What is a Lift Pump?
A lift pump is any style of pump that lifts a liquid rather than forces it through a system. These pumps are often completely mechanical in their operation; they do not have any internal motors, impellers or governed valve systems. Many of these pumps have partially-sealed chambers that create suction or bent pipe systems that keep a liquid read to siphon. A common example of a lift pump is the style of water pump common on many beaches and campgrounds—they operate totally on suction and physical lift.
Most pumps operate via a motor that forces a liquid forward. When the pump is in operation, the water around the motor moves forward and creates a low-pressure area behind it. The water behind the motor then rushes forward to fill the void, only to be pushed through the system. This creates a flow to the water, but one forcibly maintained by the pump.
Pumps that work on physical lift operate differently. They use one or more natural or mechanical forces to move the water up through a pipe system. These pump systems will often move less water than an impelled system, but they generally take significantly less power and require less maintenance. In addition, they can operate in areas with little infrastructure with no impact on their ability to function.
A force pump is a widely-used lift pump in rural areas of the United States. This style of lift pump may be found in many unpowered homes, campgrounds and hiking trails. A common force pump consists of a below-ground pipe and an above-ground piston and handle. As a person pumps the handle, it creates negative pressure in the pipe and pulls water to the surface.
When the water reaches the surface, it enters the bottom chamber of the piston. A valve on the bottom of piston closes due to the weight of the water, and a valve on the piston itself opens to relieve the pressure when it presses down. This valve allows the water to enter the upper chamber and exit out a spigot on the side of the pump. By this time, more water has entered the bottom chamber, and the process repeats.
A ram pump is a type of lift pump that operates via water pressure alone. A pipe is set at a downward slope to promote natural water flow. When the water in the pipe hits a stopper in the pump, it temporarily increases in pressure. This pressure opens a valve in the pump and a small amount of water flows through before the pressure equalizes and the valve closes. The closing of the valve triggers a restart to the sequence and water is slowly moved through the system.
The whole point of a lift pump is it doesn’t require suction to operate. When a pump sucks up water, it depends on atmospheric pressure to push on the surface of the liquid outside the pump to fill the low pressure area in front of the pump.
There is a limit to how high atmospheric pressure can lift the water. If the lift range is greater than that, the pump will not prime.
Because the lift pump is at or below the surface of the liquid, the piston lifts the liquid. The only limitation is the weight of the liquid above the pump exceeding the power available, or the strength of the components lifting the liquid.
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