Choices of Butterfly Valves

The crucial design details for the selection of shut-off valves

Using the example of a classic shut-off valve in the cooling circuit, we'll point out here which design details are crucial in order for a valve to be able to its job long and reliably. This is where you can read about what the failure of a valve in a power station may signify during an emergency.

1. Proper corrosion protection prolongs the life of a valve.

Depending on the medium and application, a variety of different surface coatings are available for valves. This will determine whether a valve works problem-free for only a few months or for several decades! Whether drinking water, media with very abrasive components, salt water or chemical process media: The right interior coating provides lifetime protection for the actual components inside a valve. Based on numerous studies and in-house testing, VAG always finds the optimal coating for your needs.

2. A reliable seat hardfacing extends the life of a valve.

Bolted or crimped on connections frequently have a tendency to be corrosively infiltrated by the medium and detach from the valve body. An infiltrated seal seat can lead to increasing torque in the valve, to leaks in the seal, and to a reduced service life of the peripheral seal. If the seat is raised from the body by corrosion, this for the most part results in the formation of edges which likewise lead to increased wear or may even destroy the seal. This problem is precluded by an armoured seat seal fixed to the base material of the body, making it absolutely safe from infiltration, such as in the VAG EKN® Butterfly Valve.

3. A secure connection between valve stem and disc.

If the valve stem has no structurally secure connection to the disc, this can quickly lead to a "loose" connection with considerable play in the stem connection. The forces occurring when opening and closing the valve can ultimately destroy the connection. Apart from water losses, a higher resistance and the resulting increase in the energy consumption of the pumps, the costly repair of the stem connection combined with a required replacement of the valves may also cause the failure of an entire plant. For this reason, for butterfly valves attention must be paid to a structurally secure connection between the valve stem and disc as is the case with the VAG EKN® Butterfly Valve.

4. A reliable stem seal prevents dirt from entering the bearing.

If the medium comes into contact with the bearing of the stems, the stems and the body will be constantly subjected to the corrosive effect of the medium. If the medium also contains abrasive particles, they can penetrate an unprotected bearing and lead to increased friction within the bearing and thus lead to increased wear of valve stems and bearing bushings. A bearing reliably sealed by multiple O-rings, as is the case with the VAG EKN® Butterfly Valve, is essential for a long valve service life.

5. A contoured peripheral seal ensures permanent tightness.

Conventional seals are fixed on the disc by means of a retaining ring. When opening and closing butterfly valves, shortly before closed position high gap flow speeds occur in the seat area, causing uncontoured seals to be pulled out of the retaining ring. Moreover, mechanical properties such as hardness and shear strength of the elastomer used for the sealing ring also play a significant role. Seals that are too soft may be pulled out at high gap flow speeds. For this reason, seals with a distinct sealing profile and sufficient hardness as well as shear strength are preferable, since they are chambered durably and stably between disc and retaining ring. Via an automated sealing system in the retaining ring operating pressure also supports the sealing effect of the profile ring in both directions of flow. The profile seals chambered in the retaining ring of the disc, as is the case with the VAG EKN® Butterfly Valve, can also be used for high gap flow speeds and support the sealing effect, regardless of the direction of flow.

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