I am working on design of the column which contains the water tanker and the pump + electronics at the bottom. I have tried different solutions and they failed. I would like to know your advice on this R&D problem with the goal to be able to achieve the the robustness, manufacturing easy process and low cost.

Objective: User put the tube as a column in vertical position. The tube is separated inside in 2 parts by the false bottom. The upper part is used as a water tank. The lower part contains the water pump. The false bottom contains the hole which is used to pass the water from the upper section to the lower section with the help of the pump. The water pipe fitting hose connector is fixed through the hole.

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Requirements: Tube + false bottom

  1. The material of the tube shall be one of the next list: PVC, uPVC, ABS, Acrylic/PMMA, PC/Polycarbonate
  2. The material of the wall separation shall be one of the next list: PVC, uPVC, ABS, Acrylic/PMMA, PC/Polycarbonate
  3. The tube shape shall be cylindrical
  4. The tube shall be separated inside in 2 sections: the upper section to contains the water and used as a water tank the lower section to contains the water pump
  5. The false bottom shall not pass the water from the upper section to the lower
  6. The false bottom thickness shall not exceed 6 mm
  7. The upper tube section shall contain minimum 4 liters of volume
  8. The upper tube section shall contain the water with no leakage
  9. The lower tube section shall contain maximum 1 liter of volume
  10. The lower tube section height shall be maximum 100 mm
  11. The tube diameter shall be >= 110 and <= 150 mm
  12. The tube height shall be >= 400 and <= 700 mm
  13. The tube wall thickness (the difference between outer diameter and inner diameter) shall be >= 2 and <= 6 mm
  14. The false bottom shall be resistant to the weight of 10 kg placed on the wall separation inside the upper section
  15. The false bottom shall be functional after 10 drop tests with different orientations from the height of 1 m

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I have designed this custom plug and 3d printed it with different sealing rings diameters. The problem is that:

  1. It is very difficult to insert the plug with sealing in the PVC pipe (12 cm diameter).
  2. The PVC pipe is not uniform and so the sealing does not works perfectly, so there is a water leakage
  3. This solution doesn't seems to be a good one for production

I am going to search more on:

  1. existing plumbing solutions to separate the water from the dry section
  2. factories if they are able to produce the tube with the inner separation wall
  3. extruded plastic disks which could be fixed to the tube walls by the heater

Do you know any existing plumbing solutions or could you advice me something to solve this problem in the most efficient manner?

Note: The solution with a silicone sealing is acceptable for a prototype but not the good one for production

  • $\begingroup$ Have you considered altering the design of the plug two or three O-rings, separated from each other vertically by 3 to 5 mm? The aim of that would be to successively reduce the amount of water leaking down. The other option, & I don't know if such an O-ring exists, but if an O-ring or rings could be inserted highly compressed state & then released when in place. Such an O-ring would exert more force against the wall of the tube creating a better seal. $\endgroup$
    – Fred
    May 31, 2020 at 1:07
  • $\begingroup$ Use a standard end cap drilled to accept the pump outlet and power supply and a waterproof pump. $\endgroup$
    – Solar Mike
    May 31, 2020 at 6:17
  • $\begingroup$ That's not a wall, that's a false bottom. wall noun an upright side of a building or room. $\endgroup$
    – Transistor
    May 31, 2020 at 18:53
  • $\begingroup$ Consider adding at least one more leg to the base insert. That way it can be guaranteed to be level when inserted. The two-leg version may tilt. $\endgroup$
    – Transistor
    May 31, 2020 at 18:58
  • $\begingroup$ @Fred, that's a good point to use a few seal rings. I noticed it is widely used in industry. I tried but with no success thank you for your advice on releasing compressed sealing. I will check it out. Someone advised to use a seal ring between 2 "disks" which could be compressed together with a screw. It will work for sure but I am not attracted by the components quantity and the assembly process. May be I am wrong to think so $\endgroup$
    – AnSLEX
    Jun 1, 2020 at 0:28

2 Answers 2


Consider the use of a double-lip seal.

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Figure 1. A double-lipped seal in the false base of the tube.

This can then be inserted from the top of the tube to take advantage of the tapered edge. It seems to me that increasing the pressure in the top side will increase the seal tightness but check with someone that uses these things. (I'm an electrical engineer.) w enter image description here

Figure 2. Having three legs will simplify horizontal alignment of the base.

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Figure 3. Doing it this way avoids the internal seal problem completely.

With the arrangement of Figure 3 the assembly, sealing and inspection becomes much simpler. With PVC, for example, a solvent can be used to fuse the plastics. This used to be quite common on plumbing waste pipes, for example. In addition, if it does leak it's visible and external to the electronics. I would consider dipping the end of the pipe into a flat-bottomed container of solvent at the right depth just prior to assembly. There is a fire risk and solvent risk here so you require ventilation and a flame-proof dispenser.

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Figure 4. A bench can with spring loaded flame arrester plate. Image: JustRite.

Read the description in the linked article for details.

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Figure 5. This design while it makes the two parts visible has the aesthetic advantage that there is no step in the outline. The disadvantage is increased difficulty in solvent bonding.

  • $\begingroup$ That's awesome! Thank you, I will try it immediately as I have few meters of double-lipped seal. Thank you for your time and design of this example And I recognized you. I used to resolve different electronics problem few years ago with the help of your responses to questions of other persons $\endgroup$
    – AnSLEX
    Jun 1, 2020 at 0:17
  • $\begingroup$ Thanks. See the update. $\endgroup$
    – Transistor
    Jun 1, 2020 at 2:25

For such a small vessel containing only water : A submersible pump would seem to solve all your problems. There are hundreds to choose from depending on capacity. These pumps start pricing around $ 10 ( US) last I looked . Search aquarium ,pond, or fountain pumps on the net ,( I often find what I want at "Big Als" - Canada).

  • $\begingroup$ Thank you! That's a great solution to manage the classic water distribution. My first prototype was based on submersible 5v pump which is very impressive by it's water flow. In my case I have a bunch of electronics to hide somewhere and to manage the water flow in different directions. Another goal is to leave an access from the top of the tube so user is able to fill it and to wash sometimes the tube with an easy access. So electronics and an access are the actual reason to hide all the staff in the bottom part of the "structure" In any way thank you for your suggestion ! $\endgroup$
    – AnSLEX
    Jun 1, 2020 at 0:10

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