How to choose a multistage submersible pump for a 4" well

A 4-inch multistage submersible pump is used to draw clean water from a well with a 4" casing (about 100 mm), for domestic, irrigation or civil use. Choose it by looking at how much water you need and from what depth it has to rise, not just the power. All the pumps in the collection have IP68 protection and continuous duty and are suited to working fully submerged at all times.

The types

• Multistage 4" ST series. Models such as ST 10, ST 13, ST 35, ST 40 and ST 55. The number indicates the pump size.
• Multistage well pumps, SP series. For example the SP 90. They have an outer jacket and shaft in AISI 304 stainless steel and a cast iron top bracket.
• Multistage SUB-Inox and SUB-Plastic. These are two distinct versions, SUB-Inox and SUB-Plastic, with stainless steel or plastic parts, as their names say. Ask which parts are used in each.

How to choose by job

Before choosing, gather three numbers: the depth at which the water stands with the pump running, the height difference up to the point of use and the flow rate you need. Adding depth and height difference (plus a margin for pipe losses) gives you the minimum head. That is what makes you choose a model with more stages.

The features to look at

• Flow rate and head. These are the two quantities that decide the pump: the first is how much water you need per minute, the second how high it has to go. In the collection's data they are not given for every model: ask for them for the one you are interested in.
• IP68 protection. It means the motor and cable withstand continuous submersion.
• Continuous duty. The pump can work for long periods without breaks, useful for irrigation and for systems that stay on for hours.
• Insulation class. The data include class F and class B; F withstands higher motor temperatures.
• Materials. Motor shaft and outer jacket in AISI 304 stainless steel, top bracket in cast iron or galvanised cast iron, mechanical seal in ceramic and graphite. Stainless steel resists rust better.
• Configuration. The motor is submerged in an oil bath, which lubricates and cools.
• Delivery outlet. The figure is 1" 1/4: the delivery pipe must have a compatible connection.

Common mistakes

• Using the pump with sandy water. It is made for clean water; sand wears out the impellers.
• Resting it on the bottom of the well. It must be suspended on a safety rope, below the minimum water level but lifted off the bottom.
• Choosing only by kW. What counts are the flow rate and head the well requires.
• Forgetting dry-running protection. If the well runs dry, the pump is ruined in a short time.
• Splicing the cable without a watertight seal. Water gets into the cable and damages the motor.
• Lowering the pump without checking the water level. If the level drops below the pump, it runs dry; if it sits too close to the bottom, you risk drawing in mud.

Frequently asked questions

How wide does the well need to be?

This pump needs a 4-inch casing (DN 100 mm). If the well is narrower, the pump will not fit.

Can I use it for dirty water or water with mud?

No, it is designed for clean water without sand. Other pumps are needed for water carrying solids.

Who connects it to the mains?

A qualified electrician, with a control panel and dry-running protection.

Stainless steel or plastic?

Stainless steel resists corrosion better. The choice depends on water quality and use: ask which parts are stainless steel and which are plastic in the model you are interested in.

What is the difference between class F and class B insulation?

The class indicates the maximum temperature the motor windings can withstand; F withstands higher temperatures than B. If the pump runs for long periods or the water is warm, class F is better.

You can see all the models in the multistage 4" collection: to choose the right one for your well, ask the AMES technicians for a quote or for advice.