2.6 COMMISSIONING The first year of operation is crucial, because when the pipe is put into service, all debris is pushed downstream, and contaminates the valves along it’s travels. With time, the pipe gets cleaner and initial problems disappear. Strainers or filters should be installed upstream of all soft seated valves. 3 . 0 O P E R A T I O N The APV double block twin seal plug valve has dual expanding seals and is a plug-type which has a mechanical means of expanding the seals when seating and retracting them prior to quarter-turn rotation. The resilient seats (Viton, Hycar) are bonded to metal seating slips (No. 13). In opening the valve, the centre plug (No. 12) is raised, thus retracting the seating slips through their tapered dovetail connections. Only after the seating slips are fully retracted perpendicularly from the body seat can the plug, which is mounted on trunnions, be rotated to the open position. Conversely, in closing the valve, the plug and seating slips are rotated freely, with no plug-to-body contact, until the seating slips are positioned over the ports. Then the plug is driven between the slips, and the tapered surfaces wedge out the seating slips for a positive upstream as well as downstream shut-off. For maximum upstream sealing, it is important to torque the valve closed. he small APV plug valves are handwheel operated, and require up to 3 turns to open or close. Up to 2 3 /4 turns expand or retract the slips, while 1 /4 turn rotates the plug. Large valves operate in a similar manner that they have enclosed weather-proof worm gearing. The plug lift/lowering/rotation action is performed in the operator assembly. The operator handwheel is rotated clockwise to close, and counter-clockwise to open - similar to other valves. At the top of the valve, a position indicator flag shows the exact lug position. It appears in line with the flow when the valve is open and perpendicular to the flow when the valve is closed. Where APV valves are used for double block-and-bleed service, the body bleed valve may be left open when the APV valve is closed, but must be closed before the APV valve is opened. Since APV valves do hold bubble-tight, for ease of opening in liquid service, it is important to prevent trapped body pressure from exceeding the working pressure of the valve. Therefore, a relief system is required to prevent pressure buildup in the body cavity. On gear-operated models, the handwheel position may be changed as follows: a. Place APV valve in full open position. Australian Pipeline Valve - Installation, Operation and Maintenance Manual 13 EXPANDING SEAL PLUG VALVE DOUBLE BLOCK & BLEED API6D - TWIN SERIES Note Remember that plug valves are like the human body; they need ‘exercise’. Keep moving them and lubricating them, and you will have fewer problems. Do not let them have a sedentary life.