## Common ground
All are pumps designed for use in fountains, moving water for decorative or functional purposes.
## Options at a glance
**8413.70 – Centrifugal (submersible)**
- **Defining trait:** Uses centrifugal force via an impeller; typically submersible and built into the fountain base.
- **Typical examples:** Submersible pool or garden fountain pumps.
- **Best fit when:** The pump is fully submerged and relies on rotation to move water upward or outward.
**8421.21 – Filtering/purifying**
- **Defining trait:** Designed primarily to clean or treat water, often integrated with filtration systems.
- **Typical examples:** Pumps in recirculating fountains with sand filters or UV sterilizers.
- **Best fit when:** Water quality is a key function—e.g., in public fountains or aquariums.
**8424.89 – Spring/spray projection**
- **Defining trait:** Engineered to project, disperse, or spray water into the air (often with nozzles).
- **Typical examples:** Water feature sprayers, decorative misters, or jet fountains.
- **Best fit when:** The main purpose is visual display through water projection or dispersion.
## Key differences
| Feature | 8413.70 (Centrifugal) | 8421.21 (Filtering) | 8424.89 (Spray/Projection) |
|---------------------|------------------------|----------------------|----------------------------|
| Primary function | Water movement | Water purification | Water projection |
| Installation | Submersible | Inline or external | Surface-mounted or jet |
| Key design focus | Flow efficiency | Filtration compatibility | Spray pattern & pressure |
## How to choose
- Does the pump move water primarily for circulation, not cleaning? → 8413.70
- Is the pump part of a filtration system (e.g., with filters or UV)? → 8421.21
- Does it spray, disperse, or project water into the air as its main purpose? → 8424.89
## Overlaps & pitfalls
A pump may serve multiple functions—e.g., a submersible pump (8413.70) in a filtered fountain could also project water. If both filtering and spraying are key, prioritize the **main function**: use 8421.21 if purification is central, 8424.89 if visual spray is primary. No option is inherently more important—choose based on the product’s defining purpose