Corny Kegs Made Easy: A guide round the keg

Discussion in 'Beer Brewing "How-To" Guides' started by Vossy1, Jan 1, 2009.

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  1. Jan 1, 2009 #1





    Jul 28, 2008
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    Manchester.....scorchio !
    History of the corny keg

    Cornelius kegs, or corny kegs as they are known to home brewers, were originally designed primarily for use in the soft drinks industry. A concentrated syrup would be placed in the keg and then either carbonated water, or water would be added. The soft drink would then be served through taps in a bar, restaurant etc, using C02 gas to push the liquid out of the keg. There are a few brands/manufacturers of corny kegs including, but not limited to, Cornelius, Challenger, Firestone etc. These kegs have now almost entirely been replaced by the 'bag in the box' delivery system.
    The main body of this text will refer to use of Cornys with beer of one type or another, however, they can be used for cider, wine, carbonated water and other drinks.
    The information in this text is based upon my own experience and it is not necessarily a definitive guide.

    Why use a corny keg?
    Corny kegs offer durability through their stainless steel construction and with a little care theyll last a lifetime. They do not allow light through to the liquid within, thus eliminating any possible skunking of beer. They are quite flexible in use, allowing naturally primed ale to be drawn via a beer engine, and at the other end of the scale, they allow force priming with large volumes of C02 or other gases. They are relatively cheap when bought 'used' and their resale value can be excellent.

    What is a corny keg?

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    The most common form of corny keg for home brewing consists of a stainless steel tank which has a rubber base and top bonded onto it. The rubber top has handles moulded into it for easy handling. It also has 2 posts screwed onto it, one is to allow liquid out of the keg, and one is to allow gas into the keg. There is also a lid and it is sited centrally. The keg can be filled with almost 19ltrs of liquid and it can then be pressurised with your choice of gas. The picture far right shows information which can be found on the outside of most corny kegs. From the top, unit number, manufacturer, maximum operating pressure, fill volume, country of origin and year of manufacture. There are other corny kegs available with smaller and larger fill volumes, some dont have a bonded rubber base or top, and the colour of the base and top material may vary.

    Tips for buying a corny keg

    Always buy the keg from a reputable supplier or one that is recommended, and check that the keg has been pressure tested. Most kegs are supplied used, and during their life span should have been regularly serviced. If the keg looks "tatty" the chances are it's had a hard life, don't buy it!
    Check the handles on the kegs rubber top are firm and not saggy/too flexible.
    Lift the keg slightly off the ground then drop it. The base should sound solid as it hits the ground. If it sounds hollow the bonded base will be coming away from the keg, don't buy it!
    Check for gaps between the rubber bonded base/top and the keg, indicating they are working loose.
    Check the exterior of the keg for any signs of deep rust/scratches. Surface rust may be repaired and shallow scratches ignored, but deeper rust/scratches may have weakened the keg wall, making it dangerous to use with pressurised gas.
    Minor dents in the steel body aren't a major issue, but it's preferable that the keg is major dent free, though they can be knocked out.
    If possible, check the posts and the threaded post ports on the keg for signs of rust. The posts can be replaced, but rust inside the threaded ports on the keg will be very hard to remove.
    Check the poppets for signs of rust and check the o-rings for cracks. Most poppets aren't serviceable and will need to be replaced if in poor condition.
    Take the lid off the keg and check it for rust or pitting. Remove the prv and check it for rust and that the o-ring/seal is in good condition. The prv is not serviceable and will need replacing if in poor condition.
    Check the inside of the keg for signs of rust, pitting and deep scratches. Be especially vigilant around the welded areas, and under the lid seating area for rust and pitting. A metal spoon can be used as a mirror to check under the lid seating area.
    Surface rust can be removed but pitting may have weakened the keg wall making it dangerous to use with compressed gas. Deep scratches are very hard to clean and sanitise, and can harbour bacteria, so should be avoided.
    Most of the kegs available will have been used in the soft drinks industry. If the o-rings smell of sweet syrup, or show any signs of cracking, they should be replaced.

    Repairing minor rust on corny kegs

    Minor surface rust on corny kegs may be treated by using a fine grade of wet sand paper.
    Gently sand the area until all the rust has been removed.
    Dry the area thoroughly and allow the affected area to be exposed to air for 24 hours.
    This allows the metal to react with the air and form a protective oxidised layer.

    Buying spare parts for corny kegs

    Parts for corny kegs are readily available within the U.K and from abroad, though prices may vary.
    Items that can be replaced include:-

    O-rings which are usually cheaper to buy as replacement kits.
    Posts and poppets, better bought together to ensure they are compatable.
    Dip tubes.
    Lids and prv's, again better bought together to ensure they are compatable.

    Items that cannot be replaced include the keg body, base and top.

    The lid

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    The picture above shows a typical corny lid. It consists of the lid body, an o-ring, a lever to open and close the lid which has removable feet attached to it, and a pressure relief valve (PRV).
    Some lids may have different types of PRV's which may not be interchangeable with other lids, and some don't have a PRV fitted at all.

    Opening the lid


    To open the lid, first lift the PRV to release any pressure in the keg. The PRV has a split ring which sits in a small recess on the top of the PRV body. Lifting the ring releases the pressure in the keg. If you turn the ring 90 degrees after lifting it, you can let go of the ring and the PRV will remain in the open position. To close the PRV simply turn the ring until it springs back into the recess in the PRV body. If there is any pressure in the keg you will hear a hissing noise, which can be quite loud if theres a lot of pressure in the keg. Once you have vented any pressure lift the lid lever to a fully vertical position. At this point the lid will detach from the keg by moving downwards. Turn the handle lever 90 degrees and the lid will fall into a vertical position, now you can lift the lid and remove it from the keg. Lid o-rings are available in various colours, and some are made of a softer material to aid sealing when in use.

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    Tips for removing the lid

    If your corny keg has been used you may find the lid does not drop down when you lift the lid lever. If this happens push down on the lid and it should come free. If it still remains 'stuck' there may still be pressure in the keg, vent as above and repeat removing the lid procedure. Also, sometimes the lid o-ring may remain 'stuck' to the mating surface of the keg body. If this happens remove the lid, then gently prise off the o-ring using your fingers.

    Corny keg posts

    On the top of the keg you will find 2 steel posts. Near the posts moulded onto the rubber body will be the words 'in' or 'out'. 'In' signifies the post allows gas into the keg and 'out' that the post allows liquid out of the keg. On some kegs the 'in' and 'out' may be found stamped into the metal of the corny body, behind the post, near the lid.

    Removing the posts


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    To remove the posts use a ring spanner of a suitable size, the most common post size being 22mm. Turn the post in a anti clockwise direction and once loose continue to turn the post by hand until it comes away from the keg body. Next withdraw the dip tube by lifting it from the threaded port on the keg.

    Each post assembly consists of a post, a post o-ring, a poppet, a dip tube and a dip tube o-ring. The 'gas in' dip tube is approximately 40mm long whereas the 'liquid out' dip tube reaches all the way to the bottom of the keg. The post o-ring can be removed from the rebate in the post by using a fine blunt palette knife, a fine pointed knife, or any method you prefer, but care must be taken not to damage the o-ring. The dip tube o-ring simply slides off the dip tube. The poppet usually falls out of the post when the post is lifted of its mounting point. If the poppet remains in the post body, simply push your thumb down on top of the post and the poppet will fall out. The poppet is the only part of the post assembly which cannot be dismantled.

    The o-rings for the posts and dip tubes are available in a variety of colours, and some are made of a softer material to aid sealing when in use. Some poppets are post specific and cannot be used with other posts and some posts are keg specific and cannot be used with other kegs. Most U.K sourced corny keg posts, use a 'ball lock' mechanism on the connector. There is a type of post which uses a 'pin lock/bayonet' mechanism, but these are generally quite rare in the U.K.

    How does a post work ?

    When the post is tightened onto the keg, the poppet is compressed and its o-ring seals against the top of the post. The dip tube o-ring seals the dip tube against the keg and it also forms a seal against the post interior. The post assembly now has an air tight seal. The only way to break this seal to allow gas or liquid into, or out of the keg, is to attach a post quick disconnect (see below)

    Post connectors (aka quick disconnects, QD)

    To get gas and liquid into and out of a corny keg post, quick disconnects are required.
    They are available in a variety of body colours, however grey and black are the most commonly used in the U.K. Grey disconnects are attached to the In post (Gas), and black are attached to the Out post (Liquid). Both QD's are virtually identical in appearance but they only fit onto the posts they are designed for.

    The picture below shows 3 QD's for liquid and gas. The basic disconnect (far left in each picture) shows the body and a branch on the body with a screw thread.
    To this thread you can add either a John Guest (JG) speedfit fitting (middle) or a barb fitting (far right). Using either fitting allows suitably rated 3/8th inch diameter tube to be attached to the QD. The JG fitting allows greater flexibility in use as a insert may be used to reduce the tube diameter which can be used. Some QD's are manufactured with a barb fitting and it cannot be removed from the disconnect body.

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    How to put a QD onto a corny post.

    A QD has a spring loaded collar around its base and when lifted, a series of ball bearings are free to move outwards. When the collar is released the ball bearings move back towards and are locked into a groove on the post.
    Lift the collar upwards whilst simultaneously pushing the QD onto the relevant post. When the QD stops moving downwards onto the post, release the collar. Without lifting the collar, give the QD a quick tug upwards to ensure it is locked onto the post.
    To remove a QD from a post simply raise the collar and lift the QD.

    How does a QD work ?

    The post when assembled on the keg is a sealed unit, and it has only one moving part, the poppet. The spring on the poppet body pushes the poppet o-ring up onto the internal surface of the post, creating a seal, stopping liquid or gas from leaking out. When a QD is put onto a post, it pushes the poppet down into the post, breaking the seal between the poppet o-ring and the post. At the same time the resistance from the poppet spring pushes the QD pin upwards, breaking the seal between the pin o-ring and QD body. This forms an open pathway for the liquid or gas to flow along.
    When a QD is removed from a post, the springs in the QD and poppet again push the respective o-ring assemblies against the bodies and the keg and QD are sealed.

    Dismantling a QD

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    Each QD has a screw located on the top. Using a screw driver undo the screw by turning it anti clockwise, and remove the screw body. The internal components of the quick disconnect should come away with the screw. If they dont, they can be easily removed by turning the QD upside down and then pushing the pin from inside the QD (see picture with pin above).
    The internal components consist of the screw body, screw seal, spring, and a pin assembly with an o-ring. The screw heads come in 3 guises including flush, recessed and proud. The pins may come in various guises including one piece moulded metal or plastic with an 0-ring, to 3 part pin bodies. The internal parts all do the same job and they are all interchangeable between posts.

    Tips for using QD's

    Never force a QD onto a post, it may be the wrong post, and once they have been incorrectly fitted, they are very hard to get off.
    Never put a QD onto a pressurised keg unless the tube is attached to something i.e., a tap or gas regulator.
    If using the barb fitting it is always good practice to secure the tube with a clamp e.g, a jubilee clip.
    If using the speedfit fitting, cut the beer or gas tubing ensuring it has no rough edges. This prevents any damage to the o-ring within the fitting. You can do this by using a sharp knife to cut the tube and then rolling the cut tube edge at an angle on a hard surface using slight pressure. This bevels the edge and minimises contact of the cut edge with the o-ring.
    If the QD collar cant be raised prior to taking it of a post, try pushing down on the QD and then raising the collar.

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