Ball Valve Working Principle
The fluid passage by rotating the sphere 90 ° on the fluid passage bore axis and turning the bore (s) to the passage open or closed, with one or more holes in the middle placed on the end of a shaft, mostly elastomer (may also be metal as required) between the two seals they cut, open and fulfill their duties.
It is preferred to work fully open or fully closed. They are not suitable for precise flow control.
Ball Valve Specification
Clean, non-solidified, neutral or aggressive liquid and gaseous fluids
Flow is possible in both directions in two-way shut-off valves. Flow direction is specified in 3 and 4 way valves.
Hot and Cold Water Installations, Natural Gas-Oil transportation main lines, Gas distribution Installations, Compressed air installations, Petrochemical Plants, Machine Manufacturing, Special Vehicle Manufacturing, Paper manufacturing, etc.
Manual, motorized, hydraulic, pneumatic actuators.
It can be from DN 8 to DN 1500.
Up to PN 500 can be reached. However, they are generally manufactured up to PN 40.
Working Temperature Range
It can expand from -2750C to + 8000C. However, they are generally manufactured for the range of –200C and + 1500C.
Copper alloys (Brass, Bronze), Cast iron, ductile iron, steel and stainless steel, and Steel and Stainless Steel, Titanium, Aluminum, Ceramic, Ball Valve PVC, PP, PTFE
Sealing gasket material
Metal material such as various Elastomers (PTFE-Teflon, NBR, etc.), Graphite, Ceramic, Nickel alloys
Connection to Installation
Screwed, Flanged, Welding Mouth, Gland.
Some related product standards
TS 3148, TS 9809, DIN 3357, DIN 3441- 3442, API 6D, BS 5159, BS 5351
Ball Valve Advantage and Disadvantage
They provide free, comfortable passage of fluid.
The pressure drop is very low, especially in 2-way valves. Armature is one of the valve types with the lowest flow resistance.
It is easy to use.
They can be used with actuators.
They are also suitable for gaseous fluids. “0 leak” can be achieved by using elastomer seals in particular.
Flow is possible from both sides of the valve.
Due to their structure, their weight is high.
As the nominal size grows, their prices become relatively expensive.
There is a dead volume between the sphere and the body cavity.
Sudden opening and closing can create ram blows.
Valves with elastomer seals have relatively low operating temperatures, depending on the temperature resistance of the elastomer
Ball Valve Types
According to the through-hole size
Full bore valves: through hole; Valves, which are given in standards depending on the nominal size of the valve and have a diameter that is very close to the value of the nominal size, expressed in mm, providing a smooth flow without turbulence.
Narrow (reduction) throughput valves: through hole; Valves with a diameter that is determined to be less than the nominal value of the nominal size in mm and generally given for a smaller nominal size than the valve nominal size.
According to the flow direction
rough hole of the full bore valves is very close to the inner diameter of the pipe to which they are connected, they show a very low flow resistance in the fully open position of the valve and the system ensures that the total resistance factor remains low.
Narrow-through valves are lighter and cheaper because smaller spheres can be used. Although resistance factors are higher than full bore, they can be easily used in places where a large number of valves are not used, as they remain lower than other types of valves.
In narrow pass valves, turbulence is formed and the valve resistance factor increases as the flow follows a narrowing and then expanding path. This increase means greater pump head height and increased energy consumption in parallel with the increasing number of valves in the system.
2-way valves are the most widely used types. 3 and 4-way valves are produced by drilling holes (holes) perpendicular to the linear transition hole in 2-way valves perpendicular to the flow axis and used as distribution or mixing valve according to the connection type to the installation.
According to the sphere bearing type
These are the valves where the sphere is bedded with sealing gaskets on both sides.
In the closed position of the valve, the opening-closing shaft is connected in a channel, which allows the ball to move on the flow axis, and the fluid pressure pushes the ball towards the gasket on the opposite side, contributing to the sealing positively.
This type of bearing can be used up to nominal sizes of DN 100-125, although the valve varies according to the rated pressure. They are used in applications with low pressure-temperature values.
Guided ball (trunnion ball)
On the axis of the sphere perpendicular to the flow axis. are the valves that are mounted directly to the shaft from the bottom and the top.
The pressure force on the closed valve transition section is met by the lower and upper bearings, not the seals.
They are used in applications with high pressure-temperature values. When we examine a DN 25, full bore PN 25 valve with a through hole diameter of 150 mm, if the fluid pressure is P = 20 Bar, the pressure force applied to the ball in the closed valve;
We see that F = [(3.14 x 152) / 4] x 20 = 3.532 kgf has reached a fairly high dimension and this force can deform the seal only if it is met by elastomer seals.
Plate spring reinforced: By placing the sealing gaskets in the plate spring, in the direction of fluid arrival, the seal is adhered to the sphere surface and a positive contribution is provided to the seal.
It can be used in both “floating ball” and “bed ball” types.
Ball Valve Parts
One-piece: The body is one-piece, the types where the spheres and gaskets are mounted on the side (Side entry) or top (Top entry) and compressed.
In top entry types, maintenance and parts can be changed without removing the valve from the line.
Two or three parts: They are the types in which the parts that make up the valve body are screwed to each other or are connected with bolts, studs and nuts.
Fully welded: These are the types where the valve is welded to one of the body parts after all parts of the valve have been installed and maintenance is not possible.
These types are generally used at high pressures and temperatures with unwanted fluids leaking from the joints to the atmosphere.
According to the control ability:
Shut-off valve: Ball valves are generally of this type and the transition section is an unobstructed hole. It is only suitable to be used fully open and fully closed.
Control valve: These are types that have gained control ability thanks to special form holes placed in the transition section.
Ball Valve Application Examples
In the refineries, gas lines, in case of fire, if the elastomer gaskets cannot melt and function, “Fire safe-Fire safe” ball valves are used. There are special test standards for these valves. (API 607, BS 6755)
Since the sealing is provided by one of the sphere and gasket surfaces sitting on one of them, if the fluid is not clean, the solid particles will enter between the two surfaces during the opening and closing process, firstly, the surfaces will deteriorate and the sealing will not be ensured and leakage will begin.
The cleanliness of the fluid is very important in these valves as well as in every valve.
When the valves are left closed for a long time, permanent layers can be formed on the surface of the sphere in contact with the fluid, depending on the type and quality of the fluid.
After these layers are formed, the sphere becomes very difficult to open. When force is applied to open, the on-off shaft can be broken, and the arm’s engagement point can be licking.
Therefore, the opening and closing of the valves for a short period of time (1-2 weeks) will prevent the formation of layers, and the life of the valve will be extended.
Due to their nature, such valves must operate fully open or fully closed. Otherwise, the fluid velocity increases significantly in the small gap between the sphere and the seal, close to the closure, that is, when the sphere hole is substantially closed by the seal.
The rapid passage of fluid leaves traces on the gasket surface. These scars grow over time and the valve begins to miss. This rapid flow also means high noise.
The gasket surface, which remains in this intermediate state for a long time, is deformed and the gasket is injured during the opening and closing of the sphere.
If the fluid used can be frozen or solidified when the temperature drops, the body should be heated in a pattern such as a serpentine and jacket.
In terms of overall energy saving; It should not be forgotten that the valves have large surfaces that will cause heat loss to the environment, and the valves where different fluid passes from the ambient temperature must be isolated.
Ball Valve Maintenance
The most common problems in such valves are again; wear of sealing surfaces (sphere and / or gasket) and leakage of packing.
In case of leakage from shaft packing, the packing should be compressed to prevent leaks. But; If the valves have reached the end of their compressibility limit, the seals may lose their elasticity and become unable to prevent leakage.
Repair is not possible in this case and the packing must be replaced.
When repair work is required as a result of damage to the sealing surfaces, processes such as grinding sphere surfaces and sealing the gas are mandatory. Therefore, it would be more correct to have this kind of repair work done at the manufacturing company.
It is generally possible to replace the damaged parts with new ones. However, it is imperative to check the valve for leak tightness after part replacement.