PaullyP wrote:

> I own a couple of espresso cafes in my city and business is good and
> turnover is brisk.
>
> We have always used a great amount of whipped cream - on drinks and
> served with deserts. I started out using the conventional disposable
> cannisters of whipped cream, and found them expensive on a per serving
> basis.
>
> So, always on he lookout for cost-cutting measures, opted to buy a set
> of iSi cream dispensers - a very good investment ... as they produce a
> thicker higher quality cream product, and also allow for addition of
> flavouring to my base cream mix ... very nice!
>
> The downside of these cream dispensers, is that I seem to go through a
> high volume of N20 (notrous oxide) bullets/charges./cartridges ...
> which are used to add a pressure base to the dispenser, turning liquid
> cream (which is added to the dispenser) into a 'whipped' final form
> (which comes out of the dispenser's nozzle).
>
> However, while a cheaper option than the disposable whipped cream
> cannisters, the number of N20 bullets/charges./cartridges that I go
> through is alarmingly high.
>
> And that is where I decided to look for a bigger and cheaper N20 supply
> alternative.
>
> I visited an industrial gas operation that imports tanks of N20 used
> for the midical market - 5 feet high, and can store some 26 kg of N20
> product - quite the volume alternative compared to a single N20
> bullet/charge/cartridge that holds a mere 8 grammes of N20 product.
>
> I need no license or permit to buy the product, and the cost per tank
> comes in at USD$175, and a rental of USD$25/month for the 5 foot
> clylinder - i.e. I am buying the N20 but not the cylinder, I have to
> rent it. Still seems a fair deal ... especially since one single N20
> bullet/charge/cartridge will cost me close to USD$1 including freight,
> etc...
>
> Doing some arithmetic .... from 1 large cylinder @ 26kg (26,000
> grammes) I should be able to get 3,250 small N20
> bullet/charge/cartridge servings of gas (26,000 / 8 grammes) .... quite
> the saving on a dollar to dollar basis. And even allowing for some
> additional wasteage from using the larger cylinder, loss of
> pressurisation, etc.... the economies of scale are still very prevalent
> in my mind.
>
> So ... how to get the N20 from the large cylinder into the cream
> dispenser?
>
> Well, took one of my dispensers to their factory and they can supply me
> with a regulator and the hosing/pipes needed to connect the big N20
> cylinder to my dispenser ... simply turn the 'tap' on the cylinder and
> the N20 should flow directly into the cannister.
>
> Now this is where it gets a little grey ...
>
> How do I gauge how much N20 to put into my dispenser?
>
> Well, my dispenser has a volume of 1litre, and I add two small N20
> bullets/charges/cartridges for a 'full load' of liquid cream base ...
> so I need 16 grammes of N20.
>
> While I can't possible measure how much N20 I am exactly filling into
> every individual cream dispenser, surely there must be a pressure
> release mechanism in the dispenser that releases some N20 gas when the
> pressure in the dispenser goes above the optimum limit?
>
> I am hoping so.
>
> I already emailed the manufacturer of my dispensers (iSi) asking about
> the pressure release function - NOT stating that I intend to use a
> large cylinder to re-charge my dispensers ... and will post their reply
> along with my test results once I get my large cylinder and hose
> mechanism sorted out.
>
> I just thought I might invite some comments about my idea and perhaps
> shed a little light on other potential (more economical) gas-refilling
> options out there.
>
> Thanks for your time everyone! :-)
>
> Regards,
>
> PaullyP
>


There is no gas metering system in an iSi. You have a premeasured
charge of N2O and it releases all of it at full pressure (minus the
pressure drop across the orifice at the puncture site) when you tighten
the cartridge holder. The pressure in the cartridge drops rapidly as
the pressure in the 1L dispenser rises, and they reach an equilibrium
when the cartridge is almost empty. The first time you dispense some of
the whipped cream, the pressure drops and the rest of the N2O goes from
the cartridge to the cream.

The bulk N2O tank can supply a relatively unlimited supply of gas at
whatever pressure the regulator is set to. So you'll need a regulator,
a hose that is good to, say, 100 psi, and a bulk gas adapter for the iSi
(I don't know if there is such a thing.) You'll probably need to set
the regulator at something like 40 to 60 pounds. To avoid wasting a lot
of N2O, what you will want to do is charge the dispenser with a shot of
gas, then remove the hose. Something like a tire valve.

You might can have a machinist make an adapter out of a stainless steel
tractor tire valve stem. (Custom design and machining is expensive.)

If you *really* use a lot of whipped cream, maybe what you need is to
adapt a 3 gallon or 5 gallon "Cornelius keg" to use N2O instead of CO2
and fill it with cream. I think that's what I'd do.

BTW, I think you are paying way too much for the nitrous.

Bob