Model FF-2500 Proportioning Unit
28
25942-1, Issue 4
f)
In most cases, the cause of the leaking valve is a particle of foreign
material preventing the ball from seating properly. If cleaning the ball
and seat does not resolve the problem, replace them.
2. PRESSURE/CHEMICAL IMBALANCE -Troubleshooting this problem requires
that two points be determined:
First
- Which chemical is missing or not mixing at the proper
proportion?
Second
- Why is that chemical missing or failing to mix at the proper
proportion?
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.
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.
After determining the missing or under-proportioned material, observe the chemical
pressure gauges on the problem side of the proportioning 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 resin component is not reaching the mixing chamber.
Dispense off target on a disposable surface and observe 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 step 3 below.
3. CAVITATION- Cavitation is the 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 can be supplied. The most common
causes of cavitation are as follows:
a) The transfer pump cannot handle the supply requirement or is
malfunctioning. The Gusmer 2:1 transfer pump is recommended for use
with the FF-2500. Also recommended is a minimum of 3/4” diameter
supply hose, as short as practical.
b) The chemical is too viscous (thick) to pump properly. Consult your
chemical supplier for the recommended material temperature required to
maintain a viscosity of 250 to 1500 centipoise (cP).
c) The inlet filter screen is restricted. Service as required.
d) An inlet valve ball and/or seat gasket that does not properly seat 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 and an off-ratio condition
will result. This malfunction will appear almost identical to cavitation, but
somewhat less severe.
4. REVERSING MALFUNCTION- For the proportioning pumps to reverse direction,
the ends of a slot machined in the rear leg of the pump yoke must contact the lever
on the reversing switch assembly. The switch lever, in turn, pushes an arm on the
reversing switch, which energizes one air valve coil and de-energizes the other. A
problem arises when the yoke fails to contact the switch lever or when the spool in
