0 o’clock.

In the above formula:
△P is any differential pressure;
Q is any flow;
△Pmax is the upper limit of differential pressure;
Qmax is the upper limit of the flow rate;
n is any percentage of flow

Flow calculation formula 2: Conversion of volume flow in standard state and working state

The conversion formula of volume flow between standard state and working state is as follows:

In the formula, qv is the volumetric flow rate under working conditions, in m3/h;
qn is the volume flow under standard conditions, in m3/h;
P is the absolute pressure under working conditions, the unit is Pa;
Pn is the absolute pressure in the standard state, in Pa;
T is the thermodynamic temperature under working conditions, in K;
Tn is the thermodynamic temperature in the standard state, in K;
Z is the gas compression coefficient under working conditions;
Zn is the gas compressibility coefficient under standard conditions;

Flow calculation formula 3: Calculation of changing range from standard orifice plate

Sometimes it is encountered in the field that the measured flow exceeds the maximum range of the orifice plate. Or the flow rate is too small and can only be displayed below 30% of the maximum range. The emergency can be met by expanding or reducing the differential pressure range.

The basis for changing the range is the formula. The maximum differential pressure and maximum flow rate of the flowmeter in use are known. With these two parameters combined with the flow calculation formula, the calculation work for changing the range can be carried out.

Tools:

DP Flow Meter Output Calculator	Flow Meter 4-20mA Current Output Calculator	Flow Velocity & Pipe Diameter to Volumetric Flow Rate Calculator
Mass Flow & Density to Volume Flow Calculator	Mass Flow Rate Unit Converter	Volume Flow Rate Converter
Volume Flow & Density to Mass Flow Calculator	Volumetric Flow Rate & Pipe Diameter to Flow Speed Calculator

Difference between integrated DP flow meter and general DP flowmeter

A general differential pressure flow meter includes two parts: a throttle and a differential pressure transmitter. The installation requires a pressure pipe system to connect the two.

The integrated differential pressure flowmeter directly assembles the throttling piece, the pressure pipe system and the differential pressure transmitter. At the same time, the integrated differential pressure flowmeter depends on the product. It can have both pressure and temperature measurement functions, temperature-pressure compensation functions, etc., all integrated in one device.

DP Flow Meter Straight Run Requirement

The accuracy of flow measurement has a lot to do with whether the installation of the differential pressure flowmeter meets the requirements. The general requirements are as follows:

When installing, it must be ensured that the opening of the throttling piece is concentric with the pipe. The end face of the throttling piece is perpendicular to the axis of the pipe.

There must be a certain length of straight pipe section upstream and downstream of the throttle.

• Orifice flowmeter requires 10D front and 5D rear
• V-cone flowmeter requires 5D in the front and 1-3D in the back
• The elbow flowmeter is installed on the elbow.

What Is Integral Orifice Plate?

The main function of the orifice is to reduce the pressure of the fluid. But it does not mean that it can be mixed, and the orifice plate should be selected according to the specific medium.

The integrated orifice flowmeter is a high turndown differential pressure flow device composed of a standard orifice plate and a multi-parameter differential pressure transmitter (or differential pressure transmitter, temperature transmitter and pressure transmitter). It can measure the flow of gas, steam, liquid and natural gas. It is widely used in process control and measurement in the fields of petroleum, chemical industry, metallurgy, electric power, heating, water supply and so on.

The integrated orifice device is simpler. No pressure tube is required. It can be directly connected to differential pressure transmitter and pressure transmitter.

Extended reading: Vortex Steam Flow Meter

Orifice Plate Flow Meter

More Featured Flow Meters

Sino-Inst offers Integral DP Flow Meters.

A wide variety of Integral DP Flow Meter options are available to you, such as brass, carbon steel. You can also choose from free samples.

Sino-Inst is Integral DP Flow Meter supplier.Integral DP Flow Meter products are most popular in Domestic Market, Southeast Asia, and Mid East.

You can ensure product safety by selecting from certified suppliers, including 375 with ISO9001, ISO14001, and Other certification.

A throttling device is also called a throttling flowmeter. A typical differential pressure flow meter. Commonly used to measure the flow of gas, liquid and steam in industrial production.

Features of Throttling Device

• The throttling device has the advantages of simple structure, firmness, reliable work, stable performance, high degree, and low price. Therefore, the amount of throttling device has an advantage compared with other flow meters.
• Wide range of pipe diameter, φ2～φ3000mm (or larger). The cross-sectional shape, round or rectangular shape is acceptable.
• The standard throttling device can determine its measurement degree without real flow calibration.
• Applicable to a wide range of tested media. It can be used for almost all gas, steam and liquid flow measurement.
• The working pressure can be as high as 32Mpa. Can also be used for negative pressure.
• Medium temperature range: -l85～+650℃. Other flowmeters are not yet possible.
• The structure of non-standard throttling device is diverse. Almost applicable to various fluid flow measurement.
• The flow range can be changed on site by setting the range of the differential pressure transmitter.
• It is simple to use, operate, easy to master, and daily maintenance is small.

Extended reading: V-Cone Flow Meter Working Principle

Throttling Device type and composition

The throttling device consists of throttling parts (such as orifice plate, nozzle, etc.). Pressure Sensors, fastening devices (flanges, bolts, nuts, gaskets, etc.), and other accessories (pressure guiding tubes, stop Valve, etc.). It can also be equipped with front and rear measuring tubes and flanges at both ends of the straight pipe section.

Throttle Parts

Code	Name	Code	Name	Code	Name
A	Restrictor orifice	K	Wide Edge Orifice	T	Machined Venturi
B	Standard orifice or eight-slot orifice	L	Venturi nozzle	U	Wedge flowmeter
C	Long diameter nozzle	M	Small nozzle	V	V cone flowmeter
D	End orifice plate	N	Orifice plate	W	Rough welded iron plate venturi
E	1/4 arc orifice (nozzle)	O	Eccentric orifice	X	Rough cast venturi
F	Low pressure loss flowmeter	P	ISA1932 nozzle or eight-slot nozzle	Y	Double orifice plate
G	High pressure lens aperture plate	Q	Round hole plate	Z	Averaging tube flowmeter
H	Annular orifice	R	Conical inlet orifice
J	Wing type wind measuring device	S	Double venturi

Extended Reading: Differential Pressure (DP) Flow Meters Technology

Pressure method

Code	Name	Code	Name
H	Corner connection pressure (ring chamber)	J	Diameter pressure
Z	Corner connection pressure (drilling)	T	Special pressure
F	Flange pressure

Note: The current limiting orifice has no such representation method

Diameter

Code	2	3	4	5	6	8	10	12	15	17	20	22	25
Diameter (mm)	25	32	40	50	65	80	100	125	150	175	200	225	250
Code	27	30	32	35	37	40	45	50	60	70	80	90	99
Diameter (mm)	275	300	325	350	375	400	450	500	600	700	800	900	1000

Pipe diameter greater than 1000 is expressed as 1/10 of the actual pipe diameter

Nominal pressure

Code	0	1	2	3	4	6	10	16	20	25	32	40
Nominal pressure(Mpa)	0.6	1	1.6	2.5	4	6.4	10	16	20	25	32	42

The special nominal pressure is filled in according to the actual design pressure value

Supply method

Code	Supply content
A	Complete device with front 10D and rear 5D measuring tubes (including connecting flange and process flange)
A1	Complete device with front 10D and rear 5D measuring tube (including connecting flange)
A2	Complete device with front 10D and rear 5D measuring tube (pipe end inverted bevel)
B	A complete set of equipment with upstream and downstream measuring tubes (including process flanges) according to petrochemical standards (HGJ516-87)
B1	According to the petrochemical standard (HGJ516-87), a complete set of equipment with upstream and downstream measuring pipes (pipe end inverted bevel)
B2	According to the petrochemical standard (HGJ516-87), a complete set of equipment without upstream and downstream measuring tubes
C	According to the standard of the Ministry of Electric Power (GD87-1101) a complete set of equipment with upstream and downstream measuring tubes
D	Flanges, ring chambers or pressure-taking flanges, throttles, pressure pipes, fasteners and other complete sets of devices without measuring tubes
E	Single throttle

Extended reading: [Working principle&Price]SI3051ANB Annubar Flow Meter

The principle of Throttling Device flow measurement

The throttling device artificially causes throttling in the pipeline through which the medium circulates (as shown in the figure). When the measured medium flows through the throttling device, it causes a local contraction. The stream is concentrated, the flow velocity increases, and the static pressure decreases.

Therefore, differential pressure is generated between the upstream and downstream sides of the throttle. There is a certain functional relationship between this differential pressure and the flow rate. The greater the flow, the greater the differential pressure generated. Therefore, the flow can be measured by measuring the differential pressure.

You may like: How does a pressure transmitter work?

Throttling Device Types

As the most important branch of the flow meter, the throttling device is divided into two categories: standard throttling devices and non-standard throttling devices.

Standard throttling devices include: standard orifice plate, ISA standard nozzle, long neck nozzle, classic venturi tube and venturi nozzle;

Non-standard throttling devices include: annular orifice plate. Quarter circle nozzle. Quarter circle orifice plate. Conical inlet orifice plate. Round missing orifice plate. Eccentric orifice plate. Double orifice plate. Low pressure loss flow tube. Rectangular venturi tube, V-cone flowmeter, wedge flowmeter, built-in orifice, restrictive orifice, etc.

Extended reading​: What is a flow nozzle?

Orifice Throttle Flow Meter

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Read more about: 5 Factors Affecting Pressure Drop

Sino-Inst offers Throttling Devices. A wide variety of Throttling Device options are available to you, such as brass, carbon steel. You can also choose from free samples.

Sino-Inst is an Throttling Device supplier. Orifice plate flow meter products are most popular in Domestic Market, Southeast Asia, and Mid East.

You can ensure product safety by selecting from certified suppliers, including 375 with ISO9001, ISO14001, and Other certification.

Differential Pressure Flow Meter is also called DP flow meter. Differential pressure flow meters use the principle of differential pressure to measure the flow of liquid, gas and steam.

Featured Differential Pressure Flow Meters

Differential Pressure Flow Meters Applications

DP flow meter applicable fluid

Clean gas /liquid

Dirty gas /liquid

Corrosive liquid

Viscous liquid

Abrasive slurry

Fiber-containing slurry

Low flow rate fluid

Steam (gas)

High temperature fluid

Cryogenic fluid

Not full of pipe

Non-newtonian fluid

Open channel

V cone

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Orifice

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nozzle

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Uniform tube

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Elbow

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Extended Reading: Differential Pressure (DP) Flow Meters Technology

Differential pressure flow meter advantages and disadvantages

Differential pressure flow meter working principle

When the fluid flows through the throttle, the fluid will be accelerated due to the fluid being compressed.

As the velocity of the fluid increases, the kinetic energy of the fluid will increase accordingly.

According to the law of conservation of energy, we know that the static pressure of the fluid being accelerated will reduce the corresponding value.

As the picture shows:

The cross-sectional area of the pipe at cross-section 1 is A1. The average flow velocity of the fluid when flowing through the cross section A1 is V1. Its density is ρ1.

When the fluid flows through cross section 2. The average flow rate of the fluid becomes V2. The density is ρ2. The cross-sectional area is A2.

According to the principle of fluid flow continuity, there is the following relationship: V1×A1×ρ1=V2×A2×ρ2.

If the fluid is a liquid, the density of the fluid before and after compression is generally considered constant. That is, ρ1=ρ2=ρ.

Therefore, the volumetric flow rate of the liquid: qv=V1×A1=V2×A2 ——–Formula①

According to the Bernoulli equation (i.e. the law of conservation of energy), Z1=Z2 on a horizontal pipe, then the following relationship is given:
—————Formula②

Applying the Bernoulli equation and the principle of flow continuity, there are the following relations on the two cross sections:

——————Formula ③

From formula ①, we get: V1=A2/A1×V2; put formula ① and formula ② into formula ③ to get:

———————Formula④

In the above formula: A1=(πD2)/4, A2=(πd2)/4, according to the definition of the diameter ratio according to the diameter ratio β: β=d/D. From formula ①, we can get: V2=qv/A2

Therefore: The theoretical flow formula can be derived from this:

————————–Formula ⑤

Also defined by the outflow coefficient C is: C=actual flow/theoretical flow,
Finally, the calculation formula of differential pressure flowmeter can be obtained:

–————————-Formula ⑥;

The expansibility coefficient of ε measured medium in formula ⑥, generally speaking ε=1 for liquid.

It can compress fluid ε<1 for gas, steam, etc.
qv is the volume flow of the fluid, unit: m3/s).
ρ1 is the density of the fluid upstream of the throttle (front) under working conditions, in kg/m3.
d is the equivalent opening diameter of the throttle under working conditions, unit: m.
△P is differential pressure, △P=P1-P2, unit: Pa.

Extended reading: Gas Rotameter Tips

Differential pressure flowmeter selection

The selection of differential pressure flowmeter should consider the following aspects:

1.Accuracy, repeatability, linearity, flow range and range

The standard parts of the differential pressure flowmeter have a strict range of use. These parameters include pipe diameter ratio, Reynolds coefficient, pipe wall thickness and other parameters.

Therefore, these series of parameters should be selected reasonably in actual selection and application. In addition, the accuracy of the differential pressure flowmeter depends to a large extent on the conditions of use on site, and generally depends on the conditions of the fluid.

2.Fluid characteristics

The characteristics of the fluid refer to the fluid’s medium conditions such as density, dynamic viscosity, pressure, temperature, corrosivity, abrasion, fouling, and dirt.
Therefore, the selection is a differential pressure flowmeter that should be reasonably selected according to the physical characteristics of the fluid medium on site. If you do not understand the physical characteristics of the fluid on site, you should actively use the instrument to measure these physical parameters.

3.Economic factors

Should consider the purchase cost of differential pressure flowmeter. Installation costs and after installation. Later maintenance costs. Calibration fee. The later operating cost of the larger diameter differential pressure flowmeter is a relatively large expense. Therefore, the proper caliber differential pressure flowmeter should be selected when selecting the model.

4.Pressure loss

Large pressure loss is one of the main disadvantages of differential pressure flow meters. Orifice plates and nozzles in various throttling devices are throttling parts with large pressure loss. At the same flow rate and β value, the pressure loss of the nozzle is only 30%-50% of the pressure loss of the orifice, which means that the nozzle has a lower pressure loss.

Various flow tubes (Venturi tube, Dole tube, Rollos tube, general Venturi tube, etc.) are throttling devices with low pressure loss. Their pressure loss is only 20% of the orifice plate, even as low as 5%-10%. The development and application of these throttling devices is a direction for future efforts.

Differential pressure flow meters are one of the most widely used types of flow meters. Sino-Inst analyzed the working principle and selection of differential pressure flow meters. It provides a certain theoretical reference basis for the selection and use of differential pressure flow meters in the future.

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Sino-Inst, Manufacuturer for differential pressure flow meters. Including Orifice plate, Venturi, Annubar, etc. Suitable for liquid, gas and steam flow measurement.

Sino-Inst’s differential pressure flow meters, made in China, Having good Quality, With better price. Our flow measurement instruments are widely used in China, India, Pakistan, US, and other countries.