evolution G-50 H
Service Manual
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Issue 3.2
Proceed as follows to check the valve balls:
a) Disconnect the machine from the power supply and close both inlet ball valves and the
supply system to the transfer pumps.
b) Depressurise the metering pump and remove the corresponding valve ball.
c) The loss from the valve ball is usually caused by foreign particles that prevent the
perfect coupling of the ball with the ball seat. Clean the ball and the seat and make sure
there are no faults from knocks, marks or scratches to the seat or the ball. If cleaning
fails to resolve the problem or any fault is observed, replace the seat and the ball.
2.
Decompensated Pressures
Pressures are decompensated when there is an obstruction in the hose or in the gun that
prevents one of the components from leaving freely through the gun chamber when it is
projected, or when a problem in the pumping system prevents one of the components reaching
the gun in the required amount.
It is relatively easy to identify which component is problematic if we bear in mind that the
chemical components used in the polyurethane foaming are of a different color. By observing
the color of the material that leaves the gun, we can determine which component is missing.
To determine whether the decompensation is caused as a result of an obstruction or as a
consequence of a problem in the pumping system, project with the gun, observe the pressure
indicated on the corresponding pressure gage to the missing component and compare it with
the pressure indicated by the gage to the other component: if the pressure of the missing
component is higher, the decompensation is the result of an obstruction, if the pressure is lower,
the decompensation is the consequence of a problem in the pumping system.
3.
Cavitation
Cavitation occurs when the metering pump requires a larger volume of material than that
supplied by the feeding system, causing the formation of a vacuum in the inlet of the metering
pump. The causes of cavitation are the following:
a) The transfer pump fails to supply the necessary volume. The problem might be in the
pump not meeting the required specifications, in the lack of air supply to the pump or
that the pump is faulty. A pump is recommended with a ratio of 2:1 for transferring the
Isocyanate and a supply hose with an interior diameter of at least 20 mm (¾ in).
b) High viscosity. The polyurethane foaming systems normally require a minimum transfer
temperature of 12º C (55 F); at lower temperatures, the product increases its viscosity,
making the pumping more difficult. When the ambient conditions prevent the products
from being maintained at a minimum temperature of 12º C (55 F) auxiliary heating
elements must be used to condition the products as the minimum temperature required
for the transfer.
c) The product inlet filter is obstructed (see Maintenance).
d) The inlet valve ball has leaks as a result of wear or possible faults in the ball or the
closing surface of the seat, which means that part of the material supplied returns to the
supply tank and that the metering pump supplies a smaller volume of material in the
discharge cycle, causing an incorrect ratio.
4.
Fault in the Reversing Switch
The metering pump system has a plate that activates the reversing switches to carry out the
change of direction. The most common cause of the fault is the deformation of the plate or the
entry of a foreign body preventing the plate from making contact with the micros.
A fault in the movement of the directional valve will cause the activation plate to pass the micro
and not make the change of direction. Proceed as follows to solve this problem:
