POLYURETHANE
MACHINERY
CORPORATION
PH-2 SERVICE MANUAL
3. CHARACTERISTICS
3.3 DOUBLE ACTING OPPOSED PISTON METERING PUMPS
The opposed double acting Pump Line is driven by a double ended Hydraulic Cylin-
der. The in-line pump system with opposed piston pumps provides a constant volume and
guarantees uniform pressures in both directions of pump movement.
3.4 PRESSURE BALANCE CONTROL SYSTEM
The Pressure Balance Control (PBC) system performs an automatic shutdown when
a chemical imbalance occurs. When the system is turned off, the Proportioner will perform
as if there is no PBC system and will continue pumping material. When the system is
turned on, it will continually monitor the pressure between the two chemicals (known as the
pressure differential). If the pressure differential becomes equal to or greater than the
maximum allowable pressure differential, the pumps will be shut off.
The Pressure Balance Control system can be simplified into a logic box diagram
with inputs and outputs. There are five inputs: the power supply from the main console, the
pressure readings from each chemical, the maximum pressure, and the maximum allowable
pressure differential. Inside the logic box, the actual pressure differential of the chemicals is
compared to the maximum allowable pressure differential. Depending on the circumstances
of all five inputs, there are only two possible outputs: either the pumps will continue to
pressurize and move material, or the pumps will shut off and flow will be lost.
Figure 2: Pressure Balance Control Logic Diagram
REVISION 1.2 9
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