The Castair DT34 is a 3/4-inch discharge tube assembly with fittings — the larger-diameter version of the DT12, designed for two-stage pumps and other compressor configurations where the pump outlet port is 3/4 inch. At the pump discharge, you're dealing with air that's just been compressed — it's at full system pressure and temperatures that can exceed 300°F. The DT34 handles this environment with a rigid tube assembly that won't degrade under the thermal and pressure load that would destroy rubber hose.
Why 3/4" vs. 1/2" Discharge Tube?
Discharge tube sizing follows the pump outlet port size. On Castair's pump lineup:
- Smaller single-cylinder pumps (PK20, DD20, PK30 — 1.5 HP class) typically use 1/2" discharge port — use DT12
- Larger two-stage pumps (C1, C2, C3 class — 4 HP and up) typically use 3/4" discharge ports — use DT34
Using an undersized discharge tube on a larger pump creates unnecessary backpressure at the pump outlet, which makes the pump work harder, run hotter, and wear faster. Using the correct 3/4" tube on a 3/4" port pump ensures the compressed air exits the pump freely and the tube can handle the volume at proper flow velocity.
What You Get
- 3/4" discharge tube — proper diameter for larger pump outlet connections
- Fittings included — compression or threaded fittings for both ends
Note: Exact tube length, material, and fitting type are not published in Castair's public catalog for this specific part. Contact us before ordering if you need to confirm dimensions for your installation.
Where the DT34 Is Used
The DT34 is used in new compressor builds, pump rebuilds, and discharge tube replacements on compressors with 3/4" pump outlet ports. The two-stage pumps it typically serves include the C1 (4–7.5 HP, 225 lbs), C2 (7.5–10 HP, 320 lbs), and C3 (15 HP, 485 lbs) — all of which are the workhorses in serious shop compressors delivering 20–50+ CFM at 125–175 PSI.
Companion Parts for the DT34
- DT12: 1/2" discharge tube — for smaller pumps
- CA3434: Compression adaptor 3/4"x3/4"
- CE3434: Compression elbow 3/4"x3/4" — for direction changes
- CNS34: Compression nut and sleeve for 3/4" — for additional compression connections
- CT75: 3/4" copper tubing (sold by the foot) — if you need more tube length than the DT34 provides
When to Replace Your Discharge Tube
- Visible cracking, pitting, or corrosion on the tube body or at fitting joints
- Persistent leak at either end that can't be corrected by tightening
- As part of any pump rebuild — new valves and rings should be paired with a new discharge tube
- If the current discharge connection uses rubber hose — replace with this rigid discharge tube immediately
Installation Notes
Discharge tube installation on a two-stage pump should include vibration isolation between the pump and the tank plumbing. If your installation runs the discharge tube directly into rigid black iron pipe without any flex section, vibration from the pump will work the fittings loose over time. Castair sells compression flex connectors and vibration pads as separate accessories to address this. If you're rebuilding a complete installation, plan your vibration isolation at the same time you replace the discharge tube.
Why Buy From Air Compressor Factory Direct?
- Specialist since 2016 — we stock Castair plumbing components and can help you select the correct parts for your pump
- Free shipping on qualifying orders
- Free tech support at 866-217-0063 — call us to confirm discharge tube sizing for your specific pump
- Full manufacturer warranty on Castair parts
- Honest guidance — if you need the DT12 or additional fittings, we'll advise you before you order
Call 866-217-0063 for quick answers and help!
