The issue of the installation direction of ball valves

Not quite sure. A two-way seal would be better, right? Tests were once conducted, and it was found that the ball valve could not maintain a seal in one direction.

When performing single-seal installation, care must be taken with the orientation of the ball valve. The direction in both ways doesn’t matter. A two-way seal is probably better.

Two-way ones are better; one-way ones sometimes fail to seal properly. Two-way ones are more reliable, though their cost is slightly higher~~~~

There is no such thing as a good or bad option; it depends on your operating conditions to determine which valve to choose. Expensive things are not necessarily the right ones. Those who are not familiar with this can contact the technical staff of the valve manufacturer for assistance in selecting the appropriate model.

It depends on the specific operating conditions; for some liquids that are prone to vaporization, a single-phase sealed ball valve is a better choice as it facilitates pressure release.

Ordinary ball valves do not indicate direction and can be installed arbitrarily. In theory, ball valves have no directionality, but in practical installation, to prevent excessive leakage between the valve body and the valve cover, the valve body is usually connected in the direction from which the tank or material flows. Some ball valves are directional, and this is usually indicated on the valve; if installed in the wrong orientation, they cannot provide a proper seal. Ball valves are divided into single-direction sealing ball valves and double-direction sealing ball valves; the former has a directionality – if installed in the wrong orientation, it cannot ensure sealing under full pressure difference – while the latter has no such directionality. Structurally, there are two types: double-seal and single-seal. Double-seals generally have no requirement regarding flow direction, while single-seals do have such a requirement. Manual ball valves have no direction, but control valves do. Both V-type ball valves and eccentric hemispherical valves are directional, and indicators showing the flow direction of the medium are usually marked on the valve body. Floating ball valves and fixed ball valves are bidirectional, while eccentric half-ball valves, V-ball valves, and lift-stem track ball valves are unidirectional. Ball valves are divided into O-type ball valves and V-type ball valves. The O-type ball valve features a floating structure; its ball core is made of precision-cast material and coated with hard chromium on its surface. The valve seat is constructed from reinforced polytetrafluoroethylene. The flow passage has the same diameter as the pipeline, resulting in high flow capacity and very low flow resistance. There is no leakage when the valve is closed. It is generally used as a on/off valve and is particularly suitable for media with high viscosity, as well as those containing fibers or particles ； The V-type ball valve features a fixed structure, with a V-shaped cut on the ball core, which enables proportional control; its flow characteristic is approximately equal percentage. Its medium flow direction is on the valve body. For users, O-type ball valves are generally used for switching purposes and offer bidirectional sealing, so there is no requirement regarding direction ； V-type ball valves are used for control; they generally provide one-way sealing and require a specific direction. In actual use, the features of the products supplied by different manufacturers may vary; it is sufficient to check whether there is a flow direction indicator on the valve body. If not, it indicates a two-way seal, and no specific installation direction is required. If so, its installation as indicated is required to achieve a good seal.

I believe that those who have in-depth knowledge are the valve manufacturers, as they understand the structure and usage of valves quite well. But when selecting valves, designers should take certain factors into account and pay attention to specific points – should they choose valves with single-direction or double-direction sealing?

Another thing that’s a bit confusing: are fixed balls all double-sealed?

It is uncertain whether fixed balls and floating balls provide one-way sealing or two-way sealing. It is not stated that fixed balls must be bidirectionally sealed. Whether it is a one-way or two-way seal depends mainly on the leakage level and the requirements of the medium, as well as the pressures before and after the valve. It mainly depends on the choice of the valve manufacturer and the owner; generally, two-way sealing will be more expensive than one-way sealing. For wear-resistant ball valves, those with coatings or cemented carbide layers are even more costly. The above refers to O-type ball valves. We are currently in contact with some well-known valve manufacturers, such as Fox, MOGOS, Venisa, Tyco, etc., and needless to say, all of them use dual-sealing mechanisms. It’s standard.

It should be noted first that soft sealing and hard sealing refer to the sealing pairs, and they have little to do with one-way sealing and two-way sealing. Whether it is a one-way or two-way seal mainly depends on the structural design of the valve. 1. Floating ball: Ball valves with floating balls achieve sealing by relying on the pressure of the medium to create a sealing force. Therefore, floating ball valves are not suitable for larger sizes; otherwise, when the medium pressure is low and the ball is heavy, the sealing effect deteriorates, or sealing may even become impossible. The floating ball can have either a single-seat seal or a double-seat seal, depending on the manufacturer’s preference. A single-seat floating ball allows for automatic pressure relief in the valve chamber. 2. Fixed-ball valve: A fixed-ball valve achieves sealing by creating a sealing pressure between a spring-supported floating seat and the valve core, thereby enabling closure and sealing. The floating valve seat consists of a valve seat, a sealing ring, a support spring, and a sealing gasket; it has a complex structure and relatively large dimensions. However, fixed balls can achieve sealing without the need for medium pressure; they provide reliable sealing and it is easy to implement dual sealing, which is why they are often used in large-diameter applications. If no special requirements are specified for the manufacturer, a fixed ball valve cannot automatically relieve pressure in its sealed valve chamber. Therefore, when necessary, it should be specified in the valve specification sheet. For example, in the case of easily vaporizable media, spheres generally have pressure relief holes to release pressure to the high-pressure side. At this point, it is a one-way seal, and the flow direction of the medium needs to be indicated on the valve body to prevent it from being installed in the wrong direction. 3. Hemispherical and V-shaped balls: The use of a hemispherical shape is intended to reduce the weight of the ball, which serves as an internal component, thereby lowering the cost of the valve. The hemispherical internal component configurations are combined to achieve the required shut-off seal pressure ratio. Semi-spherical ball valves are commonly used in pipelines for media such as in mines. The application of V-shaped balls is similar to that of hemispheres. 4. Eccentric Ball Valve: The eccentric ball valve utilizes the sealing principle of the eccentric butterfly valve (cam effect) to achieve the desired sealing pressure for shut-off, thereby reducing or preventing wear between the internal components and the valve seat. Compared to fixed-ball valves, it generates a sealing pressure through valve stem torque, and its triple-eccentric design prevents wear of the internal components and valve seat, thus offering superior performance. However, if the eccentricity is set improperly, it will instead lead to a decline in the valve’s performance. 5. Track ball valve: A track ball valve utilizes a track structure on the valve stem to cause the stem to move up and down at the moment of opening and closing the valve. The wedge-shaped structure formed between the end of the stem and the ball presses the ball against or away from the valve seat, thereby creating the desired sealing pressure or removing it. Continuing to turn the handwheel causes the sphere to rotate, thereby ultimately achieving the purpose of shutting off or opening the pipeline. Since the sphere does not come into contact with the valve seat while rotating, wear between the sealing surface of the valve seat and the sealing surface of the valve element (sphere) can be avoided. Therefore, ball valves with tracks offer better performance than fixed ball valves, and are more suitable for metal hard sealing. However, track ball valves are often used in conjunction with top-mounted valve bodies; these valves are heavy and expensive, and it is also difficult to machine the tracks on the valve stem. If the design and manufacturing are not proper, it can lead to a deterioration in the performance of the valve. In summary, there is no such thing as a better or worse option between one-way sealing and two-way sealing; it depends on the type of sealing you need. You should consider various factors based on the specific circumstances before making a choice.