Two Different Operating Principles
A ball valve is a quarter-turn rotary valve. A bored sphere sits between two seat rings and is turned ninety degrees by the stem, so that in the open position the bore lines up with the pipe and in the closed position the solid part of the sphere faces the seat. Because a quarter turn completes the stroke, the valve opens and closes quickly and the flow path is short and almost straight.
A globe valve is a linear motion valve. The disc is pushed down onto a seat by a stem and handwheel, and the medium is forced to change direction as it passes through the internal S-shaped passage. The stroke is long, the seat is a defined annular contact, and the disc position can be set anywhere between closed and fully open, which gives the design its excellent throttling behaviour.
Comparison at a Glance
| Feature | Ball valve | Globe valve |
|---|---|---|
| Motion | Quarter turn rotary | Multi-turn linear |
| Stroke speed | Very fast, suitable for emergency shut-off | Slow, stroke length is many turns |
| Pressure drop | Low in full port designs | High, due to the tortuous passage and direction changes |
| Throttling | Poor, part-open operation erodes the seat | Good, disc position gives fine control |
| Sealing | Soft or metal seats give tight shut-off, with the seats protected from the flow in the open position | Reliable metal-to-metal or soft seat closure, but the seat is exposed to the flow at all times |
| Operating effort | Low, quarter turn with a lever or actuator | Higher, particularly as the valve lifts off the seat |
| Maintenance | Simple stem seal, seats can often be renewed in line on top entry designs | Requires removal for seat and disc work, though the body is simple |
| Typical standards | API 6D and API 608, ratings to ASME B16.34 | BS 1873 and API 623, face-to-face to ASME B16.10 |
Where the Ball Valve Is the Better Choice
On-off isolation on pipelines, terminals and manifolds where a fast, low-torque, tight shut-off is wanted.
Buried or inaccessible locations, especially with a fully welded body, because there is no joint to service.
Lines carrying clean liquids, gases and many slurries, where a straight-through bore keeps pumping energy low.
Automated systems, since a quarter-turn actuator is compact, fast and inexpensive compared with a multi-turn operator.
Services with significant solids or viscous media, where the sweeping action of the ball across the seat clears debris.
Where the Globe Valve Is the Better Choice
Flow regulation, including bypass lines, drain lines and small control orifices, where the disc must be positioned accurately.
High pressure steam and hot water systems, where the long stroke protects operators from rapid pressure surges when a valve is cracked open.
Small nominal sizes where the extra pressure drop is not significant in energy terms.
Duties requiring routine seat inspection and re-lapping, because the disc and seat are accessible and simple to rework.
Systems where a slow, deliberate opening stroke reduces water hammer risk on start-up.
Selection and Installation Notes
Start from the duty: if the valve will spend its life fully open or fully closed, a ball valve gives lower pressure drop and lower operating effort. If it will be positioned part open for long periods, a globe valve will last far longer and give a stable flow characteristic. Where a single valve must both isolate and regulate, the usual arrangement is a ball or gate valve for isolation plus a globe or control valve in the regulating loop.
When ordering, confirm the bore. A reduced port ball valve has a narrower passage than a full port unit and its pressure drop is markedly higher, which matters in pumped systems sized close to the duty point. Confirm the face-to-face dimension against the piping drawings, verify the pressure-temperature rating at the actual operating temperature rather than at ambient, and confirm that the trim and body materials suit the medium. For automated installations, confirm the actuator output against the valve breakaway torque at the maximum differential pressure in the closed position, because a ball valve that is easy to turn by hand may still demand a substantial breakaway torque after a period at differential pressure.
FAQ
Q: Which valve gives tighter shut-off, a ball valve or a globe valve?
Both can achieve tight closure. A ball valve with a resilient seat is usually the easiest to seal, while a globe valve relies on a smaller contact face and a higher closing force.
Q: Can a ball valve be used for flow control?
Only with a purpose-designed characterised ball or V-port trim. A standard ball valve throttled part open erodes its seat and gives unstable flow.
Q: Why does a globe valve create more pressure drop?
The medium is forced to change direction twice through an S-shaped passage and passes a restricted seat area, so the loss coefficient is much higher than a full-bore ball valve.
Q: Which type is lighter for the same size?
A ball valve, particularly a compact or welded design, is normally shorter and lighter than a flanged globe valve of the same rating.
Q: Which valve is better for steam service?
Globe valves are widely used for steam isolation and regulation because the long stroke limits surge, while ball valves are used for fast isolation where a metal seat is specified.
Q: Does a ball valve need a bypass before opening?
Normally no. A globe valve on high differential pressure service may benefit from a bypass to equalise pressure and reduce the opening force on a large handwheel.