pump trouble with mash tun recirculation only...

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Dgonza9

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So I'm a bit stumped on this one.

I have a march 809 high speed pump. I use it with my bottom drain HLT keggle and it primes immediately and pumps strike water to my mash tun, a square cooler on a table above the HLT.

But when I try and start recirculating through my RIMS tube, it takes a loooong time to get the pump going. It may be a lack of head pressure, as the wort has to be pumped up a my hard plumbed line to a fairly high point, thru a 1 1/2" RIMS tube, then thru a barb and into the top of my sparge arm in the mash tun.

I've found no solution other than turning the pump on and off, bleeding air with an autovent or my side bleeder valve, and just submitting to a process that can take 10 minutes or more.

But if anyone can help me solve this (even a new pump would work for me, if needed) I'd be much obliged.

Once I get the flow going I rarely have problems. I use a copper manifold with slits and place a nylon bag around it as well.

Here's a pic of the setup. I use a hose barb to connect RIMS tube to the top of the square cooler.


1488a0bb.jpg
 
Anyone? My only thoughts have been that the pump has trouble pumping that high, although it's no problem with the HLT. Or maybe something about the way the mash tun drains vs the HLT.

Any theories are appreciated.
 
I can't really tell what is going on in your picture, but my guess is that your system is getting air locked at some point. It looks like your rims tube is mounted horizontally, could it be possible that water flows into it and down and creates an air pocket that is stopping the pump? That would be where I would start... the horizontal runs I see in your pic should flow slightly uphill to keep air pockets from forming.
 
Fill the cooler through the drain line, not the top, that forces the air bubble out of the pickup tube, and priming the pump after that is not an issue. It is the air trapped in the outlet tube that is the pump prime killer, eliminate that and you eliminate the problem.
 
There's a pump in the lower left corner of the picture. I have a bottom drain keggle that runs to the March 809 inlet (facing down). The pump outlet leads to the lower of the two horizontal pipes, then up to the horizonal RIMS tube. I then attach a silicone line to the top of the square cooler to recirculate.

Sorry the pic is confusing. I'm in the middle of making a panel so I have a lot of parts around.

I appreciate the comments. I will definitely try filling through the tun drain, though it thwarts my hard plumbing. :)
 
I think i can see it but i'm still not sure. Pic is kinda dark..can you take a pic of the pump and pipeing around it and post it up?
 
I use a non-march pump to recirculate (vorlauf) for about 10 minutes.

Here's my process. Keep in mind that I use soft silicone lines, and that I can see the liquid levels.

Keep pump off. I open the mash tun outlet gently, about 1/2 way. I wait for the mash liquid to equalize on the output side of the pump.

Once the liquid has equalized, I open the mash tun outlet to full. It won't draw anymore liquid now as it's equalized. I then throttle back the valve on the output side of the pump (about 1/3 to 1/2 of the way open), and I turn on the pump.

At first, my pump will push out some of the air stuck in the head, then it's usually clear sailing from then on. If I suspect a bit of air, I stop the pump temporarily (5 seconds), and start it again.

As an FYI, my mashtun has about a 2 ft of elevation advantage over the inlet of the pump (in other words, the pump is on the floor and the mashtun is 2 feet higher).

MC
 
What you are struggling with is called net positive suction head (NPSH). If you are still getting suction then you have not surpassed the maximum that can be developed but at this point you are pretty close. A couple of options are to decrease the amount of NPSH required, or use some sort of vent right at the pump discharge, or add a T with a valve to the suction side, then use a funnel to force prime the line.
 
What you are struggling with is called net positive suction head (NPSH). If you are still getting suction then you have not surpassed the maximum that can be developed but at this point you are pretty close. A couple of options are to decrease the amount of NPSH required, or use some sort of vent right at the pump discharge, or add a T with a valve to the suction side, then use a funnel to force prime the line.

The pump is already primed, though, no? I pump the strike water to the tun, so I don't see why it loses prime.

I think I mentioned it earlier, but the pump doesn't struggle to get my strike water to the tun. Makes me think that it's something in the difference between using a manifold on the tun and a bottom drain on the HLT.
 
It could be that you are trying to start the recirc with too much circulation, compacting your grain bed and starving the pump.

Open the inlet full and just crack the outlet...then adjust flow once the pump is moving fluid. You don't need to recirc at a high rate.
 
Can you take a picture of your manifold? It is possible that you are getting compacted or maybe your manifold doesn't drain fast enough to keep up with your pump. I doubt you are losing prime rather you are likely starving your pump.
 
Can you take a picture of your manifold? It is possible that you are getting compacted or maybe your manifold doesn't drain fast enough to keep up with your pump. I doubt you are losing prime rather you are likely starving your pump.

I think I've solved this problem. I upgraded the pump impeller to the high flow version. This made it clear that opening the pump up too much caused cavitation.

I think the issue had something to do with the pump needing to be wide open to push to it's max head to get the wort up where I wanted it to go, but that opening the pump outlet full starved the pump because the manifold can't drain that fast.

Anyway, the upgraded impeller setup has worked. I just need to crack the outlet open a little at first. If I open her wide it seems to lose prime.

A quick footnote, the upgraded impellers are worth it. They really increase performance, and for the recirculation I am doing, the extra head pressure is a huge help.
 
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