Ball valves leaking under suction?

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fraser_john

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For GABF I had an interesting bit of feedback that made me watch my hot side very closely last time I brewed. The comment was always around "oxidation". Now, oxidation without acetaldehyde means it has to be hot side aeration.

Don't start on about it does not matter for home brewers, because, "most" the judges at GABF were Little Creatures brewers, so I paid attention to their comments, so it really must matter to home brewers!

Anyway, I doughed in, set bed, started the pump and monitored and monitored, sure enough after the wort cleared, there was a stream of very small bubbles. I decided I must have a leak somewhere, so after the brew was done, I tore down the entire setup and reassembled everything with food grade silicone sealant on EVERY joint. Hose clamps every where, the full enclosing crimp type too, so no way was air getting in.

Filled the mash tun with water started the pump, no air bubbles whoo hoo. But, I thought, the mash bed results in a bit of suction, I wonder if the suction cause the leak, so I closed off the mash tun ball valve little by little until I could hear the pump cavitating, so air was still getting in. I opened the mash tun ball valve all the way and sure enough, out comes a heap of air from the return line.

After using the food grade sealant, all that is left is two ball valves before the pump inlet, one three way and one simple one, both similar to the pictures below.

Does anyone know if these suckers can leak under suction conditions? Are the three piece ones better under suction conditions? Pretty frustrating to spend a whole day rejigging the system just to find the same result!

ballvalve.jpg
bola_tek_3_way.png
 

Mr B

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Fraser, as I understand it cavitation can be both air getting in and causing a 'loss of grip' of the propellor etc, or it can be the propellor having enought force to essentially pull the air from solution by causing high/low pressure zones.

The latter could be your problem as you increase suction?
 

fraser_john

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Mr B said:
Fraser, as I understand it cavitation can be both air getting in and causing a 'loss of grip' of the propellor etc, or it can be the propellor having enought force to essentially pull the air from solution by causing high/low pressure zones.

The latter could be your problem as you increase suction?
Nah, cannot be that, once I opened the valve up, sure enough a bunch of bubbles came flowing out, so definitely caused by a leak.
 

fraser_john

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wide eyed and legless said:
I can't imagine a ball valve leaking, what about the threaded joints on the valves is there any possibility that could be the problem?
I had started to wonder about this last night, when you pull them apart there is a hard plastic o-ring, might measure that up and order silicone ones from oringsandmore.com, there is also a hard plastic seal where the tap shank goes through the body, could be there as well, another o-ring replacement job I think.
 

manticle

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Oxidation of ethanol results in acetaldehyde but there are other products in beer that can be oxidised (hot and cold side).

Can't help with the ball valves question though, sorry.
 

Mardoo

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fraser_john said:
I had started to wonder about this last night, when you pull them apart there is a hard plastic o-ring, might measure that up and order silicone ones from oringsandmore.com, there is also a hard plastic seal where the tap shank goes through the body, could be there as well, another o-ring replacement job I think.
Would you like to be on my new TV show, "Pimp My Ball Valve"?

Seriously though, I'm very curious about your results.
 

fraser_john

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Mardoo said:
Would you like to be on my new TV show, "Pimp My Ball Valve"?

Seriously though, I'm very curious about your results.
I'll post info once I figure the details
 

MHB

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Interesting problem.
I think that if they are leaking under suction they should leak under pressure so my first step would be to put them in a bucket of water and pressurise the circuit by hooking it up to a CO2 reg/air compressor/bike pump... apply some pressure - just like finding a pin hole in a bike tyre. Might help you to figure out where its leaking.

I have never seen a reasonably new WOG ball valve leak as you are reporting so I suspect its not a common problem, makes the odds of there being a faulty part in one of the valve a lot higher; careful examination of all the parts might show where the problem is.

Other possible fixes might involve the layout of your system, keep the pump as low as possible maximising supply pressure (head), only control flow at the outlet, make the plumbing in a bigger diameter than the plumbing out, all the basics of good hot pumping configurations.
If you are switching between multiple inputs, make sure you close the outlet control or turn off the pump before switching inputs.
Mark
 

TheWiggman

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To clarify, what a lot of people call cavitation and what cavitation is is different. Cavitation is the vaporisation of liquid due to pressure differential (i.e. suction) under flow conditions. The vaporisation point of water is about 95 kPa at 20°C, and 70 kPa at 65°C. This can be identified using a phase diagram. The Kaixin pumps are good for about 3.6m of head, so 36kPa. At best they are able to apply 36 kPa of suction so in reality your home brew pump is very unlikely to be cavitating.
I'm not being a smart arse, because this means that what you're seeing is air entrainment. There literally has to be air either in the system of being sucked into the lines.

Those ball valves don't perform any differently under suction. If you aren't seeing a leak when pressurised, it won't be letting air in under suction. I deal with them all the time industrially and the only place they will leak is through the seal where the handle connects to the ball. It's uncommon, but does happen.

I'd say with confidence what's probably happening is one of two things
  1. There is a high spot somewhere in the suction side and air is trapped there. When pressure conditions change (open/closing valve) the bubble moves and is sucked through the pump
  2. A small air leak through a barbed fitting, which is more likely to occur under suction
 

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