Castair Replacement Air Filter Element for D3, D31, D4 Rotary Pumps (RAFD3-4)
The Castair RAFD3-4 is the paper air filter element for D3, D31, and D4 rotary screw pump air ends, covering the 5 to 10 HP range of Castair rotary screw compressors. Dimensions: ID 2-7/8", OD 4-5/8", HGT 2-7/16". This is one of the smaller filter elements in the Castair lineup, sized for the compact air ends used in 5-10 HP machines. At $21.18, it is an inexpensive part that directly affects air end longevity — running a rotary screw compressor with a dirty or restricted filter damages the air end over time and is not recoverable through maintenance after the fact.
The D3, D31, and D4 designations refer to different variants in the same pump family used across Castair's lighter-duty 3-phase rotary screw models. All three use the same RAFD3-4 filter element — check your compressor nameplate for the air end model to confirm you are in the D3/D31/D4 family before ordering.
Filter Specifications
- Part number: RAFD3-4
- Filter type: Paper element, dry-type
- Inside diameter (ID): 2-7/8"
- Outside diameter (OD): 4-5/8"
- Height (HGT): 2-7/16"
- Application: D3, D31, and D4 rotary pump air ends
- Horsepower range: 5-10 HP Castair rotary screw compressors
Air End Filter Cross-Reference
- RAFD3-4 (this part): D3, D31, D4 — 5-10 HP — ID 2-7/8", OD 4-5/8", HGT 2-7/16"
- RAFD6-62: D6, D62 — 15-25 HP — ID 4-3/4", OD 6-1/8", HGT 2-7/8"
- RAFD10: D10 — 25-40 HP — ID 6-3/8", OD 9-1/2", HGT 5"
- RAFD16: D16 — 50-60 HP — ID 6-3/8", OD 9-1/2", HGT 7-7/8"
- RAFG11: G11 — 5-15 HP — ID 2-5/8", OD 3-7/8", HGT 3-1/8"
Maintenance Schedule
- Visual inspection: Check at every oil change — more frequently in dusty environments
- Hour meter: Your Castair compressor has an hour meter standard — use it to track filter intervals
- PM kit option: MKD3-4 includes 2 RAFD3-4 air filters, 4 oil filters, 1 separator filter, 5 gal CAST-LUBE oil — saves 10% vs. individual purchases and covers the D3, D31, and D4 air end families
What Is in the Box
- 1x Castair RAFD3-4 paper air filter element
Why Buy From Air Compressor Factory Direct?
- Castair authorized: OEM filter with confirmed dimensions
- Free shipping on qualifying orders
- Free tech support: 866-217-0063 — confirm your air end model if you are unsure
- Full lineup in stock: All Castair rotary pump filter elements available
Call 866-217-0063 for quick answers and help!
