How to improve mash tun flow through

[brewbrew]

I have been running a HERMS with reasonable success for a few brews - but one frustrating thing I encounter is that the grain bed blocks up and the pump (which is about 30cm below the top of the mash liquor height) gasps for liquid making the mash liquor flow pulse and generally slow down.

I can do a temporary cure by prodding it with a mash paddle - but this only works for 2 mins and then it is back to the pump struggling. Of course, when I do this, I'm breaking up the grain (but no problems with bits in the wort) and creating narrow channels that result in patchy flow through the grain bed (I'm also always slightly low on OG - yesterday's target was 1052 - I ended up 1045).

The base of the mash tun has a perforated domed "false bottom" - standard shop bought affair with approx 1.5 to 2 mm holes all over and the outlet is half inch id tubing via a plastic tap.

Has anyone else had this and found a cure?

I was thinking that placing the pump much lower might help or maybe the tap is acting as a restriction?

Thanks to anyone that can share their wisdom and experience.

[LeeH]

Rice hulls, a larger surface area of filtration, grain crush.


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[Jocky]

Sounds like the pump is running at a higher flow rate than the throughput of your mash tun, causing suction on the mash bed which compacts it until it's completely clogged.

You need a ball valve on the outflow side of the pump to restrict it so it flows out slower from the pump than the mash can provide.

[london_lhr]

What Jocky said.

You could also consider letting the mashtun drain into a hopback or any small stainless pot or kettle.
Then pump from the pot and not from the mash tun.
You can make this into a closed system.
But you would still need to restrict the pump outflo if you cannot control the pump speed.

[london_lhr]

Here is some information on building a hopback.

https://byo.com/project/build-a-stainle ... l-hopback/

[PeeBee]

What pump? I can't see what you're doing that is much different to what I'm doing. But you haven't described what pump you use.

[brewbrew]

My pump is this one from MM https://www.themaltmiller.co.uk/product ... pled-pump/

Thanks for everyone's advice - all makes sense. This forum is very useful.

[PeeBee]

Should do the job! I do know people will use the tiny 12V "solar" style pumps: They foul up with debris as soon as look at them.

Could be pumping too fast? As Jocky has already said. Seems wrong (debris clogging the pipes might be more intuitive reasoning) but those pumps can only push the wort along. Starve the pump of input and the output stalls and may not return to full flow. Even air will then clog the input (airlock) so be sure there are no rises (higher than the pump input) in the feed pipe from the mashtun. Or that air can collect in the pump. Do not restrict the flow out of the mashtun (full-bore), only restrict the flow out of the pump to control it.

[jsebright]

I had this a while ago (commented in another forum I think).
The problem was that the outlet under the perforated dome was being pushed down too close to the bottom of the mash tun blocking the outlet. I think I added an extra washer above the dome so that the thread didn't go down so low.
Have a good look at the gap underneath the outlet and check there's clearance. Remember the weight of grain + suction will push it lower.

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[mabrungard]

Flow through granular media is governed by physics. With the addition of compressible media, increasing the flow beyond it's limit is a lesson in futility, as pointed out above. I found that limiting the pumping rate to the flow rate that the bed can handle, is the best way to avoid stuck mashes. I have a manometer sight glass plumbed into the bottom of my tun and I use it to tell me when I'm pulling too hard on the bed with my pump flow. I limit the drop in the manometer to about the bottom level of the tun and that turns out to be about the maximum head drop through the grain bed that will avoid compressing the bed and causing a big drop in bed permeability.

The manometer enables you to know what the headloss through the bed is and guides you on closing the pump's discharge valve to properly set the 'allowable' flow rate through the bed. The bottom line is that you can't try and pump wort through the bed faster than the bed permeability will allow. Most pumps can place far more suction on the bottom of the tun than the bed can flow.

Sure, adding rice hulls can help, but grists with little wheat or oat should have no need for hulls if the barley husks are handled well during crushing.

[Jocky]

Flow through granular media is governed by physics. With the addition of compressible media, increasing the flow beyond it's limit is a lesson in futility, as pointed out above. I found that limiting the pumping rate to the flow rate that the bed can handle, is the best way to avoid stuck mashes. I have a manometer sight glass plumbed into the bottom of my tun and I use it to tell me when I'm pulling too hard on the bed with my pump flow. I limit the drop in the manometer to about the bottom level of the tun and that turns out to be about the maximum head drop through the grain bed that will avoid compressing the bed and causing a big drop in bed permeability.

The manometer enables you to know what the headloss through the bed is and guides you on closing the pump's discharge valve to properly set the 'allowable' flow rate through the bed. The bottom line is that you can't try and pump wort through the bed faster than the bed permeability will allow. Most pumps can place far more suction on the bottom of the tun than the bed can flow.

Would be great if you could show us a picture of this setup Martin.

[PeeBee]

Despite what I said above, people still use the suc... word. These impeller pumps cannot suck! However, the weight of wort above the pump can push the wort through the pump which will have the same effect (debris/grain compaction, etc.). There are pumps that will suck, they'll also most probably be self-priming, but they wouldn't be used for debris laden liquid because the debris will trash the blade seals or diaphragms (on diaphragm pumps).

You can get stainless steel diaphragms, metal-metal seals/valves and pumps driven at very high speeds that perhaps will "suck" but I don't think such things are appropriate for home use.

[Jocky]

Errr, yes the pumps don't suck, but surely the act of displacing liquid can cause a negative pressure on the liquid upstream of the pump and therefore the mash bed?

[PeeBee]

If the lack of seal means fluid can go around the impeller blades faster than it can be pushed along, then liquid isn't being displaced. So there is no "negative pressure". The blades just go round and round, and if any air is getting in, mixing up a fine froth.

The blades can be made to fit closer, can be "enclosed", can be spun faster. All tricks used by those little 12V pumps that makes them (at least) as efficient as the big 230V pumps. But also the reason those little pumps bung up with debris so quick.

[Jocky]

Now I have no idea what you're talking about.