Leaking or Frozen Plug Shut-off Valves Increase Probability of an Explosion!

More than 60% of Valves Leak in Closed Position!

One of the key findings in our safety inspections is that more than 60% of lubricated plug cocks leak potentially explosive levels of natural gas when in the closed position. In some cases, these plug cocks are in new or relatively new installations.

This is a serious problem when maintenance personnel are locking out, securing, and serving gas trains because they believe they are shutting off supply gas when in fact the gas is still leaking downstream through the valve.

Lubricated Plug Cock Valve Theory of Operation: lubricated plug valve
Lubricated plug cocks seal only by virtue of the lubricant that exists between the machined tapered plug the machined tapered socket that it fits into. If no lubricant or very little lubricant is present the valves can seize over time or gas can leak pass.

A seized valve prevents personnel from closing the valve in the case of an emergency (certainly not without a breaker bar or handle extension). It is also possible to cause damage to the gas train including breaking piping. This could then allow uncontrolled gas to flow making for a severe explosion hazard (if excessive force is used trying to close the gas valve).

Repair Note-01

Valve Testing:
Codes require annual valve maintenance and leak testing. A proper valve leak testing program requires the use of trained personnel and equipment.

Many leak testing approaches exist and their interaction with numerous types of safety shut-off and blocking valves goes beyond the intent of this document. Testing and checking of gas plug cocks should always be planned very carefully.

The theory behind leak testing procedures requires a means to safely relieve pressure downstream of the plug cock. One would then need to determine if the pressure again builds downstream of the valve with the valve in the closed position.


Valve Servicing: 

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Conducting a formal plug cock maintenance program requires properly installing sealant in a valve with a sealant gun. It is very important to know what type of lubricant to use on your plug cock valves. DO NOT use just any kind of “grease”. The wrong lubricant will not seal and could make matters worse.

The guns should include a swivel hose and gauge to determine whether the valve is accepting sealant or not. Different gage indications can provide important information on pressures or problems with the valve .


Honeywell Combustion Safety, formerly CEC Combustion Safety, LLC, has been in business since 1984. With engineers and staff members that sit on Code committees such as ASME CSD-1, NFPA 56, NFPA 85, NFPA 86, and NFPA 87, our inside expertise is integrated within all of our practices and our global reach ensures that customers around the world are kept safe. Contact us at +1 216.749.2992 or visit www.combustionsafety.com for additional information.

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