Project/Floodprotection
The aim of this project is to provide for a backup plan to take care of back flowing water entering through the sink in front of the emergency door in case the backflow valve fails, and also to pump away water entering through the ground into the 'beer cellar'.
This seems warranted since the problem at the source (backflow) may be unlikely to be fixed.
There's also a need for signalling and alarm/loudspeaker for people if they open the emergency door without authorization (Jasper asked for this). This can be handled on the same Raspberry Pi, hence some of the cost/effort can be shared between both projects/needs.
Concept
There are two places where water needs to be taken care of:
1. beer cellar: water entering through the ground, around the pipe from the sink. This water will come in regardless whether the backflow valve works correctly or not, and may always need to be taken care of somehow (until the source of the backflow and hence pressure on the earth will be fixed). The project uses one pump in this location in any case. Since there's not much water entering here, the small water tank already placed in there will be enough.
2. water back flow through the sink outside the emergency exit, in case the backflow valve that's now installed fails. There are two possible variants here:
Variant A: use another pump, installed below lowest step (on the side, at the wall), that pumps away the upcoming water up the wall above exit level (and a bit away from it).
Variant B: build a 10-15 mm rim from cement/sand mixture onto the platform inside the emergency door (top of the metal stairs), with a pipe embedded in it on one side, that prevents the water from flowing down the metal stairs and instead leads it into the pipe, which flows passively into a water container below the metal stairs. The kind of big water tank that Michael Trew bought for aquaponics costs around £20.
Cost / parts list
Here's the parts list with total cost for the variants A and B:
https://docs.google.com/spreadsheets/d/1A-07MvKJ07HHbb_wZoG6hT2__b73fu_lVZC-iFNi-94/edit?usp=sharing
Variant A seems to be the better idea: it is a bit cheaper, actually pumps away the water, hence is not limited by tank size and will work repeatedly without effort, seems more fool proof with regards to removing the water, and can be removed again without issue. Only *possible* issue might be stern interpretation of fire safety rules (obstruction of emergency exit, but the pump is small and mounting it under a sheet of metal should make it unproblematic).
Variant B should be even less worrisome with regards to obstruction of the emergency exit, and has an advantage in that the water collection is purely passive, but might bypass the intended path (overflow of the rim/dam, etc.), and the built-up rim/dam will probably be hard to remove and will remain when leaving the space. It's probably also more work. And it uses up the space below the metal stairs.
For this reason we prefer variant A.
Currently there's no backup power planned. A 12 V SLA battery, with some circuitry or a commercial charge controller plus a step-down to 5V for the Raspberry Pi, could easily be added to power Raspberry Pi and pumps in case power goes out in a storm. Perhaps someone donates these at some point?
