|  The Model 735 Surge Anticipating Control Valve is an automatic control valve designed to protect pumps and pipelines from pressure surge damage resulting from the sharp flow velocity changes associated with pump starting and stopping and especially with abrupt pump stoppage caused by power failures.
It is a pilot controlled, hydraulically operated, diaphragm actuated globe valve in either the oblique (Y) or angle pattern design. Valve differential pressure powers the diaphragm actuator open or closed.
The lower control chamber is connected through a fixed orifice to the downstream pressure, which serves to cushion the closing of the valve.
The upper control chamber, which operates on a two-way control principle, has varying pressure produced by the regulating pilots and the relief pilot's internal upstream restriction needle valve.
 The abrupt stopping of a pump will generally produce a drop in pressure followed by a high pressure surge The low pressure relief pilot senses this initial drop in pressure and opens allowing the main valve to open in anticipation of the returning high surge.
The open main valve relieves the high pressure surge to atmosphere. The high pressure relief pilot sensing this same high surge also opens to maintain the main valve in the open position.
A hydraulic or mechanical flow control limits the opening of the valve. This device effectively controls the surge relief and ensures the main valve closing without excess waste of system pressure. As this high pressure dissipates and approaches the set point, the high pressure relief pilot regulates to close, the pressure in the upper control chamber begins to increase and the main valve modulates closed allowing system pressure to increase to the preset pressure setting.
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