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           Pneumatics 2


                         Using a Quick Exhaust Valve as an inlet valve.


                                Below is an explanation of how a QEV valve works .

                                   There is a floating seal inside this type that shuts off the gas flow from port 1 to 3 OR  port 2 to 1.


                        On the left we have the Exhaust explanation                                         On the right  the Inlet valve explanation.
         

       
System pressure is applied to the inlet port (1)
           flow is directed to the buffer tank (2).
          
           When system pressure (1) is dropped,
           gas in the buffer tank (2) is discharged directly
           from port (3) of the quick exhaust valve into the
           ram.




 


  A Quick Exhaust Valve ( QEV )  is a simple and cheap high flow exhaust valve... but it can be used as simple and cheap  
  high flow inlet valve!
  
   A QEV attaches directly to your cylinder so ...unlike a 5/2 valve ... there are NO further losses in flow due to fittings or   
   pipe work. The amount of flow increase you could gain by using this valve varies ......it depends on how good or bad your   
   existing system is......but it flows about 50% more than a standard 5/2 valve of the same port size.
 
   NOTE:- You can ....if you want..... operate it with a much smaller 5/2.


          The following picture shows my first test assembly of the above QEV inlet adaptation.

   The Ram in the picture is a fed by gas @ 150 psi  thru a 5/2 port solenoid / QEV  inlet adaptation...it also has an adjustable retract pressure via a 
   small pressure regulator and standard  QEV exhaust.
- off / retract position gas @ 150 psi  flows via the inlet QEV into the fire extinguisher buffer tank whilst at the same time supplying gas
   to the retract port of the ram thru the regulator and QEV combination ... the exhaust of the base is solely provided by the 5 port valve.
  
   Activating the solenoid of the 5 port valve causes a reversal in the pressure lines ........ pressure is removed from BOTH QEV's  causing them
   to open .....POP!......The contents of the buffer are dumped into the ram and the pressure in the retract side of the ram is vented to atmosphere,
   there is also an additional flow supply to the extend stroke from the 5 port valve itself.
  

                Another version ->    
                                                                                             Ram has 2 ports on both the extend and retract & uses the same pressure throughout.
 


Here's another trick I use.  

Using a solenoid valve and pressure switch combo to replace the regulator...not as precise as standard regulator but I find it works well for a Fighting Robot application.

NOTE:- This only works if you have a buffer tank.

I personally have the valve / pressure switch combo wired thru a R/C switch so that when the weapon valve turns ON... it turns OFF 
....and is turned back ON to refill the buffer as the ram retracts.
Why? ....It's a waste to fill an already open ram and doing this saves on gas consumption.
My pressure recovery time is 1 or 2 seconds ... and I'm usually back up to pressure before the ram shuts.
 


A pair of buffer / ram combo ideas ....

   Wazio from the US of A has expressed an interest in the concept and Mario from Belgium is building a version of this idea for him.
                                      
                                                               

                 The drawing above is based on a QEV                                                               This drawing is based on a 2/2 servo assisted Valve

This idea is a dead end .
The math ..... Acceleration = force / mass  and  Velocity = Sqrt (2as) gives a limit to the velocity that can be obtained throwing a given mass...
from this information a MAX value for flow can be derived..... this MAX flow rate is many orders of magnitude below that of the above concept.
The large flow of the above will only succeed in accelerating the unloaded piston to a ridiculous velocity.
 

Maximum Required Flow for Pneumatic flippers.


      "I think you should post it on your website on the pneumatics page 2 section. I would be honored, your website has been and is so helpful. "
                 So ...here it is.....Australian Trent Ellis's Impressive Featherweight 4 Bar Flipper


    Trent has made a version of the base valve with an external 20oz buffer tank.
    Link to the Robowars Forum Thread  and a  Video of testing @ 600 psi

 

                                                               
                                                                  

   
Maximum Required SYSTEM FLOW for Pneumatic Flippers
Name Ram bore (mm) Ram stroke (mm) Pressure (bar) Mass to move (Kg) Leverage (ratio x:1) Ram extension time (seconds) Maximum required CV for air Maximum required CV for co2 Maximum required Kv (M3/hr) for co2 Qn Air (L/Min) Qn CO2 (L/Min)  
Example 1  
Any increase in flow beyond the calculated Max gives no extra return in terms of throw it only increases the unloaded ram extension speed.