Can a three-eccentric butterfly valve truly achieve two-way sealing?

In practical applications, it is common to observe the following issues with three-eccentric butterfly valves manufactured in China: 1. Some valves pass the pressure testing at the factory but start leaking once they are installed in the pipelines. 2. Some valves function properly at first but begin to leak internally after a few cycles of opening and closing. 3. Manual operation is barely acceptable, as these valves are not used very often anyway; however, pneumatic versions show leakage as soon as they are activated. 4. Some valves have a short service life, not even reaching one maintenance cycle. 5. Some valves, only a few months old, fail to close completely when operated, causing collision with the valve body. What is the reason for this? 6. Some valves function properly at first after being installed, but over time they fail to close tightly and do not meet the sealing requirements. 7. Some valves are claimed to offer two-way sealing, but in reality they cannot seal at all when faced with even slight reverse pressure

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This valve seems to have been invented in Denmark,,,,. Specifically, it depends on whether all the relevant technologies have been properly copied in. In principle, this type of valve design is more rational. If problems arise in actual use, a breakdown analysis should be conducted to determine whether the issue lies in the mechanical aspects, the fluid medium, or something else ? ? For reference.

Triple-eccentric butterfly valves can achieve two-way sealing. The sealing rings of triple-eccentric butterfly valves available on the market currently consist of one layer of stainless steel plate layered over another layer of asbestos plate. During pressure testing, water is used for high pressures while air is used for low pressures. When exposed to water, the asbestos plate expands, thereby providing a sealing effect. Generally, an anti-rust oil is applied to the sealing surface at the time of manufacturing. If internal leakage occurs at the installation site and the sealing surface is not damaged, it is likely that the asbestos plate has lost its moisture and contracted, losing its sealing capability. The layers of stainless steel serve a supporting role; it is actually the asbestos layers that provide the sealing function. If internal leakage occurs during pressure testing and damage to the sealing surface cannot be ruled out, then the valve should be opened during testing, filled with water so that the sealing rings are completely submerged in water for a few minutes. After that, the hex bolts on the butterfly valve should be tightened using a wrench, which will cause the asbestos plate to expand and thus achieve a sealing effect, preventing internal leakage

I have always used imported products, so I haven’t encountered such an issue

Can a three-eccentric butterfly valve truly achieve two-way sealing? Yes. Why are three-eccentric butterfly valves currently on the market generally plagued by quality issues? The valve plate and the sealing surface are in \"asymmetric engagement,\" which involves machining precision, material treatment, and matching. Domestic products still need to work harder. Why is the pressure test successful in the factory, but internal leakage occurs on-site? Positive sealing requires pressure \"borrowed from the medium\" ； Or the actual temperature is much higher than the measured value. Why doesn’t the service life of a triple-eccentric butterfly valve last long? The low closing torque of the three-way valve and its lower leakage rate compared to ordinary butterfly valves are advantages; however, it has only one sealing surface, and for reliable sealing and shut-off, ball valves or forcibly sealed gate valves are required. For regulation, a two-eccentric high-performance butterfly valve will suffice; a three-eccentric type is more cost-effective for cutting off flow. Our three-way valve from 2001 is still in use today.

The medium cleanliness not meeting the design requirements is one of the reasons.

When selecting valves, it is necessary to do so based on the actual operating conditions. Different media and different temperatures require the use of appropriate valves and materials; otherwise, problems are likely to arise

German Quadax two-way metal seal, low torque. For harsh operating conditions

There are many manufacturers that produce triple-eccentric components these days. The problems you mentioned are likely to occur with domestic products; generally, imported brands (such as VINESSA, OHL, OTEN, etc.) are less likely to have such issues, and dual-sealing also works properly in these cases.