PO Box 950 Hwy 280 West Claxton GA 30417 US

866-860-8973

Urethane Supply, Inc.

​Supplying Our Industry With Quality Graco Parts And Service

Urethane Supply features spray rigs and equipment for foam insulation and roof coatings.

Tech Tips / Spray Gun / Graco / Gusmer GAP & GAP Pro Glascraft Probler

The start-up procedures are basically the same for all of these guns. After prepping your materials and pressuring up your proportioning unit:



• Turn the air on to the gun. Purge air exiting from the mix chamber should be present at this point - The air should always be the first thing on and the last thing off.

• Trigger the gun 2 or 3 times to ensure proper mix chamber movement.

• Open one of the two material valves and, without triggering the gun, check for misting of material from the tip of the gun. If no misting is present, proceed to step #4.

• Open the second material valve and, again, check for misting. If no misting is observed proceed to step #5. If misting is observed in either step #3 or 4, STOP! It is an indication

that there is an internal leak in the gun (most likely at the side seal / mix chamber mating surface) and it is unlikely to repair itself. Allowing this material to continue to leak will cause pressure imbalances on the proportioner, gun crossover, and it’s possible for the material to back up into the air passages of the gun and even into the whip hose. If misting is present it is better to go to a second (back-up) gun or clean and repair the original gun.

• Spray a small test shot of 2-3 seconds on a disposable surface (cardboard or plastic sheeting), then check the gauges on the proportioner. If the gauges are showing equal pressure, then procede with spraying the job. If they are not showing an equal (or near equal) pressure, this is an indication of possible blockage in the gun, inadequate supply of material to the proportioner, or internal problems with the proportioner.



Proper shut-down procedures for the Graco / Gusmer GAP & GAP Pro and Glascraft Probler are as follows:

After parking your proportioner, if you intend to stop spraying for a period of time greater than 15 minutes (even if you leave the proportioner on), or if you are turning the air to the gun off for any reason:


• Close both material valves.

• Trigger the gun rapidly 3 or 4 times to expel any residual material from the mix chamber.

• Remove the air cap (and flat spray assembly, if you are using one).

• Using a grease syringe, apply grease until it is observed in the space between the mix chamber and the gun head.

• Re-install the air cap. When the air is turned on again, the excess grease will be expelled from the gun.



I cannot emphasize enough that proper cleaning during repair is critical to ensure the gun will perform well the next time it is used.

If find yourself asking, “Is this clean enough?”……it’s not! You should pay particular attention to all of the air passages in your gun, especially the passages related to the air purge. These are very critical and the most commonly overlooked areas of the gun during repair / rebuild. Using a good quality gun solvent like CU-6 (we recommend warming it in a crock pot or similar device) and purchasing a gun cleaning kit for your gun will assist you tremendously in this step of the repair process. I would also recommend that you replace all of the O-rings when doing a complete rebuild on your gun.


Another, often overlooked, area of good gun maintenance is the availability of spare parts (o-rings, side seals, & mix chambers).

You should always have enough spare parts on hand to rebuild each one of your guns at least once. As you well know, downtime

is very expensive. Additionally, overnight freight charges to rush parts to you take money out of your profits. If you need assistance

in creating a list of the parts you need to keep on hand, please contact me and I will be happy to assist you.


I hope this article will prove helpful to you. We, at Urethane Supply, are committed to the success of our customers. If you have any questions or need any assistance you can contact the Georgia home office at 1-866-860-8973 or via email atinfo@urethanesupplyinc.com. You can contact me directly at 601-693-8220 or via email at wyndell@urethanesupplyinc.com.

If you have any suggestions for future Tech Tips articles please feel free to contact us.



Wyndell Gossett

Technical Service Dept.

Urethane Supply, Inc.

Phone: 601-693-8220