March 815 Intermittent Flow During Whirlpool

Before I start, I'm a first time poster and long-time reader, so thanks for all of the great info that everyone has provided on these forums!

Now, I've sifted through a ton of the March related issues and posts on this, and other, forums and I haven't quite been able to find an answer to an issue I'm facing.

A quick note on my setup - Extract, full boil, 10gal kettle on ~18" tall burner stand, IC with "Mr Malty" style internal whirlpool, March 815 sitting on ground, 4' inlet and outlet hose on pump with a ball valve on the outlet of the kettle and the outlet of the pump.

That being said, I usually put my IC in the boil for the last 15min and start the pump to sterilize the system. I run the pump for the entire 15min and typically have no problems. The problems usually start at flameout. Almost immediately after killing the flame and turning on the cooling water to the IC, the March starts emitting a higher-pitched noise and the flow stops. If I unplug the pump, then start it back up, it will pump for a few seconds (low-pitched noise) then stop again (high-pitched noise). I have to do this several times before the pump flows continuously. Note that even when it's running continuously it makes a "rattling" noise.

I did come across several comments regarding missing thrust washers creating similar problems. So, I pulled the pump apart, expecting to find a missing washer, but there it was - my thrust washer was present and in tact.

So, can anyone comment on what might be happening? Do I need to throttle the pump outlet valve to maintain higher head pressure?

Thanks!

I've had similar issues with my chugger pump. I think it has to do with the hot wort releasing air bubbles in the pump which un-primes the pump. I solved my issues by throttling the outlet on the pump.

my $.02

Just to review: if it was bubbles during the boil that cause the pump to cavitate (a pretty common lament, actually) the OP would have had that problem while the boil was still going. He claims he doesn't - his problem starts when the boil is done - and one would assume pretty much bubble-free.

And it doesn't appear he's posting from Bizarro HBT...

Cheers!

And it doesn't appear he's posting from Bizarro HBT...

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?

@op maybe you'll find an answer here: http://www.capandhare.com/forums/archive/index.php/t-4325.html

So, I think maybe it's cavitation. I can't quite explain why it only starts at flame out, but my QD fittings are only 3/8" ID on the suction side and I'm using a modified street elbow as a dip tube. Compound that with a fairly open discharge path and I'm pretty sure I've got a pressure gradient issue.

I ordered some 3/4" QD fittings (1/2" ID) and a 1/2" ID dip tube so we'll see if that fixes the issue. If not I'll try throttling the outlet valve to keep the pump from overrunning.

I thanks for the responses.

So, another brew day and I've got an update.

After opening up the QDs to 1/2" ID and shortening the hose on the suction side I had one instance of flow stoppage. After that I choked down the pump out ball valve just a hair and had no problems from then on.

My conclusion is that the pump was cavitating and that the open flow on the IC outlet was allowing the pump to overrun and disengage the mag clutch. So, free flowing suction path + outlet pressure = problem free pumping!

Thanks everyone.

harrij4 said:

So, another brew day and I've got an update.

After opening up the QDs to 1/2" ID and shortening the hose on the suction side I had one instance of flow stoppage. After that I choked down the pump out ball valve just a hair and had no problems from then on.

My conclusion is that the pump was cavitating and that the open flow on the IC outlet was allowing the pump to overrun and disengage the mag clutch. So, free flowing suction path + outlet pressure = problem free pumping!

Thanks everyone.

Click to expand...

You got it. The NPSHrequired goes up as the flow goes up. The NPSHavailable goes down as the temperature goes up. The NPSH available at boiling is by definition the vertical head above the pump, less suction losses. The rattling sound is your pump destroying itself. It will chew up impellers and pit stuff up pretty fast. Stainless steel can look like swiss cheese from severe cavitation. It's bubbles of steam forming then violently imploding. I doubt is was your clutch disengaging, more like no flow from vapor lock.