Demand Valve or Check Valve?

[Nickmann]

I've been using 20l polypins connected directly to beer engines. A bit of reading on this forum and I see that others are using demand valves and/or check valves. My beer lines are just a straight run from the polypins to the engines, the only fittings are the size changes on the way.

What am I missing by not having valves in the line?
And do I need a demand valve, or a check valve, or both?

Cheers
Nick

[paulg]

you normally would use a check valve in the line between polypin and beer engine to stop beer being forced out of the beer engine if excessive pressure builds up in the polypin.
like this

http://www.ebay.co.uk/itm/Real-Ale-Chec ... 2583cc0aa8


A demand valve is sometimes used to describe a cask breather/aspirator which supplies co2 at atmospheric pressure to fill the space created in a cask when you draw off beer,this is not needed with a polypin as the polypin collapses when beer is drawn and therefore no space is created needing air.

hope this helps

[Nickmann]

Thanks Paul, that makes sense.

Do you think this will do the same job for considerably less cost?
http://www.ebay.co.uk/itm/John-Guest-3- ... 233a9f597b

[CJR]

I'm just thinking, if you're using a poly with an engine then you shouldn't really need a check valve if you crack the lid open as you serve?

I use a demand valve because I'll be doing it from pressurised corny to engine. A poly or Bag-in-Box method shouldn't need a valve in line.

[paulg]

nickmann
yes that would work ,I think jim used one of those with his pressure barrel.
you may need a check valve with a polypin depending on how much pressure builds up in the polypin depending on amount of priming sugars used.
dennis king recommended that you keep the pin with the tap on top while it is conditioning until you are ready to serve it cracking the tap occasionally to release pressure if the pin gets too blown up. Then setting the polypin ready to serve and allowing the beer to clear before serving

this is an interesting read if you have an hour or two to spare
viewtopic.php?f=6&t=11340&hilit=polypin+management

[Nickmann]

Ah yes I think I see the difference now. The pushfit check valve is simply a one-way valve, whereas the link you posted is a pressure-differential valve.

I've yet to have a problem with pressure in a pin (maybe I empty them too fast!). I can see the value of preventing beer creeping back downhill into the pins, and a JG valve is easier to source and fit than making a new seal and seats for the beer-engine valves.

Thanks Gents
Nick