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Pneumatic fill rates and calcs

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Ttail

Joined: 24 Jun 2013
Posts: 120

Posted: Thu Jun 30, 2022 2:30 pm Post subject: Pneumatic fill rates and calcs

To the Pneumatic Genii out there. Trying to do some numbers using Paint ball bottle to refill the main CJ 12L tank.



2L Paint Ball bottle at 4500PSI (310) bar.



Using P1V1=P2V2 if I have an empty main 12 Litre tank then the calcs say I should get 50 bar refill into the main system. However that assumes a complete transfer from one bottle to the other. In reality the transfer will stop when pressures in each bottle are equal ..... so how to calculate the residual pressure in each bottle ?



Then taking it a step further. Say I have 20 Bar in the main system what will my 310Bar 2l paint ball bottle then get ?

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_________________
Sean Trestrail
ttail[at]internode.on.net

Stressmerchant

Joined: 28 Oct 2014
Posts: 22

Posted: Fri Jul 01, 2022 12:27 am Post subject: Re: Pneumatic fill rates and calcs

You’ll have two scenarios:

    1. The pressure reaches equilibrium, or

    2. The pressure in the aircraft reaches the maximum and the filling process is halted.



The basic equation would be:

   P1C VC + P1A VA = P2C VC + P2A VA



      P1C = cylinder pressure prior to filling

      P2C = cylinder pressure after filling

      VC = cylinder volume

      P1A = aircraft pressure prior to filling

      P2A = aircraft pressure after filling

      VA = Aircraft Volume (12 litres for main?)



First scenario

The equation becomes:

	P1C VC + P1A VA = P2 (VC + VA)

              P2A = P2C since equilibrium is reached

Rearranging:

	P2 = (P1C V1C + P1A V1A) / (V1C + V1A)



Second scenario

P2A = 55 bar (Assuming that’s where the overpressure valve activates)



P2C = (P1C VC + P1A VA – 55 VA) / (VC)



In practice you’ll get a fair bit of variation from these numbers:

    • The Yak system cascades to the emergency system, so if that has lost pressure you’ll also be putting air into there as well. You can add a third term into the equations above if you would like to include the emergency system

    • The supply cylinder will cool as the air flows, the receiver will heat up. The equilibrium will be affected by this change. 

    • The equation is based on the ideal gas law. In practice the equations go non-linear at high pressures. We used to allow about a 10% reduction in effective volume for the 300 bar cylinders

    • Your supply cylinder might not be at rated pressure to begin with. This is particularly true with the 300 bar types, depends on the operator actions during the filling.



I've put this in an Excel file. Open to corrections....

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Pressure.xlsx

Description:

My guess at the pressure calcs

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Pressure.xlsx

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romaine_richard(at)yahoo.
Guest

Posted: Fri Jul 01, 2022 4:55 am Post subject: Pneumatic fill rates and calcs

Ok, I'll provide some List entertainment trying some public math with Boyle's Law...



For rough numbers, discounting the plumbing volume, 1 bar CJ initial condition and don't recall the emergency bottle volume (I'll call it E)



P1V1 is your paintball rig, P2V2 is the CJ where V2=(service tank 12L+E tank vol)...perfectly equalized should be P1V1+P2PV=P3V3 where V3 is the total volume of the combined paintball rig attached to the CJ, solve for P3...



If E tank started at higher pressure, it won't become part of the total system volume until the fill pressure exceeds E tank pressure, and the check valve prevents its higher initial pressure from backflowing to contribute during the fill.  So if E tank had a full charge at the initial state you can throw it out of the total volume.



It's July 4th weekend so return fire is anticipated!



Cheers,

Rich



Sent from my iPhone

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romaine_richard(at)yahoo.
Guest

Posted: Fri Jul 01, 2022 5:27 am Post subject: Pneumatic fill rates and calcs

..to follow up/clarify E bottle influence...if E initially full, disregard its volume in both V2 (CJ) and V3 (paintball rig + CJ)

Cheers,

Rich



Sent from my iPhone



 	  Quote: 	
		   On Jul 1, 2022, at 8:54 AM, Richard Romaine <romaine_richard(at)yahoo.com> wrote:

 

 Ok, I'll provide some List entertainment trying some public math with Boyle's Law...

 

 For rough numbers, discounting the plumbing volume, 1 bar CJ initial condition and don't recall the emergency bottle volume (I'll call it E)

 

 P1V1 is your paintball rig, P2V2 is the CJ where V2=(service tank 12L+E tank vol)...perfectly equalized should be P1V1+P2PV=P3V3 where V3 is the total volume of the combined paintball rig attached to the CJ, solve for P3...

 

 If E tank started at higher pressure, it won't become part of the total system volume until the fill pressure exceeds E tank pressure, and the check valve prevents its higher initial pressure from backflowing to contribute during the fill.  So if E tank had a full charge at the initial state you can throw it out of the total volume.

 

 It's July 4th weekend so return fire is anticipated!

 

 Cheers,

 Rich

 

 Sent from my iPhone

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Ttail

Joined: 24 Jun 2013
Posts: 120

Posted: Fri Jul 01, 2022 7:09 pm Post subject: Re: Pneumatic fill rates and calcs

Thanks for the input all.

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Sean Trestrail
ttail[at]internode.on.net

cjpilot710(at)aol.com
Guest

Posted: Mon Jul 04, 2022 11:15 am Post subject: Pneumatic fill rates and calcs

Sean, 

 

  I think you are confusing volume with pressure.  A paint ball tank does not the same space volume as the air tank on a CJ-6.  Yes, it has greater pressure but with a lower amount of air.  And it does not take as much air to fill and pressurize the CJ's system but it takes a lot of air to fill the CJ's air tank.  At 50 atmos (about 750psi normal system pressure on CJ) a paintball tank pressure (4,300psi) should get the CJ's system filled for a start but not the CJ's tank.  If I remember correctly, the QS1 valve to the brakes reduces normal system pressure from 50 atmos (750psi) to about 10 atmos (150pis) simply so as to not blow up the rubber bladders in the brakes. Also, you can start the engine with as little as 25 atoms (300 psi) of system pressure.  If you plug in your paintball tank to the normal air refill port BUT leave the main tank valve closed, you will only pressurize the system and NOT fill the tank. You will then have more then enough pressure to start your engine simply because the system does not have the same volume as the tank.

  Jim "Pappy" Goolsby

 

 

  --

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