March 21, 2008

Uneven Spray Pressure

Restriction of Fluid Flow:

A) Restriction will be on the side showing higher pressure.

B) Start looking for the problem in the gun. 90% of the time the problem will be in the gun.

C) Shut off air on transfer pumps. Close fluid inlet valves at the y-strainers or the base of your machine. Release all pressure from the system and close gun fluid valves at the gun coupling block.

D) Set spray gun to safety service position.

E) Remove the gun from the coupling block.

F) Clean the face of the coupling block to prevent material build-up.

G) If you have a solvent flush kit, which is a pressurized gun flushing system, attach the gun to the service block. Make sure that the flushing system is pressurized. Do not exceed 120 P.S.I. maximum. Hold the metal part of the flushing manifold firmly to the side of a grounded metal pail. Open the gun’s isocyanate, ISO, fluid valve trigger until the gun is flushed and clean gun solvent is flowing. Shut off the ISO fluid valve. Now open the gun RES fluid valves to flush. After this side is flushed and clean gun solvent is flowing, shut off the RES fluid valve.

H) With the fluid valves both oven and with the gun in the spray position, trigger the gun as you spray into a waste receptacle. At this time check to see that the gun solvent is clean.

I) Close the fluid valves and trigger the gun to relieve the pressure in the gun block.

J) Remove the gun from the service block. Dissemble the gun and inspect for blockage in filter screens, check valves, mix chamber, gun fluid block or pattern control disc.

K) Check module orifices sizes A and B. Look in your gun manual for correct sizes.

L) If cured material is found in the check valve, clean or replace assembly.

M) If the filter screen is more than 25 percent clogged after cleaning, it should be replaced.

N) Before reassembling the gun insure all mating surfaces are clean and free of debris or chemicals. Surface may be greased to ensure that dis-assembly will be easy.

If unequal pressure persists, the restriction is elsewhere, it may be found in:

-filters
-intake valve on bottom of transfer pump
-partially closed valve
-kinked hose
-restriction inside the pump check valves

For unequal fluid temperatures resulting in a difference in viscosity:

-always check that heaters are on and up to temperature
-make sure that the material is at least 65° in drums
-in cold weather check to see the drum heaters are on to maintain 65° temperature of material in drum.

If there is no restriction, your problem could be due to:

-worn out gun check valve on low pressure side
-worn out mixing chamber
-worn cylinder packing or cylinder bore
-worn or broken main pump check valve

GENERAL PROBLEMS:

1. If material leaks when trigger not pulled:

-coupling block seals are leaking. They are either scratched or nicked.
-leaking material around front of gun PCD body retainer not tight.

2. Low volume of material:

-restricted mixing module
-low spray pressure

3. Gun blows air while trigger is pulled. Air escapes around bottom of gun:

-”O” rings in trigger piston shaft worn or broken

4. Low spray pressure:

-restricted air flow
-solids on ISO pump rod and in cup
-regulator not adjusted properly and/or not operating correctly

5. Trigger sticks:

-build up of solids on valving rod

6. Material “steams” dose not atomize:

-low heat check thermometers and hose
-temperature setting; is the hose up to temperature
-low spray pressure

7. Spotting small amount of uncured material on surface of product:

-worn check valve
-worn module
-adjust the forward stop

8. Air leaks from gun valve assembly

-worn or broken “O” rings

9. Cross over:

-polymerized material in the check valves
-cross over is caused by material from one side pushing its way across the mixing module into the other side
-never start spraying with large difference in pressure
-always equalize pressure before spraying
-A back up into check valve assembly is a sure sign of a worn check valve. Replace check valve assembly.

General Material Problems

1. Material is soft and does not set up or sets up slowly:

-resin is insufficiently mixed. Remember to purge unmixed material from lines before starting to spray again.

2. Material Foams:

-moisture in resin. Order molecular sieve and add to resin.

3. Color is Blotchy:

-inadequate mixing of color in resin

4. Color is Translucent:

-pigment concentration too low

5. Color blushes. It lightens when sprayed:

-pigment concentration too low
-sprayed too hot or too close

6. Tiny pinholes in surface of coating:

-moisture in resin
-air bubbles in resin (mixed too vigorously)

Note: Be careful not to blend air into the material when the drum is less than half full.

Failure to follow the proper shut down procedure of the 1:1 Transfer Pump will cause build up of solids on the ISO pump shaft and in the fluid wet cup area. This will cause undue wear of the pump packing, seepage of ISO, and the pump to not cycle properly

To prevent this follow these simple rules:

A) At the end of the day, cycle the pump to the top of the stroke and clean the pump shaft of all the ISO with ISO solvent on a rag and be sure to clean wet cup area of any solids.

B) Grease the pump with Graco’s isocyanate, ISO Grease. Refill the wet cup with Graco’s ISO pump lube and cycle the pump to the bottom of the stroke. This is called parking the pump. A maintained and lubrication pump should not give you problems.

C) Check to see the packing ring is tight to keep the amount of ISO seepage to a minimum. It should be tight enough to prevent leakage, but no tighter

D) Always keep pump shaft free of solids. These solids cut the packing as they are forced through causing undue wear and seepage of ISO.