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Advantages and Disadvantages of a Triple Eccentric Butterfly Valve

February 9, 2021

Butterfly valves are commonly used in many industries, such as petroleum, chemicals, metallurgy, power and water industries, as it is used to restrict and control the flow in the system pipelines. In the conventional butterfly valve technologies, a seal coated/lined with rubber, PTFE, etc. is used as a closure member to restrict the flow of fluid. Owing to structural constraints, it is not ideal for industries where the system has high temperatures, high stresses, degradation and wear resistance.

The triple eccentric butterfly valve which uses metal hard sealing is an advanced butterfly valve technology, in this, the valve body and valve seat are connected parts, and the valve seat sealing surface is layered with heat-resistant and anti-corrosion alloy steel. When it is compared to the conventional butterfly valve, these butterfly valve has the advantages of high-temperature resistance, quick operation, frictionless opening, and closing. At the time of closing, the seal is compensated by increasing the torque of the transmission system, enhancing the butterfly valve’s sealing efficiency, and prolonging the service life.

Though technological advancement has many advantages over traditional butterfly valves, yet it has some problems during their use:

• The multi-layered soft and hard stacked sealing ring is installed on the valve plate, when the valve plate is normally opened, the medium forms the positive erosion on the sealing surface. After the soft sealing ring is washed off into the metal plate interlayer, the efficiency of the sealing would be directly affected.
• Limited by structural conditions, this butterfly valve seat structure is not ideal for valves with a diameter less than DN200, as the entire shape of the valve plate is thicker and shows a higher flow resistance.
• The valve plate is forced against the valve seat by the torque of the transfer mechanism in the concept of the triple eccentric butterfly valve structure, and then the seal forms between the sealing surface of the plate and the seat of the valve. The higher the system pressure, the stronger the effect of sealing. When the flow medium is reversed, the leaking of the seal occurs as the unit positive pressure between the valve plate and the seat is smaller than the system pressure.

Advantages or benefits of triple eccentric metal hard seal butterfly valve:
The aim is to provide a high-performance triple eccentric hard sealing butterfly valve with zero leakage, adjustable opening and closing, prolonged service life, high-temperature tolerance, high-pressure resistance, anti-corrosion capabilities, and high resistance to wear and tear.

• A high-performance triple eccentric butterfly valve is distinguished by the fact that the valve seat inserts consist of multiple layers of stainless steel sheets on either side of a soft T-shaped sealing ring. 
• The closing surface of the valve plate & seat is an angled conical design, the heat-resistant and corrosion-resistant alloy is welded to the conical surface of the valve plate.
• A spring is installed in between the adjusting ring and the adjusting bolt installation on the pressure plate. This configuration efficiently compensates for the sensitive range between the sleeve & the valve body and the elastic distortion of the valve stem under medium pressure, this solves the problem of sealing the valve in a two-way interchangeable medium conveying process.
• The sealing ring consists of a multi-layered stainless-steel plate of flexible T-shape on both sides, this has the dual advantages of a hard metal seal and a soft seal, which has zero leakage sealing efficiency at high and low temperature.
• The test shows that the pressure on the sealing surface is produced by the torque of the transmitting device and the effect of the medium pressure on the valve plate in the positive flow condition of the tank. 
• The smoother the deposition between the angled conic surface of the valve plate and the valve seat sealing surface, the more effective the sealing is as the positive medium pressure increases.
• When the valve plate is pushed against the seat in reverse flow mode by the torque of the actuator, the seal forms between the valve plate and the seat.
• If the pressure of the reverse medium flow increases, the positive pressure unit between the valve plate and the seat is lower than the pressure of the medium, and the deflection of the spring of the adjusting ring after loading will compensate for the strong pressure of the sealing surface of the valve plate and the valve seat, which plays an automatic correction function.
• The inclusion of an adjustment ring between the pressure plate and the seat is very suitable for two-way hard sealing.

The soft sealing butterfly valve shows a good sealing characteristic, and can achieve zero leakage, but the downside of these type of valve is that it is not ideal for high temperature and high-pressure conditions, not wear and tear. The benefit of the hard-seal butterfly valve is that it can adjust to high-temperature and high-pressure environment, but the sealing efficiency is poor. In order to resolve the limitations of the two types of butterfly valves and to best support our manufacturing work, triple eccentric butterfly valves have come into existence and have been widely used.


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