Analysis of the difference between Trunnion Ball Valves and Floating Ball Valves

author: ATHENA GROUP
2022-04-29
 Analysis of the difference between Trunnion Ball Valves and Floating Ball Valves

Ball Valves are widely used in on/off general service, the stem is connected at the top of the ball and allowing the valve to open and close with a quarter-turn movement to control flow.
There are two types of ball valves, Trunnion Ball Valves and Floating Ball Valves.

Trunnion Ball Valves
Designed in two or three bolted pieces with a solid double trunnion configuration and two independent seats for an easy bidirectional sealing, to ensure the greatest level of tightness and reliability under high pressure and temperature conditions in all critical isolation services.
  1. Seat Sealing Feature
a) Upstream seat: The seats can be moved slightly along the valve axis, Upstream line pressure acting on the seat area (A1) does not equalize against on the seat area (A2).The differential force in the area (D1) pushes the seat tightly against the ball surface resulting in a tight effective seal. (Fig.1)
b) Downstream seat: When the body cavity pressure is lower than the downstream pressure, the net pressure difference acting over area (D2), pushes the downstream seat tightly against the ball surface creating a positive seal. (Fig.1)
  1. Self Relieving Seat
When the body cavity pressure exceeds the downstream seat spring preloaded force, the differential force in the area (D2) pushes the downstream seat away from the ball, the body cavity pressure will automatically relieve. And then the seat returns to the ball under spring action. (Fig.1)
  1. Double Block and Bleed
When the ball is in the closed position, each seat of the ball valve can cut off the medium independently on the upstream and downstream side to realize double-block functions. the body cavity are isolated from each side of the valve, the body cavity pressure could be released through the vent valve. (Fig.2)
  1. Blow-out Proof Stem
The stem with integral T-type shoulder, supported by gland, can be guaranteed not to be blow-out by the medium even if at abnormal risen pressure in the cavity. (Fig.3)
  1. Anti-Static Device
During turning of the stem to opening and closing the valve, static electricity is easily caused by sparks generated by friction. Antistatic devices, assembled by a spring & a grounding plunger, assure the electrical continuity, between ball and stem, stem and body, to prevent the possible risk of fire or explosion. (Fig.3)

  1. Emergency Sealant Injection System
For 6 inch and larger trunnion mounted ball valves, or small valves on request, special sealants may be injected through a sealant injection fittings that are located on the adapter and the gland to obtain emergency sealing, in case of seat or stem O-ring are damaged and leakage occur by fire or other accidental. Fittings also internally installed a second check valve to provide backup sealing. (Fig.4)
  1. Firesafe Design
a) Internal leakage prevention
When seat insert, O-ring and spacer are damaged in a fire, the line pressure and the seat preloaded spring push the seat metal lip into the ball surface to cut off the line fluid and prevent the internal leakage to reach fire-safe purpose. Besides, the seat graphite packing can prevent fluid leakage from between the valve body and the seat. (Fig.5)


b) External leakage prevention
A combination of O-ring and graphite gasket on body/adapter connection, body/gland connection, and stem/gland joint, can prevent the external leakage. When O-rings are damaged after a fire, body gasket, gland gasket, and stem packing, can reach sealing function and prevents external fluid leakage. (Fig.6)

Floating Ball Valves

The valve is configured in two-piece split-body design with a small diameter, suitable for medium/low pressure working conditions.Characterized by simple design, the valve seats are directly inserted into the body.
The upstream flow pressure pushes the free-floating ball against the downstream seat-the resulting compression provides a perfect leak-free sealing solution even after years in-service.
 
  1. Fire Safe Seat Sealing



Athena floating ball valves’ fire safe is designed in accordance with API 607 & API SPEC 6FA. When non-metal resilient seats are destroyed in a fire, the upstream medium pressure push the ball into the downstream metal seat lip to cut off the line fluid and prevent the internal leakage due to a secondary metal-to-metal seals.

 
  1. Blow-out Proof Stem                                 Anti-Static Device



The stem is designed with integral T-type shoulder to provide blow-out proof effectively.
It is internally inserted as the backseat function to assure stem sealing safety at all
pressures.

Antistatic devices between ball & stem and stem & body are assembled by a spring & a stainless steel ball, which ensure all metal valve parts are grounding.

With more and more concern for environment protection in the whole world, low emission valve will be widely used. Low emission valve can prevent poisonous, flammable, explosive medium from leaking to pollute the air; and also important that low emissions valve can minimum fugitive emission of VOC to help solve the problem of ‘’Global Warming’’.

                        
 
  1. Low Emission Packing

Because of frequent opening and closing of the valve, normal graphite granule can be drawn by the stem, which will cause leakage. Athena designed low emissions valve use special low emissions packing to ensure the seal of stem. The cone packing is made of expanding graphite in die-formed rings and has features of heat resistance, less stress relaxation and low creep. With this special structure, it allows for a low-friction on rotary & rising stem valve, therefore providing the stabilized sealing performance for long cycle life. For low temperature service, the standard V shape PTFE packing rings are used for low emissions control.
 
  1. Controlled Stem and Stuffing Box Finish

Its also a key point to control the stem and stuffing box finish when machining. The stem is made by cold rolling and stem surface finish is controlled by Ra0.4, which can reduce friction for stem moving and ensure the graphite to fill and migrate into the stems micro scratches, and function as a lubricant to reduce stem leakage. The stuffing box surface is controlled within Ra1.6 and Ra3.2 for better holding of the packing ring and results in a better sealing performance.
 
  1. Live Loaded Gland Flange

In normal case, valve packing is tighten by gland and gland bolting. During the service, the gland load retention will be reduced by long time pressure from medium, which will cause possible leakage with loosened packing. Athena designed low emissions valve use a set of Belleville springs installed on each gland stud to provide a continuous compressive force on gland, which guarantees permanent load retention for the stem packing to avoid fugitive emissions.


Athena offers a high-quality ball valve at a very competitive price and fast delivery time, support you any times!
https://www.athenavalve.com/ball-valve.html