L-Port vs T-Port 3-Way Ball Valves: How to Choose | Apex Flow

You bought a 3-way ball valve to switch flow between two tanks, and now it won't behave the way the drawing assumed — it bleeds both ports at once, or it won't shut a leg off when you need it isolated. The problem is almost never the valve quality. It's the porting. An L-port and a T-port look nearly identical from the outside, but the slot machined into the ball routes flow completely differently, and you can't change it after the valve is made. Pick the wrong one and the plumbing physically cannot do what your process needs.

This guide shows exactly what each porting style does at every handle position, where each one fits, and how to specify the right valve so it arrives doing the job the first time. Apex Flow Solutions stocks 3-way ball valves in brass and stainless across both L-port and T-port configurations. Port arrangements and pressure classes below are representative; confirm against the specific valve's data sheet, since slot geometry and port count vary by manufacturer.

Not sure whether you need L-port or T-port?

Tell us what you're trying to do — divert one feed to two destinations, pick between two supplies, or blend two streams — and your line size. Our team will confirm the porting, orientation, and actuation so the valve does exactly what your process map shows.

What a 3-Way Ball Valve Does

A 3-way ball valve has three ports instead of the usual two, with a bored ball that routes flow between them as you turn the handle a quarter or half turn. It replaces two or three separate two-way valves and the tee fittings between them, saving space, leak points, and actuators. The single variable that defines everything is the shape of the passage drilled through the ball: an L-shaped bore connects two ports at a time, while a T-shaped bore can connect two or all three at once. That one difference is why an L-port and a T-port behave so differently, and why the choice has to be made before you order.

Cutaway of an L-port and a T-port 3-way ball valve showing the bored ball passages

The only real difference is inside the ball: an L-bore (left) links two ports per position; a T-bore (right) can link two or all three. The body, ports, and handle look the same from outside.

L-Port: Diverting and Selecting

The L-port ball has an L-shaped passage, so it always connects exactly two of the three ports — never all three. Rotate the handle and the open leg swings from one side port to the other, with the common (usually bottom) port shared. That makes the L-port a clean diverter (send one input to either of two outputs) or selector (draw from either of two inputs into one output). What it generally cannot do is mix two streams together, and most standard L-ports cannot shut all flow off at once — at every detented position at least one path is open. If you need a true all-ports-closed position, confirm that specific valve offers it; many do not.

Label the ports A (left), B (right), and C (common). A typical L-port routes like this:

Handle Position	Connects	Result
0° (left)	A ↔ C	Common port talks to left port; right port blocked
90° (right)	B ↔ C	Common port talks to right port; left port blocked
Mid (some models)	A ↔ C ↔ B partial	Brief transitional overlap; not a stable mixing position

The key takeaway: an L-port switches a path between two ports. It does not combine and rarely closes everything off.

T-Port: Diverting, Combining, and Mixing

The T-port ball has a T-shaped passage, so depending on rotation it connects two adjacent ports or all three at once. That extra reach gives the T-port real flexibility: it can divert like an L-port, but it can also combine two inputs into one output or mix a stream across all three ports. The trade-off is that a T-port's "straight-through" positions can leave a port live that you expected closed, so you have to read the flow pattern carefully against your process. Like most L-ports, standard T-ports are not designed as a positive shutoff for all three ports simultaneously.

Using the same A / B / C labels, a typical T-port routes like this:

Handle Position	Connects	Result
0° (left)	A ↔ C	Left port to common; right port blocked
90° (right)	B ↔ C	Right port to common; left port blocked
Center / 45°	A ↔ C ↔ B	All three open: combine two feeds or split/mix one
180° (some)	A ↔ B	Two side ports straight through; common blocked

Exact positions depend on the maker's drilling and the number of stops on the handle; always check the valve's flow diagram before piping it.

L-Port vs T-Port Comparison

Representative behavior. Specific routing, port count, and whether an all-closed position exists vary by model; confirm on the data sheet.

Capability	L-Port	T-Port
Divert one input to two outputs	Yes	Yes
Select between two inputs	Yes	Yes
Combine / mix two streams	No	Yes
Connect all three ports at once	No	Yes
All-ports-closed position	Rare / model-specific	Rare / model-specific
Best mental model	Switch / selector	Switch + blender

How to Choose by Application

Start from the verb. What is the valve supposed to do to the flow?

You Need To...	Choose	Example
Send one source to either of two destinations	L-port	Route a pump to Tank A or Tank B
Draw from either of two supplies into one line	L-port	Switch between two feed tanks to one process
Blend or combine two streams into one	T-port	Mix hot and cold, or merge two feeds
Divert and sometimes run both paths	T-port	Bypass loop that can also run full-flow
Strictly switch, never mix (avoid cross-contamination)	L-port	Keep two media from ever joining

A useful rule: if mixing two streams together would ever be a problem, use an L-port — it physically cannot join all three ports. If you genuinely need to combine or split flow, a T-port is the only one that can.

One valve, several jobs?

Many systems use a 3-way to replace a pair of 2-way valves and a tee. Send us your flow schematic and we'll mark up which ports go where and whether L or T porting matches each operating mode. Contact our team to spec it.

Actuation & Specifying Porting

3-way ball valves run manually with a lever, or automated with a pneumatic or electric actuator for remote and timed switching. One thing to watch with automation: an L-port typically uses two 90° positions, while a T-port may need three or four stops to reach its combining position, so the actuator and limit switches have to match the porting and the number of detents. Spec this together, not separately.

Because porting is machined into the ball and cannot be changed afterward, the L-vs-T decision must be stated on the order along with the flow pattern you expect at each position. A valve sold simply as "3-way" is ambiguous. State the porting (L or T), the body material, the port size and whether full or standard port, the end connections, and ideally a sketch of which physical port is your common. Apex Flow Solutions can confirm the exact flow diagram for any 3-way before it ships so there are no surprises at install.

Mounting & Port Orientation

Unlike a 2-way valve, a 3-way's three ports are not interchangeable — which port is "common" and which way the L or T opens are fixed by the casting and the ball. Mount the valve so the marked common port faces the shared line and the side ports land where your drawing puts them; rotating the body 90° or 180° to fit the bench can quietly swap which port is which. Confirm port labeling and the flow-diagram arrows on the body or data sheet before threading or flanging it in, and verify the handle's open positions clear adjacent equipment. Getting orientation right at install avoids re-piping a valve that technically works but feeds the wrong tank.

Standards & References

Ball valve design and pressure-temperature ratings follow ASME B16.34 and MSS SP-110 (threaded/welded ball valves). Stainless cast bodies follow ASTM A351 (CF8 / CF8M grades). Threaded ends follow ASME B1.20.1 (NPT); flanged ends follow ASME B16.5. Pressure class is commonly expressed as a WOG (water-oil-gas) cold working pressure rating. Always confirm the specific valve's rated pressure and temperature on its data sheet, since 3-way bodies and seats are often rated below comparable 2-way valves.

Frequently Asked Questions

What is the difference between an L-port and a T-port 3-way ball valve?

An L-port ball has an L-shaped bore that connects two of the three ports at a time, so it diverts or selects but cannot mix. A T-port ball has a T-shaped bore that can connect two or all three ports, so it can also combine and mix streams. The porting is machined into the ball and cannot be changed after manufacture.

Can a 3-way ball valve mix two streams together?

Only a T-port can. Its center position opens all three ports so two inputs combine into one output, or one input splits across two. A standard L-port physically connects only two ports at a time and cannot mix.

Can a 3-way ball valve shut off all flow?

Usually not with a standard valve. Most L-port and T-port valves keep at least one path open at every detented position. If you need a true all-ports-closed position, confirm that the specific model offers it, as many do not.

Do I have to specify L-port or T-port when ordering?

Yes. The bore shape is fixed when the ball is machined, so a valve sold only as "3-way" is ambiguous. State L or T porting, the common port, material, port size, and end connections on the order.

Which port is the common port on a 3-way valve?

It is the port shared across handle positions, often the bottom port on an L-port. Check the flow diagram printed on the body or data sheet, and orient the valve so the common port faces your shared line.