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1. Normal operating head: The pump head determined by the discharge pressure and suction pressure of the pump under normal operating conditions. 2. Maximum required head: The head of the pump when the operating conditions change, resulting in a maximum discharge pressure that may be required (with the suction pressure remaining unchanged). The head of the vane pump used in the chemical industry should be the head required at the maximum flow rate needed in chemical production. 3. Rated head: It is the head of the vane pump at the rated impeller diameter, rated speed, and rated suction and discharge pressures. It is the head that is determined by the pump manufacturer and guaranteed to be achieved, and this head value should be equal to or greater than the head under normal operation. Generally, its value is set to equal the maximum required head. 4. Head at shut-off: The head of the vane pump when its flow rate is zero. For the maximum allowable head of a vane pump, the maximum permissible operating pressure of the pump casing and other pressure-bearing components is generally determined based on the discharge pressure at this head. The pressure difference (head) of a pump is a key characteristic parameter; pump manufacturers should provide, along with the pump, a flow-rate versus pressure difference (head) curve with the pump’s flow rate as the independent variable.