The Castair RSFD3-4-6-G11-P75 is the OEM spin-on air/oil separator filter covering six Castair rotary screw air end variants: D3, D31, D4, D6, G11, and P75. These air ends are used across the 5–20 HP range of the Castair rotary screw lineup. One part number replaces the separator filter for all six configurations — Castair rationalized the filter dimensions across this range to simplify field service. If your Castair rotary is 5–20 HP and references any of these air ends, this is your separator filter.
Air End Coverage
- D3 / D31 air end: 5–10 HP rotary screw models. D31 is a variant of the D3.
- D4 air end: 5–10 HP rotary screw models.
- D6 air end: 15–20 HP rotary screw models.
- G11 air end: 5–15 HP rotary screw models.
- P75 air end: 5–15 HP rotary screw models.
Why the Separator Filter Is the Critical Maintenance Item
On smaller 5–20 HP rotary screw compressors running in busy shops, the separator filter often has a harder life than on larger units — these machines run frequent start-stop cycles or continuous duty in environments with higher ambient contamination. A saturated separator pushes oil downstream into your air tools and pneumatic equipment. On small machines, the symptom often appears first as mysteriously high oil consumption before you see oil in the lines. Replace the separator on schedule, not reactively.
Maintenance Kits Containing This Filter
- MKD3-4 — D3, D31, D4 air ends: 2× RAFD3-4 air filters, 4× ROFD3-4-G11 oil filters, 1× RSFD3-4-6-G11-P75 separator (this part), 5 gal synthetic oil — 10% savings
- MKG11 — G11 air end: 2× RAFG11 air filters, 4× ROFD3-4-G11 oil filters, 1× RSFD3-4-6-G11-P75 separator (this part), 5 gal synthetic oil — 10% savings
- MKP75 — P75 air end: 2× 20DP air filters, 4× ROFD62-P75-P90 oil filters, 1× RSFD3-4-6-G11-P75 separator (this part), 5 gal synthetic oil — 10% savings
Note: The D6 air end shares this separator filter but uses a different oil filter (ROFD6) and is part of the MKD6 kit.
Technical Specifications
- Part Number: RSFD3-4-6-G11-P75
- Filter Type: Spin-on air/oil separator filter
- Compatible Air Ends: Castair D3, D31, D4, D6, G11, P75
- Compatible Compressor HP: 5–20 HP rotary screw models
- Manufacturer: Cast Air
Why Buy From OEM Diagnostic Tools?
OEM Castair separator filters for the small-to-mid rotary screw range. Free shipping on qualifying orders. Free tech support at 866-217-0063. Full Castair manufacturer warranty. Confirm your air end with us before ordering if you are unsure.
Call 866-217-0063 for quick answers and help!
