Principle of Operation of Positive Displacement Pump

This is the operation of simple Positive Displacement Pump is given below.

Principle of Operation of Positive Displacement Pump

All positive displacement pumps operate on the same basic principle. This principle can be most easily demonstrated by considering a reciprocating positive displacement pump consisting of a single reciprocating piston in a cylinder with a single suction port and a single discharge port as shown in Figure. Check valves in the suction and discharge ports allow flow in only one direction.
During the suction stroke, the piston moves to the left, causing the check valve in the suction line between the reservoir and the pump cylinder to open and admit water from the reservoir.During the discharge stroke, the piston moves to the right, seating the check valve in the suction line and opening the check valve in the discharge line. The volume of liquid moved by the pump in one cycle (one suction stroke and one discharge stroke) is equal to the change in the liquid volume of the cylinder as the piston moves from its farthest left position to its farthest right position.

Definition of Positive displacement pump

Pumps are the basic requirement in our day to day life. These are having so much of importance. Pumps field is so good. for every mechanical engineer should have a good idea in Pumps. All the fundamentals of pumps are given below.........

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
1. Reciprocating pumps
2. Rotary pumps
3. Diaphragm pumps

Rotary Liquid Seal ring type Air compressor

Rotary Liquid Seal ring type Air compressor has forward inclined, open impeller, in an oblong cavity filled with liquid. As the impellerrotates, the centrifugal force causes the seal liquid to collect at the outer edge ofthe oblong cavity. Due to the oblong configuration of the compressor case, large longitudinal cells are created and reduced to smaller ones. The suction port is positioned where the longitudinal cells are the largest, and for the discharge port, where they are smallest, thus causing the vapor within the cell to compress as the rotor rotates. The rotary liquid seal compressor is frequently used in specialized applications for the compression of extremely corrosive and exothermic gasses and is commonly used in commercial nuclear plants as a means of establishing initial condenser vacuum.

Rotary Lobe type Air Compressor

Rotary Lobe type Air Compressor has two mating lobe-type rotors mounted in a case. The lobes are gear driven at close clearance, but without metal-to-metal contact. The suction to the unit is located where the cavity made by the lobes is largest. As the lobes rotate, the cavity size is reduced, causingcompression of the vapor within. The compression continues until the discharge port is reached, at which point the vapor exits the compressor at a higher pressure.

Rotary slide vane type Air Compressor

Rotary slide vane type Air Compressor has longitudinal vanes, sliding radially in a slotted rotor mounted eccentrically in a cylinder. The centrifugal force carries the sliding vanes against the cylindrical case with the vanes forming a number of individual longitudinal cells in the eccentric annulus between the case and rotor. The suction port is located where the longitudinal cells are largest. The size of each cell is reduced by the eccentricity of the rotor as the vanes approach the discharge port, thus compressing the air.

Types Rotary Compressors

Rotary Compressors
The rotary compressor is adaptable to direct drive by induction motors or multicylinder gasoline or diesel engines. The units are compact, relatively inexpensive, and require a minimum of operating attention and maintenance. They occupy a fraction of the space and weight of a reciprocating machine of equivalent capacity.
Rotary compressor units are classified into three general groups
Slide vane-type
Lobe-type
Liquid seal ring-type.

Types of Air Compressor

Air compressors of various designs are used widely throughout DOE facilities in numerous applications. Compressed air has numerous uses throughout a facility including the operation of equipment and portable tools.
Three types of designs
1. reciprocating
2. rotary
3. centrifugal air compressors.