Stop ISO Crystallization: Moisture Control for Polyurea Spray Rigs

Isocyanate, the A side of every polyurea and polyurethane system, reacts with water. That is part of what makes it useful, and it is why moisture is the enemy of your rig. Graco puts it plainly in the Reactor 2 manual: exposure to moisture, including humidity, makes ISO partially cure into small, hard, abrasive crystals that stay suspended in the fluid.

Those crystals plug inlet strainers, score pump rods, wear seals and gum up guns. The fix is not one part. It is a system: keep moist air out of the drum, out of the compressed air and away from the pump rod.

How moisture gets into ISO

There are three main paths on a spray rig:

• The drum vent. As the transfer pump pulls material out, air flows in. If that air is humid, it reacts with the ISO surface.
• Compressed air. Compressors concentrate water vapor. Wet air in the purge line reaches the mix chamber and causes ISO buildup at the gun.
• The pump rod. Each stroke exposes the A pump rod to air. Without a lubricant barrier, an ISO film cures on the rod and wears the throat seals.

Graco also lists moisture-proof hoses, never using reclaimed solvents (which may contain moisture) and lubricating threaded parts on reassembly as part of the same defense.

Protect the drum: desiccant or nitrogen

Graco's rule: always use a sealed container with a desiccant dryer in the vent, or a nitrogen atmosphere. Never store ISO in an open container. PMC also recommends venting drums through a desiccant dryer, which keeps the pump from pulling a vacuum while keeping moist air out.

1. Fit a desiccant dryer to the ISO drum vent bung, such as the ArmorThane Reusable Dry Air Intake Package (PKG100).
2. Keep the other bungs closed and the pump sealed in the drum.
3. Replace the cartridge (SUP101) or refill the silica beads (SUP102) when the beads change color. Check it at every drum change.
4. Avoid pouring partial drums together. PMC links consolidating drums to added debris and crystals.

Dry the compressed air

If the drum is sealed and you still find ISO buildup at the gun, look at your air. The compressor side needs two things: draining and drying.

• Drain every day. The Compressed Air and Gas Institute (CAGI) lists draining the receiver tank, drop legs and traps as a daily task. An automatic tank drain helps.
• Run a dryer, and turn it on. Graco's electric Reactor startup steps turn on the compressor, air dryer and breathing air before spraying.
• Match the dryer to the heat. Standard refrigerated dryers are typically rated for about 110 F inlet air. Hot air straight off a reciprocating compressor can overload them. Gardner Denver's RHT high-inlet-temperature models accept up to 180 F.
• Keep it working. Make sure the automatic drain actually discharges, the bypass valve is closed, and the condenser fins are clean. Gardner Denver suggests cleaning the condenser monthly, or more often in dirty areas.
• Membrane dryers (common on low-pressure rigs) need nearly oil-free air, a vertical mount and a pre-filter element that BEKO says to replace once a year.

Pump lube, TSL and parking the A pump

Graco Reactors use Throat Seal Liquid (TSL) in the ISO lube reservoir or wet cup. Graco says the wet cup circulates TSL to carry away the isocyanate film on the displacement rod.

• Check the ISO lube every day. Change it when it becomes a gel, darkens or is diluted with isocyanate.
• If it keeps going dark quickly, ISO is leaking past a worn A pump throat seal. Plan a rebuild.
• On PMC machines, PMC says to replace the ISO pump lube when its color changes or it starts to solidify.
• At shutdown, park the A pump. Graco's shutdown procedure parks it so the rod is not left exposed to air.

Use the lubricant your pump maker approves. If you are unsure whether a product such as ArmorThane HP ISO Lube fits your machine, call the tech line before you switch.

Clean out crystals already in the system

Drying the air stops new crystals, but old ones keep circulating until you remove them.

• Inspect the fluid inlet strainers daily. Graco says to clean them when more than 25 percent of the mesh is blocked; PMC uses 20 percent for its inlet screens.
• Clean the transfer pump inlet and intake valve, and replace crystallized supply hoses.
• Replace seals that crystals have scored, and never swap A-side and B-side wetted parts.
• If the ISO in the drum is heavily crystallized, call ArmorThane before using it.

Daily moisture checklist

Shop desiccant cartridges and beads in Spray Supplies, or call the tech line at (417) 831-5090 to size an air dryer to your compressor. If you already have crystal damage, our equipment troubleshooter covers ISO crystals at the drum, pump and gun, with part numbers for each fix.