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Prist / Additive  
User currently offlineAirPortugal310 From United States of America, joined Apr 2004, 3717 posts, RR: 2
Posted (6 years 10 months 3 weeks 5 days 1 hour ago) and read 2587 times:

I have been working for the past 3 months as a fuel person for a well-known private jet "broker" and have a few questions regarding Prist or other additives:

It has to be pre-mixed or mixed with the fuel as it enters the tank but, what does it really do. A google search or two tells me that it is to prevent freezing or water droplets in the fuel if they exist and also, that it acts as an anti-microbial agent.

Now, it is generally optional (i.e requested by the flight crew) and other times is a requirement for operating to colder areas such as winter time in the Northeast etc...

So, the question is really: Can someone knowledgeable (which most here on this section are) explain some things about it and if there are different kinds of it? Also, some of the reason why some planes need it more than others?

And why does the cost range from, what I have been quoted here and there, anywhere from .02 to .011 cents per gallon of Jet-A added? And does 100LL need it?

Thanks!


I sell airplanes and airplane accessories
7 replies: All unread, jump to last
 
User currently offlineKELPkid From United States of America, joined Nov 2005, 6428 posts, RR: 3
Reply 1, posted (6 years 10 months 3 weeks 5 days ago) and read 2572 times:



Quoting AirPortugal310 (Thread starter):
It has to be pre-mixed or mixed with the fuel as it enters the tank but, what does it really do. A google search or two tells me that it is to prevent freezing or water droplets in the fuel if they exist and also, that it acts as an anti-microbial agent.

Certain early jets had problems with ice crystals forming in the fuel tanks once the jet was at alititude and the fuel was getting cold soaked. These ice crystals would then get trapped by screen filters in the engine, and could lead to (best case) degraded engine performance, or (worst case) fuel starvation. This is reason #1 for the existence of Prist.

Prist does, also, inhibit bacterial growth in the fuel system, and yes, there are little nasties in nature that prefer a diet of not very purely refined oil (as both jet fuel and diesel fuel are). The trouble with private corporate airplanes is that a typical airplane can sit around for weeks or months between usage, and then be suddenly called to duty, which gives these bacteria time and possibly the right environment to do their worst in. It's not good for fuel systems components.

Quoting AirPortugal310 (Thread starter):
And does 100LL need it?

Nope. Avgas fuel systems have built-in safeguards for water (well, within reason, and providing that the PIC does his/her part...remember the big warning placards that Cessna had in the 80's and 90's as part of an AD that warned the pilot that failure to remove water from the fuel system could result in bodily injury or death?).

If you ever get the opportunity to handle Prist, be very careful with it. The stuff is one step below a toxic environmental disaster, and the safety warnings on the cans definitely need to be heeded!



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineN231YE From , joined Dec 1969, posts, RR:
Reply 2, posted (6 years 10 months 3 weeks 4 days 19 hours ago) and read 2506 times:



Quoting KELPkid (Reply 1):
Nope. Avgas fuel systems have built-in safeguards for water (well, within reason, and providing that the PIC does his/her part...remember the big warning placards that Cessna had in the 80's and 90's as part of an AD that warned the pilot that failure to remove water from the fuel system could result in bodily injury or death?).

However, Cessna does state that a 0.10-0.15% concentration of DiEGME (basically Prist) is permissible.


User currently offlineScooter01 From Norway, joined Nov 2006, 1213 posts, RR: 8
Reply 3, posted (6 years 10 months 3 weeks 3 days 20 hours ago) and read 2449 times:
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Quoting KELPkid (Reply 1):
Prist does, also, inhibit bacterial growth in the fuel system, and yes, there are little nasties in nature that prefer a diet of not very purely refined oil (as both jet fuel and diesel fuel are). The trouble with private corporate airplanes is that a typical airplane can sit around for weeks or months between usage, and then be suddenly called to duty, which gives these bacteria time and possibly the right environment to do their worst in. It's not good for fuel systems components

-Especially when water is added to the fuel. These bacterias will grow in the boundary layer between fuel on the top and water at the bottom. To avoid water in the tank, is to keep the tank as full as possible at all times, the less air in the tank the better as moisture from the air will condensate on the walls of the tank and sink to the bottom. This happens mostly on warm days/cold nights.
In my profession I deal with a lot of (diesel) pleasure-boat owners and we see this problem coming up quite often.
After the 4-6 month winter-hibernation period with a less than full fueltank, the boat gets called back to duty in the spring, makes a few cruises in sheltered waters -no problem. Next the boat gets into some waves, the fuel gets shaken up a bit in the tank and -presto, the bacterial growth which now is like black muddy gel gets mixed with the top-fuel and gets sucked into the fuelline clogging the filters, fuelpump, injectors etc. Can be a quite hairy experience when someone loses engine-power at sea.
Therefore I always recommend a dieselfuel additive year round when people are tanking up their boats.

Then again, carrying a lot of fuel burns more fuel and affects performance both with airplanes and boats, so the user must find a way to suit his own needs.


Scooter01



"We all have a girl and her name is nostalgia" - Hemingway
User currently offlineCitation501SP From United States of America, joined May 2000, 209 posts, RR: 0
Reply 4, posted (6 years 10 months 3 weeks 18 hours ago) and read 2380 times:



Quoting AirPortugal310 (Thread starter):
Now, it is generally optional (i.e requested by the flight crew) and other times is a requirement for operating to colder areas such as winter time in the Northeast etc...

Some Aircraft are placarded as requiring Fuel Additive. Most straight wing Citations, for example, require it year round. Generally mostly light jets require additive because larger aircraft have fuel heaters. The Phillips 66 brand of Jet fuel usually comes premixed. I have heard many a flight crew suggest tha all Jet fuel should just come premixed anyway. It burns the same as straight Jet fuel.



Smoke and Thunder! Stage 2 FOREVER!!!
User currently offlinePJFlysFast From United States of America, joined May 2006, 463 posts, RR: 1
Reply 5, posted (6 years 10 months 3 weeks 6 hours ago) and read 2355 times:

Quoting AirPortugal310 (Thread starter):
Also, some of the reason why some planes need it more than others?

Some aircraft have fuel heaters and others actually recirculate warm fuel back from the Fuel Control Unit to the fuel tanks to keep the temp of the fuel warm enough to prevent ice build up which can block the fuel lines. Though we still use Prist on occasion for the anti microbe agent.

Quoting AirPortugal310 (Thread starter):
It has to be pre-mixed or mixed with the fuel as it enters the tank but, what does it really do

If you don't blend it with the fuel it will not be as effective.

Quoting AirPortugal310 (Thread starter):
A google search or two tells me....

Don't miss reading the part about how PRIST is a highly toxic and dangerous material and must be handled accordingly.

PRIST is effective. Years ago I flew Lears and if it wasn't properly blended or a sufficient amount not added you would know after the first hour at cruise when one or more FUEL FILTER annuciators would come illuminate. Time to descend into warmer air and make a precautionary landing as necessary.

[Edited 2008-02-02 07:22:14]

User currently offlineTb727 From United States of America, joined Jun 2005, 1648 posts, RR: 9
Reply 6, posted (6 years 10 months 2 weeks 6 days 16 hours ago) and read 2326 times:



Quoting PJFlysFast (Reply 5):

Don't miss reading the part about how PRIST is a highly toxic and dangerous material and must be handled accordingly.

That stuff is super nasty, I had a fueler in EWR get it in his eyes when I was helping him add the can of Prist in while he was pumping fuel on our Lear. You are supposed to attach a little tube onto the nozzle and attach the other end with a clip onto the end of the fuel nozzle, I preferred to "Super Can" it. Stomp the top of the can off, take the thing apart and spray a stream right into the tank using the sprayer I took apart while they are fueling. You are supposed to do it while the fuel is going in because the Prist will puddle in the tank and is corrosive if not mixed well with the fuel. I'm just glad I am in a real airplane with a Fuel Heater now! I am still pretty sure the CJ610 on 20-series Lears will burn anything though!



Too lazy to work, too scared to steal!
User currently offlineFlyMatt2Bermud From United States of America, joined Jan 2006, 563 posts, RR: 7
Reply 7, posted (6 years 10 months 2 weeks 6 days 6 hours ago) and read 2294 times:



Quoting Tb727 (Reply 6):
I am still pretty sure the CJ610 on 20-series Lears will burn anything though!

Yeah, they will indeed burn almost anything. The problem is anything has got to get through the fuel filters and ice buildups eventually stop the flow!



"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward" Leonardo Da Vinci
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