Sealing an underground lift

Most of our underground lifts are used outdoors. Therefore, we often receive the question: How can water ingress into the shaft be prevented, eliminating the need for pumping it out of the pit?

This is not an easy problem to solve ...

Challenges with outdoor lift tables

All lift tables used outdoors face the same challenge: They must be protected from weather conditions. Therefore, our standard includes IP65-rated electrical components and hot-dip galvanisation for outdoor installations.

When the system is installed in a shaft or pit, an additional challenge arises: rain and snow can enter and must be pumped out from the pit floor. Since the underground lift is typically used to transport goods from the basement to street level, the pit floor is usually about one meter below the basement floor. Thus, natural drainage is not possible. A pump must be provided for meltwater and rain. Besides the ongoing costs for the pump, there is a risk that the pump could fail and the shaft could fill with water.

Can water ingress be completely prevented?

The goal is clear: No water should enter the shaft. Let’s be upfront: This goal is not achievable.

To ensure smooth operation, a gap is required between the platform and the surrounding shaft, through which water can enter. Therefore, a pump is absolutely necessary. However, measures can be taken to minimize the workload of this pump ...

Protective measures for underground lifts

Rubber sealing

We frequently receive the suggestion to install a rubber seal on the canopy to completely prevent water ingress. While this is a good idea in theory, it has not proven effective in practice.

Since the underground lift is located outdoors, it is exposed not only to rain but also to sub-zero temperatures. Unfortunately, rubber seals tend to freeze at low temperatures, causing them to tear during the next lift operation.

This could be prevented if the seal is regularly lubricated with Vaseline® during winter. However, this task is often forgotten in the hectic daily routine, meaning the water protection does not survive the first winter.

Canopy with overhanging tear plate

In its simplest form, the canopy has no surrounding edge, meaning no customer-supplied paving can be applied. Instead, the roof ends with a tear plate placed over the shaft opening.

This design allows for a simple reduction of water ingress. The following combination needs to be selected:

  • a canopy sheet larger than the actual shaft opening,
  • an outdoor area that slopes slightly toward the shaft and
  • a surrounding rain gutter around the actual canopy lift.

The slightly oversized lid covers the entire shaft opening, preventing rain from entering through any remaining gap. However, standing water remains a problem. Therefore, the outdoor area must be designed accordingly. A slightly sloping terrain can effectively direct the water flow, and the remaining water is subsequently drained through a sufficiently sized rain gutter.

Despite its aesthetic appeal, this solution has a drawback. Since the canopy's tear plate rests on the shaft, a tripping edge of 6 to 10 mm height is created. If the canopy is in a highly frequented area, this can become a tripping hazard.

If a flush solution is desired, a resting surface similar to an underground lift with a paved surface should be created.

Pit edge protection with integrated rain gutter

Often, the lid of an underground lift is designed to be inconspicuous. Therefore, a version that allows for the application of customer-supplied paving is chosen. In the lowered position, only the edging of the canopy and the shaft opening are visible, closely aligning with the ideal of an "invisible" helper for goods transport.

However, this better aesthetics come with more complex protection against water ingress. Let's assume an 8 cm thick paving is planned. The canopy would then be approximately 10-11 cm thick (8 cm paving + granulate layer + canopy sheet thickness). To ensure the canopy is driveable and no tripping edge is created, a resting surface for the canopy must be created within the shaft head. This means the canopy rests on the shaft in the lowered position, creating a flush surface through appropriate recess selection.

Sealing the paved surface 

To prevent the canopy from filling with water, a waterproof sealing of the paved surface is necessary. This way, water does not run over the canopy into the shaft but is directed to the edge of the canopy.

The integrated rain gutter 

For technical reasons, a gap must be present between the actual canopy and the surrounding yard area. Through this gap, water from the yard and the canopy surface runs into the shaft. While water ingress from the yard can be minimized by sloping terrain and a pre-installed rain gutter, the water cannot be entirely drained. Additionally, rain that falls directly on the canopy of the underground lift remains.

Therefore, we recommend integrating a rain gutter into the resting surface for the canopy. Before the actual installation of the underground lift, a pit edge protection with a rain gutter is installed. Although some water will run into the gap between the canopy and the yard surface, it will be immediately drained by the integrated rain gutter and will not reach the shaft pit, where it would need to be pumped out laboriously.

The remaining problem area 

Unfortunately, the solution with the integrated rain gutter can only be implemented on three sides. If a similar resting surface for the canopy were created at the loading edge, a gap approximately 10 cm wide and 10 cm deep would be formed between the yard surface and the platform of the hydraulic lift when raised. Such a gap would be impassable for most transport means. The wheel of a pallet jack, grid box or hand lift truck would get stuck, making loading and unloading impractical.

One solution could be to bridge the resulting gap with crossover plates. However, practice shows that this is not very popular with users due to the additional steps required, and thus, a larger gap should be avoided. For the loading side, we recommend reducing water ingress through appropriately sloped terrain and a pre-installed rain gutter. Any remaining water that enters the shaft is pumped out from the pit floor.

Conclusion

The protection of the shaft from water ingress begins with the appropriate design of the yard area. A significant amount of water can be diverted if the yard is designed with a slight slope and a rain gutter is placed in front of the actual underground lift.

However, there is no 100% protection against water ingress. Therefore, a drainage solution must be provided in the shaft pit for every underground lift.



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