Data Sheet

Bulletin 71.1:CS800
15
Note
In order for the Underpressure
Shutoff (UPSO) of any slam-shut to
be triggered, the downstream pipe
pressure must drop below the UPSO
setpoint. In the case of a downstream
line break, numerous factors can
prevent the downstream pipe pressure
from decreasing below the slam-shut
UPSO setpoint. These factors include
the distance of pipe to the break, the
diameter of the pipe, size of the break
and the number of restrictions, such as
valves, elbows and bends, downstream
of the regulator and/or slam-shut
device. Due to these factors additional
protections should be installed to stop
ow in the event of a line break.
Types CS805 and CS825 with
Secondary Seat™ Protection
Note
Types CS805 and CS825 regulators do not
have any means to alert when the Secondary
Seat operates at lockup. Therefore, it
is recommended that Internal relief or
high-capacity relief are also selected or
the addition of some other method of
overpressure protection be added in the
downstream system as discussed in the
Overpressure Protection section.
Refer to Figure 7. The Type CS805 provides
Secondary Seat Protection. As downstream demand
decreases and downstream pressure rises to the
regulator pressure lockup value, the regulator will
lockup. If, however, damage has occurred to the
primary disk, to the primary orice seating surface or
debris has become lodged between the primary disk
and primary orice, the outlet pressure will continue
to rise. This additional pressure causes the primary
disk to apply additional force to the orice seating
surface, which causes the Secondary seating surface
to move toward the Secondary disk or sealing surface.
If downstream demand decreases to zero, then the
secondary seating surface will contact the sealing
surface to provide lockup. See Table 6 for Secondary
Seat shutoff above setpoint.
Types CS806 and CS826 Secondary Seat
Protection with Bleed
The Types CS806 and CS826 provides small bleed
to the downstream system as an indication that the
Secondary Seat is providing lock-up. In the event that
the primary orice and disk cannot provide lockup,
the secondary seating surface will move into contact
with a metal disk. This metal to metal interface,
combined with a small drilled bleed hole, will allow
a small amount of gas to bleed downstream thereby
increasing outlet pressure until the internal relief valve
begins to discharge gas to the atmosphere. The odor
of this discharged gas provides an indication that
the regulator is relying on the Secondary Seat for
overpressure protection. See Table 6 for Secondary
Seat maximum downstream buildup.
Secondary Seat Protection Limitations
Note
Overpresssure conditions can occur in the
downstream piping when the Secondary
Seat Protection is installed. The Secondary
Seat Protection serves only as a backup to
the primary seat for lockup. Refer to
the sections on Overpressure Protection
and Maintenance.
Secondary Seat Protection does not provide additional
overpressure protection in the event the secondary seat
or disk is damaged by debris or contamination in the
pipeline or from conditions that would cause the regulator
to go wide-open.
Installation
The CS800 Series regulators may be installed in
any position. However, the spring case vent should
be pointed downward. If gas escaping through the
CS800 Series internal relief valve could constitute
a hazard, the spring case vent must be piped to a
location where escaping gas will not be hazardous.
If the vented gas will be piped to another location,
use obstruction-free tubing or piping at least equal
in size to the vent; protect the end of the vent pipe
from anything that might clog it. Regulators with
External Registration require the use of an external
control line.