^† 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°. However, when the DYNATORQUE D-Stop device is disengaged, it has no impact on the operation of the automated valve. When the device 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 partial stroke test. Because the valve is only partially closed during this test, the flow coefficient is not significantly affected and process flow continues.

Principles of operation

The DYNATORQUE D-Stop device has two internal cams. During normal valve operation, the device 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 key socket. When the redundant safety device is pulled, the engagement cam is free to rotate 90° counterclockwise. This safety feature forces an intentional, "two-handed operation" to engage the device.

When the key is turned 90° counterclockwise, 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° (this is a specifiable value).

Note that the unique key cannot be removed from the device 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 devices are serialized. If a key is ever lost, new ones can be easily obtained from the factory. DYNATORQUE D-Stop devices can be keyed such that one key fits several devices in a plant, or each device can be supplied with its own unique key.

Actuator-to-valve direct interface mounting

The DYNATORQUE D-Stop device can be provided as a component of a "new" automated valve, or it may be field retrofit to an existing valve or actuator package. The complete kit consists of a DYNATORQUE D-Stop 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.

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 DYNATORQUE D-Stop device 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.

Materials

DYNATORQUE D-Stop devicess with torque ratings up to 180,000 lbf.in have cast or ductile iron housings and covers. Units in excess of 180,000 lbf.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, and 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 coating, Cameron offers E-Coat, a cathodic epoxy coating on all units up to and including Model 60. The result is a superior black finish that is highly protective of both internal and external surfaces.

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.

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.

Level switches

A popular optional configuration includes the provision for mounting feedback devices to the DYNATORQUE D-Stop device.

Metal-to-metal safety

The DYNATORQUE D-Stop device physically prevents the valve from moving past the specified test point. Once the device 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 and simple by using a DYNATORQUE D-Stop device.

Methodologies

When considering partial stroke testing, here's why you should choose the DYNATORQUE D-Stop device.

• 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 device into the control loop or add ancillary controls, as is the case with electric systems. Often times the less complex the system, the fewer things to go wrong.
• Because the device 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.
• The basic cost of a device, 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 device, 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.
• The device 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 device is permanently lubricated, factory sealed, and requires no routine maintenance.