The pump shaft in the basement

What is referred to as a pump shaft for a cellar is nothing more than a pump sump. In the pump shaft, the water collects from different "sources" and is then pumped out by a submersible pump. Below you will find out everything that is important in connection with a pump shaft in the basement.

Tasks of a pump shaft

First of all, a distinction has to be made as to why a pump shaft should be installed at all. There are basically two different options:

  • for dewatering the cellar
  • for pumping wastewater in combination with a lifting plant

Draining the basement

Almost throughout the 20th century, the black tub was the usual construction in which a cellar was built. The basement walls are sealed with bitumen. Therefore, the term "black cellar" derives from.

White and black basement sink

Opposite is the white cellar. This is made of WU concrete (water-impermeable concrete) and designed as a tub, so it is absolutely tight. In the meantime, more and more architects and construction consultants are beginning to recommend the white bath as the standard of construction. Nevertheless, some builders still save here (unfortunately at the wrong end).

Especially effective for cellar drainage

In order to dry a cellar or to be able to keep it dry, a pump shaft is created, which is excavated in the basement floor. Water always follows the path of least resistance, which is why it seeps through the pump shaft. If a certain height of the water column is reached, an immersion pump located in the shaft (these are centrifugal pumps - here the function of a centrifugal pump) switches on and pumps off the water.

Pump shaft for a lifting system

Often basements are below the canal level. In addition, there is also the backflow level, which is completely missing in many cellars. That's the amount of sewage in the canal that would be needed to escape at the lowest point in the house.

Extended use of the cellar with lifting system

If the basement is not used appropriately (no washing machine, no toilet, no sink, etc.), the lowest connection point would be on the ground floor. From the channel level to this connection point is the backflow level.

The backflow level

In order to be able to operate sanitary facilities and washing machines in such a cellar, the wastewater above the backflow level must be introduced into the channel. Otherwise it would come under certain conditions (rain, snow melt, etc.) quickly to flooding in the basement.

So the wastewater is "lifted" above the backflow level, which gives the lifting plant its name. But now not so small amounts of water can be pumped out efficiently. Therefore, the wastewater is first collected in a pump shaft. If a certain height of the water column is reached, a float on the pump usually turns it on.

Lifting systems for gray or black water

Now, however, a distinction must be made between lifting systems for black and gray wastewater. Greywater are sewage from washing machine, sink, shower and bath. Black water, on the other hand, is sewage mixed with faeces (and sometimes other solids).

Black water lifting equipment always locked system

Alone for odor reasons, this black water is raised in closed systems. Consequently, the pump shaft is a plastic container which is sealed. For ventilation (depending on the sewage level) an appropriate filter system (activated carbon) is used. In addition, there is also an integrated cutting unit, which shreds all solids to a certain size.

Greywater lifting systems should work in a closed system

For greywater lifting systems, pump wells made of concrete are often considered, as well as for a pump sump for basement drainage. However, there may well be unpleasant odors, which is why we basically recommend a closed lifting system. By the way, here you can find out what can be the cause if the concrete pump sump stinks.

Tips & Tricks

All pump shafts in the house must be laid out so that no external discharges occur, for example from the drainage system.

In addition, some inexperienced architects also advise repeatedly to a pump shaft in a white basement bath, when the basement is lower than the sewer. However, any deviation from a straight surface means angles, etc. This increases the risk of leaking the white tub because the deeper well is not poured in one pass with the bottom plate. When building a new floor slab, you should thoroughly consider whether a pump shaft should actually be installed. There are also systems that raise wastewater above the level of the bottom plate.

The terms black and gray water were introduced in order to be able to name the exact management of such wastewater in a building. With the increasing popularity of domestic sewage treatment plants and the separate collection and separation of urine (ammonia as a valuable raw material for fertilizer), black water is also differentiated into brown and yellow waters.

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