Table of Content:
1.What is a Trunnion Ball Valve
2.How Does a Trunnion Ball Valve Work
3.What Is The Structure Of Trunnion Ball Valve
4.Trunnion Ball Valve Design Standard
6.What Is The Main Features Of Trunnion Ball Valve
7.What Are The Types of Trunnion Ball Valve
8.Where is Trunnion Ball Valve Used
9.Why and How to Maintain Trunnion Ball Valves
1. What is a Trunnion Ball Valve
The trunnion ball valve is an essential device for regulating the flow of fluids- steam, gas, or oil in pipeline. It is quarter-turn designs with a ball capable of rotating 90 degrees on its axis to either block or allow the flow of fluid. These valves have a spherical disk design at the center, which rotates to regulate the start-stop flow cycle. The disk often called the ball comes designed with a small protruding shaft at the top and bottom which are mechanically supported. In this case, flow is controlled by the position of a hole in the center of the ball. For their versatility, Trunnion mounted ball valves are useful in industries where such shut-off operation is required.
The Trunnion ball valves have adequate backing for the ball. The support is in shape similar to a shaft, and it’s called a trunnion. The Trunnion soaks up any additional pressure coming from the flow, thereby lowering the pressure on the valve seat and the ball. Trunnion mounted ball valves find their use in large-scale implementations that require low operating torque.
2. How Does a Trunnion Ball Valve Work
Trunnion valve is a device that controls the flow of fluids in pipelines by regulating the shut-off cycle. It contains the elements necessary for enabling or disabling the flow of fluids through the pipe. It is built to integrate pipe or tube sections to actualize this function.
3. What Is The Structure Of Trunnion Ball Valve
The Trunnion ball valves have a structure similar to the traditional ball valves seen around. The difference it brings is that the ball valves have more mechanical anchors to support the ball. The ball is given solid support from the two ends on its x-axis. It holds it in place and makes it very easy to control.
In the trunnion mounted ball valve, the design comes with dismal tended shafts at its top and bottom, which are mechanically supported. With this, it is made suitable for larger diameters and higher pressure. In the Trunnion mounted design, the ball is kept in position by compressing the seat rings at the two ends.
The ball, for its flexibility, enables a good measure of movement. While in use, it floats moderately downstream towards the seat ring to make a sealing. If the loads on the floating ball are much higher, the seat rings won’t be able to give the needed support to the ball. This is when the power of the trunnion comes in. In a trunnion design, the seat rings are the parts floating against the traditional design where the ball floats.
The valve’s body is the casing that holds it in place and offers support to the interior of the ball valve. The material for this design can be made of different products depending on the type of application it is used for. Some of the commonly used materials are carbon steel, low-temperature carbon steel, stainless steel, duplex, Inconel, and super duplex.
This is a sphere ball shaped disk through which it rotates to stop or start flow in a solid rotational motion. It is connected to the Trunnion at one end and the stem at the other end. The ball is fixed in a position while it rotates. The trunnion ball valve’s seats are often in contact with this ball, which reduces the torque.
The seat of the Trunnion ball valve is a design feature that surrounds the ball. When the actuator gets turned on, the seats keep the ball tightly in place, blocking off access. There are two types i.e. metal or soft (Teflon). This makes it move in the direction of the ball.
There is an extra shaft in the trunnion ball valve that grips the ball in position from beneath. This simple shaft is the Trunnion. Its function is to keep the ball firmly attached. Sometimes, the Trunnion is an extension of the spherical ball, whereas, in other trunnion mounted ball valves, it is attached to the spherical ball disk via welded joints.
The stem of the trunnion ball valve helps connect the ball and the actuator together. It is connected to the ball an additional shaft that helps secures the ball in place. Also, it regulates the ball’s movement. Trunnion mounted ball valves have strengthened anti-blowout stems, which is why they are able to handle pressurized and intense temperatures without causing any damage.
Injection fittings are designed in the seat and stem area. When sealing is compromised, and leakage is caused, the grease can be injected via a sealant injection fitting. The injected sealant functions as a partial seal to stop further leakage.
However, it must be noted that the sealant injection fittings are for emergency purposes only.
4. Trunnion Ball Valve Design Standard
The trunnion ball valve is designed by API6D or API608, and conforms to industry required standards such as ASME B16.5, ASME B16.34 and ASME B16.10. They are built to be fire resistant according to API 607.
5. Typical Material
The Trunnion ball valve is accessible in forged or cast body materials (split or monoblock). Forged structures are often used for valves of high-pressure and larger bore sizes.
5.1 Typical materials for trunnion mounted ball valve design include:
A. Body/Closures – F304L, A105, A182 F304, F316, F51, F316L, F53, A350 LF2, LF3, Inconel, Monel, Hastelloy(Forging), A351 CF3, A351 CF8, A216 WCB, A351 CF3M, A351 CF8M, A890 4A/ 5A, A352 LCC/ LCB (Casting)
B. Ball- CS+ENP, F304L, F316, A182 F304, F316L, F51, CS+TCC, CS+Ni60, F53
C. Seat retainer- A182 F304, CS+ENP, F304L, F316, F51, F53, F316L, CS+Ni55, CS+TCC.
D. Stem – A182 F51, A182 F6a, A182 F316, 17-4PH,
E. Packing- RPTFE, Graphite, PTFE,
5.2 SEAT MATERIAL
PTFE: Virgin PTFE is by far the most commonly used sealing material of exceptional quality. It has attributes suitable for most services. It’s of outstanding chemical resistance across the valve and also has low friction coefficient.
RPTFE: RPTFE (known as Reinforced PTFE) is usually created by adding 15 percent of fiberglass to virgin PTFE. It has improved pressure-temperature capabilities than the virgin PTFE and comes with enhanced wear resistance. It is effective against deformation when on load.
PCTFE: PCTFE is a chlorotrifluoroethylene homopolymer with high tensile stress and have a low deformation when on load.
Nylon 6: Nylon is a rising seat material for Valves of Class 600. It is extremely robust and can be useful in oil, air, and other media. It is appropriate for strong oxidizing agents.
Devlon: Devlon is a strong molecular weight polyamide especially suited to high temperature and pressure applications in the gas and oil industry. In addition, it is a minimal moisture absorption material.
PEEK: PEEK is an advanced high-performance thermoplastic. It is really good at continuous exposure to hot water and chemicals owing to its high resistance.
PPL: PPL(Polyparaphenylene) is an exceptional seat material which has a low coefficient of friction. It can withstand extreme pressure and also temperature resistant.
TFM: TFM (modified PTFE) is an improved chemical-modified PTFE design with improved properties whilst retaining the proven benefits of conventional PTFE.
Metal: Metal (typically stellite) seats are employed in situations of hydraulic shock, flashing abrasive media, and in extreme situations.
5.3 O-RINGS MATERIAL
NBR Buna-N: NBR Buna-N (NBR) is a durable and all-purpose polymer of hard water, oil, solvent, and hydraulic fluids.
HNBR: HNBR (Hydrogenated NBR) can be compared to NBR in terms of media stability but comes with much better oxidation and heat stability.
Viton: Viton (fluorocarbon) is an elastomer of fluorocarbons that is compliant with a wide variety of chemical Substances. It produces strong performance in mineral acids, chlorinated hydrocarbons, salt solutions, and petroleum oil.
EPDM: EPDM has good resistance to abrasion and tear, with outstanding chemical resistance to a range of alkaline and acids. This is susceptible to oil, strong acids, and strong alkaline and should not be applied in compressed airlines.
FVMQ Fluorosilcione: FVMQ Fluorosilcione is a fluorinated side-chain silicone polymer chain for better oil resistance. The physical and mechanical properties closely mimic those of silicone.