Fusion AP Crossover Problems
A material crossover can occur for several reasons. The side-seal O-ring often receives the blame, but an O-ring failure is rarely the actual cause.
1. Worn or damaged side seal
Inspect the side seal for scratches, uneven wear or excessive sanding. The sealing face must remain flat. Excessive sanding can create a U-shaped surface that no longer seals evenly against the mix chamber.
Test the side seals before connecting the manifold
After rebuilding the Fusion AP gun—but before connecting it to the fluid manifold—connect the air supply to the gun.
If a check valve pops out, air is passing underneath the side seal:
If the B-side check valve pops out, replace the B-side seal.
If the A-side check valve pops out, replace the A-side seal.
In some cases, reversing the mix chamber may move the worn sealing area and temporarily eliminate the leak. If the problem returns, inspect or replace the chamber.
2. Worn mix chamber
Excessive or uneven sanding can prevent the mix chamber from remaining flat. If the check valves repeatedly pop out during the air test—even with good side seals—the chamber may be worn.
Replace the mix chamber if its sealing surfaces are scratched, uneven or no longer flat.
3. Worn front retaining cap
On a Fusion AP, the front retaining cap applies the pressure that holds both side seals against the mix chamber. Excessive wear in the cap or its Acme threads can reduce that pressure and allow crossover.
Inspect the retaining cap for:
Replace a worn retaining cap. This problem generally does not occur with Probler P2-style side seals because those seals are individually threaded into position.
Temporary field measure
If a replacement retaining cap is not immediately available, remove one side cartridge. Remove its side seal and spring, then place one old side-seal O-ring into the bottom of the cartridge housing. Reinstall the spring and side seal.
This moves that side seal slightly farther outward and increases the seating pressure on both seals when the retaining cap is installed.
Do this on one side only. Adding an O-ring to both cartridges may prevent the retaining cap from being installed correctly. This is a temporary field measure; replace the worn retaining cap as soon as possible.
Check cartridge movement during every rebuild
Before reassembling the gun, make sure each side seal and spring can compress and return freely inside its cartridge. Sometimes the spring compresses but binds and fails to push the side seal back out. A sticking cartridge can prevent the seal from maintaining contact with the chamber and cause crossover.
Always relieve fluid pressure, disconnect the gun from the fluid manifold and wear the required protective equipment before servicing the gun.
