Closing the flood gates

With the increased occurrence of flash floods in the UK – 2023 experienced the wettest March on record for 40 years – plumbing and heating installers are being urged to prepare for sump pump projects.

In April last year, the government launched the Frequently Flooded Allowance (FFA) scheme: funding for frequently flooded communities. The FFA scheme made £100m available to aid communities where 10 or more properties have flooded twice or more over the last decade. This is expected to prompt greater interest in sump pump installations throughout Great Britain.

Caroline Douglass, executive director for flood and coastal risk management at the Environment Agency, said: “Increased flooding is just one of the impacts of climate change we are seeing in the UK and around the world. The funding will help better protect homes and businesses at risk from repeated flood incidents across the country.”

Given the projected rise in instances of flash floods, it’s critical that installers upskill on sump pump installations and seek the right products and guidance to ensure they can help homeowners.

According to Wilo, many sump pumps are used incorrectly, being placed in loose ground, which can fill up quickly with debris – causing them to clog up. Additionally, low-cost solutions, with motors that aren’t rated consistently, can prove to be a false economy, as they will overheat and fail much faster than if rated regularly.

“Installers can expect to see more sump pump enquiries and projects coming through because of these changes, so it is critical that they know how to complete these jobs, ensure they perform when required, and are future-proofed,” says Andy Thompson, national sales manager at Wilo UK.

First defence

Generally, sump pumps or wastewater pumps are used to alleviate flooding in the first instance, lifting (slightly) dirty water from a lower level to higher up; to transport water from one place to another, or to prevent backflow.

Sump pumps have various applications, including basement waterproofing, flood prevention, backflow protection, stormwater management, as a tool to dewater swimming pools and ponds, or for emergency water removal from flooded areas or basements.

“Sump pumps play a crucial role in safeguarding homes from water damage by efficiently managing excess water in basements or underfloor space,” explains Neal Saunders, sales director DBS (Domestic Building Services) at Grundfos. “Heavy rainfall can’t be stopped, so the collection and removal needs to be managed.

“Even if there is a quite effective rainwater system there might still be a risk of backflow from sewer mains if those are overloaded or blocked. Investment of a certain level in buildings or its equipment is worth it.”

Grundfos says most homes will just need a one-pump system

Inner workings

A sump pit, also known as a sump basin, is dug or installed in the lowest part of the basement or underfloor space. It collects water that may enter the space due to rainfall, drainage, or other sources. Sump pumps remove excess water from a sump pit or basin to prevent flooding or water damage in basements or underfloor spaces.

“Sump pumps aren’t necessarily complicated to install, but there are a few things to bear in mind, such as the installation method, the pump’s build and motor, flow rates and accessories,” says Thompson. “Instead of placing pumps directly in the ground, a good sump pump installation should have a sump that is lined with cement, or better still, have channel drains around the perimeter of the cellar. These drains then lead to a little plastic sump tank in which the pump is then fitted. Doing this helps stop dirt building up around pumps that could cause them to fail.”

Grundfos recommends opting for tanks with integrated pumps and controllers, which offer quick installations and great protection against odours. Installers need to specify the correct type as there are different lifting stations available for sanitary appliances and black and grey water, for example.

“Sump pumps typically use a float switch to control the pump’s operation,” explains Saunders. “As the water level in the sump pit rises, the float switch is lifted. This is the simplest way of automatic operation. In double pump solutions a controller is required to switch between the two pumps after each operation, to change over in case of failure and to activate parallel operation in terms of high peak inflow to the sump.

“When the float switch or sensor reaches a predetermined level, it activates the pump. This ensures the pump starts working as soon as water levels reach a critical point. And when the water level decreases, the pump will be switched off by the float or sensor.

“Activated pumps use a rotating component with blades, called an impeller, to draw water into the pump housing. The hydraulic is characterised on all wastewater pumps with a free passage of a certain size to fit the application. It is often protected by strainers to avoid blockages caused by bigger particles. As the impeller rotates, it pressurises and expels the water through a discharge pipe or hose. The water is then directed away from the building to a safe drainage area, preventing it from re-entering the basement or underfloor space.”

Choosing the right pump for the type of wastewater is critical

Fit for purpose

According to Grundfos, there are several key considerations specifying sump pumps for installation:

  • Local building codes and regulations: Familiarise yourself with local building codes and regulations related to sump pump installations. Compliance with these codes ensures that the installation meets safety and legal requirements. Specifying the right sump pump for the unique conditions of the building will ensure the best performance and long-term reliability.
  • Type of wastewater: In situations where there is drainage from groundwater around the building or greywater, installers can choose pumps with a free passage of 10-20mm because the particle sizes can be considered as small. For applications with higher volumes, pumps with bigger free passage will be more suitable. Inside surface water from rainfall can flush bigger particles or leaves from trees into drainage pipes and sumps, so pumps with a free passage from 35 to 50mm should be chosen to avoid blockages. High temperatures or corrosion risks, such as pumping brackish (salty) water, need to be considered when specifying a pump type.
  • Water volume and flow rate: Assess the potential volume of water that may enter the sump pit during heavy rainfall or flooding. Choosing a pump that can handle the expected water volume is crucial for effective water removal. Typical sump pumps for collecting some greywater drainage purposes are able to deal with up to 14 m³/h. When sizing wastewater pumps, consider the minimum flow rate in combination with the chosen discharge pipe. There are particles in the wastewater that need to be transported without settling due to low flow. The minimum flow velocity should be 0,7m/s, otherwise the particles tend to settle down in the pipe, which can cause blockages over time.
  • Pump head (lift height): Consider the vertical distance the pump needs to lift water to discharge it safely away from the building. It’s essential to choose a pump that can handle the required lift. The volume that needs to be pumped will impact the height and length of pipe needed.
  • Sump or tank size: The sump size or the tank size must fit to the pump type and its level detection. Float switches must operate freely for a reliable operation. The size and setting of start and stop level must also fit the maximum water inflow parameters. Too much inflow to a small sump or to a pump with relatively small on/off setting will end up in too high starts or stops and the pump will heat up.
  • Power supply and voltage: Verify the available power supply and voltage in the building. It’s important to select a pump that aligns with the electrical specifications of the building to ensure proper functionality.
  • Back-up systems: Consider whether a back-up system is needed for added reliability. Usually, domestic installations need just one pump, but depending on the risk of a flood, it’s worth considering a double pump solution with 100% redundancy. A controller makes sure that both pumps operate by switching over after each pump cycle (start/stop) and switch over in case one pump fails.
  • Maintenance and accessibility: Considering the accessibility of the pump for ease of maintenance is important for long-term functionality. One-pump systems should be checked at least once a year. Larger residential properties should be checked twice a year and commercial or industrial settings up to four times a year.
  • Warranty and support: Verify the warranty offered and the availability of customer support services. A reliable warranty and accessible support can provide peace of mind to both installers and end-users.

“There are many cheap garden pumps on the market, and the danger is that unwitting installers will choose these for a sump pump application,” warns Thompson. “By picking the right pump and installation method, installers can not only aid the fight against flooding, but also help property owners save time and expense in the long run.”

• For more information, members can download the CIPHE’s free Plumbing Engineering Services Design Guide

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