Castair S-20DP-125 Complete Air Filter Assembly — 1-1/4” Inlet, 60 CFM, Dual Foam Pre-Filter, Silencer Type
The Castair S-20DP-125 is the factory intake air filter for high-output cast iron compressor pumps with a 1-1/4” NPT inlet, rated at 60 CFM. The "DP" construction means dual pre-filter — a foam pre-filter ahead of the primary element extends service life in dusty shop conditions. The body is 6.75” outer diameter and 7.0” overall height, sized to handle the full displacement of 10–15 HP pump configurations running 1-1/4” NPT inlet ports.
The 1-1/4” inlet size is a common specification on Castair mid-to-large cast iron pumps. The S-20DP-100 uses the same body with a 1” NPT inlet, and the S-20DP-150 uses it with a 1-1/2” NPT inlet. Confirm your pump inlet thread size before ordering — these three models look identical but will not interchange.
What the S-20DP-125 Does
- Dual-stage filtration: Foam pre-filter plus primary 20DP element. Pre-filter catches coarse debris before it loads the primary element, extending element life in harsh shop environments.
- Silencer construction: Attenuates intake noise from the pump valve cycling. On a slow-RPM cast iron pump this is a meaningful noise reduction in the shop.
- Complete assembly: Ships with the 20DP element and foam pre-filter installed. No additional sourcing required for first installation.
- Sized for 60 CFM: Correct for 10–15 HP pump configurations. Using a filter rated below the pump displacement will restrict airflow and reduce pump performance and service life.
Technical Specifications
- Part Number: S-20DP-125
- Manufacturer: Castair, Inc. (Spicer, MN)
- Inlet Connection: 1-1/4” NPT
- Outer Diameter: 6.75”
- Overall Height: 7.0”
- Flow Rating: 60 CFM
- Type: Silencer-type, dual pre-filter construction
- Replacement Element: 20DP (ID 3”, OD 4-3/8”, Height 4-3/4”) with foam pre-filter
Compatible Applications
- Castair cast iron pumps with 1-1/4” NPT inlet connections rated up to 60 CFM displacement
- Castair 10–15 HP industrial and commercial compressor configurations
- Any reciprocating compressor pump with a 1-1/4” NPT inlet displacing up to 60 CFM
Replacement Element: 20DP
- Element Part Number: 20DP
- Inner Diameter: 3”
- Outer Diameter: 4-3/8”
- Height: 4-3/4”
- The 20DP element includes an integrated foam pre-filter. Do not substitute a 16D element — it is shorter and will not seat correctly in the 20DP body.
Available Configurations — Castair Air Filter Lineup
- S-20DP-100 — 1” inlet, 6.75” OD x 7.0” height, 60 CFM
- S-20DP-125 — 1-1/4” inlet, 6.75” OD x 7.0” height, 60 CFM (this unit — $71.61)
- S-20DP-150 — 1-1/2” inlet, 6.75” OD x 7.0” height, 60 CFM
- S-32DP-200 — 2” inlet, 7.5” OD x 7.5” height, 195 CFM
When Does a Shop Need the S-20DP-125 vs. Stepping Up or Down?
- Order the S-20DP-125 if your pump has a 1-1/4” NPT inlet and displaces up to 60 CFM. This is the correct thread size for this body.
- Compare with S-20DP-100 and S-20DP-150: All three use the same body and element at the same price. The only difference is inlet thread: 1” (S-20DP-100), 1-1/4” (S-20DP-125), 1-1/2” (S-20DP-150). Measure your pump inlet before ordering.
- Step up to S-32DP-200 for 20+ HP pumps with 2” NPT inlets and up to 195 CFM. The S-20DP series body is not rated for that volume.
What’s in the Box
- 1x Castair S-20DP-125 complete air filter assembly (silencer type), 1-1/4” NPT inlet
- 1x 20DP filter element with foam pre-filter (pre-installed)
Why Buy From Air Compressor Factory Direct?
- Genuine Castair OEM components — built to fit Castair pumps exactly
- Free shipping on qualifying orders
- Free tech support at 866-217-0063 — thread size questions are common; we help you get the right part before ordering
- Full manufacturer warranty
- 20DP replacement elements in stock
Call 866-217-0063 for quick answers and help!
