General hydraulic information
Pumps are machines used to pump and create all kinds of liquids, mechanical mixtures of liquids with solids and colloids and gases. It should be noted that the machines for pumping and pressure generation of gases (gaseous liquids) are separated into separate groups and called fans and compressors and are the subject of special study, so this section is not considered.
Pumps are currently the most common type of machine.
The pumps are divided into pumps according to the principle of operation:
(a) Centrifugal pumps, which are pumped and pressurized by centrifugal forces arising from the rotation of the impeller;
b) Axial (propeller) pumps with a propeller-type impeller as a working organ. Liquid in these pumps moves along the axis of rotation of the wheel;
c) piston and rock pumps in which the liquid moves at reciprocating motion of the piston or rock. To this group it is possible to carry the elementary kind of piston pumps - diaphragm pumps at which rubber or leather diaphragm making reciprocating movements serves as a working body;
d) rams working at the expense of energy of hydraulic shock;
e) jet pumps in which the liquid is transported at the expense of the auxiliary liquid, steam or gas flow energy;
f) ellifts (air water lifts) in which the working body is compressed air.
Depending on the purpose and principle of operation, the design of the pumps varies greatly. Below we consider the design, operating principle, characteristics and application of the main groups of pumps.
Design and principle of operation of reciprocating pumps
A piston pump is a positive displacement machine in which fluid is forced out of a closed pump space as a result of the rectilinear reciprocating motion of the voiding elements. Piston pumps also include plunger pumps. They differ in the design of the displacer and the nature of the seal.
Classification and basic design of reciprocating pumps
Piston pumps are classified according to several main characteristics:
1. According to the nature of the movement of the leading link: direct acting, in which the leading link performs reciprocating motion (steam direct acting); shaft, in which the leading link performs rotational motion (crank, cam).
2. By the number of discharge and suction cycles in one double stroke: single-acting and double-acting.
3. By number of pistons or plungers: single piston, double piston, triple piston and multiple piston.
4. By type of displacers: piston, plunger and diaphragm.
5. By method of actuation: mechanically operated and manual.
Let's consider the most characteristic pump designs:
Differential pumps. Double-acting pumps have one working chamber with suction and pressure valves and a second working chamber without valves. Due to the fact that the pump pumps the liquid twice in a single rotation of the shaft, the flow is evened out.
Double-acting pumps. This pump has a more uniform flow rate than single-acting and differential pumps because there are two working chambers on either side of the cylinder, each with discharge and suction valves. Therefore, the piston pumps the liquid twice in one rotation of the crankshaft. The air cap / connected to the suction port significantly reduces the fluid pulsation during discharge.
Jaw pumps. In single-cylinder pumps, the piston is driven by a cam and returned to its original position by a spring. The cam axis of rotation is offset from its geometric axis by the value of eccentricity. When the cam is rotated, the piston moves in the cylinder in a reciprocating motion on the way s=2e, suction takes place through the valve and fluid injection takes place through valve 2.
The supply in this type of pump is as uneven as in single-acting piston pumps with a connecting rod and crank mechanism. Multi-piston pumps with the number of cylinders r==3-11 in one row and with the phase shift of their working cycles by the angle φ=360°/r are used for the purpose of flow equalization.
The cam piston pumps are capable of producing high pressures. They are used in a variety of hydraulic drives, to pump fluid in hydraulic presses, as well as fuel pumps in diesel engines, which you will learn about in detail when studying cars and tractors.
Pumps with a throughput piston. Pumps of this design are compact: there is no working chamber, the suction valve is in the working cylinder and the pressure valve is in the piston. Pumps with a through piston are used to lift liquids from wells, so they are called submersible.
