Ever have control valve problems that caused you sleepless nights?
Most control valve damages are attributed to two main reasons:
1) Cavitation in the flowing medium resulting in internal damage
2) High noise resulting in damage to mechanical parts
Fisher's Severe Service product range has the answers. You can click on the following links to find out more:
http://www.documentation.emersonprocess.com/public/videos/cav_demo/english/index.html
Cavitation creates lots of challengings to a control valve and the situation becomes even worse if particulate present in fluid. Cavitation leads to unacceptable noise and vibration. Damage to control valve trim also occurs.Entrained particulate can shorten control valve life by plugging the cage and causing material erosion of the plug, cage, and seat. If the control valve does not perform as required due to cavitation damages to valve, facility could experience unscheduled downtime.
Fisher Dirty Service Trim is a multi-stage, anti-cavitation control valve trim with concept of combined axial and radial flow that features large, open flow passage to eliminate plugging issue.DST also features a protected seat design where separate the shutoff port and throttling port to signifcantly extend service life of control valve.DST trims have been successfully used in many facility of Oil&Gas, Refinery and Power Plant.
I am a severe service engineer of Fisher control valve business unit, Emerson Process Management.
In reply to Sabrina Zhang:
Pardon my ignorance - I can understand from fluid maechanics how multi stage can help to reduce cavitation...but how does a special "protected seat design" help? Isn't the seat just to make sure the closing is tight?
In reply to chowyang.neo:
Chowyang, thanks for your question. Protected seat design is available for our DST trim and Notchflo DST. As i mentioned earlier, this design separate the shutoff port and throttling port and there is a designed deadband between this two port. When valve plug lift up to 15% opening or above, there is much more flow area through shutoff port than throtting port. As a result, majority of pressure drop is taken by throttling port, and seat life can be greatly extended and tight shutoff also can be maintained for long period of time. You can click below link for more information on Fisher Anti-Cavitation technologies.
http://mtndocs.mt.na.emersonprocess.com/groups/public_valvesprodlit/documents/brochures/d351912x012_a4.pdf#xml=http://mtndocs.mt.na.emersonprocess.com/intradoc-cgi/idc_cgi_isapi.dll?IdcService=GET_XML_HIGHLIGHT_INFO&QueryText=d351912x012&SortField=dDocName&SortOrder=Asc&dDocName=D351912X012_A4&HighlightType=PdfHighlight
If you are using Fisher Cavitrol III trim, you can also upgrade your trim to Protected Inside seat.
For control valves with standard Cavitrol III trim designs, shutoff occurs when the radius tip of the plug, located on the lower outside edge of the plug, contacts the beveled seat ring. On the protected inside seat design, the plug seat consists of a bevel on the inside of the plug tip and enters a machined groove in the upper surface of the seat ring.
Since surfaces for shutoff are inside the plug tip and the radius in the groove of the seat ring, the protected seat feature does not expose shutoff surfaces to potential erosion in the flow stream.
The protected inside seat for control valves with Cavitrol III trim addresses seat leakage issues due to plug-tip erosion which commonly seen in high pressure drop application, eg. Minimum flow control valve in system like Boiler feed water
In reply to Ashleigh:
Sabrina, Ashleigh - thanks for the answers and great illustations....
Good day dears, first ask apology for my english. I am not a expert in this subject but i have a question in which you could help me. For service of recirculatión flow of feedwater pumps in boilers, which is better valve: Fisher HPT with Cavitrol III 3 stage or Fisher NotchFlow DST??
In reply to lanc:
Hi, both Cavitrol and DST are proven technologies for boiler feed water applications. Both are equally good to perform as intended. The major difference is the way they are designed. Cavitrol cage uses a series of tiny specially designed drill holes to control high pressure drop. The only disadvantage is that these holes tend to clog up in the presence of particles/weld slags that may be generated due to general pipeline corrosion. On the other hand, DST is a modular design stack on top of one another that allows bigger open passage. Hence it has less tendency to get clog up.
The posts above have those details. Send another post if your question is not being answered.
In reply to Vincent Lam:
Thank`s, here is the question: about cost?? and wich is your recomendation?
Hi Ianc, the type of solution will greatly depend on your process requirements. As Vincent has explained, if the process fluid tends to contain particles, the DST or Notchflo DST design will be recommended. Another important parameter will be the pressure drop experienced across the valve, which must also be considered when selecting a suitable valve/trim. Hence the process requirements will be neccessary to determine the type of solution offered.
Will it be convenient for you to leave your email so that we can contact you directly to have a better understanding on your process needs? Otherwise, you can also drop me an email. I will send you a private message to indicate my email address.