Powell Fabrication & Manufacturing, Inc.

Automatic Shutoff Valves

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Automatic Shut Off Valves on Flexible Transfer Hoses

Why Mount An Emergency Shutdown System Actuator On A Tank Car Valve?

There are literally thousands of railroad tank car platforms in the U.S. where hazardous chemicals are either loaded or unloaded from tank cars carrying as much as 90 tons of toxic, corrosive, or flammable material. These tank cars are typically connected to the loading or unloading process through flexible transfer hoses reaching from the valves in the tank car dome to the process platform nearby. The flexible hoses allow some relative motion between the tank car and the rigid platform, but they can only be moved a certain distance before the flexible hoses can break, releasing the hazardous chemical to the environment and endangering the community. Far too many chemical releases have occurred in just this fashion.

To protect against such a chemical release, many platforms now place automatic shut-off valves on both ends of the flexible transfer hoses: one fastened to a stabber pipe coming through the dome wall from the tank car valve and the other mounted at the other end of the flexible transfer hose on the platform. Should a leak be sensed or tank car motion cause the flexible hose to break, these valves automatically close, isolating the leak to only that amount of chemical in the flexible transfer hose when the break occurs. This type of system is certainly better than having no automatic shut-off valves at all, but it is vulnerable to a very serious leak source that still remains unprotected.

Automatic shut-off valves placed on the ends of flexible transfer hoses will not prevent a serious chemical release if the stabber pipe should break away from the tank car valve while chemicals are being transferred. In such an accident, the automatic shut-off valves would prevent any chemical in the flexible transfer hose and the upstream process from escaping, but would do nothing to stop the flow of chemicals from the tank car valve itself.

UniPro SystemThe picture at the left shows a chlorine tank car dome with a one inch stabber pipe from the valve inside the dome passing through the dome wall and connecting to a flexible transfer hose. Note that there is no automatic shut-off valve between the stabber pipe and the flexible transfer hose. Not visible in the picture is the platform mounted automatic shut-off valve on the other end of the flexible transfer hose.

Also visible in the picture is a UniPro™ Pneumatic Actuator installed on the hand wheel of the tank car valve. It is integrated into the same safety system that would close the automatic shut-off valve on the platform in the event of a leak. The UniPro™ actuator is prepared to immediately close the tank car valve, preventing further chemical release from the tank car. Only the contents of the flexible transfer hose would be released and the UniPro™ actuator would protect the contents of the tank car from escaping, even if the stabber pipe itself is broken off the valve.

Powell Emergency Valve Closure Systems automatically respond to any alarm input, closing valves with 40 lb-ft of torque in less than 5 seconds. The Powell E-Pro® Electric Valve Closure System and Powell MaxPro™ RA Pneumatic Valve Closure System offers the most protection by closing the actual container valve. Both systems automatically respond to any alarm input, regardless if the leak originates at the lead gasket or downstream at another fitting.

By installing a UniPro Valve Closure System, you can prevent a reportable release, and most importantly, offer protection to your workers and community that no other shutdown system can provide. This increased level of safety is the single biggest reason for using the UniPro™ Emergency Valve Closure System to close the actual tank car valves in the event of a leak or release.