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The trunnion ball valve is a form of quarter-turn valve which uses a hollow, perforated and fixed/supported ball to control flow through it. A trunnion mounted valve means that the ball is constrained by bearings and is only allowed to rotate, the majority of the hydraulic load is supported by the System constraints, resulting in low bearing pressure and no shaft fatigue. The line pressure drives the upstream seat against the stationary ball so that the line pressure forces the upstream seat onto the ball causing it to seal. The mechanical anchoring of the ball absorbs the thrust from the line pressure, preventing excess friction between the ball and seats, so even at full rated working pressure operating torque remains low. This is particularly advantageous when the ball valve is actuated because it reduces the size of the actuator and hence the overall costs of the valve actuation package.  Advantages of trunnion ball design is the lower operating torque, ease of operation, minimized seat wear (Stem/ball isolation prevents side loading and wear of downstream seats improving performance and service life), superior sealing performance at both high and low pressure (a separate spring mechanism and upstream line pressure is used as the sealing against the stationary ball for low pressure and high pressure applications).  The trunnion is available for all sizes and for all pressure classes but they are not suitable for throttling purposes. An article published in valve magazine discusses the unique operating dynamics of a trunnion ball valve.

For a very long time, the idea has existed that a trunnion-mounted ball valve can be opened under full differential pressure if the piping system can withstand the rapid increase in pressure and the forces induced by it. As valve sizes and operating pressures increase, however, several factors need to be considered if that valve is opening with little or no pressure downstream.  Continuing reading.

 

              

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Floating & Trunnion Mounted Ball Valves

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Floating & Trunnion Mounted Ball Valves

Floating & Trunnion Mounted Ball Valves

Southcoaster

(Mechanical)

(OP)

1 Feb 08 06:12

Guys,
With regards to floating and trunnion mounted ball valves operating in natural gas.

Looking through the manufacturers catalogues, floating ball is limited to 600lbs for some reason and trunnion mount goes to 2500lbs. Asking questions about this seems to get vague answers.

My question is;

Is there a cut off pressure or diameter where one type would stop and the other begins? i.e would floating ball be used up to 600lbs at a maximum diameter of 6", 8" at 300lbs etc.. and above this trunion. I would appreciate informed comment with regards to a possible rule of thumb.

RE: Floating & Trunnion Mounted Ball Valves

zdas04

(Mechanical)

1 Feb 08 07:17

I just looked in a couple of catalogs and both manufacturers stop making floating ball valves around 12-inch for ANSI 300 and around 8-inch for ANSI 600.

I've found that the cost savings above about 3-inch are a false economy and I simply don't spec flanged floating ball valves (i.e., if the line is too big to thread the valves in, get a trunnion).  Virtually every ball valve problem I've ever had has been with a floater.

Floating ball valves seat by the dP across the valve shifting the ball into the downstream seat. The ball in large ball valves (above about 10-12 inches) is just too heavy to shift reliably. This movement is very small, but it is required to get a good seal. Trunnion ball valves use a series of springs to shove the seat into the rigid ball. They work about the same at any dP.I just looked in a couple of catalogs and both manufacturers stop making floating ball valves around 12-inch for ANSI 300 and around 8-inch for ANSI 600.I've found that the cost savings above about 3-inch are a false economy and I simply don't spec flanged floating ball valves (i.e., if the line is too big to thread the valves in, get a trunnion). Virtually every ball valve problem I've ever had has been with a floater.

David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
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RE: Floating & Trunnion Mounted Ball Valves

C2it

(Petroleum)

1 Feb 08 10:25

IMHO floating ball valves should be avoided at the higher end of their manufacturer's specified range. I've seen a number of cases where the seal as been sheared off by rotation of the ball, resulting in massive leakage. As David says, it's false economy, use a trunnion ball instead.

RE: Floating & Trunnion Mounted Ball Valves

bcd

(Mechanical)

1 Feb 08 12:51

The size and pressure cut-off for floating versus trunnion will varu by manufacturer depending upon the type of seals used.  With floating ball, upstream pressure pushes the ball into the downstream seat and giving very effective shut-off.  However, if the pressure is too high, the resulting force on the ball can crush the downstream seat and / or create so much friction that you cannot turn the valve to open it.  This is why they have lower pressure ratings.  Trunnion valves are more expensive to make and tend to have more external joint that are potential leak points.  Normally, trunnions are upstream sealing, but not always.  Some are still downstream seat sealing and use the trunnion to limit the forces on the seat.  The trunnion bearings inside the valve withstand the force from pressure across the ball and enable a lower friction material, smaller radius to enable lower operating torque against higher pressures.  Both are good provided you use them within their limits.  If you spec. trunnions for all applications, you are wasting money.  If you use floatings balls anywhere near their limits, you will suffer reliability problems.

bcd

RE: Floating & Trunnion Mounted Ball Valves

Southcoaster

(Mechanical)

(OP)

4 Feb 08 07:22

Thanks Guys for your valuble input on this subject, most helpful.

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