What Is Pump Lift?

An Oil Refinery at Sunset
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Pump lift is the linear vertical measurement that indicates the distance a certain pump can draw a liquid from the intake into the pump body. It is then exposed to the moving parts which will compress the liquid and eject it through the outlet side of the pump.

An Example 

For example; a pump fitted to the top of a tank must be able to perform in the most challenging conditions. In the case of the tank, that's when it's almost empty.

A mostly full tank is easier for the pump to draw from since the liquid in the tank will seek the same level in the intake pipe.

In a mostly empty tank, the pump will have to draw liquid up the full height of the pump intake pipe.

The Physical Properties

The physical properties of materials like viscosity and density can impact the lift performance. Because oil is less dense than water the lift will be greater because of the ratio of weight to volume. Less weight is being lifted by the vacuum the pump creates in the inlet so a less dense material can travel higher with less energy than a denser liquid like water.

The reason a pump cannot deliver fluid to the pump body has to do with the interaction of different liquids with the partial vacuum that the pump is creating in the inlet.

An Experiment

In an experimental display, we would be able to see containers of liquid of various densities. Each container would include a clear vertical tube which has had all matter pumped out (actually impossible) to create a perfect vacuum.

We would see liquids drawn up to a certain height by the pull of the vacuum but gravity would also be pulling the liquid down

Since no pump produces a perfect vacuum in the inlet the maximum pump lift of the same liquids in a real world situation would be reduced because of the inherent inefficiency of the pump mechanism.

The Pump Type

A more efficient pump design can use several techniques to improve lift performance. The pump type has much to do with performance. A piston type pump will always be more efficient than a centrifugal pump since it's a closed chamber design.

In addition to making a closed chamber design, the number of cycles per minute can be increased to allow for the lower capacity of this type of pump. Sealing the moving parts like a piston or impeller against the pump chamber can help prevent leakage and improve efficiency.

Often, the easiest solution is to lower the pump or submerge it in the liquid which is sometimes not practical because of maintenance issues.