SOME KNOWLEDGE FOR VALVE: THE FLOW RATE OF THE VALVE MEDIUM

In chemical production, as long as a fluid passes through, various valves are used,such as ball valve, butterfly valves, check valves, forged steel valves. The importance of valves in chemical industry is self-evident. The common media for valve pressure test are water, oil, air, steam, nitrogen, etc. How do they work?

 

Valve's flow speed and flow amount

The flow and velocity of the valve mainly depend on the valve's diameter. It is also related to the resistance of the structure of the valve to the medium, and has certain internal relations with the pressure, temperature, and concentration of the medium. The flow area of the valve is directly related to the flow speed and flow amount. They are two quantities that are interdependent.

 

When the flow amount is constant, the flow speed is large, and the area of  the flow channel can be smaller; when the flow speed is small, the flow area can be larger. The medium flow speed is large, the valve diameter can be smaller, but the resistance loss is large, and the valve is easily damaged. If the flow speed is large, it will cause electrostatic effects on flammable and explosive media, causing danger. In general, the flow amount is known, and the flow speed can be determined by experience.

 

 

Valve drag coefficient

The valve diameter is the same, the structure type is different, and the fluid resistance is also different. Under the same conditions, the larger the valve's resistance coefficient, the more the flow speed and flow amount of the fluid passing through the valve will decrease; the smaller the valve's resistance coefficient, the less the flow speed and flow amount of the fluid will pass through the valve.

 

The gate valve has a small coefficient of resistance, which is only in the range of 0.1 to 1.5; a gate valve with a large diameter has a coefficient of resistance of 0.2 to 0.5; The resistance coefficient of the stop valve is much larger than that of the gate valve, generally between 4 and 7. The Y-type globe valve (DC type) has the smallest resistance coefficient, between 1.5 and 2. Forged steel globe valve has the largest resistance coefficient, even as high as 8.

 

The resistance coefficient of check valve depends on the structure: The swing check valve is usually about 0.8 to 2, the resistance coefficient of multi-turn swing check valve is large; the lift check valve has the largest resistance coefficient, up to 12 .

 

The resistance coefficient of the plug valve is small, usually about 0.4 to 1.2.

The resistance coefficient of the diaphragm valve is generally around 2.3.

The resistance coefficient of butterfly valve is small, generally within 0.5.

Ball valve has the smallest resistance coefficient, generally around 0.1.

The resistance coefficient of the above valve is the value under the fully opened state of the valve.

 

In the next article, we will share more valve knowledge, welcome to follow us into the world of ball valve, butterfly valves, check valves, forged steel valves, butt weld fittings.

 

appendix: Common flow meters for various media

Media	Use Condition	Flow Rate （m/s）
Saturated Vapor	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	ρ＜1.0（AP）	15～20
Medium pressure steam	Ρ=1.0～4.0（AP）	20～40
High pressure steam	Ρ=4.0～12.0（AP）	40～60
compressed gas	Vacuum Ρ≤0.3（GP）  Ρ=0.3～0.6（GP）  Ρ=0.6～1.0（GP）  Ρ=1.0～2.0（GP）  Ρ=2.0～3.0（GP）  Ρ=3.0～30.0（GP）	5～10  8～12  10～20  10～15 8～12 3～6 0.5～3
oxygen	Ρ=0～0.05（GP）  Ρ=0.05～0.6（GP）  Ρ=0.6～1.0（GP）  Ρ=1.0～2.0（GP）  Ρ=2.0～3.0（GP）	5～10 7～8 4～6  4～5  3～4
gas		2.5～15
Half water gas	Ρ=0.1～0.15（GP）	10～15
natural gas		30
Nitrogen	Ρ=5～10（AP）	15～25
Ammonia	Vacuum Ρ＜0.3（GP）  Ρ＜0.6（GP）  Ρ≤2（GP）	15～25 8～15 10～20 3～8
Acetylene water		30 5～6

 

 

Media	Use Condition	Flow Rate （m/s）
Acetylene gas	ρ＜0.01（GP）  ρ＜0.15（GP）  ρ＜2.5（GP）	3～4 4～8 5
chlorine	Gas liquid	10～25 1.6
Hydrogen chloride	Gas liquid	20 1.5
Liquid ammonia	Vacuum  Ρ≤0.6（GP）  Ρ≤2.0（GP）	0.05～0.3 0.3～0.8 0.8～1.5
Sodium hydroxide	Concentration l 0～30% Concentration 30%～505 Concentration 50%～73%	2 1.5 1.2
sulfuric acid	Concentration 88%～93% Concentration 93%～100%	1.2 1.2
Hydrochloric acid		1.5
Water and similar liquids	Ρ=0.1～0.3（GP）  Ρ≤1.0（GP）  Ρ≤8.0GP）  Ρ≤20～30（GP）  Heating network circulating water, cooling water Pressure backwater Backwater without pressure	0.5～2  0.5～3  2～3  2～3.5  0.3～1  0.5～2  0.5～1.2
Tap water	Main pipe  Ρ=0.3（GP）  Branch pipe Ρ=0.3（GP）	1.5～3.5  1～1.5
Boiler feed water		＞3
Steam condensate		0.5～1.5
Condensate	Artesian	0.2～0.5
Hot water		2
Sea water, slightly alkaline water	Ρ＜0.6（GP）	1.5～2.5