Brochure

Page 4 – Bulletin 90-30
ORD – (cont.)
Due to its function in the control of head pressure, the full stroke
can be utilized in selecting the ORD.
The standard pressure setting for the ORD is 20 psig. For
systems where the pressure drop between the compressor and
the receiver is higher than 14 psi, an ORD with a higher setting
is available. See Table 1 below.
APPLICATION
LAC and OROA Pressure Settings – The LAC and OROA
valves are available with three standard settings which should
handle the majority of applications: 100 psig for R-134a; 180
psig for R-22, R-407C and R-502; and 210 psig for R-402A,
R-404A and R-507. The LAC valves can also be used with
other commonly used refrigerants including R-401A. Generally,
standard settings may be used for these refrigerants but special
settings may be preferred for some applications.
The standard element is a non-adjustable dome element as
shown in Figure 3. However, there are many valves in the field
with non-adjustable remote bulbs indicated by an “R” following
the valve setting. Valves and elements with the remote bulb are
available on special order. The valve designation and setting are
stamped on the valve body. Many valves in the field have
special settings and should be replaced with the same valve to
ensure satisfactory system performance.
The LAC-4-DS has a dual setting feature that allows a choice
between two fixed settings, see Figure 2. The DS element has
an internal spring that is set to maintain the lower setting. The
element is then charged with air to obtain the higher setting
and the capillary tube is pinched and fused. An example is an
LAC-4-DS-100/180. If the capillary tube is left intact the valve
will maintain a 180 psig setting. If the capillary tube is clipped
and fused again, the valve will maintain a 100 psig setting. It is
important to fuse the capillary tube tip after clipping to prevent
moisture from entering the element.
Refrigerant Migration – During an off cycle there is a
potential for refrigerant to migrate from the warm receiver to
the cold condenser. An auxiliary check valve should be used in
the liquid line between the LAC and the receiver to prevent this
from occurring. See Figure 7.
ORI/ORD – The operation of the ORI/ORD system is such that
a constant receiver pressure is maintained for normal system
operation. Since the ORI is adjustable over a nominal range of
65 to 225 psig, the desired pressure can be maintained for all of
the commonly used refrigerants.
As shown in Figure 8, the ORI is located in the liquid drain line
between the condenser and the receiver. And the ORD is located
in a hot gas line bypassing the condenser. During periods of
low ambient temperature, the condensing pressure falls until it
approaches the setting of the ORI valve. The ORI then throttles,
restricting the flow of liquid from the condenser. This causes
refrigerant to back up in the condenser thus reducing the active
condenser surface and raising the condensing pressure. Since
it is really receiver pressure that needs to be maintained, the
bypass line with the ORD is required.
The ORD opens after the ORI has offered enough restriction to
cause the differential between condensing pressure and receiver
pressure to exceed the ORD setpoint. The hot gas flowing
through the ORD serves to heat the cold liquid being passed by
the ORI. Thus the liquid reaches the receiver warm and with
sufficient pressure to assure proper expansion valve operation.
ORD
Figure 6
Seat
Seat Disc
Maximum Pressure Drop
Between Compressor
and Receiver – psi
Head Pressure
Component Selection
Below 14
OROA-5-100 or -180
ORD-4-20 & ORI
15 – 19
*OROAB-5-100 or -180
*ORD-4-25 & ORI
20 – 24
*OROAC-5-100 or -180
*ORD-4-30 & ORI
25 – 29
*OROAD-5-100 or -180
*ORD-4-35 & ORI
Table 1
Bold type indicates pressure range.
*Available on Special Order ONLY.
Figure 7
Solenoid
Valve
Catch-All
Compressor
See-All
TEV
External Equalizer
Check Valve
LAC
Receiver
Evaporator
Distributor
Condenser
Figure 8
Solenoid
Valve
Catch-All
ORI
ORD-4-20
Compressor
See-All
TEV
External Equalizer
Condenser
Receiver
Evaporator
Distributor