POSITIVE DISPLACEMENT PUMPS

POSITIVE DISPLACEMENT PUMPS DOE-HDBK-1018/1-93 Pumps POSITIVE DISPLACEMENT PUMPS Positive displacement pumps operate on a different principle than centrifugal pumps. Positive displacement pumps physically entrap a quantity of liquid at the suction of the pump and push that quantity out the discharge of the pump. EO 2.1 STATE the difference between the flow characteristics of centrifugal and positive displacement pumps. EO 2.2 Given a simplified drawing of a positive displacement pump, CLASSIFY the pump as one of the following: a. Reciprocating piston pump b. Gear-type rotary pump c. Screw-type rotary pump d. Lobe-type rotary pump e. Moving vane pump f. Diaphragm pump EO 2.3 EXPLAIN the importance of viscosity as it relates to the operation of a reciprocating positive displacement pump. EO 2.4 DESCRIBE the characteristic curve for a positive displacement pump. EO 2.5 DEFINE the term slippage. EO 2.6 STATE how positive displacement pumps are protected against overpressurization. Introduction A positive displacement pump is one in which a definite volume of liquid is delivered for each cycle of pump operation. This volume is constant regardless of the resistance to flow offered by the system the pump is in, provided the capacity of the power unit driving the pump or pump component strength limits are not exceeded. The positive displacement pump delivers liquid in separate volumes with no delivery in between, although a pump having several chambers may have an overlapping delivery among individual chambers, which minimizes this effect. The positive displacement pump differs from centrifugal pumps, which deliver a continuous flow for any given pump speed and discharge resistance. Positive displacement pumps can be grouped into three basic categories based on their design and operation. The three groups are reciprocating pumps, rotary pumps, and diaphragm pumps. ME-03 Rev. 0 Page 18