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Thursday, April 17, 2008

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Blocked valves are normally provided upstream and downstream of Pressure Relief Valve for isolation purpose during maintenance, inspection, etc. You may noticed a word "CSO" or "CSC" attached to the block valve. What is CSO and CSC ? What is the purpose ?

Above question has been raised by some very fresh engineers in several times and i think it is worth to discuss here.

What is CSO and CSC ?
"CS" stand for Carseal while "O" and "C" are stands for Open and Close respectively. This is pretty simple.

How "Carseal" term was originated ?
The term "carseal" comes from the railroad industry. Railcars were loaded with goods. To assure that the goods were not tampered with, agents on the shipping end would but a wire though a hole in the handle and then through a hole in the car. They would then use a lead ball with a hole in it that each end of the wire was put through. A hand press would be used to squeeze the lead tight on the wires and imprint a a seal of the agency. If the wire where cut or the seal was broken, they knew the shipment was tampered with. Latter versions used stainless steel bands with serial numbers and codes on them.

What is the function of Carseal ?
In a process plant, some of block valves shall be put in a fix position for specific reason. For example, a drain block valve is Carseal Closed (CSC) to avoid loss of inventory in the event of inadvertently opening of this valve. This CSC valves can assist operator easily identify those valves position can only be altered with specific permission via stringent control procedure. Similarly, pressure relief valve inlet and outlet isolation valves are Car Sealed Open (CSO) to avoid operator inadvertently close.

How Carseal is implemented in a valve ?
Nowadays, most (if not all) valve manufactures will have hole cut in valve handles and tabs on the valve bodies. Some valve manufactures will treat this as additional feature by providing a "add-on" adapter with in-built hole. These holes can be lined up and cable seal, plastic / metal strips, etc. Following are some images for different seal type.

Heavy Duty Bolt Lock
Can only be cut by special cutting tools...

Cable Seal

Plastic Seal

Carseal enhance safe operational of a plant. For safeguarding purpose, a higher safety devices e.g locked open, key interlocked, etc shall be used.

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posted by Webworm, 10:55 PM


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January 6, 2012 at 1:02 PM  

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