# Tiny Water pump impeller size?



## kcmillin (Sep 13, 2010)

I am currently working on designing a 4 cylinder inline water cooled version of Arv's Tiny I.C. (The current project of the month winner in fact) Well I should say it is loosely based on it, but I am using all the working dimensions like bore, stroke, and valve size, however I am using cam actuated valves for both intake and exhaust. 

As you can imagine it is going to be quite small, 3 1/2 inches long, and less than 1 3/4 inches wide. Such a small engine will require an equally small water pump. OK it may not "require" a water pump, but I want to make one.

I am thinking of an impeller type pump with an impeller diameter of 1/2 inch, but no bigger than 5/8". The smaller the better. (for my design that is)

I have made superchargers for nitro R/C engines in the past, with impeller sizes around 1 inch, these also worked good for pumping water, but at that size the veins were quite small.

What my question is/are, Does the theory of impeller functionality get scaled well?

 By that I mean, do the properties of water, and most importantly centrifugal force of the impeller exponentially change in some sort of way?

Does anyone have any experience with making tiny water pumps? If I could get away with a smaller impeller that would be awesome.

Kel


----------



## dsquire (Sep 13, 2010)

kcmillin  said:
			
		

> I have made superchargers for nitro R/C engines in the past, with impeller sizes around 1 inch, these also worked good for pumping water, but at that size the veins were quite small.
> 
> Kel



Kel

I can't help you with your impeller size but I would be interested in seeing any pictures that you might have of the nitro R/C engines with superchargers. How effective were the superchargers? I can well imagine that there was some fine machining involved. :bow:

Cheers 

Don


----------



## stevehuckss396 (Sep 13, 2010)

Can't help with the impeller but a gear pump can be rather small and they move alot of water.

I would also like to see the RC charger.


----------



## kcmillin (Sep 13, 2010)

Don, unfortunatly I did not take any pictures of the supercharger. This was about three years ago. I have since sold the R/C car, and cannot get any pics.

The impeller blades were roughed out on the mill with a rotary table. And then I spent hours with a dremel and smoothed out the profiles of the blades. They had a slight curve on them. It looked a lot like a water pump impeller. I took a very amateur approach to it, but it turned out great. It was driven by a nylon "pully" which rubbed against the flywheel of the engine.

As far as performance, WOW, I almost [email protected]#$ a brick the first time I drove it. It was a .15 Cu in nitro engine, I had to turn the mixer needle 2 full turns out to compensate for the added air. It went 10mph faster with the same gearing. Although it was very tough to get the nylon pulley to last. I calculated the impeller speed at about 120,000 RPM, weather or not it got that high I don't know. But it did make a sweet screaming sound, indicating very high RPM's. 

They do make commercial versions for about $150 US, and I am sure they are better than mine. 

Kel


----------



## kcmillin (Sep 13, 2010)

Steve, Thanks for the pics of the gear pump. This may indeed be a viable solution. 

Could I get a close up pic of the inside of the pump? Specifically the outlet port connecting holes. 

I have 48DP gear cutters, do you think these would work OK? Their working depth is .047 or so. 

Kel


----------



## ghart3 (Sep 13, 2010)

Centrifugal pump works by throwing the water outward and the speed (pressure) has a lot to do with speed at the outside of the impellers.  A small impeller needs high speed to be able to pump much water.

Made a in-line 4 cylinder and the original full size engine had a centrifugal pump. When scaled down it was a .700" impeller in a .720 cavity. The pump is driven off of a gear off of a cam gear and this slow speed didn't move hardly any water. 

Wanting to keep the looks of the original designed pump, changed it to a flexible vane pump as used in an outboard boat motor.  This required moving the "impeller shaft off center but other then that it looks the same from the outside.

After trying a few different materials have settled on using nylon cable ties for the flexible vanes.


----------



## Maryak (Sep 13, 2010)

Centrifugal Pumps are not positive displacement so they need to be provided with a flooded suction or they require priming each time they are started.

If location of the pump and /or heat exchanger relative to each other is difficult then IMHO positive displacement is a much better option.

Best Regards
Bob


----------



## dsquire (Sep 13, 2010)

Kel

Thanks for the info on the supercharger Kel. Glad to hear that it was a success for you. It's always nice when something like that works out for you. Good luck on your water pump. Looks like you are going to have lots of options.

Cheers 

Don


----------



## cfellows (Sep 13, 2010)

stevehuckss396  said:
			
		

> Can't help with the impeller but a gear pump can be rather small and they move alot of water.
> 
> I would also like to see the RC charger.



Steve, I'm liking that gear pump. Are those 48 pitch gears?

Chuck


----------



## kcmillin (Sep 14, 2010)

Maryak  said:
			
		

> Centrifugal Pumps are not positive displacement so they need to be provided with a flooded suction or they require priming each time they are started.
> 
> If location of the pump and /or heat exchanger relative to each other is difficult then IMHO positive displacement is a much better option.
> 
> ...




So, would Steve's gear pump be classified as a positive displacement pump? Or how about ghart3's flexible vein pump? 


Steve, what are the tolerances of the gear pump? IE distance between the gears and the inside pump wall? 


ghart3, Am I correct in assuming that the inlet side of the pump is on the left side of your picture?


Kel


----------



## Lew Hartswick (Sep 14, 2010)

I think as a general thing, Fluid flows do NOT scale. Ether liquid or gas. 
  ...lew...


----------



## ghart3 (Sep 14, 2010)

kcmillin  said:
			
		

> So, would Steve's gear pump be classified as a positive displacement pump? Or how about ghart3's flexible vein pump?
> 
> 
> ghart3, Am I correct in assuming that the inlet side of the pump is on the left side of your picture?
> ...




A flexible vein pump is not positive displacement, if the water outlet is blocked the pump would still turn just churning the water. If the pump stopped turning water still could circulate by thermo-syphon. 

A gear pump is positive displacement what goes in must come out, if output side is blocked the gears couldn't turn or something would give so the water could get out. 


The inlet for the pump in the picture is on the right and comes into the pump cavity towards the center. The outlet is on the left and the opening inside the cavity is on the outside rim of the cavity.  
Gary


----------



## stevehuckss396 (Sep 14, 2010)

kcmillin  said:
			
		

> Could I get a close up pic of the inside of the pump? Specifically the outlet port connecting holes.



These gears are 9 tooth, cant remember the pitch but they are .225 thich i think. This pump moves a ton of water.

The hole on the right is the outlet hole. I ported it out the back instead of the side. It saved me from making a 90 degree fitting. You can drill the inlet and outlet port any way you want as long as they point to the center of the gears where they mesh.


----------

