GRACO 181978 – Seal, Piston
The GRACO 181978 piston seal is a genuine OEM component designed for use in Graco pumps. Manufactured from UHMWPE (ultra-high molecular weight polyethylene) for durability and chemical resistance, it helps maintain fluid containment and efficient piston motion inside the pump’s fluid end.
Key Features
- OEM part from GRACO for reliability and exact fit.
- Constructed of UHMWPE for high wear resistance and low friction.
- Designed specifically for certain Graco 400-series piston pumps (see compatibility section) to maintain proper sealing and prevent bypassing.
Applications
- Replacement seal in the fluid piston assembly of Graco 400-series air-powered “Glutton” pumps. (Refer to Graco manual listing part 13 as “181978 SEAL, piston; UHMWPE.”)
- Used when the pump begins to “fast cycle” on one stroke end, indicating bypassing around the piston seal.
Benefits
- Restores proper piston sealing, improving performance and reducing fluid bypass.
- Maintains consistency under high-cycle operation in air-powered pump systems.
- OEM-level quality helps preserve the integrity and longevity of the pump fluid end.
Usage & Installation Notes
- Before replacing this seal, relieve all pressure and isolate the pump
- Ensure the retaining plate is oriented correctly (flat side facing seal), especially for the UHMWPE version
- Inspect the piston rod, cylinder bore and other wear parts; replacing just the seal may not be sufficient if other components are worn.
Compatibility / Models
- This part is listed in the service parts list for Graco “Glutton” 400-series pumps (e.g., pump model 220666) as the piston seal (Ref. 13) for the UHMWPE variant. :contentReference
Why this seal matters
- If the piston seal fails or wears, fluid may bypass the piston on each stroke, causing erratic pump cycling, reduced output, and increased wear elsewhere.
- Using the correct material (UHMWPE in this case) ensures compatibility with abrasive fluids, solvents, and high cycle counts typical in industrial applications.
