a car seal valve = a valve that can be car sealedI think there is a misunderstanding of the situation. PSV's are often spared to allow testing of one PSV while a second remains active. In this way, the safety of the system is not compromised by testing and/or maintenance of the valves. However, it is imperative that both PSV's are never simultaneously out-of-service. Since it is easy to defeat the PSV by closing a block valve on its inlet or outlet line, measures are required to see that this is not inadvertently done. The most common safeguard is to car seal open all of the block valves around all of the PSV's. When a particular valve is to be tested or maintained, it is necessary to cut the carseal (normally a plastic close once/never open flat device) and this typically requires the permission of a supervisor or someone aware of the consequences of this action. Immediately after the testing or maintenance, the block valves are fully opened and car sealed in that position. Note: The car seals are on the BLOCK valves and not on the PSV's. Sorry but I don't have any pictures of car seals. Just for information, a car seal is typically just a thin metal band that prevents an operator from inadvertently opening or closing a valve. "Car Seal" is a procedure. To operate a "Car Seal" valve entails some paperwork and procedure, per your company's policies.A valve used in "Car Seal" service can be almost any valve. For most valves, you can add a locking mechanism onto the stem through which you can put the "Car Seal" (I think it is lead or tin or some other softish metal?), a lock, a chain, etc.

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