How Much Vapor Can Flow Through 3/4" Tubing? A Real-World Look at Butane Vapor Dynamics

In hydrocarbon extraction systems, especially those using n-butane, understanding flow dynamics is essential. We’re not talking about theoretical maxes in lab conditions—we mean actual flow through 3/4" stainless tubing, 10-micron sintered filters, and 6" packed beds full of molecular sieve media.

At N.B. Oler, we don’t just build ASME-certified stainless pressure vessels—we use them. Here’s a clear, field-tested breakdown of what limits your butane vapor flow and why it probably isn’t the tubing.

🔍 Common Setup

• Gas: n-butane vapor

• Tubing: 3/4" stainless steel (0.75" ID)

• Filter: 10-micron, 5-layer sintered stainless mesh (6" dia)

• Dryer: 6" column packed with 4A 4x8 molecular sieve beads

• Outlet: 3/8" tubing (for condensed liquid)

• Operating Pressure Range: 10–50 psi

• Operating Temperature Range: –40°F to 125°F

💨 1. 3/4" Tubing Flow Capacity

Even though it's the smallest diameter in the system, 3/4" tubing can flow a lot of vapor. At 50 psi inlet and atmospheric outlet, it hits choked flow, meaning the gas is moving at Mach 1 at the exit.

✨ Choked Flow Max (50 psi, 100°F): ~51 lb/min of butane vapor

At 10 psi differential, you’re still getting around 20–22 lb/min depending on temperature.

Key Insight: Unless your run is long or has lots of fittings, your 3/4" tubing is probably not the bottleneck.

🧱 2. 10-Micron Sintered Filter (6" Diameter)

These 5-layer mesh filters are built to flow. With a 6" diameter and 10–20% porosity, they handle a lot of vapor with almost no pressure drop.

✅ Estimated Drop: <1 psi at 30+ lb/min if clean

BUT if the filter is fouled with media dust or moisture, it can quickly become restrictive. Clean regularly or use blowback to prevent pressure build-up.

⚡ 3. Molecular Sieve Packed Bed (6" Column)

This is where it gets tight. A 24" tall bed of 4x8 beads has a high surface area—great for scrubbing moisture, not great for high vapor flow.

We used the Ergun equation to model flow. Here’s what you get:

∆P Across Bed	Approx. Max Vapor Flow
10 psi	~24 lb/min
50 psi	~54 lb/min

⚠ This is usually your bottleneck. If flow stalls, it’s probably your dryer column.

Design Tip: Shorten the bed, increase the diameter, or run beds in parallel to reduce pressure drop.

🌡️ Temperature Matters

• Cold vapor (–40°F): denser, lower viscosity → higher mass flow potential

• Hot vapor (125°F): less dense, more viscous → higher velocity, more friction

Always balance system temperature to stay in the single-phase vapor region and avoid unintended condensation.

✅ Summary: What Flows Where?

Component	Flow @ 10 psi	Flow @ 50 psi
3/4" Tubing	~22 lb/min	~51 lb/min (choked)
Sintered Filter	≥ 50 lb/min	≥ 100 lb/min (negligible drop)
Molecular Sieve Bed	~24 lb/min	~54 lb/min

⚙️ Build Better with N.B. Oler

Every psi counts in passive systems. We design and fabricate stainless extraction components that eliminate flow bottlenecks. Want to:

• Increase vapor speed?

• Reduce recovery time?

• Eliminate fouled filters and slow sieve beds?

Let’s talk. We offer ASME-certified vessels, custom dryer designs, and the field experience to size your system right.

☎️ Call us at 541-330-6409 or Contact Us Here

N.B. Oler — Real welders. Real vessels. Real performance.