Looking for help building a seltzer system

[ChickenRob]

Hi, I've scoured the web, searched the forum, talked to retailers, emailed suppliers, and I still can't seem to get the information I need to build the system I want.

Goals: to dispense continuous seltzer and chilled filtered flat water from a tap head in my kitchen on the first floor, with the carbonation equipment located directly below in the basement for both space and noise reasons. Dispensing temperatures would be mid to high 30s Fahrenheit.

What I think I need to do:
Build or buy a kegerator system. Get a kegland continuous carbonator lid and a corny keg, a 20 pound CO2 tank and regulator. Plumb in my filtered water supply. Run a chilled line up through the ceiling/floor to the tap.

Where I'm stuck: I don't really know this hobby. I'm not sure if I should run a chilled insulated glycol line. I'm not sure how to run chilled still water. Can I also run room temperature filtered water to the same tap head if I'm using this one: High Pressure Seltzer Tower 5443

It's not clear to me how a glycol system and a non chilled line would both connect to such a tower. In the case that I can't mix chilled and room temp lines in that same tower, I would go with the 2 line version of the system and dispense chilled seltzer and filtered flat water from it.

So, I think I know what I need to do, and I have reasonably sound DIY skills, I just need help sourcing all the parts in a way that will all come together with my desired goal. I'm surprised I can't get good help from the companies selling this stuff. My calls and emails have gone unanswered. Anyone here able to help me make some good decisions on at least major components so I can start moving this project forward?

Water source is run through a 6 stage whole house system, and then RO filtered and run through a calcite stage to raise the pH and add back some minerals. Source pressure is about 60 PSI.

 

[sodium11]

I did something similar as outlined in this thread but instead of something like the Kegland continuous carbonator lid on a corny keg I used a McCann's Big Mac Carbonator to produce the seltzer and basically ran the seltzer line through PVC pipe through my kitchen floor under the counter with a cap at the end so that the system was sealed and ran an additional hose using what is essentially a beefed up Draft Tower Fan to push cold air to the top and allow the air to return to the kegerator. That unit you're looking at states that it's designed for high pressure so it should work fine with a carbonator. The advantage to a carbonator is that it'll give you consistent seltzer during high-demand events like a party as long as you have enough cold water in reserve, and the way I achieved that is by simply adding a bunch of extra soda line hose in the kegerator. I was fortunate as the vintage soda faucet I got fit perfectly in the spot where my soap dispenser was so I could mount it in the sink.

Another alternative to the tower could be a soda gun. I had actually ran one through the soap dispenser hole years ago by carefully disassembling and labeling the lines inside the triangle portion and reassembling it one it was through the hole. It sat like that for a year or so, unfinished, before I took it out and decided to go another route. They do sell them in 2, 3, and 4 button configurations if you search around.

Either way, you could have a corny keg and some sort of carbonation setup inside a kegerator as your seltzer and cold water lines, and a line outside of the tube for your room-temperature water. There may be a touch of overlap with the cold/warm side, but you'd probably never really notice it. On the carbonated side of things, just make sure that everything is using stainless steel as any brass fittings will leach copper into the seltzer, and use a backflow and/or check valve to make sure that the carbonated water doesn't make its way back into your house lines, and finally that you use braded lines designed for soda systems.

 

[ChickenRob]

Thanks. This is helpful. I’ve been reading and watching videos and have started down the path.

I have the 2 head dispenser, an empty corny keg, a 20 pound CO2 tank, a 5 cubic foot freezer and an ink bird controller, the kegland continuous carbonation lid has been getting good reviews, and I think it’ll keep up with party volumes if I just add a second keg and lid. I’ll be building a collar hopefully over the next couple weeks as my spare time is limited, and I’m building alone.

My plan is to run 4” pvc from the collar up to the kitchen sink, and 2” pvc inside the 4” pvc. I’m going to put a fan on the 2” pvc in the freezer, pushing chilled air into the column, and have the return air come down the 4” pipe. The beverage lines will also be in the 4” pipe. I read about a build like this that was quite successful. I’ll insulate the 4” pipe to keep condensation low on the outside and temps low on the inside.

Hopefully this works out. I think it will.

I don’t have any tubes, a regulator or fittings yet. Just getting the big parts together, and doing the initial build, and running the PVC when I figure out where the tap will go. I have an RO faucet in my kitchen already, and I think the tap shank will fit there. I also have an island sink I may take over for this usage. I’ll know soon.

Very excited to get seltzer on tap! Still not sure how to get chilled still water up to the tap. Small keg in the fridge driven by water pressure alone?

 

[sodium11]

The small pipe within a larger pipe with the seltzer line inside the larger is the way to go, as it's what works in beer towers, and what I basically did. But before you commit to using ridged PVC inside the larger pipe you should consider if you have to have any bends in it because trying assemble a pipe within a pipe is a PITA. Flexible hose, like those used for dishwasher drains, vacuum cleaners, and pools come in many sizes and is, well, flexible and easy to snake through the bends. I secured mine at the top to the larger pipe by drilling a hole and securing it with a small nut and bolt. At the top I drilled a hole the size of the seltzer line, pushed it through, and sealed that with a bit of silicon calk. I used 2 inch PVC with 1 inch hose and easily had enough room to put in 4 water/seltzer lines, and for the exterior pipe I basically screwed it together with 3 screws in each joint, short enough so that it wouldn't poke through the pipe where the water lines were and then sealed each joint with duct tape followed by insulation. The reason I did this is because I know some day in the future I'll have to partially disassemble the thing for maintenance, probably when the kegerator's compressor dies and I have to replace it.

Now, the way I had to set it up there is about an inch or so of the seltzer line sticking above the top cap before it connects to the draft arm, but even on the hottest days I haven't noticed any warmness in the seltzer because if it, and the reality is I can just run it a second or so before filling my glass and any warm seltzer goes away. An advantage to this is that the draft arm isn't always cold so I don't have condensation building up on it, unless I'm going through a lot of seltzer in a short period.

As for your freezer, if you have a chest freezer you should look up keezer builds. Basically folks take the lid off and install 2x6's or 2x8's around the top and then put the lid back on that. Unless you know exactly where the wires and refrigerant lines are in the freezer you have to be careful when drilling holes in 'em because the last thing you want to do is hit one of those and render it useless. Instead you can safely cut into the wood.

As for the cold still water, your household water pressure should be fine, so a small tank reservoir or a bunch of water line in the freezer should do the trick.

I've had mine set up for nearly 2 years now and I love it. Sometimes I'll pour a glass of seltzer and put a bit of soda stream syrup in it to have a soda, and others a bit of water flavor, but most of the time I drink it plain. I'm using a 5# CO2 tank, mainly because it's easier to exchange at the home brew store down the street and go through about a gallon and a half of seltzer a day and that tank will last well over a month, so a 20# tank should last you quite a while. If you have an old CO2 regulator for draft beer laying around, you should be able to use that with the kegland system, I had to get a different one because carbonators require 100+ psi.

 

[ChickenRob]

wow. Lots of helpful info there.
I’ve been watching keezer build videos and have plans to build the collar tomorrow. Went to Lowe’s today and got some 2x10, 1x6, weather stripping, rigid insulation, paint designed to seal and prevent mold, caulking, etc. Haven’t bought the pvc yet. I’m hoping that it’ll be a 90 degree out of the collar, and the straight up to the faucet. I have to disassemble the RO tap tomorrow and see if the hole in the granite in the counter is big enough for the new tap arm. The tap arm has a 1.25” shank. I think the hole in the counter is 1.375, so I may be good to go with a straight pvc run.

What did you do to cap the top of your pvc and what did you do to pass the seltzer line through that cap.

 

[sodium11]

I used a cap like this one and drilled a hole the same side as the outer diameter to pass the seltzer line through and sealed it with a touch of calk. You could drill two holes for each of the lines, or one hole and feed them both through. Just make sure that the outer PVC pipe is sealed so that warm air doesn't get in. For all of the hose connections, I used Oetiker Clamps as that's what they use in commercial soda fountain and beer setups as they produce even pressure on the hoses and are less prone to failure than the screw types clamps, and make sure to use braded vinyl hose. I used this because it's designed to handle lots of pressure and also won't pick up any funky flavors that might appear, but it may be a bit overkill since your system won't be at the 100+psi that I have, but the last thing you want is a hose or hose connection to fail spewing water everywhere. And remember, everything after the seltzer keg must be connected using stainless steel. Unfortunately, they don't sell stainless steel fittings at hardware stores so you'll probably have to order those online, and you'll want to have a check valve on the water line going into the seltzer keg, and it's a good idea to also put one on the CO2 line so that water doesn't find its way into the regulator if the tank runs out or while you're changing tanks.

 

[ChickenRob]

Thanks @sodium11, this is all super helpful advice. I really appreciate it. It’s been a life long dream to have seltzer on tap. I’m really excited to get rid of my Aarke (or at least put it in storage for emergencies) and get this thing flowing!

 

[ChickenRob]

I used a cap like this one and drilled a hole the same side as the outer diameter to pass the seltzer line through and sealed it with a touch of calk. You could drill two holes for each of the lines, or one hole and feed them both through. Just make sure that the outer PVC pipe is sealed so that warm air doesn't get in. For all of the hose connections, I used Oetiker Clamps as that's what they use in commercial soda fountain and beer setups as they produce even pressure on the hoses and are less prone to failure than the screw types clamps, and make sure to use braded vinyl hose. I used this because it's designed to handle lots of pressure and also won't pick up any funky flavors that might appear, but it may be a bit overkill since your system won't be at the 100+psi that I have, but the last thing you want is a hose or hose connection to fail spewing water everywhere. And remember, everything after the seltzer keg must be connected using stainless steel. Unfortunately, they don't sell stainless steel fittings at hardware stores so you'll probably have to order those online, and you'll want to have a check valve on the water line going into the seltzer keg, and it's a good idea to also put one on the CO2 line so that water doesn't find its way into the regulator if the tank runs out or while you're changing tanks.

I ordered the clamps, braided tubing, a regulator with a check valve in it.

I think now I need fittings.

it’s confusing as not all the connection types are documented on the products or well understood by me.

My biggest confusion so far is how do I get from 3/8” outer diameter RO tubeto a ball lock (I assume) to feed the carbonation lid on the keg? What do I need for connecting to the tower itself?

While I wait for the build to come together I’d also like to use this tap to dispense ambient temperature filtered water from a 3/8” RO tube. The RO faucet had a threaded end with a push fit adapter. The tower connection ends look like this.

 

[ChickenRob]

Btw - those stainless tubes are .31” or 8mm.

 

[sodium11]

You're probably going to have to cut the RO hose and use a barbed hose splicer to connect to the hoses together and clamp them, then slip hose over the supply lines on the tap as far as you can and I'd use at least two clamps on those since they don't have barbed connections on them. It looks like there are 4 lines coming out of the tap, two of those are probably for a glycol remote chilling system and won't be used, if you blow into one and air comes out the other that's the glycol line, if the air comes out the tap that's the supply line. You may have to get some 1/4 ID line to slip on the ends of the tap, it's going to be a bit of trial and error as you futz around with the connectors. A trick when working with the vinyl tubing is if it's tough to get on, you can put the end in boiling water for about a minute to soften it and it'll slip on your fittings better, just make sure to have the clamp on the hose before you fit it over the connection otherwise you'll have to take it apart to put it on. When it comes time to connecting the water in the keezer, you can use a barbed T to split the water line.

 

[ChickenRob]

You’re right that 2 of the tubes are for a glycol loop and won’t be used.

So I can put the toning and a clamp right on the stainless tubes? Would Ibe better off with a duotight 8mm to 9.5mm connector and put a piece of 3/8” RO hose in the end, and then a Berber coupler to hold the vinyl?

I have been searching like crazy today and have yet to find the right connections for getting from the keg to the faucet.

As always, I continue to appreciate your help.

 

[sodium11]

If the hose fits kind of snug on the SS lines and you can shove it up close to where the black foam is and put 2 or 3 clamps on it, it should be fine. I did that when my kegerator was being used as intended and I replaced the stock tower with a fancy brass used one, but the stainless lines were cut, but of course beer is at much lower pressure than water. The duotight should work as well, and it even looks like they make barbed connections like this one. Looking closer it appears that your tower was designed to actually use them, I've just never been a fan of them after a few instances of failure but it looks like they've made some vast improvements over the last 10 years.

As for the connections for the corny keg, there are really only two types out there, and the dominating one is the ball lock. You'll need one for the gas in, and one for the fluid out, and I would guess that the connection for the kegland lid would be another fluid connection. They are slightly different so that you don't mix up your gas and liquid. The other type of connection is the pin lock, but outside of the one keg I still have in my basement that has 'em, I haven't seen another anywhere else.

 

[ChickenRob]

Thanks. Yeah, I was up to speed on the ball lock issue, that seems to be well covered. Your link got me reading deeper, and it looks like duotight might be a viable option for evabarrier tubing. Which is great on 3 fronts, taste, health and ease of connection. I use John Guest fittings in my filtration system and to plumb my ice maker/fridge/filtered tap water dispenser/water cooler/etc, and they have held flawlessly for about 6 years. At higher pressures than the seltzer system will be in some cases. The duotight seems like an improvement on the same technology. I think I just may have found the missing part of my system.

Thanks again.

Fingers crossed.

 

[ChickenRob]

Okay, I think I know what I need to do until things are assembled and I’m trouble shooting as far as the seltzer is concerned. Now I need to figure out a chilled flat water solution.

1. I could get an additional RO pressure tank and keep it in the keezer.

2. I could keep a lot of coiled tubing in the keezer, either in the ambient cold air, or a bucket of water.

3. I couldget an additional keg and let the water flow through the keg using just water pressure.

the drawbacks as I see them:

1. the RO tank would take up a lot of space

2. The coiled tubing would not hold as much volume and create a rats nest.

3. Not sure if this can even be done with a keg. Can I push water in through the gas line, and out through the beverage line? Will this restrict flow rate? I’d like to keep a reasonable flow rate.

 

[sodium11]

Sure you can use a tank to hold the water and just have the water go in on the gas side, in fact they make excellent water storage solutions once you've thoroughly sanitized them. Just make sure to purge the air by pulling the pressure relief valve on the lid until a bit of water squirts out. The short dip tube for the gas is the same size as the long dip tube for the liquid so there shouldn't be any real difference in flow.

As for the use of coiled tube, that's what I ended up doing to feed into my carbonator (if you scroll down a bit). I got the idea while working on my refrigerator as that's the way they did the cold water storage, the theory is that cold air can circulate around the tubes quickly cooling the water, much like a radiator. To keep it a little less messy I just zip tied them together.

Now, the RO pressure tank is something to consider in the system overall. I was just looking at the specifications of the Kegland lid and it states the minimum pressure the CO2 should be is 30psi, with the water pressure being 30-40psi above the CO2, so at a minimum you'll want the water pressure coming out of the RO system to be 60psi if I'm reading that correctly, and probably higher if you want fizzer water. To answer that stuff someone on these forums who actually has the Kegland Continuous Carbonated Water might better answer those questions...

 

[ChickenRob]

I have seen different specs in different places about the lid. At keglands site itself it says

Link to kegland description

“4. Set your CO2 regulator that is connected to the gas post to 30-50psi. (higher pressures will give you more carbonation so set your regulator pressure to achieve desired carbonation level).”

In the next step:

“For this unit to work well the mains water pressure should be 10-15psi higher than your regulator set pressure (from step 4).”

My pressure coming out of the RO tank is 60psi. I’m hoping that this works ok. If not I will just have to get a booster pump for the water supply. I’ll test and see. I hope I don’t need the pump, but a pump is better than flat seltzer.

 

[ChickenRob]

Still waiting on connections and tanks and doing my build on the collar, but the tower fits the hole already in the granite so I don’t need to drill the granite counter.

 

[sodium11]

That tower looks great there!

Probably the hardest part of the whole build will be securing the tower to the counter top and connecting the lines, only because of the cramped space under the sink. Looking at that reminded me of what I did: Once the 2 inch PVC pipe came up through the floor and into the cabinet, I connect it to a coupler like this one, and then ran the seltzer and cold air hoses up through the pipe. I then drilled the hole through the top cap and ran the seltzer line through it and hooked it up to the draft arm, and for the final piece of PVC I cut the length that I needed, and then cut it in half the long way so there were two halves that I could put around the hoses, securing the cold air hose to one half and putting it all into the coupler and then the cap on top and then sealed it all with tape, and then insulation. As you can see there was little room to work with:

With things like this there's a lot of trial and error. I had about 17 years of research, and a bunch of abandoned attempts ranging from soda guns to a 5 head soda fountains with a self-contained ice block before I finally successfully excited my design (frankly, I never drank enough soda to quantify having a fully functional commercial soda system). Fortunately I was able to sell a bunch of the abandoned stuff and break even and am way happier with the simplicity of a seltzer system.

Now, after you get everything set up and working optimal, if you find that after drinking a bunch of seltzer that the carbonation starts to seem a little flat, one thing you might be able to add is a diffusion stone to the CO2 side. The gas dip tube is really kind of short and looks like this, but one of the tools homebrewers use to force carbonate beer is with a diffusion lid like this. Now, you can't exactly use that lid because you'll have the continuous lid in place, but what you could do is buy a diffusion stone and connect it to the short gas tube that way the gas is exiting the line directly in the water as really small bubbles. Theoretically that would help speed up the carbonation process...

 

[ChickenRob]

Wow. A lot of great ideas in that post. The coupler, cutting the pipe the long way, using the carbonation stone. All of this is great. I just bought the carbonation stone. For under $10 it seems worth trying.

Also I was worried about water pressure. I bought:

“The SHURflo Water Boost Systems deliver quality drinks in many installations where there is an inconsistency in the pressure and flow of city water. Using one or more dispensing valves or faucets, the pump and accumulator maintain consistent water pressure to a source (for a given duration) as long as incoming water is sufficient. The system is a great back-up option for supplying water to a carbonator in case of short periods of insufficient water pressure.”

Will boost to a maximum of 90 PSI. Should hopefully keep a steady flow and pressure in the system. Might be overkill. Found it on sale for under $200.

I think I might try an idea that improves on your system that you’ve totally inspired. My shank is 1.25” in diameter. I could get a couple additional nuts and washers that fit the threads, cut a 1.25” hole in the top of a pvc cap, make a gasket out of silicone, and secure the pvc directly to the bottom of the shank. Since I’ll be using duotight fittings I should be able to attach tubing pig tails to the tubes on the tower that hang below the sink bottom, then slide a piece of PVC up that goes into the cap and let’s the tube pigtails hang out by an inch. Then using a pvc coupler, attach the long PVC pipe from the basement to the coupler.

When everything is set and ready to go, I can hold the pvc together with this stuff (I hope). It works wonders in other places I need a solid hold, but need to be able to remove it.

Amazing tape

So I like the fan you used to blow the cold air, but how did you get the beverage lines in the same hose you were blowing the air through? Did you just cut an opening in the hose and seal it up?

 

[ChickenRob]

Also, what size bottle of pine sol do I need to make this work?

 

[sodium11]

The SHURFlo booster pump will do you well, as it'll allow you to have the optimal pressure settings to get the carbonation levels high and has a pressure tank like your RO system to help maintain the pressure. Things that allow CO2 to defuse into water quickly are cold water temperatures and high pressure, which is why carbonators pump the water into the carbonation tank at 100psi with the co2 pressure usually around that as well.

My seltzer line isn't in the cold air tube, it's next to it, all within the 2 inch PVC pipe. The kegerator has a fan that blows over the coil to circulate cold air through it, as well as a tube that blew air up into the tower. Problem is it wasn't designed to push air all the way up to the next floor so instead of buying a beer tower fan I used a 110 volt van I had laying around and bought a water tight conduit box, drilled some holes for the fan and the output and extended the cold air tube all the way to the top so that it would blow the cold air up and return the air to the keg along the seltzer line.

 

[ChickenRob]

Very clever use of the conduit box. I have some 120mm and 60mm ac fans around I was going to use for this build. This looks great. I was originally thinking I’d run the lines as you did, but I read in the build thread you linked earlier (I thought) that you got the seltzer lines into the cold air hose. I’m glad this solution works. Seems a lot easier.

 

[sodium11]

I had first used one of the boxes to house the Inkbird thermostat I installed shortly after I got the kegerator when it was used for beer as seen in the other thread. The original thermostat died, and the replacement was nearly as much as I paid for the kegerator, so instead I spent 10 bucks on the Inkbird and another 10 for the box and it's been working great for over 5 years now. I liked it because it gave me more precise temperature control and I still had enough clearance to have a few 1/6 kegs in it. If you look at that thread you'll notice that the probe is in a glass of water, I did that because I noticed that the kegerator would cycle on and off more often when it was exposed to air, but in the water glass it seemed to better reflect what was happening within the carbonator. I thought about affixing it to the carbonator but haven't gotten around to it...

 

[ChickenRob]

Okay, the shipments are trickling in, and I have most of my build plan figured out. The pressure booster pump arrived with a 9.5mm barbed attachment going in and out of it. I’ve made the decision to go evabarrier and duotight to plumb this system. It looks like the biggest evabarrier tube is 9.5mm OD and 6mmID. I’ve tried googling if I can heat and stretch this on and clamp it, but as of right now, I’m not sure how to get this booster pump in line on the water supply line.

 

[ChickenRob]

Problem solved.

Help needed plumbing my seltzer keezer project (evabarrier to large barb fitting question)

 

[ChickenRob]

So the barbs on my dispenser tap are smooth and about 8mm. I was hoping a duotight 8mm fitting would do the trick, but my fitting came in today and it will not hold, the fitting is too loose.

I’m wondering if I saw he the evabarrier hose and clamp it down if it will hold under the pressure of a seltzer system.

a reminder, here are the barbs:

 

[ChickenRob]

I Swaged the hose and clamped it on the tap barb. No problems for the low pressure RO line. Will be interesting to see what happens when I get the high pressure seltzer line running.

 

[ChickenRob]

So I got one of these to get the CO2 through the collar. My CO2 tank is outside the keezer. Any thoughts about a similar fitting for the water that I’m piping through? Can I use another one of these? Will the flow be adequate?

Bulkhead adapt 1/4 mfl 2-7/8L https://www.amazon.com/dp/B07GQ5FTQS/ref=cm_sw_r_cp_api_glt_fabc_8YA40FKBKS1E6BCFPF9Y?_encoding=UTF8&psc=1

 

[ChickenRob]

Probably the hardest part of the whole build will be securing the tower to the counter top and connecting the lines, only because of the cramped space under the sink.

Even though I’m not finished building yet, I know your above prediction is wrong. I actually got the lines connected and the tower snugged fairly easily. The hardest thing is how many times I overlook some little part in my plan and then have to make yet another small order and wait for it to get shipped. That’s driving me nuts.

is there a better place than keg factory for duotight fittings in the US? I’ve been googling my brains out and have been struggling to find a single source with a better selection. Also, there are a few fittings I’m having trouble sourcing at all.

 

[rhvoodoo]

I did something similar as outlined in this thread but instead of something like the Kegland continuous carbonator lid on a corny keg I used a McCann's Big Mac Carbonator to produce the seltzer and basically ran the seltzer line through PVC pipe through my kitchen floor under the counter with a cap at the end so that the system was sealed and ran an additional hose using what is essentially a beefed up Draft Tower Fan to push cold air to the top and allow the air to return to the kegerator. That unit you're looking at states that it's designed for high pressure so it should work fine with a carbonator. The advantage to a carbonator is that it'll give you consistent seltzer during high-demand events like a party as long as you have enough cold water in reserve, and the way I achieved that is by simply adding a bunch of extra soda line hose in the kegerator. I was fortunate as the vintage soda faucet I got fit perfectly in the spot where my soap dispenser was so I could mount it in the sink.

Another alternative to the tower could be a soda gun. I had actually ran one through the soap dispenser hole years ago by carefully disassembling and labeling the lines inside the triangle portion and reassembling it one it was through the hole. It sat like that for a year or so, unfinished, before I took it out and decided to go another route. They do sell them in 2, 3, and 4 button configurations if you search around.

Either way, you could have a corny keg and some sort of carbonation setup inside a kegerator as your seltzer and cold water lines, and a line outside of the tube for your room-temperature water. There may be a touch of overlap with the cold/warm side, but you'd probably never really notice it. On the carbonated side of things, just make sure that everything is using stainless steel as any brass fittings will leach copper into the seltzer, and use a backflow and/or check valve to make sure that the carbonated water doesn't make its way back into your house lines, and finally that you use braded lines designed for soda systems.

I'm in the process of setting up a similar system. Would you mind if I message you with some questions about your setup?

 

[punkdigerati]

So the barbs on my dispenser tap are smooth and about 8mm. I was hoping a duotight 8mm fitting would do the trick, but my fitting came in today and it will not hold, the fitting is too loose.

I’m wondering if I saw he the evabarrier hose and clamp it down if it will hold under the pressure of a seltzer system.

a reminder, here are the barbs:

View attachment 743497

I know this was years ago, but for anyone else looking, John Guest Superseal is designed for clamping onto stainless tubes and should work well if Duotight isn't. I usually get JG stuff from freshwatersystems.com. When searching it can be best to use the filters to narrow down, as 5/16 and 8mm are both interchangeable in this context, but won't show up for the other if searched for.
For regular tubing DMfit stuff can also work well, but Duotight can be had cheaper for most fittings.