There are different types of piston pumps (reciprocating piston pumps):
the submersible piston pump, also called plunger pump,
the disc piston pump and
the diaphragm pump.
By asynchronously opening and closing the inlet respective outlet of the pump chamber, the fluid will moved in the pump chamber and then pressed to the discharge side.
Reciprocating pumps are generally used for applications that require relatively low flows and high pressures. Since each cylinder delivers a definite volume of liquid to the system, these pumps are also applicable for dosing and metering tasks. The disadvantage against rotating pumps is the pulsating operation.
Liquid pumps are divided into centrifugal pumps and positive displacement pumps according to their operating principle. There are also special designs such as jet or mammoth pumps.
A single-start conveying spindle rotates in a double-start worm housing made of elastic plastic.
The eccentrically rotating screw conveyor conveys the medium in the free screw channel of the housing from the suction side to the discharge side in a continuous flow.
Eccentric screw pumps are particularly suitable for the transport of highly viscous fluids, mushy, slurry or paste-like media. Like screw pumps, they are suitable for highest viscosities where the use of centrifugal pumps is not possible.
In building services, especially for pumps for heating and air-conditioning technology, the classification of the pump design according to the sealing (wetting of the motor) is widespread:
Design
Description
Glandless Pump
Glandless pump with canned rotor motor
Glanded Pump
Centrifugal pump with shaft seal
In addition, the subdivision according to the type of installation or the arrangement of the drive is common:
Monobloc with flange-mounted motor
DIN-standards with motor and coupling on common baseplate
The required shaft power of the pump is given as a performance curve depending on the flow rate. The performance curve changes when the speed of the pump changes in accordance with the affinity laws.
The shaft power of the pump is directly proportional to the density of the pumped medium. In the case of highly viscous media, the shaft power also depends on the viscosity.
Depending on the application and size of the pump, the drive is designed so that the motor power is either greater than or equal to the viscosity of the pumped medium.
the shaft power at the operating point or
the maximum power of the characteristic curve,
in each case plus a security surcharge of at least 5%.
The required safety margin depends on the required engine power. While the safety margin is reduced to up to 5% for larger motors, surcharges of over 20% are applied for smaller power values. In addition, the nominal motor power for standard motors must be converted to the ambient conditions.
P2 is used as the symbol for the shaft power.
Newtonian fluids, at laminar flow, create shear tension and pressure super-imposed normal tensions which are proportional to the deformation velocity, the proportionality factor being the absolute viscosity.
The kinematic viscosity is defined as:
The viscosity depends on temperature and pressure, whereby pressure dependency of fluids is of negligibly small characteristics.
Viscosity of non-Newtonian fluids can moreover be time-related (thixotropic or rheopexic flow characteristics); its characteristics then becoming undefined.
The viscosity of a medium has an influence on both the system curve and the pump performance curve. For centrifugal pumps, the pump curves are converted in practice at a kinematic viscosity of more than 10 mm²/s.
Increasing the available static pressure at the pump location (positioning the pump at a lower level, e.g. from a roof plant room into the basement to benefit from the increased static head from the higher water column. The pump performance remains unchanged).
Lowering the fluid temperature (reducing the vapour pressure pD).
Changing the pump characteristics (reducing the driven speed and/or different pump design with a lesser Pump NPSHrequired).
In a narrower sense, in contrast to blowers and compressors for gases and compressible media, pumps for incompressible media are referred to as liquid pumps. This means that the volume of the fluid remains approximately constant as the pressure increases. In practice, this also includes liquid mixtures with a low solid or gas content.
Depending on the direction of the energy flow, pumps belong to the working machines.
nsync = synchronous speed
f = frequency of the 3-phase power supply
p = number of pole pairs of the 3-phase motor
Kindly note that the above noted relation results in revs per second if the frequency unit is Hz.
Pole pair numbers
1
2
3
4
5
6
Synchronous speed (at 50 Hz) n [rpm]
3000
1500
1000
750
600
500
Synchronous speed (at 60 Hz) n [rpm]
3600
1800
1200
900
720
600
The rated full-load speed of three phase asynchronous motors is, due to slip, a few percent below the synchronous speed.
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The kinematic viscosity is defined as:
The viscosity depends on temperature and pressure, whereby pressure dependency of fluids is of negligibly small characteristics.
Viscosity of non-Newtonian fluids can moreover be time-related (thixotropic or rheopexic flow characteristics); its characteristics then becoming undefined.
The viscosity of a medium has an influence on both the system curve and the pump performance curve. For centrifugal pumps, the pump curves are converted in practice at a kinematic viscosity of more than 10 mm²/s. 
nsync = synchronous speed
f = frequency of the 3-phase power supply
p = number of pole pairs of the 3-phase motor
Kindly note that the above noted relation results in revs per second if the frequency unit is Hz.