A ball valve is a shut-off valve that controls the flow of a liquid or gas by means of a rotary ball having a bore. By rotating the ball a quarter turn (90 degrees) around its axis, the medium can flow through or is blocked. They are characterized by a long service life and provide a reliable sealing over the life span, even when the valve is not in use for a long time. As a result, they are more popular as a shut-off valve then for example the gate valve. Moreover, they are more resistant against contaminated media than most other types of valves. In special versions, ball valves are also used as a control valve. This application is less common due to the relatively limited accuracy of controlling the flow rate in comparison with other types of control valves. However, the ball valve also offers some advantages here. For example, the valve still ensures a reliable sealing, even in the case of dirty media.
Standard ball valves consist of the housing, seats, ball and lever for ball rotation. They include ball valves with two, three and four ports which can be female or male threaded or a combination of those. Threaded valves are most common and come in many varieties: ball valves with approvals for specific media or applications, mini ball valves, angled ball valves, ISO-top ball valves, ball valves with an integrated strainer or a bleed point and the list goes on. They have a wide range of options and a large operating range for pressure and temperature.
Hydraulic ball valves are specially designed for hydraulic and heating systems due to their high operating pressure rating and hydraulic and heating oil resistance. These valves are made of either steel or stainless steel. Besides these materials, the seats also make hydraulic valves suitable for high operating pressure. The seats of these valves are made of polyoxymethylene (POM), which is suitable for high pressure and low temperature applications. The maximum operating pressure of hydraulic ball valves goes above 500 bar while the maximum temperature goes up to 80°C.
Flanged ball valves are characterized by their connection type. The ports are connected to a piping system via flanges that are usually designed in accordance with a certain standard. These valves provide a high flow rate since they typically have a full-bore design. When choosing a flanged ball valve, besides the pressure rating, you also have to check the flange compression class which indicates the highest pressure this connection type can withstand. These ball valves are designed with two, three or four ports, they can be approved for specific media, have an ISO-top and everything else a standard ball valve could have.
Vented ball valves look almost the same as the standard 2-way ball valves when it comes to their design. The main difference is that the outlet port vents to the environment in closed position. This is achieved by a small hole that is drilled in the ball and in the valve body. When the valve closes, the holes line up with the outlet port and release the pressure. This is especially useful in compressed air systems where depressurization provides a safer working environment. Intuitively these valves look like 2-way ball valves while in fact they are 3/2-way due to the small borehole for venting.
The valve may have two, three or even four ports (2-way, 3-way or 4-way). The vast majority of ball valves are 2-way and manually operated with a lever. The lever is in line with pipe when the valve is opened. In closed position, the handle is perpendicular to the pipe. Manually operated ball valves can be quickly closed and therefore there is a risk of water hammer with fast-flowing media. Some ball valves are fitted with a transmission. The 3-way valves have an L-shaped or T-shaped bore. As a result, various circuit functions can be achieved such as distributing or mixing flows. In the image below, the circuit functions 3-way ball valves are shown schematically.
The assembly of the valve housing can be divided in three commonly used designs: one-piece, two-piece and three-piece housings. The difference is how the valve is assembled and this affects the possibilities for maintenance or repair. The operation of thevalves is the same in each embodiment.
The most common design is the "floating ball design". The ball is suspended in the media and held in place by two sealing rings. Some high-quality valves have a "trunnion ball design". The ball is supported at the top and bottom to reduce the load on the valve seats.
The hole through the ball may have different profiles such as a full bore, reduced bore or V-shaped.
The most common housing materials for ball valves are brass, stainless steel and PVC. The ball is usually made of chrome plated steel, chrome plated brass, stainless steel or PVC. The seats are often made of Teflon, but could also be made of other synthetic materials or metals. More information on this topic you can find on the page: Chemical resistance of materials.
Brass ball valves have the largest market share. Brass is an alloy of copper and zinc and has good mechanical properties. Brass valves are used for (drinking) water, gas, oil, air and many other media. Chloride solutions (e.g. seawater) or demineralized water may cause dezincification. Dezincification is a form of corrosion where which zinc is removed from the alloy. This creates a porous structure with a greatly decreased mechanical strength.
Stainless steel ball valves are used for corrosive media and aggressive environments. They are therefore often used in seawater, swimming pools, osmosis installations, with high temperatures, and many chemicals. Most stainless steel is austenitic. Type 304 and 316 are the most common, 316 has the best corrosion resistance. 304 is sometimes referred to as 18/8 because of 18% chromium and 8% nickel. 316 has 18% chromium and 10% nickel (18/10). Stainless steel valves usually require a higher operating torque than for example brass or PVC valves. This must be taken into account when a stainless steel valve is operated by an electric or pneumatic actuator.
PVC ball valves often have a lower price (except for ISO-top valves) and are widely used in irrigation, water supply and drainage or corrosive media. PVC stands for polyvinyl chloride. PVC is resistant to the most of the salt solutions, acids, bases, and organic solvents. PVC not suitable for temperatures higher than 60 °C, and is also not resistant to aromatic and chlorinated hydrocarbons. PVC is not as strong as brass or stainless steel, therefore PVC ball valves have lower pressure rating. A more in-depth article about PVC ball valves can be read here.
|Brass||Durable, suitable for most applications||Sensitive to dezincification|
|Stainless steel||Very abrasive resistant, inert, corrosion resistant||Higher price, often more torque needed to rotate the ball|
|PVC||Cost-effective, not prone to corrosion||Shorter lifetime, limited pressure and temperature ranges|
Most valve seats are made of PTFE (Teflon). PTFE stands for PolyTetraFluorEthylene. This material has a very good chemical resistance and a high melting point (~327°C). Besides that, the friction coefficient is extremely low. A small disadvantage of PTFE is that the material shows creep, which can cause a deterioration of the sealing over time. Besides that, PTFE has a rather high thermal expansion coefficient. A solution for this problem is to use a spring in order to apply a constant pressure on the Teflon seal, like for example a cup spring. Other popular sealing materials are enforced PTFE and Polyamide (Nylon). The harder the material of the valve seat is, the more difficult it is to maintain proper sealing. For some application in which soft materials are not possible to use, for example with very high temperatures, metal or ceramic valve seats are used.
For certain applications, approvals are desired or required. Drinking water and gas are the most common. Choosing a certified ball valve, assures that the product meets important safety requirements.
These ball valves are suitable for drinking water applications and have a WRAS, KIWA or DVGW approval.
These valves are approved for application in gas appliances.
Ball valves can be driven manually, electrically or pneumatically. Electric ball valves use an electric motor to rotate the ball. The electric actuator often consists of a protective housing with an internal electric motor and a reducing gear mechanism. This reduces the speed of opening and closing and reduces the risk of water hammer. Furthermore, the operating torque is increased. Usually, the actuator can be disconnected from the valve. The most common flange connection between the valve and actuator is the ISO 5211 standard. The photo below shows an example of a ball valve with ISO 5211 flange, often called ISO top.
Most electric ball valves use the electric motor for both opening and closing. Spring closed or battery closed actuators are less common, and close (or open) automatically once the power supply is shut down. More luxury versions often have a visual position indicator and the option of manual control.