Graco 15C766 Diffusion Tube

Engineering Highlights

• Material: 17-4 PH stainless steel, H900 temper – resists corrosion and maintains hardness after repeated solvent flush cycles.
• Manufacturing accuracy: centreless-ground to ≤ 0.0006 in concentricity; inferior aftermarket copies typically exceed 0.002 in.
• Six helical micro-vents: precision-drilled at a 45° pitch to dissipate pressure spikes by up to 95 % at 3 300 PSI (228 bar).
• One-piece construction: no brazed seams or weld inclusions that could fail under dynamic load.

Technical Specification

Platform Compatibility

The 15C766 diffusion tube is installed as standard or optional equipment in the following Graco models:

• Ultra Max II 490, 495 and 595 (Hi-Boy & Stand models)
• GMax 5900 and 7900 gasoline hydraulic sprayers
• LineLazer V 3900 and 5900 road-marking units
• Classic 395 PC (revision D onward)
• Fusion Pro spray guns fitted with manifold 24J245

Identification tip: if your parts diagram lists “Diffuser A (Ø 5 mm)” or displays a six-vent spiral sleeve, 15C766 is the correct replacement.

Operational Advantages

Installing the OEM diffusion tube delivers measurable benefits:

1. Pressure stability: reduction of pulsation at the manifold decreases operator fatigue and improves coating transfer efficiency.
2. Extended packing life: smoother flow minimises check-ball chatter, delaying premature wear of the upper and lower packing stacks.
3. Improved finish quality: uniform atomisation results in sharper fan edges and lower overspray, particularly when applying high-solids elastomeric or block-filler materials.
4. Predictable maintenance intervals: OEM tolerances restore the sprayer’s baseline performance, allowing service cycles to follow the factory schedule.

Installation Guidelines

1. Disengage the sprayer, relieve pressure, and flush the fluid section with a compatible solvent.
2. Remove the valve body retaining nut and withdraw the existing diffusion tube using non-marring pliers.
3. Inspect the seat and check-ball for pitting; replace if required.
4. Install the new 15C766 with the vented section oriented towards the outlet side; torque the housing to 80 in-lb (9 N·m).
5. Prime the system with clean water or solvent and verify that pressure fluctuation is within ±1 PSI at operating set-point.

Maintenance Recommendations

• Flush the tube after each shift—solvent or warm water—until discharge runs clear.
• Perform a quarterly dimensional check; outer diameter below 0.310 in indicates metal fatigue and warrants replacement.
• Replace the diffusion tube concurrently with the upper and lower packing sets every 500 gallons of latex or 350 gallons of high-solids material.
• Store a spare diffusion tube in each service kit; the part is compact, lightweight and eliminates unplanned downtime.

Frequently Asked Questions

Can the original tube be re-machined instead of replaced?

Reaming or polishing raises the surface roughness, disrupts port geometry and compromises pressure damping. Replacement is the recommended solution.

The pump operates correctly, but the spray fan pulses—could the diffusion tube still be responsible?

Yes. Blocked or eroded vent holes cause check-ball resonance even when the pump maintains set pressure. Inspect and replace if required.

Is thread sealant necessary during installation?

No. The diffusion tube is retained by a compression fit; introducing sealant can obstruct the micro-ports.

Comparative Analysis: OEM vs Aftermarket

Logistics & Ordering Information

Qualifying orders confirmed by 12 PM Central Time are despatched the same business day, shipping directly from Graco’s warehouse to ensure traceability and shelf-life integrity. Bulk order pricing is available upon request for maintenance departments managing multiple rigs.

A consistent spray pattern starts with stable fluid dynamics—secure the Graco 15C766 Diffusion Tube today and safeguard finish quality on every pass.