L-Port vs T-Port 3-Way Ball Valves: Flow Paths and Applications
Short answer: an L-port 3-way ball valve has an L-shaped bore that connects the common port to one of the two side ports at a time, so it is used to divert flow from one inlet to either of two outlets (or select one of two inlets). A T-port 3-way ball valve has a T-shaped bore that can connect two ports or all three at once, so it can divert, mix or pass flow straight through. An L-port valve with the right positions can shut off; a standard T-port valve cannot isolate all three ports.
How 3-way ball valves are arranged
A 3-way ball valve has three ports, usually two on the run of the valve and one at the bottom (the common or centre port). The flow path depends on the drilling in the ball and on how far the handle or actuator turns it: 90° or 180°. Port configurations are normally shown as small diagrams on the data sheet, and it is worth checking them against your P&ID before ordering, because manufacturers draw and number positions differently.
L-port 3-way ball valves
The L-port ball has two openings at 90° to each other. Typical behaviour:
- 90° rotation: switches the bottom port between the left and right side ports. Used as a diverter (one supply to two destinations) or selector (two supplies to one destination).
- 180° rotation: adds a third position. Depending on the design, the intermediate position connects the two side ports or closes all three.
- The L-port cannot connect all three ports together.
L-port valves are the usual choice for change-over duties: duty/standby pumps, twin filters, switching between two tanks or routing product to one of two lines.
T-port 3-way ball valves
The T-port ball has three openings, so it can:
- connect all three ports together (mixing or splitting flow);
- connect the two side ports straight through, with the bottom port closed;
- connect the bottom port to either side port, as a diverter.
A standard T-port valve cannot close all three ports at once, so it should not be relied on for isolation. T-port valves suit mixing, bypass and sampling arrangements.
L-port vs T-port: comparison
| L-port | T-port |
|---|
| Ball drilling | Two openings at 90° | Three openings in a T |
| Connect all three ports | No | Yes |
| Straight-through flow (side to side) | Only in some 180° positions | Yes |
| Shut off all ports | Possible with 180° rotation on some designs | No (standard designs) |
| Typical use | Diverting, selecting, change-over | Mixing, splitting, bypass, diverting |
Actuating a 3-way ball valve
For two-position diverting duty a standard 90° pneumatic actuator or electric actuator is enough. Three-position duty needs 180° travel, which means a 180° actuator or a multi-position electric actuator. Spring return actuators fail to one end position only, so decide which flow path the plant should default to on loss of air or power. Our actuated ball valve packages are built with the port configuration and fail position you specify.
3-way ball valves available from Ball Valve UK
Browse the full range of 3-way ball valves.
Frequently asked questions
Can a 3-way ball valve replace two 2-way valves?
Often, yes. An L-port valve on a change-over duty replaces two interlocked isolating valves, saves space and removes the risk of both being open at once. Check that the valve's intermediate position is acceptable for the process during switching.
Which port is the inlet on a 3-way ball valve?
For diverting service the common (bottom) port is normally the inlet. Some valves are bi-directional and some are not, so confirm against the manufacturer's flow diagram.
Is a T-port valve suitable for mixing hot and cold water?
A manual T-port valve can blend two streams, but it gives coarse control. For temperature control a dedicated mixing or control valve with a modulating actuator is the better choice.
Send us your P&ID or a sketch of the flow paths and our technical team will confirm the correct port configuration.
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