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Flow Control -   DYNATORQUE D-Stop Partial Stroke Test Device

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).  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 DYNATORQUETM D-Stop®  (Patent #6,935,610), you can do both: You can test your valves and allow the process (revenue) flow to continue. 

 

The 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 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.

 

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.

Mounting Adaption Kits
 
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 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.

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.
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.

Optional limitswitch brackets, installed switches (see below), remote operation, full lock-in / tag-out capability.



Materials 
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, Cameron 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 phosphate 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 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.

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.
Limit Switches
A popular optional configuration includes the provision for mounting feedback devices to the D-Stop.  The picture to the left, 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. 
 

 

 

 

 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. 
 
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.
 

 
Metal-to-Metal Safety
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. (See photos below)
  • 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.  Obviously if you can tolerate the valve closing, you do not need a Partial Stroke Test Device.
Solution: When performing Partial Stroke Testing: Keep it safe, keep it simple – specify D-Stop.
 
Photo to the left is a fabricated DT 260 D-Stop in factory assembly.  Note the engagement cam has not been installed.  This unit is manufactured of special materials for low temperature application.
 
Cameron manufactures D-Stops up to 4,000,000 in-lb. capability.






 
 
 
Picture at right shows the same DT 260, but with the engagement cam now installed.
 
Photo shows the engagement cam not engaged.
 
  







Photo shows the D-Stop fully engaged with Metal-to-Metal Safety, preventing the valve from going to the closed position during the test mode.



 


 




D-Stop® is Modular
 
The D-Stop is modular – it can be used and applied many different ways.

The figure at left shows the D-Stop in its most economical and manual format. The device is manually operated by a key—simple and safe

 







The D-Stop may also come equipped with its own data point device (such as limit switches, as shown in this middle illustration) for positive annunciation to the control room indicating whether the device is engaged for testing the Safety Instrumented System.
  
Some users may want to use such devices to gather information for their data acquisition system such that auditable reports, testifying to time and date of the test, can be generated (Reference ISA-S84.01, para 9.8.1).
 





For remote and/or automated applications the Key and Safety Release are not required. By adding a pilot actuator (as shown in the illustration at the left) the D-Stop can be remotely controlled.  The top actuator controls the valve, while the pilot actuator on left engages and disengages the D-Stop.
  
Using control system logic, the user can program the device to be configured to automatically disengage the D-Stop in the unlikely event of an ESD occurring during the partial stroke test.







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 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.
 
  • It’s Safe: Once the D-Stop is engaged, the drive mechanism prevents the actuator from causing the valve to stroke past a specified set point--the partial stroke. 
    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. Obviously if you can tolerate the valve closing, you do not need a Partial Stroke Test Device.
Solution: 
When performing Partial Stroke Testing: Keep it safe, keep it simple – specify D-Stop.
D-Stop Partial Stroke Test Device
 
Features
DYNATORQUE Sandwich Mount Partial Stroke Test Device D-Stop, is a device used for the periodic testing of emergency shutdown valves (ESD) and other safety related process flow applications. The test may indicate whether the valve and actuator package is inoperable due to valve blockage, mechanical failure, control system anomalies, or misalignment.
 
Additionally, use of the D-Stop can also aid in compliance with ISA S84 and IEC 61508/61511 requirements for testing of the Safety Instrumentation System (SIS), especially in applications where exercising the final trip element may not be practical, such as when the ESD is installed in an active process flow line. The device limits the travel of the valve actuator to 20 degrees (or customized to other specifications), thus avoiding significant reduction of process flow. NOTE: Failure Modes, Effects and Diagnostic Analysis (FMEDA) available on request.
 
Materials
D-Stop models up to and including D260DS have iron housings and covers. Larger models are fabricated of carbon steel. Engagement cams and shafts are stainless steel, drive cams are cast ductile iron; shaft and drive cam seals are Viton, bushings are oil impregnated copper nickel steel alloy, cover-to-housing seal is RTV #732. Engagement keys and socket covers are stainless steel. Standard D-Stops are supplied with blank drive couplings.
 
The D-Stop is totally enclosed, IP-67 certified, weatherproof, and permanently lubricated. Standard temperature application range is from –20F to +350F.
 
D-Stop models up to and including D21DS are black epoxy e-coated inside and out. Larger models are coated with black enamel painted interiors and black epoxy coating exteriors.   
Double Acting Actuators
Maximum Air Start Torque
NOT TO EXCEED
Spring Return Actuators
Maximum Spring Start Torque
NOT TO EXCEED
Model
Unit Wgt.
Lbs.
Inch
Lbs.
Foot Lbs.
Newton Meters
Inch
Lbs.
Foot
Lbs.
Newton Meters
12.5
3,000
250
339
2,250
188
254
19.5
6,700
558
757
5,000
417
565
38
10,700
892
1,209
8,000
667
904
54
17,300
1,442
1,955
13,000
1,083
1,469
110
42,000
3,500
4745
31,500
2,625
3,559
208
120,000
10,000
13,558
90,000
7,500
10,170
681
174,000
14,500
19,658
130,000
10,833
14,690
D500DS
*
333,000
27,750
37,623
250,000
20,833
28,250
D1000DS
*
667,000
55,583
75,359
500,000
41,667
56,490
D2000DS
*
1,333,000
111,083
150,604
1,000,000
83,333
113,000
 
Model
Std Output
Bore
Std. Keyway
Size
Std. Mounting Pattern
Qty. & Size
(Bottom Flange)
BCD
(Top & Bottom Flange)
Qty. & Size
(Top Flange)
1.250”
.250x.188
(4)5/16-18
2.756 (ISO F07)
(4).344
1.750”
.500x.375
(4)3/8-16
4.016 (ISO F10)
(4).406
2.000”
.375 sq.
(4)1/2-13
4.921 (ISO F12)
(4).562
2.500”
.500 sq.
(4)5/8-11
5.512 (ISO F14)
(4).688
3.250”
.750 sq.
(4)3/4-10
6.496 (ISO F16)
(4).781
4.000”
1.000 sq.
(8)5/8-11
10.000 (ISO F25)
(8).688
6.250”
1.50x1.00
(8)1 1/8-8
14.016 (ISO F35)
(8)1.188
D500DS*
7.000”
1.50x1.00
(8)1 ½-6
15.984 (ISOF40)
(8)1.562
D1000DS*
9.000”
1.75x1.50
(12)1 ½-6
19.016 (ISO F48)
(12)1.562
D2000DS*
10.000”
1.75x1.50
(12)1 ½-6
19.016 (ISO F48)
(12)1.562
 
 
*Application modifications significantly affect product weight.
 
Diagnostics with the D-Stop
Some end users are investigating diagnostic technology for valve maintenance considerations. The data acquired from these systems may be helpful in determining the present or future operational status of an automated valve.

Even though the D-Stop does not require ancillary controls, such controls may be added if the end user specifies them. For example, if the user would like to gather data to determine if the valve/actuator package is experiencing a change in run time trends, standard actuator top works diagnostic tech­nology may be used. 
 
 
 
 
 
But because the D-Stop is mechanical, once it is engaged the end user has assurance that the actuator will not stroke the valve past the test set point.  
 
 
 
 
 
 
 
 
 
 





The Valverciser™

In addition to safety applications, the D-Stop can also be used to enhance the operation of valves in severe applications.

In many process applications the chemical composition of the flowing fluid causes material to build-up on the valve internal body and trim surfaces. Over time, this build-up may cause the valve to “stick” in position and not stroke. In other applications, extreme heat and dry gasses may cause the valve to lock up. 

Use of the D-Stop allows plant operators to periodically “exercise” the valve or actuator by allowing it to partially stroke—even while the valve is flowing process fluids. This “exercising” of the valve can be automated simply by installing a pilot actuator on the D-Stop as shown above. If both the valve actuator and the D-Stop actuator are logically or timer controlled, this “exercising” can be a truly automated process.


The D-Stop can also be configured to accommodate maintenance lock-in, tag-out requirements.
 
 
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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