## Common ground
All are devices designed to clean debris from swimming pools or spas.
## Options at a glance
**8421.21 – Underwater cleaning robots**
- **Defining trait:** Operates autonomously underwater while the pool/spa is full of water.
- **Typical examples:** Robotic pool cleaners like Dolphin, Wynd, or Aiper models.
- **Best fit when:** The device cleans while submerged in a filled pool or spa and uses built-in filtration.
**8479.89 – Pump-action spa vacuums**
- **Defining trait:** Relies on water flow from the pool’s pump system to create suction; used only in filled hot tubs or small pools.
- **Typical examples:** Manual vacuum heads connected to skimmer lines, often with a hose and filter bag.
- **Best fit when:** The device is attached to the pool’s existing pump system and works only when the water is circulating.
**8508.60 – Rechargeable electric vacuums (dry use)**
- **Defining trait:** Battery-powered, operates above ground or when the pool/spa is empty; used for dry debris removal.
- **Typical examples:** Handheld vacuums like the Karcher or PoolMaster models for sand and grit.
- **Best fit when:** The device is used to clean the floor of an empty pool or spa, especially after draining.
## Key differences
| Feature | 8421.21 (Robots) | 8479.89 (Pump-action) | 8508.60 (Rechargeable) |
|-----------------------|------------------------|----------------------------|----------------------------|
| Water level required | Yes (full pool/spa) | Yes (full pool/spa) | No (empty) |
| Power source | Built-in battery | Pool pump system | Rechargeable battery |
| Operation mode | Autonomous | Suction via pump | Manual, portable |
## How to choose
- Does it work only when the pool/spa is full of water? → 8421.21 or 8479.89
- Is it powered by the pool’s pump system? → 8479.89
- Does it run on battery and work when the pool is empty? → 8508.60
- Is it fully autonomous and self-propelled underwater? → 8421.21
## Overlaps & pitfalls
- A rechargeable vacuum (8508.60) might be used in a partially filled spa, but its primary use is dry cleaning—so prioritize function over context.
- Pump-action vacuums (8479.89) may have batteries for lights or controls, but their core operation depends on the pump system.
- If unsure, choose based on **main function**: autonomous underwater cleaning → 8421.21; pump-driven suction → 8479.89; battery-powered dry use → 8508.60