Our DYNATORQUE 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 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 184.108.40.206.b). One of the terms associated with these industry standards is "valve partial stroke testing."
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)
Double Acting Actuators Maximum Air Start Torque
(Not to Exceed)
Spring Return Actuators Maximum Spring Start Torque
(Not to Exceed)
- Bottom Flange)
(Quantity and Size
- Top Flange)
||2.756 (ISO F07)
||4.016 (ISO F10)
||4.921 (ISO F12)
||5.512 (ISO F14)
||6.496 (ISO F16)
||10.000 (ISO F25)
||14.016 (ISO F35)
||19.016 (ISO F48)
||19.016 (ISO F48)
*Application modifications significantly affect product weight.
What is 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.
Principles of Operation
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 D-Stop 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).
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 its own, unique key.
Actuator-to-Valve Direct Interface Mounting
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. 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 Cameron 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, including 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 packages, limit switches, and option for remote operation.
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.
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 Silicon RTV 732 to assure against water ingress. Engagement keys and key sockets are stainless steel.
Protective External Coating
As a standard superior coating, Cameron offers E-Coat, a cathodic epoxy coating on all units up to and including D60D's. 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.
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.
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.
A popular optional configuration includes the provision for mounting feedback devices to the D-Stop.
The D-Stop physically prevents the valve from moving past the specified test point. Once the D-Stop is engaged, the valve cannot move past the set point.
- Theory: Electronic Systems rely on instrumentation, software and controls to limit valve travel past the set point to closure
- Reality: The valve is in a real pipe with real process flowing through it. If the valve closes there may occur anything from loss of revenue to a catastrophic event, depending on the plant and the application
- Solution: When performing Partial Stroke Testing: Keep it safe, keep it simple - specify D-Stop
When considering Partial Stroke Testing, plants have two basic methodologies to choose from: Mechanical or Electrical. The D-Stop is a mechanical device and we believe the mechanical methodology is superior to electrical, and here’s why:
- It's Simple: When it comes to testing systems, the temptation is to take what might be an already sophisticated control valve system and make it even more complex! It is not necessary to integrate the D-Stop into the control loop or add ancillary controls, as is the case with electric systems. It’s simple. In the real world, often times the less complex the system, the fewer things to go wrong.
- True Safety System Tests: Because the D-Stop requires no extraneous controls, when the valve is tested all the actual SIS components, controls and elements used in an ESD or safety valve will be activated. You have real information about the exact controls that will be relied upon to protect your plant and personnel.
- It’s Economical: The basic cost of a D-Stop, depending on torque requirement, is typically hundreds or thousands of dollars less than an electric or controls-driven system. Instrumentation personnel and software programmers are not required to install the D-Stop, so installation costs are lower. Commissioning or routine calibration of controls is not required, because there aren't any. Most process plants have qualified in-house mechanics or Valve Automation Centers nearby and, since there are no additional controls required, installation cost savings can be substantial.
- Built for a demanding, industrial environment: The D-Stop is vibration resistant. It is externally corrosion protected with coatings and independently certified to IP 67 to prevent water ingress. Stainless Steel trim is used for keys, shafts and sockets. The D-Stop is permanently lubricated, factory sealed and requires no routine maintenance.