Overpressure Protection; Installation - Emerson Fisher 299H Series Instruction Manual

299H Series
This creates a higher pressure on the top side of the
main diaphragm (E) than on the bottom side, forcing
the diaphragm downward. This motion is transmitted
through a lever, which pulls the valve disk (K) open,
allowing inlet pressure to flow through the valve.
When the demand in the downstream system has been
satisfied, the outlet pressure increases. The increased
pressure is transmitted through the downstream control
line (for external or dual registration) or through the
port (G) (for internal registration) and acts on top of the
pilot diaphragm (F). This pressure exceeds the pilot
spring setting and forces the diaphragm down, closing
the orifice (C). The loading pressure acting on the
main diaphragm (E) bleeds to the downstream system
through a bleed restriction (H).
With a decrease in loading pressure on top of the
main diaphragm (E), the main closing spring (B)
exerts an upward force on the diaphragm post which
is connected to the main diaphragm (E), pulling it
upward. This moves the main valve disk (K) toward its
seat, decreasing flow to the downstream system.
Type 299HR
During normal operation the Type 299HR performance
is identical to the Type 299H. If an overpressure
condition occurs, the pilot diaphragm head will
separate from the pilot diaphragm post and travel until
it contacts the pilot spring case. The movement of the
diaphragm head creates a path and a token or small
amount of gas will be released.
When the overpressure condition ceases, the pilot
diaphragm head will return to the diaphragm post and
the regulator will return to normal operation.
Type 299HS
The Type VSX-2 slam-shut device on the Type 299HS
regulator is a fast acting slam-shut valve which provides
overpressure or overpressure and underpressure
protection by completely shutting off the flow of gas to
the downstream system. The slam-shut module's actions
are independent of the Type 299HS main regulator and
of the variations to the inlet pressure. The Type VSX-2
has internal or external registration. External registration
requires a downstream sensing line.
The slam-shut disk is held in the open position (reset
position) by a small ball holding the disk stem. If
the pressure below the diaphragm increases (or
decreases) reaching the Type VSX-2 setpoint,
the diaphragm will travel upwards (or downwards)
operating a lever which in turn releases the ball.
6
Once the ball is released, the spring force on the stem
will push the stem and disk to the closed position
against the seat shutting off all gas flow. The pilot
supply pressure is also shut off when the Type VSX-2
is closed. The manual reset has an internal bypass to
equalize the reset pressure on either side on the
slam-shut disk.
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 flow in the event of a line break.

Overpressure Protection

Like most regulators, the Type 299H has outlet
pressure ratings lower than the inlet pressure ratings.
Complete downstream overpressure protection is
needed if the actual inlet pressure exceeds the outlet
pressure rating.
Overpressure protection for internal parts is built
into the main and pilot diaphragms by means of a
small spring on each post. The springs will allow
the diaphragm heads to move farther on the posts
avoiding damage to or bending of the valve trim.
Overpressuring any portion of a regulator or
associated equipment may cause leakage, parts
damage or personal injury due to bursting of
pressure-containing parts or explosion of accumulated
gas. Regulator operation within ratings does not
preclude the possibility of damage from external
sources or from debris in the pipeline. A regulator
should be inspected for damage periodically and after
any overpressure condition.
The pilot vent is provided with a 1/4 NPT tapped
connection in the spring case.

Installation

WARNING
!
Personal injury, equipment damage or
leakage due to escaping gas or bursting
of pressure-containing parts might result