How do you add hinges and latches to a metal lid on a concrete water tank?

Steve5

I replaced the heavy concrete lid on my in-ground water tank with a metal plate.

It is screwed down into wall plugs in holes drilled in the concrete top.

After numerous times unscrewing to check water levels, I want to add hinges and latches to make access easier.

Since the top of the concrete water tank is curved like a dome, the metal plate edges don’t contact concrete near the edge when it’s not screwed down. (See yellow lines on the photo)

With 3 hinges on one side and 3 latches on the other side placed near the screw holes, the latches would need to pull the metal lid down like the screws.

I like these strap hinges since they spread out the concrete drill holes.

https://www.bunnings.com.au/pinnacle-100mm-stainless-steel-heavy-duty-strap-hinge_p4150030

A toggle latch seems like the best approach to pull down the metal lid but there’s no give on the concrete lid like a box trailer cage.

https://www.bunnings.com.au/pinnacle-60mm-stainless-steel-adjustable-toggle-latch_p3962537

The existing seal is a 3mm felt strip but I might use a thicker foam or D shape weather strip.

The biggest gap is on the corner closest to the concrete top edge.

Thicker foam or D shape strips would compress so latching does not need as much pressure to bend the metal plate to mate with the dome concrete top.

But then I need to address the additional height difference between the metal lid and the concrete which will depend on how much compression of the D shape weather strip.

The adjustable toggle latch will allow easy adjustment so I’ll probably put these on the side of the metal plate closest to the edge of the concrete top.

The metal lid is about 3mm thick.

The toggle latch and strap hinges come with screws so I can use wall plugs in the concrete but need to use bolts/nuts/washers on the metal lid. 

Stainless rivets might be better since they won’t stick out as much on the bottom of the metal lid.

Stainless steel flat washers can be used to adjust the contact heights on the concrete.

Is there a way to find out what size bolts/nuts/washers would fit the latch and hinges? 

Same question for rivets for latch and hinges.

Now the big question, have I been so focused on hinges and latches that I’ve missed out on a better approach?

Any ideas/thoughts greatly appreciated! 

MitchellMc

Hi @Steve5,

I think the best approach to determine the size of the bolts/nuts/washers and rivets would be to have a helpful team member assist with their selection in-store. I could speculate on what might fit, but due to the application, I think it's best to try a few different options to find the best solution. 

Regarding a better approach, have you considered installing an access port in the lid to check water levels? If you were to cut a 100mm hole in the lid and use Sikaflex 11FC to glue a Holman 100mm PVC DWV Threaded Access Coupling into the hole, a Holman 100mm PVC DWV Threaded Access Cap could be screwed onto it. A couple of rotations of the cap would be all that is needed to secure it, and it could be taken off and put back on far quicker than having to undo all those latches. It would also save the work needed to implement your method above. Combine the access port with a timber depth measuring stick, and you can check water levels conveniently.

Following a similar theme, other smaller inspection outlets would likely work, too, like this Kinetic 100mm Square Clear Out Floor Grate.

Please let me know if you have any questions.

Mitchell