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On-Off Valve Interlock Dilemma


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#1 deltaChe

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Posted 23 August 2010 - 06:07 AM

Dear professional engineers
I have a simple and mundane question need to bother you.

I have a storage tank and the product there need to be send to drumming area and isotank area.(Please see the attached drawing)
The on-off valve A will be closed through the interlock trip if the tank level is high high. Beside, the on-valve C and E can't be open at the
same time. If on-off valve C open, the interlock will trip to close he conrol valve D.Also, there is a local hand-switch push buttom needed
to be actived when product is selected to transfer to isotank.

My question is
Any valve can be open/close to protect the system if operater open the control valve D by accident or
the control valve C can cause any on-off valve failure?
Thank you very much.

Attached Files

  • Attached File  test.bmp   576.05KB   42 downloads


#2 Art Montemayor

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Posted 23 August 2010 - 09:29 AM


hswang2:

I don’t think yours is a mundane question. I believe this is an important issue in establishing a safe and dependable filling operation in a process area. Therefore, I have given it a detailed study and have had to edit your original post in the following manner in order to better understand your scope of work and operational needs:

“I have a storage tank whose product needs to be sent to a drumming area as well as to an isotank area. (Please see the attached drawing)

The on-off block valve A will be closed through the interlock trip if the tank level is high-high. Besides, the on-off block valves C and E can't be opened at the same time.

If on-off valve C is opened, the interlock will trip to close the control valve D. Also, there is a local hand-switch push button that is activated when product is selected to transfer to the isotank filling.

My question is:
Can any valve be opened/closed to protect the system if an operator opens the control valve D or the control valve C by accident, and can this cause any on-off valve failure?”

Please verify that my understanding of what you meant to write down is correct and also note the following comments which I add because I believe we need additional data (and Scope) in order to make correct and practical recommendations that will ensure a safe operation. My main concern here is that this should be instrumented in accordance with a SAFE and practical operating instrumentation logic that is in keeping with your local operational needs and constraints. In order to facilitate our members is furnishing you with safe and practical recomendations, I have made the editing and follow with my comments:

  • The drawing supplied is not accurately drawn. Please try to draw in Excel so that our members can quickly and efficiently add comments and modifications to your sketch. A .bmp drawing does not allow engineers to make comments or modifications on the drawings as well as other details.
  • Your drawing shows what you call an “on-valve” (on-off?) as a CONTROL valve – in other words, it is shown as a normal, diaphragm-actuated, control valve that regulates flow. Is this intended? – or a mistake? Is it mis-labeled or described wrong?
  • I would normally expect to have a pneumatically-operated, on-off, 90o turn, ball valve acting as a block valve – and this would be typical of valves A, B, C, and E. You don’t give an scope of how you intend to fill your drums or Iso-containers, but I would assume that you intend to regulate the flow in order to control the rate of filling each type of container. If that is the case, then I would expect to use a flow-regulated control valve on the smaller, faster, drumming operation and a simple, on-off ball valve on the Iso-container operation (depending on the size of the Iso-containers. Therefore, I would normally change the way you show the two filling operations.
  • You should state whether your filling operations are manual or automated. This makes a BIG difference on the instrumentation controls on your tank. This is part of the Scope of Work that you don’t supply.
  • You should supply a minimum flow by-pass valve on your filling pump.
  • Your drawing should show all the instruments and valves employed on the tank – including over-fill and pressure/vacuum protection on the tank.
  • What is the fluid you are storing and filling?
Await your reply.


#3 deltaChe

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Posted 24 August 2010 - 06:44 AM

Dear Sir

Thank you very much for your kindly reply.
I would like to clearify the point you mention in the following:

1. The new drawing pdf file was attached but I still miss the inlet line with its on-off valve to the tank.
2. The valve C in the previous post should be control valve. This is my typo.
3. The PEG is the product in the tank and will be transfered to the drumming and isotank.
4. The valve to the drumming is 1-1/2" with 68% opening. (This is vender information and I would really appreciate that you show me any useful sofeware website for calculating %open and cv value)
5. The filling operation are manual operation. Operator can manualy open the block valve first, and the light will kept green for 1 min if the block valve is not closed by this operation. And, then operator will start the
process through lock push button in 1 min to start the flow control valve D.
6. The minimun flow by pass valve is on-off valve and orfice ( not show in the drawing). The on-off valve setting is for the fully recircultion flow when the drumming/isotank not in operation state..
7. Sorry, I still not show the level transmitter on the tank and psv valve on the tank. The tank is operatiing in ATM.
8. The flulid storing is PEG.

My question is:

1. Is any premissive interlock should be put on the valve upstream drumming/isotank? For example, if ZSO-B(on-off vlave B limit swith is not actuated), the wrong message will show on the DCS panel.

Thank you very much for your help.

Attached Files

  • Attached File  test.pdf   24.28KB   45 downloads


#4 Narayanan.u

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Posted 29 October 2010 - 12:12 PM

Hi,

On what parameter control valve is operating?Based on level? Valve C&E interlocked. Valve C&D interlocked.
when valve C opens valve D will close. When valve D opens valve C should be closed. If interlock not working operator shall intervene.If operator make error all valve shall fail safe.

Fail safe is meant for that as I understand.

Narayanan

#5 Ravi22

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Posted 02 November 2010 - 09:37 PM

is there any low level interlock there




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