User Guide

BULLETIN 10-9 / Page 13
The Rapid Pressure Balancer (RPB) Feature — The
thermostatic expansion valve with the Rapid Pressure
Balancer (RPB) feature was developed by Sporlan in response
to an industry demand for a TEV which would equalize sys-
tem pressures during off-cycle more rapidly than a TEV
with a permanent bleed port. In some cases, the bleed port
has proved somewhat slow at equalizing system pressures
creating restart problems for low starting torque compres-
sor motors. The RPB feature, however, has been proven to
reduce equalization times, normally to within two minutes
after system off-cycle.
The RPB feature is actuated following system off-cycle.
Immediately after compressor shutdown, the evaporator
pressure rises forcing the valve’s pin carrier to a more closed
position. When the RPB feature is used, the pin carrier con-
tinues its motion and opens a secondary spring loaded bleed
port allowing rapid pressure equalization to occur. Upon
compressor restart, evaporator pressure falls closing the
spring loaded bleed port. The bleed position and the normal
operating position of the RPB are illustrated in Figure 12.
The RPB feature has a specific application. The feature
should only be used on small air conditioning and heat pump
systems which use a low starting torque single phase com-
pressor motor. On heat pump applications, the RPB feature
should only be used on the indoor coil. Since the outdoor coil
may be exposed to cold ambient temperatures, there exists a
possibility the evaporator pressure may fall too slowly upon
compressor restart to reset the RPB feature. In addition, the
RPB feature is not recommended nor is it required for any
system employing electrical hard start components.
The RPB feature is available with the Type RI TEV, and it
can be specified on a special order basis for Types C and S
TEVs up to and including 4 tons R-22 nominal capacity.
Refer to the valve specification sheets for further information.
For OEM type TEVs, contact the Sporlan Division of Parker
regarding the availability of the RPB feature. A Catch-All
®
Filter-Drier should be installed near the inlet of a TEV hav-
ing the RPB feature to assure proper valve operation.
The normal capacity of the valve is increased by 15% when
the rapid pressure balancer is used. A cross drilling is part of
the internal construction of the RPB feature and this drilling
provides the additional refrigerant flow.
R-717 (Ammonia) Applications
The traditional Sporlan ammonia product line is cur-
rently manufactured and marketed by Parker Refrigerating
Specialties (R/S) Division. The following information has
been included in Bulletin 10-9 for reference only.
Thermostatic expansion valves for ammonia applications
require special design considerations due to the erosive
effects of ammonia vapor. TEVs Type D and A have been
developed for this type of application. Like other compo-
nents of any ammonia system, the Types D and A valves are
made from steel and steel alloys. The materials used in the
manufacture of these valves are listed in Catalog R/S 717,
Refrigerant 717 Ammonia Products, a transitional reference
guide from Sporlan to R/S valves.
With ammonia systems, the formation of flash vapor at the
expansion valve port causes valve seat erosion or wire draw-
ing to occur. This effect is further aggravated by high velocity
ammonia mixed with dirt or scale passing through the port of
the expansion valve. Fortunately, seat erosion can be mini-
mized and valve life extended if the following steps are taken:
1. Maintain vapor-free liquid at the TEV inlet at all times.
2. Maintain clean ammonia through effective filtration.
3. Reduce the velocity of the ammonia through the TEV
port by reducing the pressure drop across the port.
Step 1 can be accomplished through proper system design.
Liquid line vapor is prevented by adequately sizing liquid
lines and providing sufficient subcooling. Step 2 can be
assured with the use of a Sporlan Catch-All
®
Filter-Drier.
This filter-drier is an effective scale trap when used on
ammonia systems. For further information on the use of the
Catch-All Filter-Drier with ammonia systems, contact
Parker Refrigerating Specialties.
Step 3 is accomplished through the use of a removable dis-
charge tube located in the outlet of all Type D valves and
the nominal 20, 30, and 50 ton Type A valves. This discharge
tube represents the principal difference between ammonia
TEVs compared to TEVs used with other refrigerants. The
discharge tube functions by removing a portion of the total
pressure drop across the valve resulting in a lower pressure
drop across the valve port. Liquid velocities and the formation
of flash vapor at the valve port are reduced, extending the life
of the valve. Discharge tube sizes are listed in the Types D
and A valve specifications located in Catalog R/S 717.
The discharge tube should be removed and discarded when a
refrigerant distributor is used with the ammonia TEV since
the function of the discharge tube is accomplished by the dis-
tributor nozzle. If the discharge tube is not removed from the
valve, the combination of the discharge tube and distributor
nozzle may create an excessive pressure drop resulting in a
substantial loss of TEV capacity. Refer to Catalog R/S 717
for further information on ammonia distributors.
The nominal 75 and 100 ton Type A valves do not employ
a discharge tube since their valve outlets are designed to
Typical Valve Cross Section
Bleed or Equalizing
Position
Normal Operating
Position
RIVE
With
RPB
Figure 12