IC Engine Water Pumps

[Roger B]

That's some very interesting research    Thank you for posting it   

[Charles Lamont]

MJM460, you raise several interesting points.

I agree the pressure produced by the regenerative pump is impressive, especially as I think I am running these little pumps at speeds way below their optimum. However it does not match the reqirements of the cooling curcuit. This is something I have not said much about yet. From the tests I have done, the circuit needs greater flow at lower pressure than this particular pump offers. The centrifugal pumps appear to be better matched.

Friction is an important consideration in pumps this small, and I think that the problem with the curved blade impeller may be that the flow is too restricted near the eye. Observe also that, except at zero flow, the brown curves for the six bladed radial impeller are slightly worse that for either of the four bladed ones, when one would otherwise expect the progression of the rake angles to give it a performance intermediate between the two. I ought really to make an impeller with shorter curved blades, and one with just three or four radial blades. (I could easily remachine the existing ones, but then I would not have the originals for any further testing)

In view of the close clearance requirements and friction, I do want to try some time an impeller with a front shroud (though probably not a wear ring!).

I think the inlet manometer problem is one of too much resistance in the inlet tube. Probably the easiest way to get more suction head is to raise the inlet tank, but a bigger bore hose fitting at the tank outlet might be more practical.

On the matter of the gear pump as a fallback option; not long before things got nasty, I acquired on Ebay from a Russian, a full set of 0.6 module gear cutters. They were cheap enough to buy against an idea of building a clock, if I ever get the time (pun intended). Aaanyway, 0.6mod, 12T, and a 3mm face width would give the output I think I need.

[Charles Lamont]

Following all this playing about, I have been prevaricating over the final design of the pump for the Seagull engine. A good way to fabricate the pump casing eluded me, and while the bearing housing was not so difficult, a fabrication would still have been more work than I really wanted. Discussion on this forum in recent months of 3D printed metal parts prompted me to consider that route. I soon decided that my 3d CAD skills needed extending to produce a smooth progressive shape for the spiral volute passage in the casing.
 
I had the pump parts modelled fairly quickly, at last giving me a design I was happy with. While I was at it, I also produced a printing version of my modified carburettor body. The costings meant that it seemed sensible to get two of each made, to give a sample of the as-printed part, or a spare if I nurgled the first. The parts printed pretty well, but it is worth noting that tolerances are on the plus side, this means that holes are generally a little smaller than the model. Machinability is good.

Looking at the finished parts, it may be observed the stainless shaft will run directly in the aluminium housing. There is enough metal in the housing to bush it if that does not work out. The shaft has a slightly reduced diameter for the viton o-ring seal to bear on, as reduced squeeze is recommended for rotary applications. The impeller has a larger blade height than the test pumps, at 0.1" rather than 5/64". It was intended to be 3/32, but I forgot to make a machining allowance on the inside face of the printed casing. This needs machining, as the experimental work showed that it is important to minimise the axial clearance between impeller and casing. I had to make two impellers to get this right. I am happy with the second one which turns freely but with no end float that I can feel. There is clearance at the pulley end. The bought MXL pulley has been modified to remove the mounting hub, and the flange has been reduced in diameter. It should perhaps have been reduced a bit more.

In view of another recent discussion on achieving good finish, I also point out the use of proper studs with a short plain central shank and domed and polished ends. These 8BA stainless ones were a right pain to make. When cutting the second, outer, thread it was just not possible to tighten the stud box backing screw enough to prevent the die from unscrewing the stud when backing it off. I had to cut the thread with the die set slightly closed to cut the thread to the right diameter, then use the jacking screw in the die holder to expand the die to release the stud. With a non-adjustable button die, I think the job would have been impossible. The washers are home made, but I have used commercial nuts.       

The grease stauffer is intended for use and is filled with proper pump grease. The casing joint is sealed with Wellseal - no gasket. It took me half an hour to get the four casing nuts in place. The inlet and outlet flanges are positioned for show. The pipe runs will come next after I have made a stand for the pump.

[Dave Otto]

That looks really nice Charles!

Dave

[MJM460]

Hi Charles, All that preparatory work followed by 3D printing resulted in a beautiful little pump.  Well done. 

It will be most interesting to see how it works at such a small scale.  It will certainly look the part mounted on an engine, but it’s a fascinating line of exploration on its own.

Have you done any work to compare the performance of those impeller blades with straight radial blades?  Or how you might produce curved blades?

MJM460

[Sanjay F]

Looks great, I like the finish on the surface 

[Charles Lamont]

Thank you, chaps.

MJM460, if you look back up the thread to post #2 from 2023 (heck!) you will see some of the experimental impellers. The curved blades were made using a jig mounted eccentrically on a rotary table and in which the impeller could be indexed on its own axis.

Sanjay, the surface texture on the printed parts is bead blasted, as supplied. It is a bit rougher than my own sanded and bead blasted finish on the rest of the engine.

 

[Zephyrin]

absolutely superb little pump, clearly this approach using 3D printing really seems to play a major role in model making...