Pipe sizing and pump capabilities

[kolektiv]

Hello! I'm designing a tiny 3V system (about 5-7.5l batches) and am looking at pumps and piping. At the moment I'm thinking that a fairly small pump (something like a Topsflo TS5, or a similar non-branded equiv) would do (about 12l/min), combined with 12mm (OD) piping/valves, etc. By my reckoning this would give about 2.2-2.5m/s max velocity, and I generally hear a rule of thumb of about 1.5m/s for recirculation, etc. and 2m/s+ for cleaning. So it seems like this would work passably well.

However, I'm no fluid dynamics expert. To me that pipe size seems small but proportionate, as does a pump with about that capacity, but am I missing anything? Do I need to think about anything in particular with valve sizing, etc.? At the moment I can't see any reason not to settle on 12mm (1/2") as a standard, as having bigger valves than piping doesn't seem to be particularly required.

Can anyone see any immediate problems?

EDIT!

Immediate problem I'm finding is pipe and braided hose in 1/2"! 3/4" seems to be fine, no problem, but then my flow velocity at 12l/min seems like it would be far too slow. Am I overthinking that? If I went with 3/4" pipe/valves in general, I suppose I could always step the diameter down in a few places if a faster velocity seems needed? (If the pump will take it)

 

[day_trippr]

fwiw, the vast majority of pumped home brew rigs are using 1/2" tubing. On my rig I can get at least 6 gpm from vessel to vessel at max flow through roughly 5' lengths of 1/2" tubing using March 815pl pumps...

Cheers!

 

[kolektiv]

I guess I'm trying to work out what would go wrong if I used 3/4" fittings and pipes/tubes throughout! And possibly larger for some intakes/drains, etc.

 

[McKnuckle]

I've noticed that hose with a larger diameter than whatever is inside the kettle, such as a pickup tube, will not fill completely with liquid, and seems to draw in air. So there are air bubbles in the output along with reduced flow, despite the wide hose. This is even worse when it's hot wort and a pump is involved, as it tends to cause cavitation.

In these cases, I have dropped down the diameter and it's resolved the problem.

 

[kolektiv]

I'm hoping that particular problem might not surface, as I'm designing all of the vessels to be bottom draining (with some filters inline for certain phases). So with any luck it'll stay reasonably well filled. I might need to up the pump capacity though with 3/4" fittings.

(The rationale here is that I'm going TC pretty much everywhere, and 1/2" TC pipes/hoses are effectively non-existent, despite being able to get plenty of 1/2" valves, etc. It's annoying, but I'd like to hard line most things, or use SS braided where I can't - and 3/4" is about the minimum size I can find.)

 

[Vale71]

Can anyone see any immediate problems?

For such a tiny batch size even a 12 l/min pump would be way too powerful. You'll definitely need some form of pump speed control to make your system work properly.

 

[kolektiv]

Yes, that's a fair point - at the full 12l/min, it would be recycling the whole batch twice per minute, which probably isn't needed (although would it do any harm? Not sure...)

Ideally, in a way, you'd want to scale pipe size directly to batch size, but then you'd be looking at pipes and pumps which just don't exist. At the moment I think my plan is to broadly speaking "ignore" the pipe size (and go with 3/4" which is the most versatile and available), focus on fluid circulation and then forget the specific fluid velocity - it'll probably be down to 0.5m/s or somewhere like that, but that's still probably not too awful. I hope... Of course for cleaning it doesn't matter too much in general, if it's just hot water and sanitiser I can sluice it through with no concerns.

In terms of speed control, I'm always assuming a magnetic pump here so just a ball valve or similar to exert variable back pressure should be fine I think. One day I might motorise that but I suspect it's easier than trying to control actual pump speed.

 

[Vale71]

Yes, that's a fair point - at the full 12l/min, it would be recycling the whole batch twice per minute, which probably isn't needed (although would it do any harm? Not sure...)

That depends. If you're just going to pump water or cleaning solution it shouldn't be a problem. If you intend to implement some sort of recirculation mash system (either RIMS or HERMS) then you're going to have to throttle down a lot to avoid compaction and a stuck mash. For your referemce I have a batch size of 40l and I recirculate at about 5 l/min in my RIMS system based on an SSB 20g kettle. Faster than that and I get compaction/stuck mash issues.

A magnetic pump is just like any other pump, meaning you should always regulate it by changing the actual rotor speed and not by throttling it with a valve. A DC pump is very easy to regulate using a PWM controller.

 

[kolektiv]

Yes, the plan is HERMS, so it'll definitely need to be carefully flow limited to avoid a stuck mash. To some extent I suppose that's going to be a function of the size/depth of the grain bed that forms (ideally the grain will be circulating not forming a bed, but not sure that's possible with flow happening).

That's interesting in terms of your point on the pump regulation - the pump specs I'd read had mentioned being able to control flow with a valve/back pressure. There's also a distinct chance that if I need to have a more powerful pump in there (for cleaning, etc.) it won't be a DC pump, at which point PWM doesn't seem so applicable?

 

[Vale71]

You can't recirculate solids with those pumps, you'll drive them kaputt in no time. An AC pump requires a variable frequency inverter and those are way too expensive for such a small system. I wouldn't worry about that though as you really won't need powerful pumps at such a scale. Just get a PWM controller for the 12 l/min pump and you can run it full throttle for cleaning and heating to strike temp and throttle it way down for mash recirculation.

 

[kolektiv]

Yes - I'm not planning on recirculating solids anyway, the HERMS circulation should be the other side of a filter/false bottom which will keep any significant chunks out. I'll start with a couple of small DC pumps (Topsflo TS5s most likely) and see how it goes. Can always modify things there. With 12l/s through 3/4" pipe (OD) it'll be about 1m/s, which is (way!) more than enough for any actual brewing process given the batch size I think, and hopefully enough to do a reasonable clean if the pipe runs aren't too convoluted.

Anything at this size is a bit of an experiment, to say the least, so to some extent I'll just need to start getting some tests done with pumps etc.