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D-Stop
Partial Stroke Test Device
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Partial Stroke Test Device for
1/4 Turn Valves
D-STOP™ it!
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Email us for a copy of our Failure Modes, Effects and Diagnostic
Analysis (FMEDA) for information necessary to calculate SIL values for
your application, such as Probability of Failure on Demand (PDFavg) |
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What is
it?
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Click on the picture for a
larger image |
It’s a Catch-22 situation: To maximize revenue you want to keep your plant running 24/7 for as many months or years as you can--and you want to do it safely. To do it safely you need to periodically test your automated Emergency Shutdown Valves (ESD Valves). Here’s the catch: To test the ESD Safety System you have to close the valve. If you close the valve, you shutdown the process flow. If you shutdown the process flow, you stop revenue flow.
Now, with the DynaTorque D-Stop (Patent #6,935,610), you can do both: You can test your valves and allow the process (revenue) flow to continue! |
Background
DynaTorque's D-Stop Partial Stroke Test Device is for use in automated quarter-turn valve applications where compliance with standards such as ISA-S84.01 (Application of Safety Instrumented Systems for the Process Industries) and IEC 61508/61511 (Functional Safety Of E/E/PE Safety-Related Systems) is of concern. The
D-Stop allows testing of the entire Safety Instrumented System (SIS) in applications where exercising the final trip element (the valve) may not be practical, such as when the valve is installed in an active process flow line (reference ISA-S84.01, paragraph 9.7.5.2.b).
One of the terms associated with these industry standards is "valve partial stroke testing". A "partial stroke test" might be defined as, for example, allowing the safety system to close the valve only 20 degrees. However, when the D-Stop is disengaged, it has no impact on the operation of the automated valve. When the D-Stop is engaged, the device limits the travel of the valve actuator to the specified travel limits. In that case, all of the valve control elements (solenoids, positioners, relays, limit switches, etc.) are tested. If the automated valve is inoperable due to valve blockage, mechanical failure, misalignment, or some other control system anomaly, it will become apparent during a D-Stop Partial Stroke Test. Since the valve is only partially closed during this test, the flow coefficient is not significantly affected and process flow continues.
To
view a D-Stop video click here.
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How does
it work?
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The D-Stop has two internal cams. During normal valve operation, the D-Stop is disengaged and the actuator is free to stroke the valve on demand.
When the Partial Stroke Test is to be performed, the stainless steel engagement key is inserted into the DStop key socket.
When the redundant safety device is pulled, the Engagement Cam is free to rotate 90 degrees counter-clockwise. This safety feature forces an intentional, “two-handed operation” in order to engage the D-Stop.
When the key is turned 90 degrees counter-clockwise it is locked into the device and the Engagement Cam rotates--the device is now “engaged”. At this point, when the valve actuator is sent a test signal to go to the ESD or safety-test position, the Drive Cam that is attached to the actuator through the drive coupling, rotates until it comes into contact with the Engagement Cam, normally 20 degrees (this is a specifiable value).
Click
here to view a video of how the D-Stop works.
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D-Stop
Disengaged |
D-Stop
Engaged |
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Note that the unique key cannot be removed from the D-Stop while the unit is engaged. Therefore, if the key is kept in a control room or lock box, the plant operators are assured that the device has not been accidentally left in the engaged mode.
All keys and D-Stops are serialized. If a key is ever lost, new ones can be easily obtained from the factory. D-Stops may be keyed such that one key fits several D-Stops in a plant, or each D-Stop can be supplied with it’s own, unique key.
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Mounting Adaption Kits
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Actuator-to-Valve
“Sandwich Interface”
The
D-Stop can be provided as a component of a “new” automated valve
or it may be field retrofit to an existing valve/actuator package.
As shown to the right, the complete kit consists of a D-Stop
Test Device, Engagement Key, and a Drive Coupler for customer
adaptation to the valve and actuator. (Custom machined drive
couplers are available from DynaTorque on application. Consult the
factory or your authorized representative.)
D-Stop
housing flanges can be factory drilled to accommodate a wide variety
of valve and actuator combinations.
A
“Driver” connects the actuator and valve through the D-Stop.
As the actuator turns the valve, the Driver also rotates the Drive
Cam by means of a keyed connection.
Click here for pictures of Sandwich
Mounting.
The
D-Stop is totally enclosed, weatherproof, and permanently
lubricated. No routine maintenance is required. The
standard device has been independently certified to IP 67 for
protection against water ingress.
The
D-Stop is available for applications up to 4,000,000 lb-in of
actuator torque!
For detailed information regarding sizing, ratings, materials
of construction, coatings and special construction, refer to the
product specification sheets or contact the factoryOptional
limitswitch brackets, installed switches (see below), remote
operation, full lock-in / tag-out capability.
Materials
of Construction
D-Stops
with torque ratings up to 180,000 lb-in have cast or ductile iron housings and
covers. Units in excess of 180,000 lb-in are fabricated of carbon
steel. Engagement cams are stainless steel, drive cams are cast
ductile iron, input shafts are stainless steel, shaft and segment
seals are viton rubber, bushings are oil impregnated copper
nickel steel alloy, cover-to-housing sealant is
Loctite
51580 to assure against water ingress.
Engagement keys and key sockets are stainless steel.
Protective
External Coating:
As a standard superior coating, DynaTorque offers E-Coat, a cathodic epoxy coating
on all units up to and including D21's. In this process, substrates are cleaned and
pretreated with a phosphated conversion coating to prepare the body
and housing for electro coating. Parts are dipped into a bath where
direct current is applied between the parts and a
"counter" electrode. The coating material is attracted by
the electric field and is deposited on the part. Coated parts are
removed from the the bath, rinsed and then baked to cure the
paint. The result is a superior black finish that is highly
protective of both internal and external surfaces. For more
detailed information, visit the PPG
Powercron web site and refer to Powercron
590 for complete specifications.
Contact the factory for pricing and availability.
Other Options:
Custom and ISO bolt patterns on either or both
flanges, custom bores, custom factory drive adapters for direct
mounting to actuator and valve. Increased or decreased travel
limits, automation mounting package, limit switches, remote
operation, lock-in tag-out configuration..
IP
67 Certified!
Bodies
can be factory drilled to accommodate a wide variety of valve and
actuator combinations. The D-Stop is totally enclosed,
weatherproof, and permanently lubricated.
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Feedback |
Limit
Switches
A
popular optional configuration includes the provision for mounting
feedback devices to
the D-Stop. This picture (below) shows a typical NAMUR-mount limit
switch providing
"engaged" / "disengaged"
information to the plant I/O system.
Note that on our larger
D-Stops, brackets may not be required as the body is optionally
milled and tapped to accept the limitswitch mounting pad directly. |
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Limitswitches
that indicate whether the D-Stop in engaged or disengaged inform the
control room of the status of the device and, with the appropriate
plant I/O system, can help to provide auditable reporting of
compliance with standards.
A
wide array of mounting configurations and switch styles are
available. Contact the factory or your DynaTorque authorized
representative for more details.
The
illustration at left shows a switch pack with "on test / off
test" indicators and an additional switch to indicate when the
device has been moved to the 20 degree test position.
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