SLURRY KNIFE GATE VALVE
Red Valve Company, Inc. introduces the durable and user-friendly Series DX Slurry Knife Gate Valve
It is designed especially for heavy slurry applications in the power and mining industries.
When the Series DX valve opens, the reinforced elastomer sleeves seal against each other and provide a 100% full port opening, minimizing turbulence which in turn minimizes wear. The seats isolate
and protect all metal parts of the valve from coming in contact with the process. When the valve is
closed, the sleeves provide a drop tight seal. Another unique feature to this valve is its ability to provide drop tight shut-off in both directions.
Each time the Series DX valve strokes, it is designed to discharge a small amount of slurry out of
the valve, keeping the gate path and seat area clear of entrapped particulates. Unlike traditional knife
gate valves, the DX prevents slurry build up in the seat area which might otherwise prohibit the valve
from closing.
CIRCLE READER SERVICE #88
CASE STUDY:
Safety Only Takes a ‘Moment’ with Custom PS/ESD Software
When one North American oil refinery
discovered a possible safety liability
during partial stroke testing of their
emergency remote-operated block
valves, it was important to find the right
solution to keep their personnel and
plant safe. Partial stroke testing is necessary because the valves are called
upon only during an emergency, meaning they could spend many years dormant. The test involves partially opening or closing the valves to ensure the
valves are not “stuck,” giving an
increased level of confidence that the valve will be available for emergency operation, if necessary.
However, there is a chance that a partial stroke test
signal could coincide with an emergency shutdown (ESD)
signal, possibly causing interference. In the rare event this
happens, the actuator might not be able to perform its
ESD function. Obviously, plant safety engineers knew they
had to find a way to be confident the block valves would
operate during an emergency even if a partial stroke signal had been sent.
To address the problem, the refinery developed new
specifications for the Flowserve Limitorque MX actuators
installed on the block valves. The specifications called for
momentary contact emergency shutdown and partial
stroke emergency shutdown custom software, which would
have to be developed especially for the refinery. Flowserve
agreed to take on the challenge of creating a customized
solution for the plant in October 2007.
The key to the new specifications was momentary contact, which meant the ESD signal would be activated for a
short period of time and then removed. This is contrasted
with closed contact, where the signal
must be maintained and interrupted by
switching the contact to its opposite
position.
The momentary-contact ESD require-
ment added to the complexity of develop-
ing the software. However, it was neces-
sary because the cables running from the
actuator to the control room—which
would deliver the signal—were contained
in conduits. With fire being the most like-
ly cause of an emergency shutdown, there
was a possibility the conduits could be
compromised, making communication between the control
room and the actuator impossible. If the signal were closed
contact, the actuator might fail if the cable were to become
damaged, because the signal could be interrupted. However,
with a momentary-contact ESD, only one 800-millisecond
signal would be required to interrupt a partial stroke test
and initiate emergency shutdown.
“The safety feature provides peace of mind and simplifies the digital control process by driving the control logic
at the actuator closest to the event,” said Flowserve Limitorque marketing and product manager Earnest Carey Jr.
“This software allows you to initiate one single command
that breaks the partial stroke and initiates emergency
shutdown rather than sending out multiple signals and
having to check on adjacent valves.”
The software passed the first factory acceptance test in
December 2007 and helped eliminate a major safety liability. The plant has since standardized on the PS/ESD
software with Flowserve for its emergency remote-operated block valves.
