August 5, 2020
Can Valves Be Repacked Under Pressure?
NO!
The simple answer is: NO! Repacking a valve which is under pressure can cause personal injury and/or property damage, and should never be done.
 
Repacking a valve is part of routine maintenance. Valve packing forms a pressure seal to keep the process media (water, steam, other) from leaking. Over time, the packing will wear, relax, or loosen and begin to leak due to media temperature, seasonal ambient temperatures, or even valve cycling. Media that leaks out of a valve can be costly, messy or even harmful to health and environment. 

Repacking a valve is not a difficult or lengthy process. Proper preparation, with trained personnel and factory-provided packing made specifically to fit your valve should make the process go very quickly. When done correctly, service interruption will be minimal… minutes, not hours… of system down-time.
Certain manufacturing standards require that gate, globe, and angle valves include a backseat in the design. The backseat is not a seal, and the function of the backseat is not to permit repacking under pressure. Examples of the related standards for valves are: MSS SP-70 Gray Iron Gate Valves, Flanged and Threaded Ends, MSS SP-85 Gray Iron Globe and Angle Valves, Flanged and Threaded Ends, and MSS SP-80 Bronze Gate, Globe and Angle Valves. Each of these standards calls for a backseat, and in the same paragraph of each standard, all state that repacking of valves under pressure is hazardous and not recommended.
In the case of ball valve specifications where there is no requirement for a backseat to be present, the answer still remains - NO! Ball valve standards, almost universally, call for blow-out proof stem retention. This is normally accomplished (for end-entry valves) by retention of an internally inserted stem via a hard shoulder. Examples of the pertinent standards are MSS SP110 Ball Valves and API 608 Metal Ball Valves. This stem retention feature doesn't allow the ability to repack under pressure.
For all these reasons, the answer from the factory to our original question of can valves be repacked under pressure will always be a resounding NO!
 
For more information, contact your Milwaukee Valve or Hammond Valve sales representative, your regional manager or our application engineers today.
262.432.2700
262.432.2702
262.432.2700
16550 West Stratton Drive, New Berlin, WI 53151