Air in my pumps

[calumrobertson]

Hi,
I recently purchased two mag pumps to replace mini solar ones which i had. I've always had a bit of an issue with air in the pumps but my first brew at the weekend with the new pumps was a bit of a nightmare with air switching the pumps on and off (they have a sensor which prevents them running dry). I've seeled all the connections with PTFE tape and tried my best to minimal air in the pumps from the start but still seems to be an issue. I cannot understand how air gets in at all when im pumping between two vessels containing only water or wort!
I've read that if i put a three way ball valve after each pump you can get rid of air pretty effectively by running through one outlet before turning the lever to the position you want to pump fully too.
Just wandering if anyone has had similar experiences and any wisdom to pass on as a result?!
Thanks

[Andy]

Are you flooding the pump head with water/wort before turning the pump on?

[calumrobertson]

Yup, leaving the valve full open to 'prime' it.

[guypettigrew]

Which pumps are you using? The idea of having pumps with sensors to ensure they don't run dry is very appealing!

Guy

[dloper]

I've noticed bubbles in the line when pumping hot wort from the bottom of my kettle to my heat exchanger and on to the fermenter. I don't think air is getting in and I was wondering if the pull of the pump was creating a partial vacuum in the line causing vapour bubbles in the hot wort, in the same way that water will boil at a lower temperature if the ambient pressure iss reduced. Probably beer induced nonsense, but it's a thought

[irv]

this is probably more relevant when priming the pumps: Is the pump lower than the pot? also if you can, orientate it so that the output of the pump is facing up, then any air should be expelled rather than rattling around the pump head.

[calumrobertson]

Cheers for all the advice..yup done all that...pumps are below pots, outputs point up etc...will try with three way valves and see if i can purge all air before switching to outlet to mashtun or boiler

[Jocky]

I found I was having the same problem until I always ensured that the open end of the hose I was using on the outlet side passed above the point of the valve on the pot I was drawing liquid from.

Otherwise the liquid naturally syphons itself out. Ideally you want to empty from the bottom of a pot and fill at the top.

Also the pump needs some back pressure - either having the eventual outlet higher than the liquid level on the inlet side, or (initially) restricting the flow on the outlet side. This is particularly important when trying to pump out the mash tun, and the grain restricts how much liquid the pump can draw in.

I'm probably going to buy a cheapy PWM circuit off eBay to give me direct speed control of the motor in future, rather than battle with the valves.

[Fil]

afaik the problem is identified by the term 'cavitation' if you want to look it up, and can ocour when there is gas 02/co2 disolved in the liquid, the agitation of the pump impellar will 'knock' the gas out of suspension just like shaking a can of fizzy drink.

the simplest way to eliminate it afaik is to preheat the liquor to boiling temps which will eliminate any absorbed/dissolved gas in the liquor, however its not always practical,

another solution would be to add a T fitting post the pump with a short length of tube pointing upwards, any escaping gas would then rise up the tube, where you could fit a screw fitting to seal and bleed off the gas.

hope thats useful

[calumrobertson]

Thanks v Mich for the advice..I've ordered some 3 way valves which should allow me to bleed the airmen fingers cross will work well!