CONTROL VALVES
Flow control valves for corrosive and abrasive chemicals
Control valves are often short lived in corrosive chemicals, particularly in the presence of particles. It is an area of chemical engineering where applying traditional knowledge simply does not work.
Techlink Flow Control valves are designed to offer the best resistance to corrosive and erosive chemicals and a low pressure recovery at a very attractive price!
The purpose of a control valve is to create a pressure drop following the requirements of the process. TECHLINK V-orifice flow control ball valves are designed and built according to the process data. The V-orifice is shaped by CNC machining to deliver the required flow characteristic curve. All new patterns are tested on a loop to confirm the flow curve. The ball and the V-orifice mask are usually made of PVDF to provide the maximum resistance to erosion.
Benefits
Economical with an attractive price and low maintenance.
Erosion and corrosion resistant.
Low pressure recovery (high FL factor).
Lightweight and mechanical strength.
Excellent regulation performance.
Applications
Industries:
- Chlor-Alkali Plants
- Water treatment plants
- Paper pulp mill
- Battery materials plant
Typical fluids:
- Brine
- Wet chlorine
- Hydrochloric acid
- Caustic soda
- Sodium carbonate
- Sodium hypochlorite
- Ferric chloride
- Zinc sulfate
- Copper chloride
- Sodium chlorate
- Sulfuric acid
- Chlorine dioxide
- Sodium sulfite
- Bromine
- Lime water
- Aqua regia
- Copper sulfate
- And more!
The "Vena Contracta"
Any type of flow control valve has a restricted passage area called “Vena Contracta”. In this area, the flow is accelerated to a high speed. Turbulence is created, dissipating energy and therefore creating the desired ΔP. Where the flow velocity is high, corrosive chemicals cause all sorts of damage to the materials.
Download our learning resource below to understand better the Vena Contracta phenomenon, its consequences, and our solutions.
PVDF: the best material against abrasion
The corrosion resistance of metals is generally determined in still fluids. But at high flow speeds and in the presence of turbulence, a process known as “erosion induced corrosion” starts destroying even the so-called “corrosion resistant” metals. In such situation, solid polymers offer an economic solution that will outperform even “special metals” and other exotic materials.
Polymers are not equal when it comes to resisting high flow velocities, turbulence and erosion, as well as chemical attack. The table here shows the abrasion resistance of several polymers, as determined by the “TABER” ASTM D4060 test (wheel CS-10). Materials which resist best to erosion have the lowest figure on this table: the lower, the better. Note that PVDF has a better resistance than stainless steel.
Apart from polyamid, which cannot be used because of its low chemical resistance, the best abrasion resistant material is PVDF. This material should be preferred for all parts of the valve making up the “Vena contracta”. When PVDF cannot be used for chemical reason, such as in concentrated hydroxides, then PPH and ECTFE are acceptable alternatives.
It is readily seen that PTFE, which has the lowest abrasion resistance of all polymers, is the worst choice for contact with the flow in the Vena Contracta. However, because of its almost universal chemical resistance, PTFE is often found as a liner in control valves, either globe valves or diaphragm valves. Such valves suffer a fast deterioration of the flow throttling parts, such as discs, seats, diaphragms etc.
|
Materials
|
Weight loss mg/10000 rev.
|
|---|---|
|
PVDF homopolymer SOLEF®
|
5 - 10
|
|
PVDF SOLEF® 21505/31508
|
5 - 8
|
|
PA 6 polyamid
|
5
|
|
ECTFE Halar ®
|
13
|
|
PP homopolymer
|
15 - 20
|
|
PTFE
|
500 - 1000
|
|
304 stainless steel
|
50
|
|
PVDF homopolymer SOLEF®
|
PVDF SOLEF® 21505/31508
|
PA 6 polyamid
|
ECTFE Halar ®
|
PP homopolymer
|
PTFE
|
304 Stainless steel
|
|---|---|---|---|---|---|---|
|
5 - 10
|
5 - 8
|
5
|
13
|
15 - 20
|
500 - 1000
|
50
|
V-Orifice seats and Needle valves
Depending on the type of valve (globe, diaphragm, butterfly, V-port ball, etc.) the pressure drop in the Vena Contracta will be more or less pronounced. A big pressure drop induces high flow velocity. High flow velocity in the Vena Contracta is what causes damage in corrosive and abrasive media.
Globe valves have a shallower pressure drop in the Vena Contracta than diaphragm , butterfly and full port ball valves.
But with proper design, V-orifice ball valves have a pressure drop as shallow as a globe valve. The pressure drop in the “vena contracta” is characterized by the “Pressure Recovery Coefficient” FL of the valve. The value of FL varies between 0 and 1. A value close to 1 means a smaller pressure drop.
The velocity in the Vena Contracta varies in the opposite way to the pressure drop. Globe and V-Orifice ball valves therefore have a lower maximum velocity in the Vena Contracta. Diaphragm and butterfly valves are the worst.
Thanks to their unique design, TECHLINK V-orifice ball and needle V-notch valves have a FL similar to Globe valves.
|
Type of valve
|
Typical FL values
|
|---|---|
|
Globe control valve
|
0.8 ~ 0.98
|
|
TECHLINK needle V-notch
|
0.95
|
|
TECHLINK V-orifice ball
|
0.8 ~ 0.9
|
|
On/off ball valve (full bore)
|
0.7
|
|
Segmented ball
|
0.6 ~ 0.7
|
|
Butterfly
|
0.6 ~ 0.7
|
|
Diaphragm
|
0.5 ~ 0.6
|
|
Globe control valve
|
TECHLINK needle V-notch
|
TECHLINK V-orifice ball
|
On/off ball valve (full bore)
|
Segmented ball valve
|
Butterfly valve
|
Diaphragm valve
|
|---|---|---|---|---|---|---|
|
0.8 ~ 0.98
|
0.95
|
0.8 ~ 0.9
|
0.7
|
0.6 ~ 0.7
|
0.6 ~ 0.7
|
0.5 ~ 0.6
|
Characteristic curves
The characteristic curve must be adapted to the process. There are various “depth” of Equal% depending on the process data.
Techlink valves offer adapted orifice and needle profiles that are designed according to customer-specified process conditions for the best results. And if you are not sure which design you need, Techlink engineers are here to help you.
Positioner and actuator
Non-metallic components are preferred for corrosive environments. Hence, Techlink valves come with corrosion resistant accessories. Techlink engineers have experienced the best results with the positioners Samson (made in Germany) with polyphthalamide casing, and with the actuators Max-Air (made in Italy) with polyarylamide cylinder body.
All Techlink designs can be adjusted to customer specifications.
Tested and approved!
Plant: Aditya Birla Chemicals, Thailand.
Service: Sodium Hypo.
In service since 2013.
Techlink Flow Control Valve equipped with: SAFI Valve PVDF/FKM (VITON), Samson Positioner, Max-Air Actuator.
