All Serck Audco plug valves, no matter which type, are pressure balanced. Pressure balanced means, that the plug is protected against the possibility of seizure due to taper locking. Taper locking is caused by an imbalance of forces acting on the plug due to line of pressure finding its way into the lower and wider part of the plug chamber.
As shown by the arrows in Fig. 1, the resultant force tends to push the plug upwards, jamming it in its tapered bore. Pressure Balancing Super-H valves incorporate pressure balanced plugs as shown in Fig. 2. The drilling and check valve in the top section of the plug allow the line pressure itself to counteract the upwards force, preventing any possibility of taper locking.
Protected Pressure Balancing - a Flowserve patent
For increased reliability in service and where there is risk of many particles in the media Protected Pressure Balance can be incorporated. See fig. 3. Protected Pressure Balancing is a standard design on all DB&B valves and an option on Super-H valves. The design ensures that the balancing holes are not exposed to the line media in the plug port, providing added security compared with the normal balancing.