Selection Between Ball and Globe Valve

[chicopee]

What is the criteria used when selecting a ball or globe valve in the piping system of propane bulk storage installation? Such valves would be 2", 2-1/2" and 3" size fitted in the liquid and vapor transfer lines (loading and unloading). I get the impression that it is a matter of preference by the engineer or availability by the supplier.

 

[zdas04]

Oh my god, you are not serious here? If you had said "the choice between ball, gate, and plug valves seems to be a matter of opinion or availability" this would have been a reasonable question, but the valves you mentioned have very different purposes.

A ball valve is intended for on/off service and should not normally be throttled (they have terrible throttle characteristics).

A globe valve is designed for throttling and even fully open will impose a dP.

If a particular line should always be fully open or fully shut, then a ball valve is often a very good choice (the further choice between a floating ball and a trunnion ball depends on the process). A valve to control flow within a stream should have good throttling characteristics--if the required position changes frequently then a regulator is a better choice, but if it changes infrequently then a manual globe valve can occasionally be the best choice.

The specification of either a throttling or block valve requires that the design engineer have knowledge of the performance of each sort of valve that could be used. To think that a ball valve and a globe valve are interchangeable is amazingly dangerous.

David

 

[JimCasey]

If you are just speaking about isolating valves (on-off) the globe valve is at a disadvantage on almost every parameter.

Shutoff: a metal-seated globe valve will require use of a cheater to torque the seats together. Ball valves can be expected to have resilient seats and to shut off tightly.

Convenience: Globe valve requires 4 or 5 turns of the handwheel to open or close. Ball valve: 90-degrees. (Ball valves were initially developed for USNavy. Tactical advantage to being able to yank a valve shut while at a dead run, vs having to stop and grind away at a handwheel.) Somebody over-eager to close a ball valve may yank it shut too quickly and cause liquid-hammer.
In fairness: Larger ball valves need a gear-operator.

Position of a ball valve is easy to read. Lever is aligned with the pipe when the valve is open. Position indication of a globe valve is on a small plate inside the yoke.

Environmental: Rising stem in globe valve drags packing particles out, and environmental dirt in, every time the valve is cycled. ALso if you figure 4 turns to open, globe valve packing sees 16 times the wear on each stroke. Ball valve packing stays tighter-longer.

Installation: Globe valve is taller and heavier and usually longer F-F, than a ball valve of the same size.

I started to say something about Globe valves having a fire-safe advantage, but ball valves are offered in firesafe meeting API standards.

Capacity: Globe valves have a convoluted s-shaped flow path. Ball valves are straight through. Even a "regular" port ball valve has no more friction loss than an elbow, while "full" port ball valves have loss no gtrater than an equivalent length of straight pipe-probably less since the ball is machined to better surface finish than the inside of the pipe.

 

[gerhardl]

After all being said in the previous two answers: within the probably normal pressure range and the normal sizes you have mentioned, ball valves would be readily commercial available in different quality, standards and constructions.

At least up to two inch sizes a price/performance/lifetime comparison would be in favour of ball valves, and I believe also for the larger dimensions in your range.

I would suggest you start having a look at all SS ball valves, floating PTFE seats, three-piece (midsection to swing out for inspection or change) construction , welding or screwed ends, perhaps flanged for larger sizes or if not three-piece.

If unsuitable or to high in price: two piece construction and CS house.

For automated valves for on off, you could have a look at solenoid (globe-construction) on/off valves with forced lifting. Theese valves will open if downstream pressure increases above upstream pressure and will relief overpressure backwards if propane resting in downstream pipeline are heated and increases in volume/pressure.

Drawback is the pressure loss over the globevalves, as mentioned by others, if the main pressure is low.

For electric operated valves (solenoid valves) check if EX protectioon is required (sometimes it is).

 

[JLSeagull]

Many bulk plants used gate valves for the distribution header. The gate valve is another multiturn rising stem design that is not suitable for throttling.

To maintain liquid phase the propane lines require back pressure. Thus propane could be flashing across some of the valves if releasing to a flare. Consider hard trim for valves in flashing service. Other valves to release vapor back to the bullets or cavern would still have pressure on the return side.

 

[chicopee]

Thanks for the replies, participants. I already knew the answers, however, I wanted other opinions mainly to back me up for "inquiring minds" that will not take just one person's opinion.

 

[AntonTRN]

I am always using globe valves in gas or in flashing service: you have the possibility to slightly increase the pressure. If you do not have a large pressure drop a gate or ball valve are suitable.

 

[Zapster]

There are exceptions. There are V-ball valves that work fairly well for throttling. Whereas they are still ball valves, the V allows for greater control compared to a standard ball valve.