Full Bore vs Reduced Bore Ball Valves: Flow, Pressure Drop and Selection
Short answer: a full bore (full port) ball valve has a bore through the ball that matches the internal diameter of the pipe, so flow passes with almost no restriction. A reduced bore (standard port) ball valve has a smaller bore, typically around one pipe size down, which gives a higher pressure drop but a smaller, lighter and cheaper valve that needs less torque to operate.
What is a full bore ball valve?
In a full bore ball valve the ball and body are oversized so that the hole through the ball is the same diameter as the connecting pipe. When the valve is open the flow path is effectively a straight length of pipe. That gives:
- the lowest pressure drop and highest flow coefficient (Cv/Kv) for the line size;
- a clear path for pipeline pigs, cleaning balls and line scrapers;
- less turbulence and fewer places for solids, fibres or viscous product to hang up.
Most of the industrial ranges on Ball Valve UK are full bore, including the BV-L2000 2-piece and BV-L3000 3-piece stainless steel valves and the PN16, PN40 and ANSI 150 flanged ranges. See all full bore ball valves.
What is a reduced bore ball valve?
A reduced bore valve uses a smaller ball, so the bore is narrower than the pipe. The valve body is more compact and the operating torque is lower, which also means a smaller actuator if the valve is automated. The trade-off is a step change in diameter at each seat, which increases pressure drop and velocity through the valve.
For many isolation duties on water, air and general services the extra pressure drop is insignificant, and a reduced bore valve is the economical choice. A good example is the 3-way BSPP reduced bore stainless ball valve, which sits alongside a full bore 3-way version in the same size range.
Full bore vs reduced bore: comparison
| Full bore | Reduced bore |
|---|
| Bore diameter | Matches pipe ID | Smaller than pipe ID, often one size down |
| Pressure drop | Minimal | Higher |
| Flow coefficient (Cv/Kv) | Highest for the line size | Lower |
| Pigging | Possible | Not possible |
| Valve size and weight | Larger and heavier | More compact |
| Operating torque / actuator size | Higher | Lower |
| Cost | Higher | Lower |
To put numbers on the difference for your own line, use our valve Cv and Kv calculator and valve pressure drop calculator.
When to specify full bore
- Lines that are pigged or cleaned with a ball or scraper.
- Slurries, viscous fluids, fibrous media and anything that can build up at a step in the bore.
- Systems where the pump or compressor has little pressure margin, or where the valve sits in a long run with many other losses.
- Hygienic process lines, where a smooth, crevice-free flow path matters for cleaning.
When reduced bore is the better choice
- General isolation where the valve is either fully open or fully closed and pressure drop is not critical.
- Tight installations where a compact body is useful.
- Automated valves where lower torque allows a smaller, less expensive actuator.
Frequently asked questions
Is full port the same as full bore?
Yes. Full port is the more common term in the US; full bore is used in the UK and Europe. Reduced port and standard port mean the same as reduced bore.
Can I use a ball valve to throttle flow?
A standard full bore or reduced bore ball valve is designed for on/off duty. Holding it part-open concentrates flow on the edge of the seats and can damage them. For control duties look at characterised or segmented ball control valves, such as the SAMSON rotary ball and segmented ball control valves.
How do I tell if an existing valve is full bore?
Open the valve and compare the bore through the ball with the pipe ID, or check the product data sheet. Full bore valves are usually noticeably longer and bulkier than reduced bore valves of the same nominal size.
If you need help sizing a valve for flow, talk to our technical team with the flow rate, media and allowable pressure drop.
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