Graco 108528 Piston Nut

The Graco 108528 Piston Nut is an OEM replacement part used in specific Graco industrial pump lowers. It ensures secure connection of the piston rod for reliable operation under high pressure.

Fits selected High-Flo 4-Ball pump lowers
Compatible with President, Viscount / Viscount II, and NXT powered systems
OEM-grade durability for long service life

$221.54

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Description

About the OEM Graco 108528 Piston Nut

Compatible Machines / Pump Families

The Graco 108528 Piston Nut is an internal OEM component used in selected Graco industrial pump lowers. Compatibility is determined by the specific lower (fluid) section used on the machine.

Graco High-Flo 4-Ball lower pump assemblies (selected sizes)
Packages powered by President air motors using compatible 4-Ball lowers
Packages powered by Viscount / Viscount II hydraulic motors using compatible 4-Ball lowers
Packages powered by NXT air motors paired with compatible High-Flo lowers

What is the Graco 108528 Piston Nut?

The Graco 108528 Piston Nut (often shown in diagrams as “Nut, Piston”) secures the piston/rod assembly inside the pump’s lower (fluid) section. As an OEM part, it’s engineered to maintain proper alignment, sealing stack compression, and long-term durability under high pressure.

Authentic Graco OEM internal fastener for specific 4-Ball lowers
Critical for rod/piston retention and correct packings preload
Designed for high-duty industrial coating and fluid transfer pumps

Key Details

OEM Part Number	108528
Part Name (Catalog)	Nut, Piston
Used In	Selected High-Flo 4-Ball lowers (President / Viscount / NXT packages where diagram specifies 108528)
Typical Dimensions (approx.)	~1.8 in × 2.4 in × 2.2 in (reference from supplier listings)
Installation Note	Torque per your pump manual (examples in Graco service docs range ~75–100 ft-lb depending on model). Always follow the exact spec for your lower.

When to Replace

Thread damage or rounding on the piston nut flats
Unable to hold torque / loosening during operation
Packings won’t maintain proper preload after rebuild
Specified as a new component in a complete lower rebuild

Installation Tips (Summary)

Clean and inspect rod, piston, spacers, and seals; replace worn parts.
Thread the rod into the 108528 Piston Nut and tighten to the torque specified for your lower.
Ensure packing orientation and wet-cup setup match the manual.
After assembly, flush and pressure-test for smooth operation and leaks.

Frequently Asked Questions

Check the lower (fluid) section parts diagram in your model’s manual. If the diagram lists “Nut, Piston — 108528” you’re good. You can also share your model and serial with us and we’ll verify before you order.

Selected High-Flo 4-Ball lowers paired with President, Viscount / Viscount II, and some NXT packages. Always confirm against your lower’s exact part list.

Follow your pump manual. Graco service documents show example ranges around 75–100 ft-lb depending on the exact lower. Use only the value specified for your model.

No. This listing is for the authentic Graco 108528 OEM part (“Nut, Piston”) for compatible lowers.

Use fresh packings and seals, set correct torque, keep the wet-cup filled as specified, and flush compatible solvents after each shift. Inspect threads/flats each service cycle.