AAON LL-540 - Manual (Page 33)

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Figure 12 - Piping Schematic of Example System using the OROA Valve.
ORI/ORD Valves
This system uses a two valve arrangement.
The head pressure control valve is an inlet
pressure regulating valve and responds to
changes in condensing pressure. This valve
is located in the discharge of the condenser
and is called an ORI valve (Open on Rise of
Inlet pressure). As the ambient temperature
drops, the condenser capacity increases and
the condensing pressure falls, causing the
ORI to modulate toward the closed position.
The condenser bypass valve is a pressure
differential valve that responds to changes in
the pressure differential across the valve.
This valve is called an ORD valve (Open on
Rise of Differential pressure). As the ORI
starts to restrict liquid flow from the
condenser, a pressure differential is created
across the ORD. When the differential
reaches the setpoint, the ORD starts to open
and bypass hot gas to the liquid line. The
ORI valve is adjustable from 65 to 225 psig
(factory setting of 180 psig). The ORD is
not adjustable. On refrigeration systems that
are too large for a single ORI and ORD
valve, there will be two ORI and two ORD
valves in parallel. The following schematic
shows an example system using the
ORI/ORD valves.