Ball Valves Introduction
Ball Valves are quarter turn valves that uses hollow ball and seat combination to allow or prevent flow of fluid. Ball valve types includes floating ball valve, trunnion ball valve, stainless steel ball valve, brass ball valve, bronze ball valve etc. A ball valve is open when the ball’s hole is in line with the flow. Turn is one quarter (90 deg) by either a handle (3" or below) or geared handwheel, the ball is seal on the seat thereby preventing fluid flow. Any position in between open and close can be used for throttling. Ball valves can be full port or reduced port. Pipeline applications prefer full port ball valve to allow passage of cleaning pigs thought them. Stainless Steel and Brass ball valves are commonly used in industrial and home applications in size 3" or smaller and comes an open close lever.
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Ball valves are used to control flow of liquid or gas and can also be used for on/off throttling. For critical throttling applications however, the profile of the opening in the ball valve is designed mainly for controllability over its range of positions. The orifice cut into the ball is machined in the shape o and of triangle and also called V Port Ballvalve.
Standard ball valves are quarter-turn valves.The stem rotates 90 degrees to go from close to open position. The ball is usually metal with a hole drilled through it for fluid flow. Ball valves are easily turned with levers in sizes up to 3 inch nominal pipe size. Bigger size ball valves are usually equipped with geared handwheels which indicate the position of the valve with an arrow located atop the operator.
It is important while specifying ball valve to ensure that the bore size is appropriate for the application. The standard bore is actually one size smaller than the nominal ball valve size. For example, a 4" standard bore ball valve has a 3" bore and is therefore smaller than the inside diameter of pipe it is attached to. It is also called "reduced-port" ball valve. If the application require full bore opening, the ball valve should be specified as "full-port" ball valve.
Double reduced bores are also available in smaller sizes such as 2 in and under. The bore in these valves are 2 size smaller than the adjoining pipe.
Types of Ball Valves
Ball valves are available in three types: Full Port, Reduced Port and Venturi Port. As mentioned above, full port valve has ball opening that matches the adjoining pipe size. Reduced port and venturi port has ball opening that is one size smaller
Different body configurations of the ball valve includes;
- Top Entry Ball Valve: This allows maintenance of the valve internals by removing the valve bonnet cover. This prevents removing the entire valve from the piping system.
- Split Body Ball Valve: This type of valve consist of two parts, where one part is smaller. Ball is inserted in the larger body part and smaller body part is assembled as a bolted connection.
Ball Valve End Connections
While specify the ball valve, it is important to specify the valve end connection. Most common end connections are: Butt Weld, Socket Weld, Flanged, Threaded and Propriety Connections.
Ball Valve Components
Material: Balls in a a ball valve is usually made of metal while the seats are made of a soft material such as Telfon, Neoprene or Thermoplatics.
Stem Design: Stem has rectangular portion at the ball that fits into slot cut into the ball. This permits rotation of the ball as the valve is operated.
Bonnet: Bonnet of the valve is fastened to the body which holds the stem assembly and ball in place. Bonnet can be adjusted to change compression of the packing which supplies the stem seal.
Ball Valve Sealing Mechanism
One of the critical ball valve component is sealing interface between the ball and the seat. This sealing surface relies on both the sealing method and seat material. Sealing is achieved by one of the four methods as below;
- Compression of the ball and seat.
- A floating ball valve, with a floating ball, that is pressed into the seat when high pressure is applied.
- A trunnion ball valve type where the ball is held in place with a trunnion. In this case the seat is compressed against the ball via line pressure or springs.
- A floating ball with a pressurized seat.
Seats are often made with a low friction material such as PTFE. These material have upper temperature limit of 350 F at 100 psi. For higher temperature, metal to metal seal is used.
Ball Valve videos
Video below shows the working of a floating ball valve.
Video below shows working for Trunnion mounted ball valve
Q&A with a Valve Distributor
We recently sat down with a valve distributor which specializes in smaller size valves (up to 4") mainly for O&G customers. Below is the transcript of the session;
Speaker 1: Alright these are ball valves. We cover everything from a forged brass, stainless steel and carbon ball valve. We'll first discuss our brass ball valve. This is a forged brass we cover everything from a one-inch through a four-inch, I mean quarter-inch. Quarter-inch through a four-inch and do also offer in a two-inch heavy duty as well. We've had a lot of success with these, in regards to testing these valves we test these in house. Typically anything over two-inch or two-inch and above we test a hundred percent. Below that we have certain percentages, we've had a lot of success with these valves. They do not have a locking handle although we get a few request every now and then on those but that is our brass ball valves.
Speaker 2: And the main reason we don't have a locking handle on this is because it's rated at 600 pounds. It's just a low-pressure valve, brass can not withstand a very high pressure, and that's when you get into your carbon steel, and your stainless steel.
Speaker 1: Go ahead and talk about the carbon steel first.
Speaker 2: So you know essentially it comes down what the customer wants, of course your going to pay more for your stainless steel. But this carbon steel ball valve this is going to be a high-pressure ball valve. It's one-inch, it's a two-piece locking handle one-inch up to four- inch.
Speaker 1: Quarter inch.
Speaker 2: Yes quarter-inch up to four-inch and your 2,000 pound, your SRT is going to be your reduced port your SFT is going to be your full port 2,000 pound and then when you get into your high pressure you'll have a 3,600 class and a 6,000 class. Now when your get to the two-inch on a 3,600 pound and a 6,000 pound it will go into a reduced port. Now your stainless steel is going to be a stainless steel 316, as you can see this here will be a two piece but this has got a seal weld on it. Ok, this ensures just another safety feature that we add to our stainless steel ball valve. This is probably our number one seller our SWFT. It's going to be a full port, two piece, 2,000 pound locking handle. We also offer this in an SRT, which is your bar stock, this is going be your one piece and it will be at a reduced port. Then you also get into the high-pressure valves which will be your SFTB 3,600 class, your SFTB 6,000 class, that's going to be your higher pressure two piece steel weld 316 ball valves.
Speaker 3: And those are NACE as well?
Speaker 2: Yes.