Automation and Pump Cavitation

[FourSwitch]

Hey all, Ive been brewing electric for some time now as a "Four Switch" semi auto system, but am making a move to Full auto with the help of a BCS-462 and Arduino Mega (Thanks to Brundog for controller inspiration, though i purchased the 462 before i knew about "Brucontrol") Anyways.... the 462 programs very easily for my system [A standard horizontal 3 tier herms], and most all safeties are easily covered except pump cavitation!

Not that cavitation is a big issue or anything in my system, but incase I'm inside making lunch or who knows what, id like to plan for some sort of safety. which brings me to the RIB Current Sensor/Relay (http://www.ebay.com/itm/FUNCTIONAL-...176535?hash=item33c75e4697:g:b7gAAOSwCU1Ytqk3)

and: (http://www.ebay.com/itm/New-5V-DC-D...rn-off-Switch-Module-with-Timer-/181961529809)

So thats first in the running in my research so far for a nice cheap price point, with an adjustable trip point it should be able to trip easily when amperage drops incase of cavitation, (which is also usually happens when i finish my first runnings before batch sparging)

So Heres the plan...

i am going to use the 5vdc time delay relay to bypass the current relay safety for 5 seconds on pump startup, then switch back to the current relay.

so assuming everything goes wrong, and the pump cavitates, i can drop back to a 30 second prime rest or something of that effect as needed, or forward in my process in the case of batch sparging


So after that whole long winded explanation, i have two questions mainly;
1. Have any of you automation gurus even found this to be an issue worth pursuing?

and 2. Do any of you guys have a better way of accomplishing this goal?

let me know!
Thanks
Matt

 

[timdillon36]

For positive displacement pumps cavitation can be a problem, mainly because they use the fluid they are pumping to lubricate the moving parts inside.

If you are using an impeller type pump such as a March or chigger the only thing that will happen when you stop feeding it liquid is it will become a tiny little air pump. A centrifugal blower if you will.

In a typical setup it cant over come the pressure of the liquid in the discharge line to even contribute to hsa.

In short i think you are looking for a solution to a problem that doesn't exist.

 

[FourSwitch]

For positive displacement pumps cavitation can be a problem, mainly because they use the fluid they are pumping to lubricate the moving parts inside.

If you are using an impeller type pump such as a March or chigger the only thing that will happen when you stop feeding it liquid is it will become a tiny little air pump. A centrifugal blower if you will.

In a typical setup it cant over come the pressure of the liquid in the discharge line to even contribute to hsa.

In short i think you are looking for a solution to a problem that doesn't exist.

Hey Timdillon! Some good info there, I do like the point about the HSA being a non issue and it is true that I may be digging up a problem that may not be haha

I do know that chugger pumps, as non positive displacement centrifugal pumps will cavitate, decouple and usually send the radial impeller grinding along the Volute wall, also because it has a magnetic coupler, every time it decouples and jars the magnets on that link they become slightly weaker (in short I'll end up damaging the equipment) which was really my main worry I should have emphasized that more in the first post

Anyways long story short I think this will be a good way to protect the pumps, and I hope I can keep a bit of a knowledge share going on the subject I may get a few sweet tips before I build

 

[BrunDog]

Since I am named, I'll chime in (thank you for the props by the way). First, technically speaking, air ingress or loss of prime is not cavitation. Cavitation happens when certain areas in the pump's medium pressure drops enough to cause local boiling. This will happen in our world when boiling wort is pumped or when it passes through a restriction or similar diffuser. Cavitation will damage a pump's impeller or other parts over time, and it may cause our pump's to magnetically decouple. Usually adding a restrictive orifice downstream of the pump creates enough back pressure to reduce or eliminate cavitation. That said, it's not likely to have cavitation when the wort is well below boiling. That's probably just air ingress or loss of prime.

That said, I think if this is a problem for you (I suggest you don't chase it unless it is), I think it's worth solving. But doing it on the pump current draw may be a tough way to tackle it as AC motors often draw more current when they are under less load. I don't know for sure if that occurs here - you should test it with an ammeter to see measurable differences before going that route.

I think a better way is to use a flow switch. They are simple to install, are inexpensive and are reliable. They are used here to stop a RIMs from heating when flow stalls effectively. You could easily tie one into your automation controls and incur a recovery/alarm loop.

Also don't sweat damage to your pump when it loses prime. As long as the impeller is wet it will be fine. You don't want to run it dry for long, but a few seconds is no biggie. You are right about magnetic decoupling - I think it wears the magnets. But you know when it happens... the motor takes forever to spin down and you hear it "click" as the magnets recouple at the end.

 

[FourSwitch]

Good points as well Brun i feel a bit better with that explanation(maybe I've just heard too many pump horror stories from other brewers). Since i have started down this path anyways i figure ill probably pursue it anyways even if its nothing more than exercising the mind

I did a quick check on amp draw of my first chugger pump with flow, and again with loss of flow or lack of prime, and i have to say i was rather disappointed with the results, the pump was pulling 1.5A at 120vac with prime, and 1.4a without prime. so my current sensors would be nowhere near sensitive to trip on that (it was a pretty snazzy idea though!). I think Flow switches are the next easiest option! ill start looking into those tonight!

Thanks
Matt

 

[BrunDog]

These are inexpensive and can be put right inline with current hardware as they come female or male threaded. You can wire directly to a BCS input. In BCS you can create a state which checks for it and handles if it is not, or use the ladder logic, though that may be trickier because you need the pump to be on before checking, so would probably need to use a register as a gate.

Also, given you are using an Arduino (not sure in what capacity), you could use a flow-meter and utilize it for more than one duty. More work to implement, but if you want to know the flow rate beyond a binary setting, you could go that route. Note there aren't many cheap-o's which can handle boiling wort.

 

[FourSwitch]

Hey Brundog, yeah i've looked up a few different examples of high temp flow switches, which should do the job, (an at 6-12$ a piece thats not a bad deal either)! [Automationdirect has a piston module thats an adjustable set point! looks pretty good, but 125$ ish] i would probably still need that 5vdc time delay relay module just to keep things simple and easy, i already have my bcs looking for a lack of input on that pin when the pump is running, so that'd be an easy drop in solution for now

You caught me on the arduino mega! Honestly ill be able to easily run the rig on the bcs with little to no issues! i do plan on doing little upgrades and additions here and there though, and that'll definitely give room for expansion! I really like you're kettle volume measurement system but i hate cleaning little fittings and such... lately i ran across a post from a clever guy in finland i think it was? Hop rod garage (something close to that) and he was using a load cell (or possibly 3 or 4 in parallel) to calculate weight and volume of his kettles! so i may mess around with that once this is up and running!

but with everything, its a learning process for me so its a lot of try, fail, learn, so i may end up changing course on that later too, who knows! or just using the mega to control a fermentation! either way its always good to leave room for future projects, i find its often more fun building the panel than it is brewing with it haha

Matt

 

[BrunDog]

Cool. Building this stuff is 90% of the fun!

I think the load cell method has been with moderate to low success, but give it a go. I will tell you I dont have to clean any fittings (theoretically) with my method - PBW takes care of that!