Description
The 3Z-series nitrogen compressor — manufactured under the 3ZW model designation — is a three-column, three-stage reciprocating machine built for applications that require 3.0 MPa discharge pressure at modest flow rates of 5–6 m³/min. Where the Z-series two-stage frames reach their pressure ceiling at 1.5 MPa and the LW three-stage frames start at 7 m³/min, the 3ZW fills the gap: a compact, 380 V unit that compresses nitrogen to full cylinder-filling pressure without the footprint or power infrastructure of a larger machine.
Two models are available — 3ZW-6/30 at 6 m³/min and 3ZW-9.5/30 at 9.5 m³/min — both running on standard 380 V supply at 75 kW and 110 kW respectively. The three-column arrangement distributes the three compression stages across separate cylinder banks, which keeps the per-stage compression ratio below 4.7:1 and discharge temperature at each stage within safe limits for oil-free packing materials.
Three-Stage Nitrogen Compressor 3MPa: Why Three Columns and Three Stages Are the Right Architecture at This Pressure
Compressing nitrogen from atmospheric pressure (0.101 MPa) to 3.0 MPa is an overall pressure ratio of approximately 29.7:1. Handling that ratio in two stages — as the ZW series does up to 1.5 MPa — would require each stage to work at a compression ratio of around 5.4:1 in the first stage and 5.5:1 in the second. At 3.0 MPa outlet, a two-stage machine would need a second-stage ratio exceeding 8:1, which drives discharge temperatures above 200°C and rapidly destroys PTFE piston rings and rod packing.
Three stages distribute the same overall ratio across three steps of approximately 3.1:1 each. The result:
- Discharge temperature per stage: Stays below 140°C with inter-stage cooling, well within the continuous service limit of PTFE-composite packing (~160°C). This is the fundamental reason for choosing a three-stage architecture at 3.0 MPa rather than pushing a two-stage frame harder.
- Valve service life: Lower per-stage pressure ratio means lower differential pressure across each valve plate. Valve fatigue life increases significantly — typically 6,000–10,000 hours between replacements on a properly maintained three-stage unit vs. 3,000–5,000 hours on a two-stage machine at the same final pressure.
- Three-column layout: Assigning one stage per column eliminates the cylinder-bore size disparity that would occur if two stages shared one column at this pressure level. Each column is individually sized for its stage inlet volume, keeping piston speed uniform and minimizing unbalanced forces on the crankshaft.
- Inter-stage cooling: Two water-cooled inter-stage coolers with moisture separators are fitted between stages 1–2 and stages 2–3. Condensate must be drained from each separator — install automatic drain valves if the unit runs unattended.
- Lubrication: Force-feed oil lubrication to crankshaft, connecting rod, and crosshead bearings. Gas cylinders on all three stages use oil-free PTFE-composite piston rings and rod packing — no lubricator in the gas path.
3Z-Series Nitrogen Compressor Technical Specifications — Three-Column Oil-Free N₂ Compressor 380 V 75–110 kW
Both 3ZW models share the same three-column, three-stage (三列三级) configuration and run on 380 V / 50 Hz. Capacity is measured at atmospheric inlet (0.101 MPa, 20°C).
| Model | Pattern | Capacity (m³/min) | Discharge Pressure (MPa) | Dimensions L×W×H (mm) | Weight (t) | Power (kW) | Voltage (V) |
|---|---|---|---|---|---|---|---|
| 3ZW-6/30 | Three-col, Three-stage | 6 | 3.00 | 1845×1660×2360 | 3.00 | 75 | 380 |
| 3ZW-9.5/30 | Three-col, Three-stage | 9.5 | 3.00 | 1845×1660×2360 | 3.50 | 110 | 380 |
Stage-by-Stage Pressure Profile (3ZW-6/30 reference frame)
| Stage | Inlet Pressure (MPa) | Outlet Pressure (MPa) | Compression Ratio | Max Discharge Temp (°C) |
|---|---|---|---|---|
| Stage 1 | 0.101 | ~0.32 | ~3.2 | ≤ 135 |
| Stage 2 | ~0.30 (after cooler) | ~0.95 | ~3.2 | ≤ 140 |
| Stage 3 | ~0.90 (after cooler) | 3.00 | ~3.3 | ≤ 145 |
Pressure values are nominal design points. Actual inter-stage pressures vary slightly with gas temperature, cooling water conditions, and valve condition. Data for 3ZW-9.5/30 follows the same profile with higher swept volumes per stage.
Where a Three-Stage Nitrogen Compressor 3MPa at Small Flow Rate Gets Specified
Nitrogen Cylinder Filling Stations
Standard 40 L industrial nitrogen cylinders are filled to 150 bar (15 MPa) from a high-pressure cascade — but the first-stage filling compressor needs to push supply nitrogen from PSA/ASU outlet pressure (0.12–0.5 MPa) up to approximately 3.0 MPa before a booster takes it higher. The 3ZW-6/30 is the standard specification for small cylinder-filling stations with 3–8 cylinders filling simultaneously; the 3ZW-9.5/30 covers stations running 8–15 cylinders.
High-Pressure Pipeline Leak Testing
Small-bore process piping (DN15–DN80) in chemical plants and refineries is hydrostatic-tested at 1.5× design pressure, which for 2.0 MPa design pressure means a test pressure of 3.0 MPa. Where water cannot be used — stainless steel lines sensitive to chloride, systems in cold climates, or lines already insulated — pneumatic testing with nitrogen at 3.0 MPa using the 3ZW frame is the practical alternative.
Instrument Air System Backup (N₂ Substitute)
Some facilities maintain a backup nitrogen supply at 2.5–3.0 MPa for critical instrument air loops where moisture-free, hydrocarbon-free gas is essential. The 3ZW-6/30 at 6 m³/min can supply a medium-size instrument manifold continuously. Because the unit runs on 380 V, it can be installed in a pressurized instrument room where MV cabling is not permitted.
Rubber & Plastics Vulcanization Press
Nitrogen is used in autoclave vulcanization and bladder-type tire curing presses at 2.5–3.0 MPa. A single 3ZW-6/30 or 3ZW-9.5/30 can supply a cluster of 4–6 presses, eliminating the cost and handling risks of liquid nitrogen dewars or cylinder banks for mid-size rubber product manufacturers.
Selecting the Right Oil-Free Three-Stage N₂ Compressor at 3.0 MPa: 3ZW vs ZW vs LW Frame
At 3.0 MPa discharge pressure, three different frame families overlap. Here is how to choose:
| Parameter | ZW (Z-series modular) ZW-4/30, ZW-13/30 |
3ZW (3Z-series) 3ZW-6/30, 3ZW-9.5/30 |
LW (L-series) LW-7/30 → LW-33/30 |
|---|---|---|---|
| Capacity at 3.0 MPa | 4–13 m³/min | 6–9.5 m³/min | 7–33 m³/min |
| Column count | Two-col, Three-stage | Three-col, Three-stage | Two-col, Three-stage |
| Motor power | 55–160 kW | 75–110 kW | 75–350 kW |
| Voltage | 380 V | 380 V | 380 V / 6–10 kV |
| Machine weight | 4.0–6.0 t (skid pkg) | 3.0–3.5 t | 2.7–6.6 t |
| Crankshaft balance | Two-col opposed | Three-col — lower vibration at this stage count | Two-col opposed |
| Best fit | Small flow, fully packaged turnkey unit needed | 5–10 m³/min, lower vibration priority, 380 V | 10–33 m³/min; larger sites |
The 3ZW frame’s three-column arrangement distributes dynamic forces more evenly than a two-column machine at the same stage count, which can matter in installations where vibration transmission to the building structure is a concern — a compressor room on an upper floor, or a facility with sensitive measurement equipment nearby.
Installation Requirements and Commissioning Checklist for 3ZW Three-Stage Nitrogen Compressor
The 3ZW frame is not a packaged skid in the same sense as the ZW-4/30 or ZW-13/30 — it is a unit-mounted compressor where peripheral components (coolers, separators, discharge piping, safety valves) are typically supplied as part of the unit but field-piped on site. Allow for the following site preparation:
- Foundation: A level concrete pad is sufficient for the 3ZW-6/30 (3.0 t). Vibration isolation mounts are supplied with the unit. No special anti-vibration grouting is required for ground-floor installation, but confirm with structural engineer for upper-floor siting.
- Cooling water: Inlet temperature ≤ 30°C; flow rate approximately 3–5 m³/h for 3ZW-6/30 and 4–7 m³/h for 3ZW-9.5/30. Both inter-stage coolers and the after-cooler connect to the same cooling water loop. Pressure drop across the cooling circuit: approximately 0.05 MPa at design flow.
- Condensate drains: Two inter-stage separators and one after-cooler separator produce liquid condensate whenever the gas is not perfectly dry. Install automatic timed drain valves; manual draining is acceptable for attended operation but not for 24-hour unattended duty.
- Safety valve: A certified pressure relief valve set at 1.1× design pressure (3.3 MPa) is mounted at the third-stage outlet as standard. Vent the relief valve discharge to a safe outdoor location — not into the compressor room.
- Inlet filter: Fit a 1 μm coalescing filter at the compressor inlet if your N₂ source is from a membrane or PSA unit with entrained moisture or hydrocarbon traces. Compressor warranty is conditional on clean, dry inlet gas.
- Commissioning run: Initial startup on clean nitrogen only — never start on air or oxygen. Run for 30 minutes at minimum flow before loading to full pressure. Check all inter-stage pressures against the stage profile table above; deviation of more than ±0.05 MPa from design indicates a valve fault or cooler blockage.
Maintenance Schedule for the 3ZW Three-Column Oil-Free N₂ Compressor at 3.0 MPa
| Component | Check Interval | Replace / Action | Note |
|---|---|---|---|
| Suction / discharge valves (all 3 stages) | 2,000 h | Replace at 6,000 h | Stage 3 valves wear fastest; keep 1 set on site |
| Piston rings — Stage 1 (largest bore) | 4,000 h | Replace at 8,000 h | PTFE-composite; replace as a set |
| Piston rings — Stages 2 & 3 | 4,000 h | Replace at 10,000 h | Smaller bores, lower wear rate than Stage 1 |
| Rod packing (all 3 stages) | 4,000 h | Replace on leakage or at 8,000 h | Stage 3 packing sees highest pressure — monitor closely |
| Inter-stage cooler bundles (×2) + after-cooler | Annual | Chemical clean or replace on fouling | Monitor inter-stage temperatures — rising temps = fouled cooler |
| Crankcase oil | 1,000 h / sample | Change at 2,000 h | ISO VG 100 compressor oil standard |
| Main bearings | At major overhaul | 16,000–20,000 h | Inspect at 8,000 h during valve/ring service |
Intervals assume continuous operation on clean, dry nitrogen (dew point ≤ −40°C at line pressure) in an ambient temperature of ≤ 40°C. High humidity, high ambient temperature, or contaminated inlet gas will shorten consumable life.
Request a Quote for the 3ZW Nitrogen Compressor
Tell us your required flow rate (m³/min), your N₂ inlet source and inlet pressure, whether you need the 3ZW-6/30 or 3ZW-9.5/30, and any site-specific constraints (room dimensions, floor load limit, ambient temperature). We’ll respond with a formal quotation within 2 business days.
