The Castair 20DP is a replacement air filter element for the P75 class filter assembly, used on larger industrial Castair compressor pumps including the C4U configuration. This element is physically larger than the 16D and 16DP elements — 3" ID, 4-3/8" OD, 4-3/4" height — and it includes a foam pre-filter for additional particulate protection. At $23.72, it is priced appropriately for a larger, higher-flow element serving bigger pump configurations. If your compressor runs a 1-1/4" or 1-1/2" inlet filter assembly (S-20DP-125 or S-20DP-150), this is your replacement element.
Filter Element Specifications
- Part Number: 20DP
- Fits Assembly: S-20DP-100, S-20DP-125, S-20DP-150 (1", 1-1/4", 1-1/2" inlet assemblies)
- Compatible Pumps: C4U configurations and other pumps using S-20DP series housings
- Inner Diameter: 3 inches
- Outer Diameter: 4-3/8 inches
- Height: 4-3/4 inches
- Pre-filter: Yes — foam pre-filter included
- Assembly CFM Rating: Up to 60 CFM (S-20DP housing series)
- Price: $23.72 per element
Filter Element Size Comparison
Castair offers three main filter element sizes for industrial compressors. Selecting the wrong size is a common mistake, so here is the breakdown:
- 16D ($7.70): 3"IDx4-3/8"ODx2-1/8" height. For S-16D-075 (3/4" inlet). A4/A8 pumps. No foam pre-filter.
- 16DP ($10.01): 3"IDx4-3/8"ODx2-1/8" height. For S-16D-100 (1" inlet). C1/C2/C3U pumps. With foam pre-filter.
- 20DP ($23.72): 3"IDx4-3/8"ODx4-3/4" height. For S-20DP series (1" to 1-1/2" inlet). C4U and larger pumps. With foam pre-filter.
The 16D and 16DP have the same OD and ID but are 2-1/8" tall. The 20DP is more than twice as tall at 4-3/4" — it will not fit in a 16-series housing. Confirm your housing model before ordering.
S-20DP Housing Ratings
- S-20DP-100 (1" inlet): 60 CFM rated
- S-20DP-125 (1-1/4" inlet): 60 CFM rated
- S-20DP-150 (1-1/2" inlet): 60 CFM rated — this is the most common housing for C4U pump applications
The Foam Pre-Filter Advantage
Like the 16DP, the 20DP includes a foam pre-filter layer. In a high-duty-cycle industrial environment, the foam pre-filter catches larger airborne particles before they reach the paper element. You can inspect and clean the foam pre-filter during routine maintenance to extend the main element's service life. Replace the entire element assembly when the paper element is visibly dirty or when you notice reduced compressor output.
About the C4U Pump
The C4U is one of Castair's largest industrial pumps — a 15-25 HP, two-stage, V4 configuration weighing 800 lbs. It uses a 48"x32"x7.5" belt guard (5BG). At this size, proper intake filtration is especially important: the larger the pump, the more air it moves per minute, and the more damage a contaminated intake can do to cylinder walls, pistons, and valve seats over time.
What's in the Box
- 1x Castair 20DP replacement air filter element with foam pre-filter
Note: Filter housing (S-20DP-100/125/150 assembly) sold separately. Element insertion requires removing the housing end cap — no special tools needed.
Maintenance Interval
Castair recommends inspecting filter elements at every oil change. For a C4U pump in heavy-duty service, plan element inspection every 500-1,000 hours of operation. In dusty environments, check the foam pre-filter monthly. A significantly restricted filter will cause the pump to run hotter and output to drop — if you notice those symptoms before the scheduled interval, check the filter first before diagnosing anything else.
Why Buy From Air Compressor Factory Direct?
We stock Castair replacement parts including the full range of filter elements, assemblies, oil, and belts. We can help you identify the correct element for your specific pump and housing configuration. Free shipping on all orders, free technical support at 866-217-0063, and full manufacturer warranty on all Castair parts.
Call 866-217-0063 for quick answers and help!
