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Excess Flow Operation
The internal valve contains an excess flow function, or
"integral excess flow valve", which is designed to close
when the flow exceeds the flow rating established by MEC.
MEC integral excess flow valves installed on a bobtail truck
or transport can provide protection against the discharge
of hazardous materials during an unloading operation of a
bobtail truck or transport in the event that the pump or
piping attached directly to the internal valve is sheared off
before the first valve, pump, or fitting downstream of the
internal valve, provided that the cargo tank pressure
produces a flow rate greater than the valve's excess flow
rating.
Likewise, if the internal valve is installed on a stationary
tank or in the related downstream piping system, the
integral excess flow valve can provide protection against
an unintentional release of hazardous materials in the
event that a pump or piping attached directly to the
internal valve is sheared off before the first valve, pump,
or fitting downstream of the internal valve, provided that
the flow of product through the internal valve reaches the
rated flow specified by MEC.
!EXPLOSION HAZARD!
Restrictions incorporated in the discharge system of a
bobtail truck or transport or of a stationary tank (due to
pumps, pipe and hose length and dimensions, branching,
elbows, reductions in pipe diameter, or a number of
other in-line valves or fittings), low operating pressure as
a result of ambient temperature, or a partially closed
valve downstream from the integral excess flow valve,
can restrict the rate of flow through the internal valve
below the level necessary to actuate the integral excess
flow valve. Therefore, DO NOT USE the excess flow
function of the internal valve for the purpose of providing
protection against the discharge of hazardous materials
in the event of a rupture of hose or piping at a point in
the discharge system downstream from the first valve,
pump, or fitting downstream of the internal valve.
The internal valve is designed with an internal bleed
feature for equalization of pressure. After the integral
excess flow valve closes, the leakage through the bleed
must be controlled or a hazard can be created. For this
reason the operator must be familiar with the closure
controls for the internal valve and must close the internal
valve immediately after the integral excess flow valve
closes.
Failure to follow this warning could result in serious or
fatal personal injury or property damage from a fire or
explosion.
DOT Passive Shutdown Equipment Requirement--
DOT regulations 49CFR§173.315(n){2) require certain
cargo tanks transporting propane, anhydrous ammonia
and other liquefied compressed gases to be equipped with
passive emergency discharge control equipment that will
FORM #1132 ME990-3F IOM
ME990-3F
automatically shut off the flow of product without human
intervention within 20 seconds of an unintentional release
caused by complete separation of a delivery hose. The
design for each passive shutdown system must be certified
by a Design Certifying Engineer (DCE) and all components
of the discharge system that are integral to the design
must be included in the DCE certification. The DCE
certification must consider any specifications of the
original component manufacturer.
In the case of downstream ruptures in hose or piping, a
variety of operating conditions routinely encountered
during an unloading operation restrict the rate of flow
through the integral excess flow valve and make such a
valve unsuitable to serve as the means of passive
shutdown required under 49CFR§173.315(n)(2). Such
variables include restrictions incorporated in the discharge
system (due to pumps, pipe and hose length and
dimensions, branching, elbows, reductions in pipe
diameter, or a number of other in-line valves or fittings),
low operating pressure as a result of ambient
temperature, or a partially closed valve downstream from
the excess flow valve. Due to the variety of conditions, in
the case of a hose separation, that can restrict the rate of
flow below the level necessary to activate the excess flow
valve, the integral excess flow function of ME990 series
internal valves cannot be used to satisfy the passive
shutdown equipment requirement under/in
49CFR§173.315(n)(2}. Also, a Design Certifying Engineer
cannot include the integral excess flow valve of a ME990
series internal valve as a component of the discharge
system in any DCE certification under
49CFR§173.315(n)(2).
!EXPLOSION HAZARD!
DO NOT USE the excess flow function incorporated into
ME990 series internal valves to satisfy the passive
shutdown equipment requirement in
49CFR§173.315(n)(2). DO NOT include the excess flow
function incorporated into ME990 series internal valves
in a DCE certification under 49CFR§173.315(n)(2). The
cargo tank manufacturer must install some other
equipment that satisfies the requirement for passive
shutdown capability under 49CFR§173.315(n)(2).
Failure to follow this warning could result in serious or
fatal personal injury or property damage from a fire or
explosion in the event of an unintentional release of
product during an unloading operation.
Rev C 2/3/21
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