March Pump Woes.....

[Paraops]

Ok...WTF??? For several batches now, I've had multiple loss of prime issues with the pump when recirc during heat application to the mash tun, or during vorlauf. (My MLT is a 10gal Blichmann and the silicone tubing is connected with brass QD's). Intitally I assumed my flow was too high during recirc and I was getting the effect of a stuck sparge.... but even with significantly lower flow rates I am still having the same problem. To fix it, I have to re-prime the pumphead with water from the HLT and start over. Ideas????

 

[AnonyBrew]

Leak in the line somewhere? Or the pump?

 

[The Pol]

Air being introduced.

When adding heat, small bubbles from he bottom of the kettle can get in the line and cease the prime.

During varlouf... dunno? Do you have clamps on all of your hose connections to keep them tight?

 

[Paraops]

I was thinking air off the bat.... I have zip ties on the barbs now.... I'm going to change that to hose clamps asap. I checked the screws on the pump head to make sure none were loose...they were all tight. When applying heat I've always made sure to use just enough heat to raise the temp a degree or so over 1.5-2.0 min to make sure i was creating very little or no bubbles under the false bottom. i can't imagine air getting in around the zip ties because of how tight I applied them... but it's completely possible.

 

[eriktlupus]

check your fittings also, make sure your using pipe tape on all pipe to pipe joints and they are TIGHT!

 

[Catt22]

I suspect the problem is with too fine of a grain crush which is causing some degree of grainbed compaction. When this happens, the pump suction can then cause a pressure drop beneath the false bottom resulting in vapor pockets forming which can cause the pump to lose its prime. This is a form of cavitation. Has your crush changed any for whatever reason. Try a slightly coarser crush next time.

I recently added a vacuum gage on my MT tee'd off the output just before the valve. This is used to monitor the pump suction and it can aid as an early warning signal that the grain bed is beginning to compact. The gage measures 0-30 iches of mercury. One inch of mercury is about 1/2 psi. I have run the gage up to 3 in Hg without problems and that provides a very good flow rate of about two gallons a minute or so, maybe a little more than that. Without the gage, I was eyeballing the flow rate and always afraid to push the envelope. The gage lets me explore higher flow rates without fear of the mash sticking and I can pour on the heat without overheating the wort. I'm sure it will stick at some point if I push it fast enough. Next I need to find out what that limit is and how close I can approach it without danger. Stay tuned for future updates on this. So far, the vacuum gage is working extremely well for me.

 

[Paraops]

.....vac gauge........excellent idea. I have a couple in the shop! I didn't suspect too fine a crush...another excellent avenue to explore! Would too fine a crush be evident by a layer of sediment on top of the grain bed the consistancy of baby powder after vorlauf and lauter?

 

[AnonyBrew]

Would too fine a crush be evident by a layer of sediment on top of the grain bed the consistancy of baby powder after vorlauf and lauter?

I don't think so, I'm used to seeing that on top of my mash after I lauter.

 

[missing link]

The most likely culprit is air being drawn in through a quick disconnect or loose fitting. I believe the brass quick disconnects we all use are meant to seal under pressure. I'm not sure what they do when in a vacuum condition.

Linc

 

[The Pol]

The most likely culprit is air being drawn in through a quick disconnect or loose fitting. I believe the brass quick disconnects we all use are meant to seal under pressure. I'm not sure what they do when in a vacuum condition.

Linc

Huh, I never have a problem either priming my pump, or keeping a prime for 90 minutes while I am mashing with it. I have the brass QDs, and according to everyone, I have my pump mounted wrong... but you dont see me having problems priming. Weird.

 

[SpanishCastleAle]

This is a form of cavitation.

That would be my guess. Hot liquids are very volatile and if you pull any vacuum on them they immediately boil and release gas and the pump cavitates. I see this at work all the time when we try to pump uber-volatile solvents through SS tubes that sit out in the Florida sun...we actually have to insulate the lines and sometimes go as far as chilling the solvent in order to prevent all the cavitation.

But I don't have a pump in my brewing rig so I'm just going from my 'work' experience.

 

[Paraops]

Maybe I should use even less heat when bumping mash temps then????

 

[Catt22]

Maybe I should use even less heat when bumping mash temps then????

I've been down this road more than a few times, so I am speaking from direct experience. The solution is a faster flow rate, not lower heat, although you will be forced to reduce the heat if the flow rate is slow or you risk both cavitation and possible scortching.

I'm doing the direct fired RIMS thing and I've been tweaking the system for a very long time getting it to work right.

1. Use large inside diameter hoses throughout and keep the bottleneck restrictions to an absolute minimum. It all adds up quickly. GET BIGGER HOSES
2. Keep the hoses as short as possible, especially on the suction side of the pump. Every foot counts, so shorten up if you can. USE SHORT HOSES
3. Don't crush the grain too fine. It's not worth the small gain in efficiency. Efficiency is not that important, or shouldn't be anyway. CRUSH OPTIMALLY
4. Install a vacuum gage on the suction side of the pump. This was a major improvement. You can really see what's going on while pumping.MONITOR PUMP SUCTION
5. Monitor return wort temp with a digital thermocouple type thermometer. This was another major improvement that I don't know how I got along without. Prevents overshooting temps easily. MONITOR RETURN WORT TEMP ACCURATELY

The above key points took me forever to figure out by trial and error. Not a problem as I like playing with this stuff. Don't make the mistake of dismissing any of these items as unimportant. Because there are multiple factors working simultaneously, they can compound and aggravate each other which makes problems more difficult to pin down. Check all of the above, correct as needed and watch the problems disappear.

 

[Paraops]

Thanks a lot Catt!