What is a bellows seal globe valve

What is a bellows seal globe valve?

Bellows globe valve is a new type of stop valve. The valve stem seal is a double seal design of bellows + packing. The sealing performance is more reliable than that of ordinary stop valve. The metal barrier formed by the bellows can prevent leakage, and the filler can also provide sealing effect after the bellows fails. The application is safer, energy-saving, environmental protection and zero leakage.

20210816032716 82252 - What is a bellows seal globe valve
The key part of the bellows seal stop valve is the metal bellows. Through the connection between the automatic roll welding cover and the valve stem, it can ensure that the bellows assembly has no leakage. The rupture of bellows is the main problem in the use of bellows stop valve. There are three main reasons for the rupture of bellows:
Column instability: refers to the transverse offset of the corrugated connection of the bellows, so that the actual axis of the bellows after offset becomes an arc or S-shape. Due to the insufficient total thickness of bellows, it is difficult to resist the test pressure or operating pressure. Excessive wave number of bellows and large coaxiality deviation of bellows are easy to cause column instability. When used in steam system, stem deformation or valve head displacement caused by water hammer is easy to cause column instability.
Plane instability: one or several corrugated planes are inclined due to rotation relative to the axis of the bellows, but the center of the bellows is basically on the axis of the bellows. The reason of plane instability is that the bellows has plastic deformation under the combined force of meridional bending stress and circumferential membrane stress caused by internal pressure. Plane instability often occurs when the bellows is in compression; The column instability or plane instability can not be controlled, the ripple shape changes greatly, which is separated from the original calculation model, and the displacement is concentrated on one or several ripples, which will eventually lead to the rapid fatigue fracture of the bellows. Sometimes it will not break immediately, but it greatly reduces the fatigue life and pressure bearing capacity of the bellows.

Structural characteristics of bellows seal valve

  • 1. Double sealing design (bellows + packing) if the bellows fails, the valve stem packing will also be avoided.
  • 2. Reasonable structure, reliable sealing, excellent performance and beautiful appearance.
  • 3. No fluid loss, reduce energy loss and improve plant equipment safety.
  • 4. The sealing surface is overlaid with Co based cemented carbide, with good wear resistance, corrosion resistance, friction resistance and long service life, so as to reduce the number of maintenance and reduce the operating cost.
  • 5. The rugged bellows sealing design ensures zero leakage of the valve rod and provides conditions without maintenance.
  • 6. The stop valve stem is subject to quenching and tempering and surface nitriding treatment, with good corrosion and friction resistance;
  • 7. The valve rod lifting position indication is more intuitive.

Parts and materials of bellows seal globe valve

Number
Model
WJ41H-16C WJ41H-25/40
WJ41W-16/25P
1
Valve body
WCB carbon steel
CF8M stainless steel
2
Valve cover
WCB carbon steel
CF8M stainless steel
3
Sealing surface
304/F4
304/F4
4
Valve disc
2Cr/3Cr13
304/316
5
Valve stem
2Cr/13Cr/304
304/316
6
Handwheel
WCB carbon steel
WCB carbon steel
7
Filler
Flexible stone surrounding ink
8
Gasket
304 composite graphite gasket/spiral wound gasket/F4
9
Corrugated pipe
304/316L
10
Beads and locking pieces
304/316L
11
Stem nut
Copper
12
Gland
WCB
304
Material and performance of main parts of bellows seal stop valve
Parta name
Body
Bonnet
Stem
Disc
Sealing face
Paking
GS-C25
GS-C25
GS-C25
13Cr
2Cr13
2Cr13
GRAPHITE
STL
304
CF8
CF8
304
304
304
GRAPHITE
STL
PTFE
316
CF8M
CF8M
316
316
316
GRAPHITE
STL
PTFE
304L
Cf3
CF3
316
304L
304L
GRAPHITE
STL
PTFE
316L
CF3M
CF3M
316
316L
316L
GRAPHITE
STL
PTFE
Boundary dimensions and connection dimensions of bellows seal stop valve
PN
DN
L
D
D1
D2
B
f
H
N-ф
△H
(STRODE)
1.6
15
130
95
65
45
16
2
191
4-14
6
20
150
105
75
58
18
2
191
4-14
6
25
160
115
85
68
18
2
197
4-14
8
32
180
140
100
78
18
2
200
4-18
8
40
200
150
110
88
18
3
218
4-18
13
50
230
165
125
102
20
3
220
4-18
13
65
290
185
145
122
20
3
238
4-18
16
80
310
200
160
138
20
3
257
4-18
20
100
350
220
180
158
20
3
340
4-18
25
125
400
250
210
188
22
3
360
4-18
32
150
480
285
240
212
22
3
390
8-22
40
200
600
340
295
268
24
3
530
12-22
50
2.5
15
130
95
65
45
16
2
191
4-14
6
20
150
105
75
58
18
2
191
4-14
6
25
160
115
85
68
18
2
197
4-14
8
32
180
140
100
78
18
2
200
4-18
8
40
200
150
110
88
18
3
218
4-18
13
50
230
165
125
102
20
3
220
4-18
13
65
290
180
145
122
22
3
238
4-18
16
80
310
200
160
138
24
3
257
4-18
20
100
350
235
190
162
24
3
340
8-22
25
125
400
270
220
188
26
3
360
8-26
32
150
480
300
250
218
28
3
390
8-26
40
200
600
360
310
278
30
3
530
12-26
50
4.0
15
130
95
65
45
16
2
191
4-14
6
20
150
105
75
58
18
2
191
4-14
6
25
160
115
85
68
18
2
197
4-14
8
32
180
140
100
78
18
2
200
4-18
8
40
200
150
110
88
18
3
218
4-18
13
50
230
165
125
102
20
3
220
4-18
13
65
290
185
145
122
22
3
238
4-18
16
80
310
200
160
138
24
3
257
8-18
20
100
350
235
190
162
24
3
340
8-22
25
125
400
270
220
188
26
3
360
8-26
32
150
480
300
250
218
28
3
390
8-26
40

How to select bellows seal globe valve

Different materials of bellows and valve stem have different weldability. When welded together, it is easy to cause welding defects, resulting in easy perforation of bellows.
The sealing failure of valve core and valve seat is another main problem that is easy to occur in the use of bellows sealed stop valve. In the daily use of large-diameter stop valve users, we often reflect a problem, that is, when the bellows sealed stop valve is used for media with large pressure difference, such as steam, high-pressure water and other pressurized work, it is often difficult to close. No matter how hard it is closed, it is always found that there will be leakage and it is difficult to close it tightly, The reason for this problem is caused by the insufficient structural design of the valve and people’s ultimate horizontal output torque. It also has a great relationship with the structure, material, heat treatment and machining accuracy design of valve core and valve seat sealing pair. When used in steam system, the traditional plane valve seat design has a considerable impact. If the hardness of the valve seat is too small, it is easy to be affected by erosion. If the hardness of the valve seat is too large, it is easy to cause problems in the coordination between sealing pairs.
The latest conical disc design, when the valve is closed, the conical sealing surface with “scraping effect” can automatically remove surface impurities, which can ensure reliable sealing and longer service life of the disc. Generally, various disc designs are provided according to the requirements of working conditions, which can be designed as throttle disc, stop check disc, plane soft seal and other disc designs.
When the steam system is started, it is necessary to preheat the steam pipeline (warm up the pipe), and the preheating process generally requires a small flow of steam to pass through, so that the stop valve can be fully opened only after the pipeline is heated slowly and evenly to a certain extent, so as to avoid excessive expansion caused by rapid temperature rise of the pipeline and damage to some connecting parts. However, in this process, the valve opening is often very small, resulting in the erosion rate is far greater than the normal use effect, which seriously reduces the service life of the valve sealing surface.
Watt’s energy-saving steam engineer found that the damage of valve core and valve seat is often manifested in that when the valve is about to be closed at the throttle, V2 = V1P according to the formula of flow rate and differential pressure;, The normal steam flow rate V1 = 40m/s. if the steam pressure is 10barg, the flow rate V2 = 126m / s, which is 3 times of the normal flow rate! It has strong kinetic energy. In this way, the scouring force on the sealing surface increases exponentially, which can quickly punch the valve core and valve seat surface out of the linear fine groove, so as to reduce the service life of the valve exponentially. On the other hand, according to the principle of energy conservation, with the increase of speed, the pressure will drop sharply and flash will occur at the outlet. A strong pressure shock wave will be generated in an instant, so that the materials on the valve core and valve seat surface are impacted into honeycomb holes, and cause vibration and noise, which is cavitation. Therefore, it is required that the hardness and erosion resistance of the disc seat material are very excellent to ensure the service life of the valve.
Products above DN150 must be equipped with triangular positioning device to effectively prevent the trembling, noise and internal parts damage of the valve in use, and the service life can be effectively increased by more than 150%.
It is better to use coated sand casting or silica sol casting technology for the valve body, so as to improve the surface finish and mechanical properties of the valve body, reduce the occurrence of pores, sand holes and cracks, and enhance the tensile strength of the casting.
Handwheel of the valve shall be designed to ensure easy grip and no protrusions such as burrs. The diameter of the hand wheel is too large, which is easy to cause artificial contusion of the valve core and valve seat when closing; If it is too small, it is not easy to close. The use of afterburner wrench will cause stem deformation and seal pair damage.
The valve rod is best treated by nitriding and other processes to increase the wear resistance of the valve rod. The valve stem thread adopts fine thread rolling thread to avoid dead zone leakage after the valve is closed.
When leaving the factory, the valve must undergo 100% pressure test, and the test pressure is 1.5 times the design pressure; When used for steam, 100% tightness test is required, and the sealing grade must be higher than the level 4 leakage standard.
Generally, the maximum diameter of bellows sealed stop valve shall not exceed 350mm. When the diameter is greater than 350mm, the bellows stop valve is not the most appropriate choice. Regardless of size, weight, product complexity and operation difficulty, the bellows stop valve is no longer the appropriate choice. The selection of bellows gate valve and eccentric butterfly valve is more economical and reliable.

Source: Network Arrangement – China Bellows Seal Globe Valve Manufacturer – Yaang Pipe Industry Co., Limited (www.ugsteelmill.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.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@ugsteelmill.com

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