The No-Leak MLT bulkhead design

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Bobby_M

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I've been pretty hard on weldless setups and I won't concede on that for metal vessels but if you HAVE to use a weldless setup, this post is for you. Of course, when you're converting a cooler for use as a MLT, you have no choice but to use weldless. This design is similar to all of them with a couple nit-picky details that I think are absolutely important to keeping it from leaking. First, sorry for the big pic...

bulkhead.jpg


1. 1/2" coupling, 1/2" NPT hose barb (for stainless braid designs), or 1/2" male adapter if using manifold.

2. 3/4" SS washers (meant for use with 3/4" bolts so the ID is close to the 1/2" NPT OD. Use enough washers so that the Oring's inside diameter sits on NON THREADED portion of nipple. The washer touching the oring should be slid all the way down to where the threads end and it should stop there.

3. Silicone ORING AS568A Dash Number 314 3/4" ID.

4. Inside wall of the cooler drilled to 7/8" hole.

5. Stainless pipe nipple 1/2" NPT (.84" OD actual)

6. short piece of schedule 40 3/4" PVC pipe, just long enough to reach from the inside wall to the outside wall of the cooler. Slit lengthwise with a hacksaw to stretch over 1/2" nipple.

7. Outside wall of cooler (and insulation) drilled out to 1-1/8" so PVC will fit inside.

8. 3/4" washers (meant for use with 3/4" bolts so the ID is close to the 1/2" NPT OD. Use as many washers as necessary to make up for a slightly "too long" nipple. You may have to dremel out the ID to fit over the unthreaded portion of the nipple or use a slightly larger washer. These don't have to be stainless.

9. 1/2" NPT brass Locknut. Can also get away with an electrical conduit nut for very cheap.

10. 1/2" NPT ball valve.


So why is this a superior design? First, having the inside (and only) Oring sitting on the nipple flat doesn't require any huge buildup of teflon tape to keep liquid from getting past the Oring through the threads. Second, the PVC reinforcement holds the inside wall from caving in and ruining the seal. Third, No Orings used on the outside. Any design that suggests trapping liquid inside the wall of the cooler is flawed. Do you want wort soaking into the insulation if the inner seal fails? If you ever smelled a 2 day old mash, you know the answer.

Discuss...
 
I like it. On one of my conversions I actually cut away the outside of the cooler and insulation for a 3x3" area and made my watertight seal just on the inner wall itself. So I really like that you've taken the compression of the cooler wall out of the equation.
 
Nice design. I just followed your blueprint to make one, I'm at 45 minutes now and no drips. Thanks very much!
 
going to use for my step up to 10 gall batches and famous orange cooler

Is this as simple as Fly Guy's ?
 
conpewter,

how long of a nipple did you use on the conversion where you cut away in the outer shell?

Hmm with that build I actually used the spigot that you'd find on a bottling bucket. I had it sitting around already and the hose I was planning on using for transfer fits on it very nice. I've retired that mash tun for the most part, I bought out a guy getting out of the hobby and got a 10 gal round cooler, it just fits better into my setup.

My next brew will be using both coolers though, I can't fit the grain bill in the 10 gal cooler, this is for a 5 gal batch! :drunk:
 
First, having the inside (and only) Oring sitting on the nipple flat doesn't require any huge buildup of teflon tape to keep liquid from getting past the Oring through the threads.

I'm going to ask what's probably a really stupid question here, but does this statement suggest that no teflon tape is necessary on the inside threads, or just not a ton of it?

I've been trying to get this exact setup not to leak with no success. I'm just trying to eliminate potential points of failure.
 
If it's setup just right, with the oring touching the flat of the nipple and the cooler wall, it shouldn't leak. If the Oring is over any threads at all, it will leak without teflon tape. The only solution there is to pack the threads.
 
Bobby,

This is the same setup I have on my cooler minus the pvc piping. That is an excellent addition and seems to solve the issue of reinforcement for the whole unit. If we explore that area more I bet we could make it even better. What about using a 2"-3" disc of HDPE?

1) Insert it into the wall of the cooler (don't know what the best way would be yet).

2) Use some expanding foam (or something else) to fill in the gaps.

3) Drill out a hole of the appropriate diameter for the piping.

Continue with the rest of the design as laid out.
 
Bobby,

This is the same setup I have on my cooler minus the pvc piping. That is an excellent addition and seems to solve the issue of reinforcement for the whole unit. If we explore that area more I bet we could make it even better. What about using a 2"-3" disc of HDPE?

1) Insert it into the wall of the cooler (don't know what the best way would be yet).

2) Use some expanding foam (or something else) to fill in the gaps.

3) Drill out a hole of the appropriate diameter for the piping.

Continue with the rest of the design as laid out.

I like this design, but the inner wall of the coleman 'xtreme' does seem a little weak for all of the load.

I'm considering cutting a piece out of the bottom, then sliding a spacer up between the walls. I was thinking of using wood because it would be easy to shape. The wood shouldn't get any moisture, but if it did, the bottom would be open to dry out.

Plastic might be a better idea, but it might be easier to shape wood (and maybe conform to any residual insulation on the wall, without creating pressure points).
 
If you use a cooler for an MLT, here's a cheap and easy method that doesn't leak.

Run a tube through a drilled rubber stopper.
Plug the stopper in the hole.
Install an inline valve outside of the cooler.

This is Denny's idea. Look at the "Cooler Detail" section of his page. dennybrew
 
I'd "like something a little snazzier" than Denny's design. :D

I do see one problem with the coleman 'xtreme'. The space between the walls is really thick, and even with a 2" nipple, I don't think I could get the o-ring off the threads & onto the smooth part.

If I spaced it out (#2 washers in diagram), I don't think there would be enough thread outside for the ball valve (which needs a spacer for handle clearance). Maybe it would work with a different ball valve...

Canadian source for nipples longer than 2.5":
https://www.pieco.ca/
 
If you use a cooler for an MLT, here's a cheap and easy method that doesn't leak.

Run a tube through a drilled rubber stopper.
Plug the stopper in the hole.
Install an inline valve outside of the cooler.

This is Denny's idea. Look at the "Cooler Detail" section of his page. dennybrew

After about 10 brews with the coleman cooler extreme, the whole valve area gets flimsy. As Bobby_M has pointed out through his design - something to firm up the walls is needed.
 
Okay, I cut a slot in the bottom of the xtreme & removed the insulation from around the recessed area. {There's not turning back now!}

I think I could wedge a spacer in there, but I'm wondering if it would be better to just fill that whole section with something that'll harden up? Fibre glass resin? (I'm not sure how much it heats up as it sets)? Epoxy resin? Any other options that are considered food safe?
 
I think it would definitely be best to have some sort of an insert to ensure that the surface is flat for the o-ring seal.

The shedule 40 pvc is 26.67 mm OD and 20.42 mm ID. I've got a friend in a machine shop, so I think I'll have something machined a little sturdier (brass or stainless steel?): 35 mm OD; 22 mm ID; 17 mm thickness

The inner wall around the hole is convex (I'm not sure if it was originally, or if that's from me tightening it down & pinching the walls together). A larger disk/insert would only really be supporting a few mm around the hole anyway.

I still think I'll fill the surrounding space with something supportive as well.

Fibreglass resin exothermic as it cures, and I'm afraid that much between plastic might get too hot. It shrinks as it cures form the inside out as well (so it would pull away from the walls).

RTV (room temperature vulcanizing) silicone, with platinum catalyst for an addition cure rather than a condensation cure (since it's deep & sealed), seems to be what I want. I'll need less than 4 oz, but it seems to be sold by the pound ($40 CAD).
 
One option I can think of is polyester resin, aka BONDO which is what auto body shops use to fill dents, etc. You could even just dig out whatever insulation you can via the hole the assembly is going to fit into and fill that new space with bondo or that epoxy stick that has the green skin with white center. The idea is to create a rigid "donut" to hold the inner and outer walls of the cooler apart when you tighten down.

If this is done correctly, there should be no worry about food safe or not because the wort shouldn't touch it.
 
The problem with fibreglass resin is that can generate a lot of heat and it cures from the inside out. So it would shrink away from the walls as it dried. It would also be very permanent.

The RTV silicon is food safe, has minimal shrinkage, and should seal it up as well. But it's pricie.

I've currently got it together with a delrin spacer and no other filler. I figured I could see if it leaked this way... and I may just leave it like this. But man is the 'xtreme' inner wall thin! I didn't use an o-ring, I used a thicker rubber washer from the faucet section to try & spread out the load a little. The inner wall compressed nicely against the inner spacer.

I wouldn't go smaller than 35 mm OD for the spacer. When the cooler is full of water, the inner wall is pushed up against it. It doesn't seem to be bulging around it though.

By the way, 2.5" pipe nipple was a good length. Lock nut with rubber washer on the inside; big stainless washer on the outside with another lock nut. Once you know it all fits, I suggest threading the ball valve on first (before inserting the assembly).

I was hoping to not have any teflon, but the hose adaptor on the ball valve is dripping.
 
I like the additional of the piece of PVC.

Not to piss in the punch bowl, but this design can still leak if the o-ring isn't tightly sealed around the nipple (and once you compress the o-ring, especially if you over compress it, they have a tendency to squeeze out). There isn't anything putting external radial force on the o-ring towards the nipple. So, the design isn't inherently leak-free, even though it may be more leak free than most designs. It's certainly more leak free than the weldless set-up on my HLT. That thing leaks like a sieve.

Perhaps you could add a 3rd washer between the cooler inner wall and the existing stainless washers that would have a slightly smaller ID than the OD of the outside of the o-ring. That way you would have the o-ring completely captive, and compressed on both of the sealing surfaces. It might be overkill, but it would slightly improve the design.
 
The easier improvement on the design is to use a flat silicone washer that fits around the nipple snugly. It won't be squeezed out. The intent of the design was to solve two major problems with the popular designs. Putting the oring over threads. Clamping two thinwall pieces of plastic together with no internal support.
 
I used this design more or less for my MLT. A few brews ago I accidentally dropped my MLT from my two-story deck onto the brick patio below (empty). It still does not leak. ;)
 
The easier improvement on the design is to use a flat silicone washer that fits around the nipple snugly. It won't be squeezed out. The intent of the design was to solve two major problems with the popular designs. Putting the oring over threads. Clamping two thinwall pieces of plastic together with no internal support.

The flat washer is probably better, but I still think leaks are possible with that setup. Unless the gasket is radially compressed, there is leak potential.
 
I agree. Another way to negate the concern is to solder the inside coupling to the washer. In that way, the seal is made between the washer and cooler wall. A little teflon tape on the threads and you're good to go.
 
I agree. Another way to negate the concern is to solder the inside coupling to the washer. In that way, the seal is made between the washer and cooler wall. A little teflon tape on the threads and you're good to go.


Good idea. I like that.
 
Hi there -

I'm probably going to build my MLT this week, and I'm really liking this method, since, as you note, it does seem to avoid some of the basic problems with cooler bulkhead designs. I'm really trying to get everything straight in my head before I build it, so I have a few questions - many apologies if they're kind of basic or newb-y:

1) When you guys are talking about using Bondo or something of that sort between the cooler walls, this would be a substitute for the PVC, right, not in addition to it? i.e. that would firm up the cooler walls even better than the PVC would? My cooler doesn't have a spigot, so I have to drill a hole anyway, so I'm thinking that I might just drill a 7/8" hole, dig out some of the insulation around it, fill the area with Bondo, and install the rest as directed, without needing to drill the outside to 1-1/8".

2) With this design I'm assuming you attach the braid to the hose barb the same way you do with Flyguy's method? i.e. you'd use stainless hose clamps or zip-ties or whatever works for you. Do you recommend putting tubing (with holes cut in it) inside the braid, a la Flyguy, or would you just do without it?

3) Just to be clear, the reason you're not just sealing the nipple to the inside cooler wall with food-grade silicon (which should prevent all leaks) is that you want this bulkhead build to be removable? If one doesn't care about that (i.e. if I'm really only planning on building one MLT for the time being), then would there be any reason why I wouldn't just go ahead and seal it in?

Thanks in advance, and again, apologies if these are basic questions.
 
1. Right, the PVC was one way to firm up the wall to wall gap. Bondo, etc, would do the same thing.

2. You shouldn't have a problem with a plain braid, but I've found the larger diameter ones meant for water heater connections is a little more hefty.

3. I'm not sold on silicone's ability to stick to the HDPE liner of the cooler long term. As recently mentioned, I like the idea of a silicone washer more than an Oring.
 
wow - thanks for the quick response! Ok, I'm building it this week. Will keep posted. Thanks again.
 
Initially I considered just filling the space, but I think using the spacer (with or without filler) is actually a better idea.

The two walls typically aren't parallel (the inner one typically slopes in). The inner wall on the xtreme cooler had a lot of curvature around the factory spigot as well. With a spacer, everything should compress down making the walls perpendicular to the nipple & providing a nice flat surface for the washer to seal.

I guess you could open it up; fill it; and compress it down (to some extent) to get everything lined up as it hardens...
 
3. I'm not sold on silicone's ability to stick to the HDPE liner of the cooler long term. As recently mentioned, I like the idea of a silicone washer more than an Oring.


At least for Igloo coolers, the interior liner is polypropylene. From an adhesive bonding perspective, HDPE and PP are essentially the same, they're both very low surface energy plastics. It's extremely hard to get anything to permanently bond to them.
 
At least for Igloo coolers, the interior liner is polypropylene. From an adhesive bonding perspective, HDPE and PP are essentially the same, they're both very low surface energy plastics. It's extremely hard to get anything to permanently bond to them.

Aquamend epoxy will bond to it. Its the only retail product I found that would.
 
(edit - save some time, I added pics a few posts later)

Hey,

I don't have any pics, but I'll get some taken and post them. Here is how I put mine together for 10 gal Powerade cooler ('cause blue is better), and it hasn't leaked.....

I used a similar design as the OP, but instead of 1 and 10, I used two 1/2" cpvc female adapter which threads right onto the brass nipple.

MH658468.jpg


I took two stainless washers for the inside dremel-ed the hole out so that they would fit snug on the smooth portion of the nipple, and bent (I guess curved) them so that they matched the profile of the cooler. I also found some large rubber washer that fit really snug over the smooth surface and trimmed it to the same size as the stainless washers.

On the outside, I used some washer and the original bushing for the spigot as spacer for the other female adapter to push against before bottoming out in its threads.

I put it together by placing the rubber washer on the smooth part and then the curved wahers so that the first washer is just to the threads. The second washer is there so that the female adapter on the inside hits it before the threads bottom out. Place it through the hole and assemble the outside portion, tightening the outside while holding the curved washers in place on the inside.

I finish the inside off with a small piece of 1/2" cpvc, then a 22* angle, and another small piece of 1/2" cpvc and a water heater stainless braid "finger-locked" onto the 1/2" piece sticking out and clamped with a stainless hose clamp. The 22* fitting serves to get the braid on the bottom and lower the standing water volume left behind to a mere 1/4" or so.

On the outside I used 1/2" cpvc to a 1/2" cpvc ball valve, then a 45*, then some sorta cpvc fitting with female threads and a male brass nipple and braided vinyl tubing attached to it. (I don't remember what I used exactly)

(edit - clicked post not preview) The only thing I am going to do different is cement portions together, as it tends to get a little loose when it all heats up - and things (the ball valve mostly) start to shift when you use it hot and not cemented.
 
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