March pump priming or cavitation with boiling wort

[billtzk]

I'm not sure if this is cavitation or a priming problem with my March pump. In fact, it may be neither. It only happens with my BK and only when the wort is very hot, boiling or close to it.

During the last 15 minutes of the boil, I attach my silicone hoses from the BK ball valve to the inlet of the March pump, and from the pump outlet to the Therminator Wort In connection, and from Wort Out connection back to a return fitting in the lid of my BK. A pipe in the lid delivers the wort back to the BK below the liquid level. I start recirculating in the last 15 minutes to sanitize everything in the wort cooling drain path.

The physical configuration is like the original Lonnie Mac Brutus where the Therminator and the March pump are mounted on the brew stand middle cross beam on the same level next to each other below the BK.

I attach the hose to the BK, hold the end up, open the valve, let air purge out, then lower the end of the hose until the wort completely fills the hose, close the BK ball valve, hook up the hose to the March pump inlet. Then I connect the other hoses, open the ball valve on the outlet side of the March pump, open the BK valve, and turn on the pump.

At this point, if all goes well, the flow starts, the hoses and Therminator downstream of the pump fill with wort and purge of air, and the wort makes the complete circuit back to the BK. If something goes awry, it will be one of two things:

1) The wort makes it through the Therminator, but won't push up the final return hose to the fitting in the lid. It's only a rise of about 3 feet. When this happens, I usually see air in the lines at the exit from the pump. I can usually hold the lid up so the return pipe is above the wort level and stop and start the pump a few times and it'll start flowing.

2) The wort flows, but not at full speed, and there is air in the hose between the BK ball valve and the inlet to the March pump. The air gap in the hose appears when I turn on the pump, and it looks like wort only dribbles from the BK ball valve too slowly to feed the hose. If I turn off the pump, the hose fills immediately, but when I turn on the pump, it's as though something is restricting the flow from inside the BK. When this happens, it is much more difficult to resolve. I shut off the pump, close all valves, and try to reprime from the BK to the pump. Sometimes it works, sometimes not. Slowing down the pump by throttling it at the outlet side ball valve sometimes helps, but sometimes it just causes the whole loop to stop flowing. If I wait for the temp to drop a few minutes after flameout, I can get everything to flow properly without air in the lines.

I don't have any problem using the exact same configuration after a brew when I'm pumping 140 degree PBW solution through pump, Therminator, and back to BK for cleaning.

I don't have any problems with pumping sparge water from my HLT to my mash, or recirculating my mash. The temperature of the water or wort in those cases is much lower than in the BK. I use a different pump and dedicated hoses for the HLT to MLT sparge loop, but I've swapped things around and tried both pumps and all hoses in both situations, and it is still just the boiling wort BK loop that has the problem.

I don't believe any of my hoses are actually leaking and pulling in air, despite the apparent entry of air into the hose where it connects to the BK ball valve.

I came across some threads about a larger 2.156 inch diameter pump impeller that fits certain models of March pump. I have a compatible pump from Morebeer, a HS model with 3500 RPM part number 0809-0196-1000, so I just placed an order with Tesco for the new impellers (part number 0809-0107-0200). I'm hoping that will solve the problem, but I'm not sure if the problem I'm having is related to the impeller.

Has anyone experienced a problem like this or have any suggestions to resolve it?

 

[DeafSmith]

I had a problem losing prime on my March pump, only when trying to pump near boiling water from the kettle I use for heating water. This kettle had a dip tube from the ball valve inlet to the center of the kettle. Once I removed the dip tube I have no more problems. I leave some water in the kettle now without the dip tube, but it isn't a problem for me in this case because it's just strike water or sparge water.

 

[outside92129]

i had air-lock and priming issues and solved 95% of them with a auto-bleed device. I got four of them off ebay for $10, Watts FV-4M1. They come in different threaded sizes. Watts also makes a Duovent, it has both auto-float and a manual bleed button.

 

[billtzk]

DeafSmith, I have a dip tube that goes to the middle of my BK also. I wondered if that might be a problem during a hard boil, with large air bubbles coming off the bottom of the keggle. I don't want to remove the diptube altogether since I'd be leaving a couple gallons of wort in the kettle (ball is a couple inches up above where the keg bottom angles down). But maybe I could try a side dip tube.

outside, I've never come across those automatic vent valves before. Where did you install that?

 

[outside92129]

I put them on the output of the pump, i saw a Dutch fellow with the Duovent on youtube and copied him. I would have preferred the duovent but at the time 4 FV-4M1 for $10 was too good to pass up. It's basically a float valve so there are things to keep clean. But i haven't been super cautious about cleanliness and haven't had any issues yet. I just run boiling water + starsan through everything. If one were so inclined these units can be taken apart for detailed inspection/cleaning.

p.s. see my ghetto pump setup below. It's destined to be mounted to the stand but i haven't had the time to do that yet : )

 

[klyph]

How are you straining the hops and protein break in the kettle?
I also suspect your diptube may be preventing a complete purge, that's why bottom drains have become a design requirement for any system I build.
Try filling the hose like you describe and then raise and lower it a few times to push any trapped air out of the diptube. Impeller pumps are very finicky about air and restrictions in the lines. All the stars have to align for them to work smoothly, especially at boiling temps. If you could post detailed pics of your plumbing arrangement with hose and fitting types and sizes, we may have a better idea of what causes the issue. It could be something simple like a quick connect that slowly leaks bubbles into the intake side.

 

[billtzk]

Nice setup, outsider. Thanks for the picture. That would be easy for me to do, but I hope I won't need to. How effective is it? I would imagine that some air would get past the T in that configuration. The ball valve coming off the horizontal T and the vent valve straight up might vent air better.

How well do those cam and groove couplers work? Do they seal well, and are they quick to connect and disconnect? I was thinking of replacing my brass hydraulic moldmate couplers with those. They are pretty nice looking.

 

[billtzk]

How are you straining the hops and protein break in the kettle?
I also suspect your diptube may be preventing a complete purge, that's why bottom drains have become a design requirement for any system I build.
Try filling the hose like you describe and then raise and lower it a few times to push any trapped air out of the diptube. Impeller pumps are very finicky about air and restrictions in the lines. All the stars have to align for them to work smoothly, especially at boiling temps. If you could post detailed pics of your plumbing arrangement with hose and fitting types and sizes, we may have a better idea of what causes the issue. It could be something simple like a quick connect that slowly leaks bubbles into the intake side.

Paint strainer hop spider for pellet hops. I don't use whole / leaf hops. No FB in the kettle, just a naked dip tube. I've tried stuffing a stainless scouring pad under it, but it tends to clog up with hot break. So I just let the hot break and the pellet debris that escapes the net circulate through my plate chiller and pump. It winds up in my conical, and I dump it after it settles. I've never had any sort of clog.

I'll try to figure out a way to post pics tomorrow.

 

[BBL_Brewer]

I used to have the extact same problems you're describing. Pumping boiling water or wort was hit or miss. Pulling the dip tube will definitely help, especially in the HLT, but in the BK that's not really a great option. Your best remedy is to let it cool a bit before you start pumping. Once it gets around 200F you can pump just fine. It's the rolling boil that gets ya. I haven't had any problems since I started doing this.

 

[WalterAtMarchPump]

A rolling boil (or very near it) will have air bubbles at the bottom of your kettle. Depending on how much air you suck into the pump it will be hit or miss to keep it primed. What you can try if you are having issues and insist on trying to pump in that condition it to choke off the outlet of the pump and slow the velocity of the liquid coming out of the pump. This way the liquid going into the pump will be slower and there will be less suction velocity trying to bring the air bubbles into the pump. The pump will also be able to pass small amounts of air through it as well.....but suck a big enough bubble into it and it will cavitate.

-Walter

 

[outside92129]

billtzk- air getting past the T is already past the pump so it's not a problem. The contraption is only there to get air out of the pump to stop cavitation and help the unit prime. The camlocks work great. Not a drop leaks through. I did replace all the gaskets with silicon gaskets, you can get them real cheap. I source all my fittings from bargainfittings, proflowdynamics, or brewhardware- note that proflow has a slightly larger barb ID than the others. Of course many folks just put tubing directly on the threads for a cheaper and larger ID use.

316 Stainless Steel Cam and Groove Couplings for Homebrewers
Quick Disconnects / CAMLOCKS
Stainless Fittings

 

[billtzk]

BBL_Brewer and Walter, thank you both for the confirmation that the problem is related to the boil. The only reason I try to recirculate during the boil is to sanitize my plate chiller, pump, and hoses in preparation for wort chilling. It sounds like I need to rethink that approach, and maybe pump Star San through pumps and Therminator instead.

 

[billtzk]

billtzk- air getting past the T is already past the pump so it's not a problem. The contraption is only there to get air out of the pump to stop cavitation and help the unit prime. The camlocks work great. Not a drop leaks through. I did replace all the gaskets with silicon gaskets, you can get them real cheap. I source all my fittings from bargainfittings, proflowdynamics, or brewhardware- note that proflow has a slightly larger barb ID than the others. Of course many folks just put tubing directly on the threads for a cheaper and larger ID use.

316 Stainless Steel Cam and Groove Couplings for Homebrewers
Quick Disconnects / CAMLOCKS
Stainless Fittings

Thank you for the clarification on the vent valve, outside, and especially for those links. As for the air getting past the T, I was thinking that letting any of it remain in the recirculation path might lead to HSA. But I guess that may not be a problem during the boil?

 

[bucfanmike]

BBL_Brewer and Walter, thank you both for the confirmation that the problem is related to the boil. The only reason I try to recirculate during the boil is to sanitize my plate chiller, pump, and hoses in preparation for wort chilling. It sounds like I need to rethink that approach, and maybe pump Star San through pumps and Therminator instead.

Have you tried with chocking down the output as Walter suggested. I do the same as you and start recirculating with 15 minutes left and recirculate all the way thru the chilling. I have to mostly close the valve on the output side of the pump during the boil to keep from cavitating, then as soon as i cut flame and turn on the water to the chiller i can open up the valve.

 

[billtzk]

Mike, yes I do that. Quoting myself is bad form I know, but I said in the first post: "Slowing down the pump by throttling it at the outlet side ball valve sometimes helps, but sometimes it just causes the whole loop to stop flowing."

That was a long post, so "tl;dr" would be a fair reaction.

It's a juggling act. If I throttle it too much, the whole thing just stalls. If I don't throttle it enough, I get the air. And I have to keep watching it, because when it works, it may only be for a few minutes.

I wonder what temp and time is really needed to sanitize the chilling loop.

 

[klyph]

You can sanitize with 170 deg F liquid. You don't have to have it rolling boil when you sanitize.