A Pump is a device that moves fluids, or sometimes slurries, by mechanical action. Pumps can be classified into three major groups according to the method they use to move the fluid: direct lift, displacement, and gravity pumps.
Types of pumps
The two types of pumps behave very differently regarding pressure head and flow rate:
• The Centrifugal Pump has varying flow depending on the system pressure or head.
• The Positive Displacement Pump has more or less a constant flow regardless of the system pressure or head.
The pump is powered by an electric motor that drives an impeller, or centrifugal pump. The impeller moves water, called drive water, from the well through a narrow orifice, or jet, mounted in the housing in front of the impeller. Its function is to slow down the water and increase the pressure.
Centrifugal pumps are a sub-class of dynamic axisymmetric work-absorbing turbo-machinery. Centrifugal pumps are used to transport fluids by the conversion of rotational kinetic energy to the hydrodynamic energy of the fluid flow. The rotational energy typically comes from an engine or electric motor.
A reciprocating pump is a class of positive-displacement pumps which includes the piston pump, plunger pump and diaphragm pump. In reciprocating pumps, the chamber in which the liquid is trapped, is a stationary cylinder that contains the piston.
Stages in a Pump
A pump that contains different stages within the piping system where force is applied to the water. Each stage consists of one impeller as well as its accompanying diffusion components. The term “multistage” is usually used in reference to centrifugal pumps.
Centrifugal Pump vs. reciprocating Pump
Reciprocating pump works like a positive displacement pump. It is considered that centrifugal pumps are less efficient because they need high maintenance cost as compare to reciprocating pumps. In reciprocating pumps, there is constant flow rate despite of pressure
Specific speed of a Pump
Suction Specific Speed. The Suction Specific Speed of a pump is defined by the following equation, in US units: Click here to enlarge image. Suction specific speed is an index number for a centrifugal pump similar to discharge specific speed and is used to define its suction characteristic.
Efficiency of a Pump
The centrifugal pump converts mechanical energy into hydraulic energy (flow, velocity and pressure), and the AC motor converts electrical energy into mechanical energy. Many medium and larger Centrifugal pumps offer efficiencies of 75 to 93 percent and even the smaller ones usually fall into the 50 to 70 percent range.
Pump Hydraulic Efficiency (%) = Pump Hydraulic Power Output (kW) x 100 / Pump Input Shaft Power (kW). The AUP can be calculated from eletricity bills - it is the total amount charged (in €) in a period (including standing charges) divided by the total number of units used in that period
Parts of a Centrifugal Pump
Some of the most common components found in centrifugal pumps are:
• Pump main housing.
• Impeller seal.
• Impeller bearings.
• Shaft seal
Advantages of a Centrifugal Pump
Centrifugal pumps are fairly simple in nature. They use the kinetic energy of a motor to move liquids. An engine is attached to the axis, which then rotates the pump impeller, which is reminiscent of an old ship's “water wheel”. As with all pumps, there are advantages and disadvantages.
A submersible pump (or sub pump, electric submersible pump (ESP)) is a device which has a hermetically sealed motor close-coupled to the pump body. The whole assembly is submerged in the fluid to be pumped. Submersible pumps push fluid to the surface as opposed to jet pumps having to pull fluids.
Volumetric efficiency of Pump
Volumetric efficiency in a hydraulic pump refers to the percentage of actual fluid flow out of the pump compared to the flow out of the pump without leakage. In other words, if the flow out of a 100cc pump is 92cc (per revolution), then the volumetric efficiency is 92%
An impeller is a rotating component of a centrifugal pump which transfers energy from the motor that drives the pump to the fluid being pumped by accelerating the fluid outwards from the center of rotation.
Head on a pump
In fluid dynamics, Total Dynamic Head (TDH) is the total equivalent height that a fluid is to be pumped, taking into account friction losses in the pipe. TDH = Static Height + Static Lift + Friction Loss. where: Static Height is the maximum height reached by the pipe after the pump (also known as the 'discharge head').
Net Positive Suction Head
Net Positive Suction Head (NPSH) NPSH can be defined as two parts: NPSH Available (NPSHA): The absolute pressure at the suction port of the pump. AND. NPSH Required (NPSHR): The minimum pressure required at the suction port of the pump to keep the pump from cavitating.
A Suction Head exists when the liquid is taken from an open to atmosphere tank where the liquid level is above the centerline of the pump suction, commonly known as a Flooded Suction.
Simply defined, cavitation is the formation of bubbles or cavities in liquid, developed in areas of relatively low pressure around an impeller. The imploding or collapsing of these bubbles trigger intense shockwaves inside the pump, causing significant damage to the impeller and/or the pump housing