Low agitation mixing pump design

[steveh2112]

hello everyone,

i run a small microbrewery and i have a need for a unique pump design, here are the requirements:

1) low agitation of pumped liquid (cider in my case) because its full of CO2 in suspension and i don't want the gas to come out in the pump
2) the pump will be used to mix 2 fluids in-line in precise proportions. the fluids are cider (gassy) and fruit juice (flat). the mix ratio is 14% juice to 86% cider and must be exact. this is because excise tax is based on alcohol content and the ABV of the cider is know exactly so the ABV of the mixed (diluted) product must be know exactly too.
3) flow rate is 400liters/hr
4) needs to be food and beverage grade stainless throughout.
5) the pump pumps cider from the tank to the bottle filling machine, though a .5micron filter. the back pressure in the filling machine tank is 3bar of CO2 and the filter adds some resistance too, but not sure how much yet.
6) the port on the air cylinder is on 1/4" on the 2" cylinder and 1/8" on the 3/4" cylinder. this is no doubt fine for air but too small for liquid i think. i plan to bore it out to 1/2" for the 2" cylinder and 1/4" for the 3/4" cylinder. the one way check valves are 1" and the main feed pipes are 1/2".

i've looked for mixing and meter pumps and found nothing suitable and everything close is crazy expensive, $2000 and up.

so i designed my own pump using pneumatic air cylinders from Bimba which are all stainless and easily available on ebay

so i have some questions, first off, 1) does my math look ok on the attached slide?

2), what about the mechanical design of the crank wheel, crank shaft and coupling to the air cylinder piston shafts. i assume i have to allow some movement on the connections from the piston shaft connecting bar and the piston shafts since its unlikely with my welding still that i can make this 100% perfect.

note that I'm only planning to use 6" of the total stoke length of 9". this is so there is always at least 3" of piston the cylinder which i hope will help stabilize the piston shaft and reduce side to side stain on the shaft and cylinder caused by the rotating crank. how low do you think the crank shaft should be and would you use an extra linear guide of some kind to keep the piston shaft connector bar on the straight and narrow?

3) on the fluid flow side, you can see the idea is 2 check valves cause the fluid to flow in one direction only from tank to filling machine through the action of the reciprocation pump. any problems with this?

thanks for your thoughts on this

steve

 

[steveh2112]

hi again

i just had a new idea. i was thinking about making this whole thing air operated vs. motor/crank driven. i though of using another air cylinder but then i had an idea.

you will notice from my original diagram that there are 2 air ports on these cylinders, they are 'double acting'. I'm only using one end to pump the liquid so the other end is free.

by connecting the shafts end to use using some kind of semi-rigid connecting rod, i can make the two air cylinders operate in a push-pull way on the 2 liquids and have 2 air inputs to control the push-pull action pneumatically.

the only part I'm not sure about is the control aspect since I've never worked with air powered actuators etc. before.

if you go on ebay and search for 'Air valve 4 way' you will see something like the unit in the attached picture.

the idea is that the connecting rod connecting the two piston shafts has two (possibly adjustable) arms that contact the toggle on the air valve. if my understanding of a 4 way 2 position air valve is correct, then i can use that switch to automatically push the pistons one way, then the other. i would control speed by controlling the feed air pressure.

this seems far simpler and cheaper than my last design, any thoughts about this?

thx steve