What is a Centrifugal Pump?
A centrifugal pump only has an impeller as a moving part. Impeller is attached to a shaft that is driven by a motor. The other main part of the pump is a diffuser. Impellers are usually made of stainless steel, cast iron, bronze, thermoplastic, or a variety of different materials. A diffuser, also called Volute, houses the impeller and captures the water coming off of the impeller.
Water enters the impeller and is thrown out by centrifugal force created by the motor spinning the shaft and impeller. As the water leaves the eye of the impeller, a low-pressure area is created, causing more fluid to be sucked at the inlet due to atmospheric pressure and centrifugal force. As the water leaves the impeller, velocity is created and collected by diffuser (volute) and converted to pressure by specially designed pathways that direct the flow to the discharge piping system or another impeller in case of a multistage impeller pump system. Each stage further increases the pressure until the fluid exits.
The pressure head of the pump is directly related to impeller diameter, the number of impeller, inlet opening size and the speed of the shaft spinning the impeller. Capacity is determined by the exit width of impeller. All these factors affect the horsepower of the motor. If more water or pressure is needed, higher horsepower motor is required.
It is important to note that centrifugal pump is not a positive acting pump. As the depth to water increases, it pumps less water. Also, when the discharge is against a high pressure, the pump pushes less water. For higher pressure or greater lifts (against a higher pressure), two or more impellers are needed. Sometimes a jet ejector can be added to assist the impellers in raising the pressure.
What pump I need? The two most popular centrifugal pumps are jet pump and submersible pump.
Submersible Pump
A submersible pump or submersible well pump is a multi-stage centrifugal pump. Submersible water pump has advantages over other centrifugal pumps since all stages of the pump and motor are joined and submerged in water. There is no need to recirculate or generate drive water and hence most of the energy goes toward pushing the water rather than fighting the gravity and atmospheric pressure to draw the water.
Impellers of multi-stage submersible pump are mounted on a single shaft and all rotate at the same speed. Each impeller exits water into the inlet of the other through a diffuser. The diffuser slows down the water and converts velocity into pressure. Each impeller and diffuser combo is called a “stage”. Each time the water waters through one impeller-diffuser stage, the pressure is increased.
The pump and motor assembly are lowered into the well below the water level with connected pipes. A submersible pump is always submerged in water and hence no priming is needed. Because the motor and pump are under water, they operate more quietly than above ground pumps. With submersible pumps, pump freezing is not a concern.
Submergible pumps are very commonly used as sump pump. A sump pump is used to remove water in a water-collecting sump basins.
Jet Pumps
Jet pumps are centrifugal pumps. A jet pump requires the inlet piping filled with water to function properly. This is also called priming. Jet pumps are commonly used to pump water out of deep wells. Especially when water levels are gradually lowering, a proper jet package is required for efficient water pumping.
There are two type of jet pump installations.
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Shallow-Well Jet Pump: A shallow-well jet pump has the ejector mounted close to the pump impeller. A jet pump also has a nozzle and venturi at the inlet. The venturi changes the high-speed jet stream to a high pressure for delivery to the pump. The jet nozzle and venturi is also called Ejectors or Ejector Kit. On a shallow-well jet pump, the ejector kit is located at the pump housing, in front of pump impeller. A portion of the suction water is circulated through the ejector with rest going to impeller.
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Deep-Well Jet Pump: A deep-well jet pump has the ejector mounted just above the water level in the well or submerged below the water level. A deep-well jet pump differs from shallow-well jet pump by the location of the ejector kit. In deep-well jet pump, the ejector kit is located at the suction side of the pump. This considerably increases the effective suction lift from 20 ft to as much as 28 ft. However the amount of water delivered to storage tank becomes less as the distance from the pump to water increases.
Jet Pumping Action: See the schematic below to understand how the jet ejector works. Water is supplied under pressure to the jet ejector. The jet ejector, submerged in water, pushes the surrounding water up the column, there by creating a lift. A jet lifts water from the well to the level where the centrifugal pump can finish the lift by suction. Hence a small portion of inlet water is always circulated through ejector kit to create jet action.
A jet pump well has no ability to pump air. It is important to remove the air from suction line when starting the pump. An air leak in the suction line will cause the pump to stop pumping. This is also called losing the prime.
Pressure Tanks
A pressure tank provides means of storing water, initiate pump operation and deliver water to the water-use system. Pressure tank is made of steel and has plastic lining inside. Pressure tank has a rubber diaphragm for smooth operation of tank. A pressure tank can be free standing or an in-line model. Sizes commonly vary from 2 gallon to 119 gallons. Pressure rating is usually up to 100 psi. A pressure tank has 4 stages of operation
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Start up Cycle: In this cycle the rubber diaphragm is pushed completely against the bottom of the chamber. This allows for pump to start operating and suck water.
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Fill Cycle: In this cycle the water is pumped into the water chamber, pushing the diaphragm upwards into air chamber.
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Hold Cycle: When enough water is filled, the tank reached the pump cut off point. The diaphragm is pushed to its upper most position which is usually the cut off point for pump.
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Delivery Cycle: When water is needed, the tank act as an accumulator pushing the stored water to the delivery system with diaphragm pushing the water down. Air pressure in the top chamber also pushes the diaphragm downwards.
Pressure switch is mounted in tank, creating pump initiation and cut off.
Booster Pumps
What is a booster pump: As the name suggest, a booster pump provides pressure or flow boost during low pressure, low flow or during peak demand. In the pressure mode, a booster pumps starts when pressure drops to a pre-determined level. In the flow mode, the booster pump starts and stops by sending the flow. In conservation mode, the booster pump starts during peak demand times.
A booster pump has following typical components.
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Pressure tank: Allows for storage of water
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Pressure gauge: Monitor pressure to trigger pump operation
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Circuit board: Allow for operating logic to be executed
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Digital control: An interface for pressure adjustment and on off pump operation
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Pressure transducer: Constantly monitors system pressure
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Inlet valve: For water inlet
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Electrical Motor: Totally enclosed fan-cooled motor for quiet operation and low power consumption
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Centrifugal Pump: Usually all stainless construction for tough water application.
A Y McDonals’s DuraMAC™ Booster Pumps are one of the most popular booster pumps in United States. Backed by 160 years’ experience, they are widely used in residential, light commercial and commercial applications.
Irrigation Pump & Superbooster Pump
Irrigation Pumps: Irrigation pumps are used to move water from a lower level to a higher level from which the water then flows to the channels to water the irrigation field. Irrigation pump creates the required pressure head so that the water can be sprayed on the field via sprinkler system.
Superbooster Pump: A superbooster pump is a centrifugal pump used for general purpose pumping along with residential, commercial, pressure washing and agricultural purposes. Superbooster pump ranges from ½” through 2” horsepower and with a flow rate ranging from 5 to 25 gpm. AY McDonald’s superbooster pumps offer keyed shaft motor with shaft extension for easy motor replacement. Material is heavy duty corrosion resistant with no-lead brass intake and discharge. Impellers and diffusers are thermoplastic offering corrosion free operation and a long life. Shell and shaft are made of stainless steel with ¾” ceramic/carbon rotary mechanical seal. It has 1 ¼” intake and discharge and a drain plug.
Sump Pump | Sewage Pump | Effluent Pumps
Sump Pump: A sump pump is a centrifugal pump used to drain water from basement of the house. Sump pumps remove water from the basement. A sump is a hole dig in the basement of the house to collect ground water. The sump pit holds water. The pit is also known as basin and holds the sump pump. The sump pump monitors the water level and pumps the water out when it reaches a certain level. The discharge line that is used to move the water out of the house is also called “effluent”. It connects the sump pump to the drainage area.
What are the types of sump pump? There are two main type;
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Submersible Sump Pump: Submersible sum pump contains the pump and motor in one unit and is submerged under water.
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Pedestal Sump Pump: Pedestal sump pump has separate motor and pump. The motor is on a pedestal above the basin and a hose connect the suction line from the basin to where the pump is placed in the pit.
Sump pump battery backup: A battery backup sump pump is a great 2nd line of defense against a flooded basin. If the power goes out during a storm, the primary pedestal or submersible pump won’t operate. A battery backup with a float switch allows the pump to operate when power is out.
Sewage Pump: A sewage pump transfers sewage liquids and solid from the sewage basin or septic system. The sewage includes soft solids to be pumped from a swage basin to a septic tank. A sewage pump is a submerge centrifugal pump. The sewage pump could be automatic or manual. An automatic sewage pump monitors the fluid level in the sewage basin and moves fluids once a certain fluid level is reached.
Effluent Pump: Effluent pump is the most common type of sewage pump. They are designed to pump effluent out of septic system. The effluent is relatively clear liquid because the solids break down in the septic system, leaving effluent. Effluent pump is also called grey-water pump. For raw sewage, you need a sewage pump or a grinder pump to prevent clogging the effluent pump.
Effluent pumps are available in different material housings such as stainless steel, brass. Also common are cast iron and thermoplastic. Thermoplastic effluent pumps hold well against corrosion and they are more affordable. They are easier to install due to their lower weight.
Dewatering Pumps
Dewater pumps are used to remove groundwater from large construction sites, excavation water, water collected during storm or any application that requires water to be removed from the area, on-demand. Dewater pump is usually a horizontal pump, mostly mounted on a skids, and driven by an electric motor. The electric motor can be AC powered or driven by a gasoline engine to provide portability. It generally has a suction and drain line that is connected to suction and discharge hoses. Dewatering pumps are centrifugal pumps and could be single stage or multi-stage.
AY McDonald also offers a mini transfer pump that can handle most domestic and commercial pump applications. It is made of durable cast brass and stainless steel and can be used to empty water heaters, bilge pumping, bait tanks, clogged sinks and other small dewatering applications.
AY McDonald’s Handymac Pump is a powerful and portable pump and can operate on any 12-volt truck or automobile batter. It has a convenient 30 ft cable and very useful in dewater applications for utility companies, contractors and municipalities.
SludgeMaster Pump: AY McDonald offers an air-powered sludge pump that can be hooked up to a compressed air supply and lowered into a manhole or sump basin to remove small trash and sludges. The SludgeMaster has no fuel tank, gas cans, electrical connection, or electric motor to overload. Its high capacity and low head operation meet nearly every emergency or daily use. SludgeMaster pump is used in applications to handle mud, leaves, twigs, sand, sludge, mill-scale, bilge-gunk, sewage, and trash-laden water. It can also handle most substances in a chemical processing, marine, mining, and petrochemical industries.
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