breakdown or shearing of the gel structure under high pressure injection and under the pressure between seating surfaces. It must be stable over a wide range of temperatures, and not freeze. It must not react chemically with the fluid and become solid, or rubber like (i.e. polymerize). Depending on the service, the best greases are fully synthetic; if you have any doubt or concern, consult a valve maintenance expert. Field experience has shown that greases and sealants may cause severe problems with the seat and seal arrangement if used regularly during preventative maintenance. If a non-leaking ball valve is lubricated with an adhesive grease/sealant, the floating, spring loaded seats can become stuck within their seat pockets. When the ball floats due to a pressure differential across the valve, the seals cannot track the ball and leakage can occur. Grease manufacturers produce low viscosity synthetic ball valve lubricants such as Clare UK “601-Fluid”. Such light greases offer the following advantages to heavier emergency sealant greases and cheaper brands of light greases: • Enhanced resistance to hydrocarbon fluids and gases. • Will not dry out or form a gum like some other greases when used within its application temperature range. • Will not disrupt the operation of the seat and seal arrangement. Of course, be warned any type of grease, especially synthetic grease can become hard or sticky causing torque problems and seat spring jamming in which case a line flushing agent like Clare 601 Valve Cleaner may be required. Of course, for leaking seats a heavier sealant like Clare 601 lubricant must be used for temporary emergency sealing. 2. Use an appropriate high pressure grease-injection pump, capable of overcoming the pipe pressure and the high pressure build-up caused by the grease itself, during it’s injection in the grease passages. 3. Inject a generous amount of grease in the seats before flushing. The object is to cover them all and to fill the groove between seat carrier and ball with grease. The dirt will get stuck to the grease during flushing, but it will not come inside. And before turning the valve for the first time, inject again a small amount of grease into the seats. A little is enough (1/4 of the normal quantity per seat, see 8.4.1). The dirty grease will be pushed into the pipe by the fresh grease, and the turning action of the ball will drag fresh grease towards the seats, not dirty grease. 4. Do not turn the valve during flushing. Australian Pipeline Valve - Installation, Operation and Maintenance Manual 11 EXPANDING SEAL PLUG VALVE DOUBLE BLOCK & BLEED API6D - TWIN SERIES Note Do not operate the valve during flushing or entrained particulates could damage soft seat or enter stem or seat pocket area. Beware of greases made of synthetic oil with a mineral thickener. The natural gas (or storage prior to use) washes away the oil, leaving the thickener behind. The thickener is like a powder that caulks or bakes hard on the seats, increasing the operating torque. Always wipe the seats clean as much as possible prior to installation.