How to improve mash tun flow through

[PeeBee]

You started it! Trying to confound me with "negative pressure" 'stead of "suck"

[mabrungard]

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

Well, I don't have a place that can host a pic. So I can't show you. But I'll attempt to describe a bit better.

My tun has a threaded elbow fitting drilled into the side wall of my tun near the bottom of the tun. Its sealed through the wall. There is a length of clear vinyl tubing running up the outside of the tun and you can see where the liquid rises to in that tube. With the recirculation flow shut off, the water level in the tube is the same as in the tun. As I open the recirculation valve, the water level in the tube drops. If I increase the circulation too high, the tube will be drained and it will suck air into the tun (not a good thing). So I typically adjust the flow rate so that there is about an inch of water in the tube.

PS: Yes, a rotten pump like a March pump can pull a couple of feet of water uphill. So they can 'suck'. They just aren't very good at it. But its more than enough to compact a grain bed.

[Jocky]

Thanks for the explanation. Basically it’s a sight glass that’s below the false bottom of the mash tun?

[PeeBee]

… PS: Yes, a rotten pump like a March pump can pull a couple of feet of water uphill. So they can 'suck'. They just aren't very good at it. But its more than enough to compact a grain bed.

Don't say that ! You'll encourage people too put such pumps in "sucking" situations and then to wonder why they don't work.

Anyway "pull a couple of feet of water uphill" is a bit of an exaggeration! I've got a "rotten" March-May pump (all you could get not so long ago). The good thing about such rotten pumps (very open impeller types, probably mains driven and over-powered to counter inefficient impeller) is they keep pumping even if the liquid is full of muck (grain) when not-so-rotten pumps just pack up.

[f00b4r]

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

Well, I don't have a place that can host a pic. So I can't show you. But I'll attempt to describe a bit better.

My tun has a threaded elbow fitting drilled into the side wall of my tun near the bottom of the tun. Its sealed through the wall. There is a length of clear vinyl tubing running up the outside of the tun and you can see where the liquid rises to in that tube. With the recirculation flow shut off, the water level in the tube is the same as in the tun. As I open the recirculation valve, the water level in the tube drops. If I increase the circulation too high, the tube will be drained and it will suck air into the tun (not a good thing). So I typically adjust the flow rate so that there is about an inch of water in the tube.

PS: Yes, a rotten pump like a March pump can pull a couple of feet of water uphill. So they can 'suck'. They just aren't very good at it. But its more than enough to compact a grain bed.

Martin, you can upload pictures directly to the forum if you wish.

[brewbrew]

I thought I'd give you and update on this. I fitted a ball valve on the mash recirculating pump outlet. Holding the flow back did reduce the problem slightly but it was not the full solution. After some further investigation, I realised that the nut that holds the 1/2 inch BSP outlet elbow in the centre of the perforated false bottom was only 3 mm or so from the bottom of the bucket (despite the dome depth of the false bottom being more than 10mm). I concluded that the bottom of the polypropylene bucket (that goes a bit soft at 65/66 degC) was getting sucked onto the bottom of the elbow nut when the pressure in the void under the false bottom was restricted by the packed grain bed. My solution was to cut 2mm wide, 5mm deep slots on all 6 faces of the nut and threaded stem of the elbow. Eureka! it works - no more pulsing and stopping.