RTV on bulkheads?

[MarsRover]

Hey Folks,

Anyone ever done/considered using RTV sealant with their bulkheads?

I'm talking about putting a small bead-line with the gasket before screwing it down to make darn sure that gasket won't fail?

The reason i'm asking is because i'm doing a custom build, and if my bulk heads fail on my overflow "box" it's going to be a huge PITA to replace without draining the tank.

thanks

 

[bobman]

Nope you do not need anything and to be honest its not a good idea. RTV can leach toxins into your water. If you used something 100% silicone is all you could use which I also dont recommend. Think about this for a second you are going to use silicone on a gasket if the gasket fails wouldnt it still leak? Also once you add chemicals to rubber it can cause the rubber to break down increasing risk of gasket failure. Silicone I dont think would be an issue. However once the bulkhead is properly installed and not messed with again you have very little chance of gasket failure for a long long long time.

 

[MarsRover]

how long is a long long time?

I thought a lot of tank makers use an RTV to make tanks?

 

[KJAG]

No, Momentive RTV does Not leach toxins into a tank, but it's not advisable to use it on bulkheads.

 

[Fin]

Nope, nothing on bulkhead gaskets.

https://www.reef2reef.com/threads/installing-bulkhead-tips.34973/

 

[MarsRover]

What about using RTV INSTEAD of a bulkhead gasket?

I find rubber gaskets to be....concerning. And in my application, it will be possible.......but miserably difficult and complicated to replace the seals should they leak.

 

[AlexG]

The correct RTV such as Momentive RTV 108 is aquariums safe. I will note though that RTV 108 is an adhesive and not just a sealant. I would not apply RTV or silicone to the gasket sealing surface of the bulkhead. In my large build the bulkheads that are not on even surfaces I did put silicone 1 on the thread side of the bulkhead where there is no gasket and then I tightened the bulkhead down with the gasket side held against the tank. If it is a glass or acrylic tank I would not bother with silicone as the gasket alone should be enough for the seal. If your bulkheads start to leak over time or you are worried about leaks I would be concerned about how the plumbing connected to these bulkheads is supported. If you are relying on the bulkhead to support the weight of the plumbing with water in it will greatly increase the chance of a failure on the bulkhead seal.

 

[MarsRover]

@AlexG and others...

I saw your tank build with a PVC bottom. My tank also has a PVC bottom. I will be having sch80 PVC bulkheads threaded both sides.

Instead of bothering with a rubber gasket on the flange-intank side.....why not forgo to gasket and just use PVC glue (really a chemical bond or "weld" rather than an adhesive....) and bind the bulkheads to bottom of the tank? Have a forever bulk head?

 

[KJAG]

Have never associated a bulkhead gasket with any sort of "bother" or inconvenience, but perhaps it exclusively is so in your system, for whatever reason. Most use gaskets because of the vulcanizing phenomenon(highlighted by @AZDesertRat) they achieve, which is just as efficient as a solvent weld and allows for removal if necessary for cleaning/ maintenance etc etc. I would look into what your sheet is made of however as I believe most pvc sheets are UPVC, and I'd research the solvent weld properties of gluing pvc to upvc or whatever the sheet happens to be made of before just gluing it and filling the tank.

 

[MarsRover]

Have never associated a bulkhead gasket with any sort of "bother" or inconvenience, but perhaps it exclusively is so in your system, for whatever reason. Most use gaskets because of the vulcanizing phenomenon(highlighted by @AZDesertRat) they achieve, which is just as efficient as a solvent weld and allows for removal if necessary for cleaning/ maintenance etc etc. I would look into what your sheet is made of however as I believe most pvc sheets are UPVC, and I'd research the solvent weld properties of gluing pvc to upvc or whatever the sheet happens to be made of before just gluing it and filling the tank.

If you go to my build thread you'll see my application.

My concern with the current embodiment I have for my standpipes, the bulkheads won't be accessible without removing pretty much my full intended rock structure (integrated with standpipes) to get at the bulkheads to replace them. This wouldn't require draining.....but it'd probably be easier to drain it at that point vs doing what would be necessisary to replace without draining....

So I'm trying to find a bullet proof solution for bulkheads that will **never** require servicing or repair OR allow access.... I came up with a new solution for access but I'm not thrilled with it yet... will post soon. Just landed

 

[hart24601]

As others have said, I would be concerned that messing with the bulkheads would cause them to be more prone to failure down the road, not less. Since there are not many people who have tired to make a permanent bulkhead in that fashion you will be essentially testing the concept, which considering how hard it will to be replace if there is a failure really isn't a spot I would want to be in.

 

[AlexG]

@AlexG and others...

I saw your tank build with a PVC bottom. My tank also has a PVC bottom. I will be having sch80 PVC bulkheads threaded both sides.

Instead of bothering with a rubber gasket on the flange-intank side.....why not forgo to gasket and just use PVC glue (really a chemical bond or "weld" rather than an adhesive....) and bind the bulkheads to bottom of the tank? Have a forever bulk head?

I looked at your build thread briefly and the main question I have is how is your PVC bottom attached to the tank? I do have PVC lining the bottom of my 720 gallon tank but it is held in with glass RTV & epoxy but I don't consider it water tight. From the pictures I saw in your build thread it appears that the tank is glass if so the actual bottom is glass and PCV is on top I am not sure how the two would be bonded together in a way that will not allow water to get in between the glass and PVC. I am not aware of any reliable means to bond glass to PVC which could be considered water tight. If water does get in between the glass and PVC then there is a possibility of a leak. The bonding of ABS plastic bulkheads to PVC could be done with the correct glue but I am not sure if I would do that because while it might seal better the only option for replacement would involve tearing the entire bottom of the tank out and replacing it. I know that would basically have to tear down/drain the tank now for a replacement but its one less step to take for replacement. The difficulties of replacing bulkheads that are located in the bottom of the tank is the reason I avoid them and prefer bulkheads that are through the side of a tank towards top.

 

[Even Further]

RTV can leach toxins into your water.

RTV is not a specific chemical product. It just means the product cures at room temperature. Silicone can be an RTV type product.

Mars: Consider using a premium high end sch.80 bulkhead. Using a strong heavy duty quality bulkhead, properly installed is your best bet. BTW sch.80 BH requires different hole sizes.

 

[KJAG]

I looked at your build thread briefly and the main question I have is how is your PVC bottom attached to the tank? I do have PVC lining the bottom of my 720 gallon tank but it is held in with glass RTV & epoxy but I don't consider it water tight. From the pictures I saw in your build thread it appears that the tank is glass if so the actual bottom is glass and PCV is on top I am not sure how the two would be bonded together in a way that will not allow water to get in between the glass and PVC. I am not aware of any reliable means to bond glass to PVC which could be considered water tight. If water does get in between the glass and PVC then there is a possibility of a leak. The bonding of ABS plastic bulkheads to PVC could be done with the correct glue but I am not sure if I would do that because while it might seal better the only option for replacement would involve tearing the entire bottom of the tank out and replacing it. I know that would basically have to tear down/drain the tank now for a replacement but its one less step to take for replacement. The difficulties of replacing bulkheads that are located in the bottom of the tank is the reason I avoid them and prefer bulkheads that are through the side of a tank towards top.

This is a valid point. Solvent welding the flange on the bulkhead(if possible at all depending on if the two plastics are compatible, which they may or may not be even if they are both a pvc product) is irrelevant. A bead of silicone sandwiched between two panes of glass (what holds all of our glass tanks together) seems to me at least, to be a different application than simply running a bead around a flat piece of plastic resting on your bottom pane of glass, in that the top edges of the bead are more susceptible to potentially compromising variables such as peeling. Its possible to make it watertight however with enough silicone under the bottom plastic sheet, but its definitely not something I would ever try. I would personally cut the plastic so as to fit around the rock structure, so as to accomodate a standard gasketed bulkhead against the glass.