BAUER Junior II-B (petrol) Troubleshooting: Why Final Pressure Cannot Be Reached and How to Fix It
"It runs but it will not reach pressure" is the most common high-pressure breathing-air fault we are asked about, and on a BAUER Junior II-B (petrol) it has a finite list of credible causes. The disciplined way to find it is not to start replacing parts, but to compare stage pressures with the commissioning data: the faulty stage identifies itself.
1. Equipment overview
The BAUER Junior II-B (petrol) delivers about 100 L/min (3.5 cfm) at a maximum working pressure of up to 330 bar, driven by petrol engine (Honda-type industrial engine). Typical duty: mobile refill vehicles, remote dive sites, emergency response without mains power. It is a petrol-driven field unit, engine speed directly influences output, which shapes how the fault shows up in service.
| Parameter | Typical specification |
|---|---|
| Free air delivery | about 100 L/min (3.5 cfm) |
| Maximum working pressure | up to 330 bar |
| Drive | petrol engine (Honda-type industrial engine) |
| Filtration | P21 filter cartridge system |
| Typical applications | mobile refill vehicles, remote dive sites, emergency response without mains power |
These values are typical market configurations. Confirm every value against the data plate and the manual of the individual unit before ordering parts or planning service.
2. The stage-pressure method
On a multi-stage machine each stage is designed to work to a defined pressure ratio. If one stage loses capability, the stages around it move off their design points. In practice:
- A stage whose discharge pressure is low, with that stage running hot, is usually losing gas through its own discharge valve or piston rings;
- A stage whose interstage pressure is high usually means the next stage's inlet valve is leaking back;
- All stages drifting together points to a shared cause: intake restriction, speed loss, ambient temperature or a big external leak.
Log pressures at a defined load point, at the same ambient conditions, and compare with the values recorded at commissioning. This turns a guessing game into a single-stage decision.
3. Symptom-cause-check-fix table
| Symptom | Likely cause | How to confirm | Corrective action |
|---|---|---|---|
| Delivery falls short even though engine sounds normal | Engine speed below governed RPM or slipping drive belt | Measure engine RPM under load and check belt tension | Restore governor setting, replace or tension belt |
| Engine stalls when the compressor loads | Load applied before warm-up or carburettor mixture issue | Warm up and observe load behaviour | Service carburettor, adjust idle, verify load sequence |
| Exhaust smell traced to the inlet | Intake scoop positioned downwind of the engine exhaust | Observe inlet placement relative to exhaust | Relocate intake to clean upwind position, re-test air |
| Hard starting after storage | Stale fuel or fouled spark plug | Inspect fuel age, plug condition | Drain fuel, fit new plug, run to operating temperature |
4. Checks that cost nothing
- External leak survey with leak-detection fluid on every joint, valve cap, gauge connection and the safety valve;
- Intake filter condition and intake air temperature;
- Drive speed: belt tension and slip, or engine governor speed on petrol-driven units;
- Gauge sanity check against a calibrated reference gauge;
- Condensate drain: a drain left open is a permanent leak that grows with pressure.
Only after these are cleared does it make sense to strip a valve.
5. After the repair
Re-establish the baseline: record stage pressures and discharge temperatures at the same load point, compare with the pre-fault trend, and keep the sheet in the machine file. On breathing-air systems, any intervention upstream of the filter cartridge must be followed by an air test before gas is released to users.
6. Service scope
BAOSI / DEJUE (Shanghai) supplies high-pressure breathing-air compressors and also supports third-party service and consumables for mixed fleets. For the BAUER Junior II-B (petrol) and comparable units we can supply compatible filter cartridges, valve plate kits, belts, lubricants and seals, and provide troubleshooting support, overhaul guidance and annual maintenance planning. Where a brand-specific part number is required, we match it from your serial number and filter housing type.
Need parts or a second opinion on a fault? Send the model, serial number, operating hours and the recorded stage pressures or temperatures - our technical team will respond with a parts list and a diagnostic plan. Contact the BAOSI technical team.
Disclaimer: This article is provided for general reference only. Specifications vary by serial number, build year and market configuration - always verify against the original equipment manufacturer's manual and your unit's data plate before service. Work on high-pressure equipment should be performed by qualified, trained technicians, and any safety-critical repair should follow local regulations and the OEM procedure.