Graco 288400 important safety instructions Proportionting System

Troubleshooting

Proportionting System

Problems

Try the recommended solutions in the order given for each problem to avoid unnecessary repairs. Also, determine that all circuit breakers, switches, and controls are properly set and wiring is correct before assuming there is a problem.

Problem	Solution
Proportioning pump does not hold pressure	1
when installed.
Proportioning pump does not build pressure	1,6
on the upstroke.
Pressure imbalance between pumps.	2,3,1
Cavitation in the proportioning pump.	2,3,1
Pump movement is erratic.	5,6
Failure of pump to reverse.	4,5,6

Solutions

1.Leaking Ball Check Valve - Determine which inlet ball check valve or piston ball check valve is leaking. If the pump (A or R) is losing pressure on the upstroke, check the piston ball check valve of the respective pump. If the pump is losing pressure on the downstroke, check the inlet ball check valve of the respective pump. To repair, see manual 309577.

2.Pressure/Chemical Imbalance - To troubleshoot this problem, first determine the following two points:

First - Which chemical did not exit the mixing chamber?

Determine the first point by checking the color of the material exiting the gun. Since two-component foam systems are usually a combination of light and dark material, the missing or under-proportioned material can be readily determined in most cases.

Second - Why did the chemical fail to get there?

The second point is due to a restriction in the gun or because the proportioning pump did not function properly in pumping its designed volume. This is determined by checking the chemical pressure

gauges on the unit. Focus on the pressure gauge corresponding to the missing chemical.

After determining the missing or under-proportioned material, observe the chemical pressure gauges on the problem side of the unit to see if the malfunction is due to a restriction at the gun or a lack of material produced by the pump. To prevent misinterpretation, focus on the pressure gauge corresponding to the missing chemical.

For example: Assume that the R-component is not reaching the mixing chamber. Spray off target and note the resin pressure gauge; if the resin gauge is considerably higher than the isocyanate gauge, the problem is within the gun. Refer to the gun manual to resolve the problem. If the resin gauge is considerably lower than the isocyanate gauge, see Solution 3.

3.Cavitation - Formation of a partial vacuum or void created within the pump cylinder during the fill stroke. It is actually a “short fill”, since the fill chamber is not completely full of chemical when the pump reverses to start the discharge stroke. Cavitation occurs when the proportioning pump demands a greater volume of material during its fill stroke than the supply system can deliver.

The most common causes of cavitation are as follows:

a.The transfer pump cannot handle the supply requirement or is malfunctioning. The Graco- Gusmer 2:1 transfer pump is recommended for use with the unit. Also recommended is a minimum of 3/4 in. diameter hose, as short as possible.

b.The chemical is too viscous to pump properly. Consult your chemical supplier for the recommended material temperature required to maintain a viscosity of 250 to 1500 centipose.

c.Inlet strainer screen is restricted. Service as required.

d.An inlet ball check and/or seat o-ring that does not properly seal will permit some of the proportioned material to flow back towards the supply drum. When this happens, the proportioning pump will not pump the proper volume of material during the discharge stroke

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