The flowmeter selection

With the development of air system solutions, more can provide users with more and more products and services, such as air flow meter, is a series of new products in recent years.

but speaking of flowmeter, in all the compressed air at the scene of process instruments, flow transmitter is definitely one of the most unpredictable, it will be affected by the accuracy of condition, pressure, temperature, medium velocity, pipe diameter size, installation, and so on a variety of factors, so how about proper selection and how to guarantee its accuracy has been a lot of problems. To solve this problem, the control team special invited meter instrument opened a technical discussion of experts, managed to understand many common problems. Here and share a few of the more important knowledge,

basic concept: there are many kinds of flow meter on the market at present, turbine, and vortex, orifice plate, heat type, ultrasonic, electromagnetic. For compressed air system is of high cost performance of vortex flowmeter, broad standard flowmeter product also is such.

for compressed air flow, often use two nouns, the state of the working condition of traffic and traffic.

tag of flow temperature is 20 ℃ pressure 0. 1 mpa, the flow, the unit is generally Nm3 / min. We usually say air compressor gas for 20 m3 is actually the case flow;

condition of flow is in the working status of the temperature and pressure of flow, unit expressed in m3 / min. Great product standard flowmeter parameters of the flow measurement range is working flow ( The unit is the m3 / h) Second, the big flowmeter selection:

1. Such as the mark of flow unit is Nm3 / min, should first & times; 60 become Nm3 / h;

2。 Put the mark of flow Nm3 / h put into working flow m3 / h;

for our compressed air system, the algorithm is simple: ( Among them, the gage pressure unit is kg. )

( The complete formula ( For reference only) : = working flow gage pressure unit is kg, table units is ℃ temperature)

3。 Calculated according to the working condition of flow in the selection table corresponding to the selection, the important principle is

a) The flowmeter is 1/3 to 2/3 range within the scope of b) In principle, not shrink tubing or expanding.

example: such as air compressor gas production of 20 nm3 / min, pressure is 8 kg, are: 1)

20 nm3 /分钟× 60 = 1200 Nm3 / h; 2) 1200 / ( 8 + 1) Nm3 / h≈ 133 m3 / h; 3) Look-up table, according to the principle of flow meter in the scope of 1/3 to 2/3 range, namely selection (flow meter. Parts name

diameter mm measurement range M3 / h

32 gas flowmeter

20. 25 - 144. 69

40 gas flowmeter

31. 65 - 226. 08

50 gas flowmeter

49. 45 - 353.

25 gas meter 65

83. 57 - 596. 99

3, installation note

gas meter installation position is very critical, if the installation is not correct, will not accurate measurement. Several basic considerations are as follows: 1)

Cannot be installed in the pipeline vibration, so the compressed air system should be installed on the air tank after mother tube, cannot install on the road at the pipe of compressor outlet

2) Must be installed on the straight road, usually flow meter installed front-end should have at least 10 d ( Which is 10 times the pipe diameter) The length of the straight pipe sections, such as the back-end to have 5 d length of straight pipe section.

3) It's best not to install the valve upstream of the flow meter, valve should be installed in the downstream of the 5 d. If the valve must be installed in the upstream of the flow meter, you must ensure the upstream flow of 50 d straight pipe sections, such as the downstream straight pipe section should be not less than 5 d.

4) If upstream line have elbow flowmeter or expansion or shrinkage tube, requirements for the length of the straight pipe is higher, the specific requirements see flowmeter installation manual.

insertion ultrasonic flow meter mass flow meter, device for producing rosemount coriolis mass flow meter, endress hauser coriolis mass flow meter, and other coriolis density meter, consisting of v shape coriolis mass flow meter.

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