Blending trimix > air comp or booster ?

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Etmutt

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Hello all,

New around here ; I hope this section is the right one.

I’ve been diving trimix recently but the nearest dive shop that fills trimix is a few hours away. So here i am : looking into doing my very own blend!

From what I gathered on this post, there are 2 main low tech ways and I’m not too sure which one to go with. I'm not really looking for a short and efficient fill time ; but rather for a simple, compact, not too expensive setup.
Any advice between the 2 setup below ?

  • Mini air compressor to fill in helium and then top up with nitrox in a dive shop
    • Plus : fast, rather cheap with a simple compressor
    • Unclear :
      • Blow by : Assuming I will never fill above 120bars of helium, what % of blow by should I expect?
      • I read the air quality of the air compressor might be an issue, but I don’t understand how it is different from the standard air fill we get in any dive shop

  • Booster to fill in helium and then top up with nitrox with the booster
    • Plus : setup compact, can top up nitrox as well from a tank
    • Unclear :
      • Drive gas consumption: can I expect to fill in a twin set with helium, using another twin set of air as drive gas?
      • Scavenging capacity : what is the left over in your experience ?
 

_Ralph

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Have no experience with a dive compressor, and have just got my booster setup completed...


Drive gas... it depends on 3 factors... drive gas pressure, supply gas pressure and output cylinder pressure.


Scavenging, again, depends primarily on your booster design, and output cylinder pressure.

I have a double acting, 2 stage booster that has a 40:1 ratio. I have drained cylinders down to ~12bar while boosting it on 200bar.. but it starts to use up a lot of drive gas as you go along.

If you are getting any booster larger than a ‘mini’ or ‘baby’ booster, that are really only setup for small CCR bottles, it makes sense to invest in a shop compressor (bigger the better) with filters to drive the booster, than using a scuba tank to run it.


_R
 
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Etmutt

Etmutt

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Hi Ralph,

I ve spent a bit of time looking at the setup the nearest dive shop has this weekend ; and to my surprise they have ... no setup. They just buy a bunch of tanks and cascade them to scrap the helium down to 10 bar.

I've runned a few simulations and with 3 He tanks it adds up. Assuming I will mainly fill 35 to 45% He, it will be leaving about 10 to 15 bar in the tank which seems acceptable.

It means it will not be possible to top up whatever is left in my twinset at the end of the dive; but anyway I plan it down to 0 and I use a 3rd tank with the bottom mix that shouldn'nt be touched.

So I will start with this and if I end up throwing away too much gas at the end of my dives I will go for the booster option, it seems like the easiest one
 
https://www.shearwater.com/products/teric/

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