How to Calculate the Head on a Submersible Pump

Oil in the ground can be hard to reach. Engineers need methods of pumping oil to the surface so they can process it appropriately. Submersible pumps give researchers a way of obtaining oil. The head of a submersible pump tells you how high the liquid can reach through the pump system.

Submersible Pump Head

You'll find submersible pumps lifting fluids from the ground across oil fields as well as from subsea areas. They became popular because they're generally cheaper than dry motors are when installing. You use it by submerging the pump in fluid so that pump cavitation, breaks in the stream of fluid caused by the elevation difference between a pump and a fluid, doesn't occur. The submersible pump's motor is sealed in an air-tight case.

These pumps are generally efficient because they don't need to use as much energy moving water into the pump as other types of pump do. They work through a series of chambers, known as stages, connected to add lift to the pump above the motor at the bottom of the pump. When the motor creates flow in the liquid, it flows from the bottom to the top, and this flow rate is inversely related to the head pressure. Calculating lengths of each stage is pertinent to letting fluid flow.

Pump Head Calculation Example

The submersible pump stage calculation tells you how many stages are required. You find it by dividing the total dynamic head (TDH) by the length of each stage. The TDH is the equal to the sum of the pumping level, head length, drop pipe friction loss and check value friction. The check valve is on top of the stages to let fluid rise to the surface, and drop pipe friction loss is the friction affecting liquids and materials at the top of the pump.

A pump head calculation example can demonstrate this. If you had 200 feet of pumping level, 140 feet of the head of the pump, 4.4 feet of 8-inch drop pipe friction loss and 2.2 feet of check valve friction loss, you would have a TDH of 346.6 feet. The submersible pump stage selection can use this value 346.6 for 125-foot stages to tell you to use three stages to give you sufficient pressure to use this pump.

Other Uses

Submerged motors may be useful in obtaining crude oil from the ground, but they're at a disadvantage compared to other motors in that you can't directly observe them operating. Improvements in motor designs since they were first invented, however, have given these motors more insulation and methods of checking the pump performance to overcome this hindrance.

Electric submersible pump (ESP) systems are useful for wells in the ground that don't have enough pressure in and of themselves to bring liquid to the surface. The electricity of ESP systems lets them increase flow rate for applications involving wells, caissons and flowline risers. The ESP stages are stacked one on top of the other. They use rotating chambers that create a centrifugal force to let fluid rise to the top.

When using ESP systems, you need to pay close attention to gas in the chambers that may interfere with the flow of liquid. Many ESP setups let the gas flow to the top when mining from petroleum reservoirs. Using an appropriate casing head pressure can prevent gas from thwarting the flow of liquid. These types of pumps require high amounts of voltage, and sometimes you may need to use a transformer to ensure an electric power source has enough voltage.

Hydraulic submersible pump (HSP) systems use a turbine downhole pump to take advantage of varying pressure among fluids in bringing substances to the surface. These types of pumps are well-suited for high-suction lift applications for purposes such as sewer bypass. You can also see them being used in the dewatering of mines and gravel pits. They have advantages of being free of suction lines and electricity while functioning even when unattended.