The PA B31 is a compact reduction gearbox designed for petrol and diesel engine-driven pressure washer systems up to 31 HP (23 kW). Manufactured by P.A. S.p.A. in Italy, the B31 converts engine output speed of 3,100 RPM down to approximately 1,450 RPM — the ideal operating speed for most triplex plunger pumps. Its hardened steel helical gears ensure quiet, efficient power transfer with long service life, making it a reliable choice for commercial and industrial waterblasting rigs across New Zealand.
| Model | B31 |
| Manufacturer | PA (P.A. S.p.A., Italy) |
| Type | Reduction Gearbox |
| Max Engine Power | Up to 31 HP (23 kW) |
| Input Speed | 3,100 RPM |
| Output Speed | ~1,450 RPM |
| Gear Type | Hardened steel helical gears |
| Gear Ratio | 2.176:1 |
| Oil | SAE 90 / SAE 80W90 (0.35 L capacity) |
| Engine Flange | SAE J609B |
| Pump Bolt Pattern | 62 mm × 62 mm centre-to-centre |
| Weight | 3.95 kg |
| 50.0071.00 | 1-1/8″ (28.6 mm) | 24 mm |
| 50.0071.30 | 1-1/8″ (28.6 mm) | 30 mm |
The PA B31 gearbox is compatible with a wide range of triplex plunger pumps from leading manufacturers, including:
AES Waterblasters stocks genuine PA gearbox parts and complete B31 units for prompt dispatch across New Zealand. Whether you need a replacement gearbox, seals, or technical advice on matching the right gearbox to your engine and pump combination, our team can help. Contact us on 09 271 4782 or visit our Auckland showroom.
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