How to choose the right valve according to the medium flow meter?
How to choose the right valve according to the medium flow meter?
As we all know, the flow and velocity of valve depend mainly on the diameter of valve, and also on the resistance of the structure to the medium, and at the same time, it has certain internal relations with the pressure, temperature and concentration of the medium.
Contents:
- Valve nominal diameter to inch
- Valve diameter (DN) and pipe diameter
- kilograms and pounds in valves
- Valve pressure rating
- Pressure bearing directions and installation directions of valves
- Selection principles of valves
The flow area of valve is directly related to flow velocity and flow rate, and flow velocity and flow rate are two interdependent quantities. When the flow rate is constant, the flow rate is large, and the area of the runner can be smaller. Conversely, the flow path area is large, its flow velocity is small, the flow area is small, and its flow velocity is large.
- 1. The flow rate of the medium is large, the valve diameter can be smaller, but the resistance loss is large, and the valve is easy to damage.The flow rate is large, which causes electrostatic effect and danger to inflammable and explosive medium. The flow velocity is too small, the efficiency is low, and the economy is not economical. For large viscosity and explosive medium, a smaller flow rate should be taken. Oil and a large viscosity liquid flow with viscosity, generally 0.1 ~ 2m/s.
- 2. Under normal circumstances, the flow rate is known, and the velocity can be determined by experience. The nominal diameter of the valve can be calculated by flow rate and flow rate.
- 3. The valve diameter is the same, its structural type is different, the fluid resistance is also different. Under the same conditions, the greater the drag coefficient of valve, the more the flow and flow rate of fluid flow through the valve. The smaller the resistance coefficient, the less the flow and flow rate of fluid passing through the valve.
The flow rates in various media are shown below.
| Fluid name | Conditions of use |
Flow rate (m/s)
|
| Saturated steam |
DN > 200
DN=200 ~ 100
DN < 100
|
30~40
25~35
15~30
|
| superheated steam |
DN > 200
DN=200 ~ 100
DN < 100
|
40~60
30~50
20~40
|
| Low pressure steam | P < 1 (absolute pressure) | 15~20 |
| Medium pressure steam | =1.0 ~ 4 (absolute pressure) | 20~40 |
| High pressure steam | =4.0 ~ 12 (absolute pressure) | 40~60 |
| Compressed gas |
vacuum
Less than 0.3 (gauge pressure)
=0.3 ~ 0.6 (gauge pressure)
=0.6 ~ 1 (gauge pressure)
=1.0 ~ 2 (gauge pressure)
=2.0 ~ 3 (gauge pressure)
=3.0 ~ 30 (gauge pressure)
|
5~10
8~12
10~20
10~15
8~12
3~6
0.5 to 3
|
| oxygen |
=0 ~ 0.05 (gauge pressure)
=0.05 ~ 0.6 (gauge pressure)
=0.6 ~ 1 (gauge pressure)
=1.0 ~ 2 (gauge pressure)
=2.0 ~ 3 (gauge pressure)
|
5~10
7~8
4~6
4~5
3~4
|
| coal gas | 2.5 to 15 | |
| Semi water gas | =0.1 ~ 0.15 (gauge pressure) | 10~15 |
| Natural gas | Thirty | |
| nitrogen | =5 ~ 10 (absolute pressure) | 15~25 |
| ammonia |
vacuum
< 0.3 (gauge pressure)
< 0.6 (gauge pressure)
Less than 2 (gauge pressure)
|
15~25
8~15
10~20
3~8
|
| Acetylene water |
Thirty
5~6
|
|
| Acetylene gas |
Rho < 0.01 (gauge pressure)
Rho < 0.15 (gauge pressure)
Rho < 2.5 (gauge pressure)
|
3~4
4~8
Five
|
| chlorine |
Gas
liquid
|
10~25
One point six
|
| Hydrogen chloride |
Gas
liquid
|
Twenty
One point five
|
| liquid ammonia |
vacuum
Less than 0.6 (gauge pressure)
Less than 2 (gauge pressure)
|
0.05 to 0.3
0.3 to 0.8
0.8 to 1.5
|
| sodium hydroxide |
Concentration 0 to 30%
Concentration 30% to 505
Concentration 50% to 73%
|
Two
One point five
One point two
|
| sulphuric acid |
Concentration 88% to 93%
Concentration 93% to 100%
|
One point two One point two |
| hydrochloric acid | One point five | |
|
Water and viscosity similar liquids
|
=0.1 ~ 0.3 (gauge pressure)
Less than 1 (gauge pressure)
Less than 8 gauge pressure)
Less than 20~30 (gauge pressure)
Circulating water and cooling water in heat supply network
|
0.5 to 2
0.5 to 3
2~3
2 to 3.5
0.3 to 1
|
| Water and viscosity similar liquids | Pressure backwater | 0.5 to 2 |
| Water and viscosity similar liquids | No pressure backwater | 0.5 to 1.2 |
| tap water |
Supervisor =0.3 (gauge pressure)
Branch tube =0.3 (gauge pressure)
|
1.5 to 3.5
1 to 1.5
|
| Boiler feed water | > 3 | |
| Steam condensate | 0.5 to 1.5 | |
| Condensate water | Gravity flow | 0.2 to 0.5 |
| Superheated water | Two | |
| Seawater and slightly alkaline water |
< 0.6 (gauge pressure)
|
1.5 to 2.5 |
Note: the unit of DN value is mm; the unit of value is MPa.
For example:
- The resistance coefficient of the gate valve is small, only in the range of 0.1-1.5; the resistance coefficient of the gate valve with large caliber is 0.2-0.5; the resistance coefficient of the necked gate valve is larger.
- The resistance coefficient of stop valve is much larger than that of gate valve, generally between 4 and 7. The resistance coefficient of Y-type stop valve (DC type) is small, between 1.5 and 2; the resistance coefficient of forged steel stop valve is large, even up to 8.
- The resistance coefficient of check valve depends on its structure: swing check valve is generally about 0.8-2, among which the resistance coefficient of multi disc swing check valve is large; the resistance coefficient of lift check valve is large, up to 12.
- The resistance coefficient of plug valve is small, usually about 0.4-1.2.
- The resistance coefficient of diaphragm valve is generally about 2.3.
- The resistance coefficient of butterfly valve is small, generally within 0.5.
- The resistance coefficient of ball valve is small, generally around 0.1.
Note: the resistance coefficient of the above valves is the value of the valve in the fully open state.
The selection of valve diameter shall take into account the machining accuracy and dimensional deviation of the valve, as well as other factors. The valve diameter should have a certain margin, generally 15%. In the actual work, the valve diameter depends on the process pipeline diameter.
Table for conversion of valve nominal diameter to inch
Valve nominal diameter definition:
The nominal diameter (or nominal diameter), also known as the mean external diameter, refers to the size of all piping accessories in the piping system. Nominal diameter is a convenient garden integer for reference. The nominal diameter of the valve is followed by a digital symbol followed by the letter DN. DN represents the inner diameter of the pipe, and the unit is millimeter, for example, DN50, that is, 50 millimeters. American Standard valves are usually expressed in inches (“), and a few valves represent the internal diameter of pipes by inches. The conversion formula is 1 “=25.4mm, such as 8”, which is equivalent to DN200mm in China.
Valve nominal diameter comparison table:
The nominal diameter of the valve (NPS-NOMINAL PIPE SIZE) is not always consistent with the diameter of the runner. The size of the valve is calculated according to the requirements of the delivery fluid. The Cv value is then calculated by the Cv value (reference manufacturer directory). The nominal diameter of the valve suitable for valve diameter (NPS) is used to represent the nominal diameter of the valve caliber. The GB is DN, and the unit is mm. The US standard is expressed in inches. The conversion relationship between British NPS and metric DN is as follows:
|
|
|
Valve diameter (DN) and pipe diameter comparison table
Valve size and size of the pipeline has a certain relationship, usually speaking of how large diameter (outer diameter) with large valves. The valve caliber needs to be calculated according to the actual parameters. Generally speaking, the pipeline will be larger, and the valve should be relatively small. It depends mainly on the size of the flow that the valve position needs to be controlled, and the pipeline size only needs the circulation capacity enough.
(1) pipe size and valve diameter and inch contrast table:
|
|
(2) valve diameter DN (nominal diameter) corresponds to outer diameter of pipe (mm):
|
|
Conversion of pounds and kilograms, conversion of kilograms and pounds in valves
Conversion between pounds and kilograms, conversion between kilograms and pounds.
Kilograms (kg, also known as kilograms) is a statutory unit of measurement in the international system of units. Lb is the British system of quality units used by the United Kingdom and the United States, and is used as a code for weight measurement. So how much is 1 pounds? How many kilograms are 1 pounds?
According to the international measurement conversion standard, 1 pounds =453.6 grams, and 1 jin =500 grams, so 1 pounds =0.972 Jin, that is 1 pounds = 0.4536 kg.
Common weight conversion methods:
| 1 kg = 0.001 tonnes (or “ton”) | 1 ounce = 437.5 Valley = 28.350 grams. | ||
| 1 kg = 1000 grams | 1 pounds = 16 ounces = 0.4536 kilograms. | ||
| 1 kg = 1000000 mg | 1 U.S. dollars = 100 pounds = 45.359 kilograms. | ||
| 1 kg = 1000000000 micrograms | 1 BT = 112 pounds = 50.802 kg | ||
| 1 kg =2 Jin | 1 US ton = 2000 pounds = 0.9072 tonnes | ||
| 1 kg =20 two | 1 tons = 2240 pounds = 1.0161 tonnes | ||
Conversion of kilograms and pounds in valves:
Because of the different standards of valves, some valves are expressed in pounds (class), and some are expressed in kilograms (PN). How do they convert pounds and kilograms in valves? Kilogram PN is a code that is related to pressure. It is the nominal pressure commonly used by domestic valves, class. api valve The nominal pressure, kilogram (PN) and pound (CLass) are the means to indicate pressure. The difference is that the pressure they represent corresponds to the reference temperature.
Comparison table between valve class and nominal pressure unit:
|
Pound class (Class)
|
One hundred and fifty | Three hundred | Four hundred | Six hundred | Eight hundred | Nine hundred | One thousand and five hundred | Two thousand and five hundred | |
|---|---|---|---|---|---|---|---|---|---|
|
Kg (PN)
|
Two | Five | Six point three | Ten | Thirteen | Fifteen | Twenty-five | Forty-two | |
Note: kilogram (PN) European system refers to the corresponding pressure at 120 degrees Celsius, while the pound (CLass) US standard refers to the corresponding pressure at 425 degrees Celsius. So in engineering interchange, we can not simply carry out pressure conversion.
Example: CLass300# should be 2.1MPa only for pressure conversion, but if the temperature is taken into account, the corresponding pressure will rise. According to the temperature and pressure test of material, it is equivalent to 5.0MPa.
Valve pressure rating conversion Division
How many kilograms of pressure valves do we usually talk about is equivalent to Mpa. Conversion of Mpa and kg, for example 1.0MPa=10 kg, 2.5MPa=25 kg pressure.
Valve pressure conversion:
Valve pressure conversion:
PN and CLass are all expressions of pressure in valves. The difference is that the pressure they represent corresponds to the reference temperature. The PN European system refers to the corresponding pressure at 120 degrees Celsius, while the CLass American Standard refers to the corresponding pressure at 425.5 degrees Celsius. Therefore, in engineering interchangeability, pressure conversion can not be simply carried out. For example, CLass300# should simply use pressure conversion to be 2.1MPa, but if the temperature is taken into account, the corresponding pressure will rise. According to the material temperature and pressure test, it is equivalent to 5.0MPa.
Valve pressure division:
Valve pressure division:
National standard, American Standard, Japanese standard valve nominal pressure, pound (Lb), MPa (Mpa), Pakistan (bar), Japanese standard (K) conversion table.
|
Pressure level pound (Lb) and MPa (Mpa) conversion comparison table |
||||||||||
|
Pound class Class |
One hundred and fifty |
Three hundred |
Four hundred |
Six hundred |
Eight hundred |
Nine hundred |
One thousand and five hundred |
Two thousand and five hundred |
Three thousand and five hundred |
Four thousand and five hundred |
|
MPa Mpa |
2.0MPa |
4.0MPa |
6.8MPa |
11.0MPa |
13.0MPa |
15.0MPa |
26.0MPa |
42.0MPa |
56.0MPa |
|
|
Pressure level MPa (Mpa) and BA (bar) conversion table |
|||||
|
0.05 (0.5) |
0.1 (1) |
0.25 (2.5) |
0.4 (4) |
0.6 (6) |
0.8 (8) |
|
1 (10) |
1.6 (16) |
2 (20) |
2.5 (25) |
4 (40) |
5 (50) |
|
6.3 (63.3) |
10 (100) |
15 (150) |
16 (160) |
20 (200) |
25 (250) |
|
28 (280) |
32 (320) |
42 (420) |
50 (500) |
63 (630) |
80 (800) |
|
100 (1000) |
125 (1250) |
160 (1600) |
200 (2000) |
250 (2500) |
335 (3350) |
|
Comparison table between pound class (Lb) and Japanese standard (K) and nominal pressure conversion |
|||||||
|
Pound class (Lb) |
One hundred and fifty |
Three hundred |
Four hundred |
Six hundred |
Nine hundred |
One thousand and five hundred |
Two thousand and five hundred |
|
Level K |
Ten |
Twenty |
Thirty |
Forty |
Sixty-three |
One hundred |
/ |
|
Nominal pressure (MPa) |
Two |
Five |
Six point eight |
Ten |
Fifteen |
Twenty-five |
Forty-two |
Pressure bearing directions and installation directions of valves
As the name implies, pressure bearing of valve refers to the pressure that the valve can bear, that is, the pressure level of valve is not lower than the design pressure level of pipeline. The pressure bearing direction refers to the direction of the valve body arrow is recommended to bear the pressure when the valve is applied to the closed state after the pipeline working condition. If the valve is installed incorrectly, the leakage failure of the valve that is not tightly closed may occur. Generally, it is determined according to the use process or use conditions. The same direction refers to the same pressure bearing direction (the side with high medium pressure on both sides of the valve RAM) and flow direction, and the opposite direction refers to the opposite pressure bearing direction (the side with high medium pressure on both sides of the valve RAM) and flow direction of medium.
Many valves have directionality, such as stop valve, throttle valve, pressure reducing valve and check valve. If they are installed reversely, the service effect and life (such as throttle valve) will be affected, or they will not work at all (such as pressure reducing valve), or even cause danger (such as check valve). For general valves, there is a direction mark on the valve body; if not, it should be correctly identified according to the working principle of the valve.
The arrow marked on the valve body is the recommended pressure bearing direction of the valve, not the flow direction of the pipeline medium. The valve with two-way sealing function can be marked with arrow instead of indicating arrow, because the arrow of the valve refers to the recommended pressure bearing direction, and there is always a better direction between left and right or up and down. It is usually installed wrongly by the engineering installation company as the flow direction mark of the medium, resulting in leakage and even pipeline accidents.
The valve cavity of the stop valve is not symmetrical. The fluid should be allowed to pass through the valve port from bottom to top, so that the fluid resistance is small (determined by the shape), the opening is labor-saving (due to the upward pressure of the medium), and the medium is not pressurized after the closing, which is convenient for maintenance. This is the reason why the stop valve can not be reversed. Other valves have their own characteristics.
The installation position of the valve must be convenient for operation; even if the installation is temporarily difficult, the long-term work of the operator should also be considered. It is better to make the valve handwheel flush with the chest (generally 1 away from the operating floor). 2 meters). In this way, opening and closing the valve is relatively energy-saving. The hand wheel of landing valve shall face up, and do not tilt to avoid awkward operation.
The valve of the wall leaning machine and the equipment shall also leave room for the operator to stand. It is not safe to operate in the sky, especially in acid and alkali, toxic media, etc.
Do not install the gate valve upside down (i.e. the hand wheel is downward), otherwise, the medium will remain in the valve cover space for a long time, which is easy to corrode the valve stem, and is forbidden by some process requirements. At the same time, it is inconvenient to change the packing. Open stem gate valve shall not be installed underground, otherwise exposed stem will be corroded due to humidity. When installing the lift check valve, make sure that the valve disc is vertical, so that the lift is flexible. The swing check valve shall be installed with its pin shaft horizontal so that it can swing flexibly. The pressure relief valve shall be installed vertically on the horizontal pipeline and shall not be inclined in all directions.
The installation position of the valve must be convenient for operation; even if the installation is temporarily difficult, the long-term work of the operator should also be considered. It is better to make the valve handwheel flush with the chest (generally 1 away from the operating floor). 2 meters). In this way, opening and closing the valve is relatively energy-saving. The hand wheel of landing valve shall face up, and do not tilt to avoid awkward operation.
The valve of the wall leaning machine and the equipment shall also leave room for the operator to stand. It is not safe to operate in the sky, especially in acid and alkali, toxic media, etc.
Do not install the gate valve upside down (i.e. the hand wheel is downward), otherwise, the medium will remain in the valve cover space for a long time, which is easy to corrode the valve stem, and is forbidden by some process requirements. At the same time, it is inconvenient to change the packing. Open stem gate valve shall not be installed underground, otherwise exposed stem will be corroded due to humidity. When installing the lift check valve, make sure that the valve disc is vertical, so that the lift is flexible. The swing check valve shall be installed with its pin shaft horizontal so that it can swing flexibly. The pressure relief valve shall be installed vertically on the horizontal pipeline and shall not be inclined in all directions.
Selection principles of valves in petroleum and chemical industry
In the face of so many valve classifications and such complicated working conditions, the most suitable valve products for piping system installation should be selected. First, the characteristics of valves should be understood; secondly, the steps and basis for selecting valves should be grasped; furthermore, the principles of selecting valves for petroleum and chemical industries should be followed. The principle of selecting valves for petroleum and chemical industries is that the flow path is a straight through valve, and its flow resistance is small. It is usually chosen as the valve for closing and opening the medium. The valve that is easy to adjust the flow is used for controlling the flow rate; the stopcock and the ball valve are more suitable for diversion and shunting; and the sliding and wiping valves on the closed parts along the sealing surface are most suitable for the medium with suspended particles.
One. valves for cut-off and opening of medium
The flow path is a straight through valve, and its flow resistance is small. It is usually selected as the valve for closing and opening the medium. The downward closed valve (stop valve and plunger valve) is less selective because of its tortuous flow path and higher flow resistance than other valves. Closed valves can be used when high flow resistance is allowed.
Two. Valves for controlling flow volume
Usually, the valve that is easy to adjust the flow is selected as the control flow. The downward closed valve (for example, globe valve) is suitable for this purpose, because its valve seat size is directly proportional to the stroke of the closing piece. Rotary valves (plug valves, butterfly valves, ball valves) and flexible valve bodies (clamping valves, diaphragm valves) can also be used for throttling control, but they are usually applicable only to a limited range of valves. The gate valve performs cross cutting movement on the circular valve seat by means of disc gate. It can control flow only when it is close to closing position, so it is usually not used for flow control.
Three. Valve for reversing diversion
There are three or more passages for this valve according to the need for diverting diverts. Plug valves and ball valves are more suitable for this purpose. Therefore, most of the valves used for diverting diverting valves are one of the valves, such as plug valves and ball valves. But in some cases, other types of valves can be diverted as long as two or more valves are properly interconnected.
Four. Medium valve with suspended particles.
When suspended particles are applied in the medium, it is most suitable for the valve with the wiping effect on the sliding cover along the sealing surface. If the closing piece is vertical to the back and forth movement of the seat, then it may be gripped particles. Therefore, unless the sealing surface material can allow the particles to be embedded, it is only suitable for the basic cleaning medium. Ball valve, plug valve, butterfly valve in the process of opening and closing of the sealing surface wipes, so it is suitable for use with suspended particles in the medium.
At present, no matter in petroleum, chemical industry or in other industries, the most important and critical equipment is to control or eliminate the leakage of valves. The final control of the pipeline is valve and valve. The service and reliable performance of valves in various industries is unique.
Source: China Valves Manufacturer – Yaang Pipe Industry Co., Limited (www.pipelinedubai.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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