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Difference between soft seal butterfly valve and hard seal butterfly valve

The difference between soft seal butterfly valve and hard seal butterfly valve:

A butterfly valve hard seal refers to a “hard seal” in which both sides of the seal pair are made of metal materials or other harder materials. This kind of seal has poor

ductile iron, DI, butterfly valve, manufacturer, center line, TH valve

ductile iron, DI, butterfly valve, manufacturer, center line, TH valve

sealing performance, but high temperature resistance, wear resistance, and good mechanical properties. For example, : Steel + Steel; Steel + Copper; Steel + Graphite; Steel + Alloy Steel; (The steel here may also be cast iron, cast steel, alloy steel or surfacing, sprayed alloy).

The soft seal seal pair is made of metal materials on one side and elastic non-metallic materials on the other side. It is called “soft seal”. This kind of seal has better sealing performance, but it is not resistant to high temperatures, easy to wear, and mechanical Poor performance. Such as: steel + rubber; steel + tetrafluoropolyethylene; etc. The soft sealing seat is made of non-metallic materials with certain strength, hardness and temperature resistance, with good sealing performance, zero leakage, but life And the adaptability to temperature is relatively poor. The hard seal is made of metal, and the sealing performance is relatively poor, although some manufacturers claim that it can achieve zero leakage. The soft seal cannot meet the process requirements for some corrosive materials, and the hard seal can solve it! These two types of seals can complement each other. In terms of tightness, the soft seal is relatively good, but now the tightness of the hard seal can also meet the corresponding requirements! The advantage of the soft seal is good sealing performance, but the disadvantage is that it is easy to age, wear, and has a short service life. The hard seal has a long service life, but the tightness is relatively worse than that of the soft seal.

The main differences in its structure are as follows
1. The difference in structure

Soft seal butterfly valves are mostly centerline type, and hard seals are mostly single eccentric, double eccentric, and triple eccentric butterfly valves.

2. Temperature resistance

The soft seal is used in normal temperature environment. Hard seal can be used in low temperature, normal temperature, high temperature and other environments

3. Pressure

Soft seal low pressure-normal pressure, hard seal can also be used in medium and high pressure conditions

4. Sealing performance: The soft sealing and triple eccentric hard sealing butterfly valves have better sealing performance. The triple eccentric butterfly valve can maintain good sealing under high pressure and high temperature environment.

In view of the above characteristics, the soft sealing butterfly valve is suitable for the two-way opening and closing and adjustment of ventilation and dust removal pipelines, water treatment, light industry, petroleum, chemical and other industries. Hard-sealed butterfly valves are mostly used in heating, gas, gas, oil, acid and alkali environments.

With the widespread use of butterfly valves, its features of convenient installation, convenient maintenance and simple structure become more and more obvious. Electric soft-sealed butterfly valves, pneumatic soft-sealed butterfly valves, hard-sealed butterfly valves, etc. have begun to replace electric gate valves and globe valves in more and more occasions.

Installation instructions of double eccentric butterfly valve

Installation instructions of double eccentric butterfly valve:
1. Before installation, you must carefully check whether the valve’s mark and certificate of conformity meet the requirements for use, and clean it after verification.

double eccentric butterfly valve (3)

double eccentric butterfly valve (3)

Uninstalled valves should be stored in a dry room. Valves stored for a long time should be cleaned regularly, dried and coated with anti-rust oil. Blind plates shall be used to protect the flange sealing surface at both ends of the valve.
2. Install according to the flow direction of the medium; horizontal installation is preferred.
3. The connecting bolts of the butterfly valve and the pipeline should be tightened several times in the diagonal direction during installation, and no single piece should be tightened at a time to prevent the flange connection from leaking due to uneven force.
4. When installing the butterfly valve, the butterfly plate should be in the closed position to prevent debris from entering the valve cavity and scratching the sealing surface. When the user wants to test the pressure, be sure to install the flange pair on both ends and test the pressure.
5. When connecting the valve to the pipeline, it is required to use butt-welded steel flanges or special butterfly valve flanges on the pipeline. If flat-welded steel flanges are used, the inner hole of the flange must be the same size as the inner hole of the gasket to ensure the effective sealing surface of the gasket.
6. When the electric butterfly valve leaves the factory, the opening and closing stroke of the control mechanism has been adjusted. In order to prevent the direction from being wrong when the power is turned on, the user must manually move to 1/3 of the closed position before turning on the power for the first time. And check whether the direction of the indicator plate is consistent with the opening direction of the valve.
7. When the valve is in use, if any malfunction is found, stop using it immediately

Tanghai Valve is the best manufacturer of double eccentric butterfly valve in China. We produce the best quality products with competitive low prices. Main products: butterfly valve, lug type butterfly valve, wafer type butterfly valve, U-type butterfly valve, double flange butterfly valve, gate valves, check valves, globe valves, valve parts (Valve body, Valve disc, Valve shaft, Valve seat…)

Classification and features of Eccentric butterfly valves

Eccentric butterfly valves are divided into single eccentric butterfly valves, double eccentric butterfly valves, triple eccentric butterfly valves, and variable eccentric

double eccentric butterfly valve (1)

double eccentric butterfly valve (1)

butterfly valves. Contrast with concentric butterfly valve. A butterfly valve whose stem axis deviates from the center of the disc and the center of the body at the same time, and the sealing pair is an oblique vertebra is called an eccentric butterfly valve.

Structure classification of eccentric butterfly valve:
Single eccentric butterfly valve
In order to solve the problem of the extrusion of the butterfly plate and the valve seat of the concentric butterfly valve, a single eccentric butterfly valve was produced. Its structural feature is that the shaft center of the valve stem deviates from the center of the butterfly plate, so that the lower end of the butterfly plate no longer becomes the rotation axis. Disperse and reduce the excessive squeezing between the lower end of the butterfly plate and the valve seat.
Double eccentric butterfly valve
On the basis of the single eccentric butterfly valve, the double eccentric butterfly valve is the most widely used double eccentric butterfly valve. Its structural feature is that the axis of the valve stem deviates from the center of the butterfly plate and the center of the body. The double eccentric effect enables the butterfly plate to be released from the valve seat immediately after the valve is opened, which greatly eliminates unnecessary excessive extrusion and scratching of the butterfly plate and the valve seat, reduces the opening resistance, reduces wear and improves The life of the valve seat is improved.
Triple eccentric butterfly valve
To withstand high temperatures, hard seals must be used, but the amount of leakage is large; for zero leakage, soft seals must be used, but they are not resistant to high temperatures. In order to overcome the contradiction of the double eccentric butterfly valve, the butterfly valve was eccentric for the third time. The so-called third eccentricity means that the shape of the sealing pair is not a positive cone, but an oblique cone.
Variable eccentric butterfly valve
The uniqueness of the variable eccentric butterfly valve is that the valve stem shaft where the butterfly plate is installed is a three-segment shaft structure. The three-segment shaft type valve stem has two shaft sections concentric, and the center line of the central shaft is offset from the two ends of the axis by a center distance , The butterfly plate is installed on the intermediate shaft section. Such an eccentric structure makes the butterfly plate a double eccentric shape when in the fully open position, and a single eccentric shape when the butterfly plate rotates to the closed position. Due to the effect of the eccentric shaft, when close to closing, the butterfly plate moves a distance into the sealing cone surface of the valve seat, and the butterfly plate matches the sealing surface of the valve seat to achieve reliable sealing performance.

Features of eccentric butterfly valve:
The butterfly valve and the upper and lower valve shafts are connected by special-shaped holes and special-shaped shafts. During the opening and closing process of the butterfly plate, the function of the butterfly plate floating up and down, left and right, without a pin link, reduces the interference area between the butterfly plate and the valve seat. Thereby greatly reducing the torque. The floating structure of the butterfly plate realizes the single eccentric manufacturing process and the use function of variable eccentricity.
There is an over-position stopper for the butterfly plate in the inner cavity of the valve body to ensure that the butterfly plate is not in place when it is closed.
Bushings are used between the upper and lower valve shaft holes of the valve body cavity and the upper and lower valve shaft holes of the butterfly plate to prevent large particles in the medium from entering the valve shaft holes.