From ease of service to efficiency: What are the differences and similarities of dry-installed and wet-installed pumps?

Types of water supply pumps: Comparing apples and pears

Handling different heads, fluctuating water quantities and pipelines that often span several kilometres – supplying the ever-increasing population and agriculture with clean water is one of the key challenges for the future. 

Making sure that water is extracted, transported and treated reliably and efficiently, KSB is at your side with decades of experience and a comprehensive portfolio of high-efficiency pumps. So, what type of pump is suitable for what pumping task?

Let’s look at the differences and similarities of dry-installed and wet-installed pumps and discuss their respective advantages and disadvantages.

Submersible borehole pumps and classic high-pressure pumps differ significantly both in design and in application limits. Both pump types suit very specific applications, performance ranges and ambient conditions. Based on these factors, the decision on what type of pump to use may be obvious in most cases. However, particularly interesting are cases in which factors overlap and, theoretically, either pump type can be used.

Direct comparison of dry-installed pumps and submersible borehole pumps

For our comparison we are using a dry-installed Multitec high-pressure pump and a wet-installed UPA submersible borehole pump from KSB. They are representative of their pump types.

Multitec high-pressure pump: dry-installed and openly accessible

With KSB’s Multitec, a classic dry-installed high-pressure pump, motor and pump casing are freely accessible in the room they are installed in. The motor is practically completely sealed off from the fluid handled and is cooled by the air surrounding it. This type of installation has a number of advantages and disadvantages:

Advantages:

• Vertical, horizontal or angled: highly flexible choice of installation positions.
• Easy to service and maintain as all areas of the pump and all connections are freely accessible.
• Easy to automate and digitalize as the pump can simply be fitted with sensors to monitor the pump operation and enable predictive maintenance.
• Highly efficient operation can be achieved by combining the pump with a synchronous reluctance motor.

Disadvantages:

• Comparatively high noise levels caused by the motor being free-standing in the room rather than being surrounded by the fluid.
• Wear parts requiring regular maintenance at defined intervals.

UPA submersible motor pump: in a pressure shroud, completely surrounded by the fluid handled

Unlike Multitec, UPA has a wet motor. This means the motor is filled with water and designed for permanent use in the fluid handled. Nevertheless, depending on the application, UPA’s benefits can also be made use of in dry installation in the form of a hermetically sealed pump installed in a pressure shroud.

Advantages:

• With its hydrodynamic bearings UPA is completely maintenance-free. When installed in a pressure shroud, it can be used for the same applications as dry-installed pump sets.
• UPA’s shroud connections can be chosen as required. Horizontal or vertical installation is possible, optionally with radial or axial flanges. 
• On the inside, the UPA submersible motor pump runs permanently in water, which means: Flooding of the system will not harm the motor in any way.
• The noise levels are considerably lower, making the pump sets suitable for installation in residential areas, for example.

Disadvantages:

• The pump set’s enclosure makes it hard to access. If in doubt, the pump set will have to be removed from the system.
• The choice of automation and digitalization accessories is smaller than for dry-installed pump sets.

Overview of main differences between UPA and Multitec ©KSB 2021

Multitec 

• Standardized motor
• Rolling element bearing and mechanical seal
• External lift check valve
• Runs in air only
• Motor- or cabinet-mounted FI
• No filter necessary
• Highest efficiencies

UPA 

• Wet motor
• Maintenance-free
• Integrated lift check valve
• Runs in water only
• Cabinet-mounted FI + motor cable
• Output filter recommended
• Highest efficiencies thanks to high-efficiency hydraulic systems and UMA-S high-efficiency motor

UPA and Multitec from the point of view of efficiency and life cycle costs

What about efficiency? Many plant operators are of the opinion that submersible borehole pumps cannot achieve the same efficiencies as dry-installed pumps. This used to be the case for a long time. With new technologies, however, the pumps’ efficiencies are almost even: When looking at the latest generation of high-efficiency pumps, UPA partly surpasses comparable dry-installed type series in a direct comparison.

In this context, a comparison of complete life cycle costs of dry-installed and submersible borehole pumps shows that, with submersible borehole pumps being maintenance-free, energy input makes up the lion's share of costs for this pump type. Without incurring additional servicing and inspection costs for bearings and sealing elements (as are necessary for conventionally installed pumps), wet-installed pumps in a pressure shroud can cut costs by more than 30%.

Submersible borehole pumps and classic dry-installed high-pressure pumps differ considerably in their design. And even though pump sets with wet rotor motors may partly not quite reach the efficiency of dry-installed pumps yet, it is worthwhile having a closer look: Over the entire life cycle, wet-installed pumps in a pressure shroud cut costs by more than 30%. In addition, they are also much quieter, use up less space and are maintenance-free.

Any further questions? KSB will be pleased to provide you with advice and help you plan your wastewater pumping station. Don’t hesitate to contact us.