Model gearwheel pump

These pictures are of a little gearwheel pump that I found in a deceased friend's workshop. It is 1 1/4" high and 7/8" wide on the cover plate. The drive shaft is 3/16" diameter. Inside, the gears are 15/32" diameter and 9/16" long.

It does not look as if it belongs in or on a specific machine, but it does have the look of something intended to be driven by a "toy" steam engine. There is no drive pulley, and if anyone has any knowledge of these pumps, I would be most grateful for a picture of a complete one.If no picture, then the pulley diameter and appearance would be good.

I would also like to know who made it of course. I have a facsimile of a "Stevens Model Dockyard" catalogue, and there is nothing in there; but of course it only covers one particular year.

I am considering making a close copy of it. I have some suitable gears, and the rest looks straightforward; unless I'm missing something! Has anyone seen anything similar?

Maurice ( I hope the moderator can put all the pictures after the text please. This always happens to me!).

Edited By JasonB on 21/02/2019 19:29:07

Pumps of this type were used in car engines along with a couple of other types and usually driven off of the distributor drive. I suspect that this is very old technology now and most, if not all, current engines have pumps fitted around the crankshaft at the auxiliary drive end are often of the crescent type. Google types of oil pump and have a look at the images to see a load of types.

This somewhat larger item might be of interest: **LINK**

https://www.cds-johnblue.com/pumps/sprayer-applications/spray-pumps/brass-gear-pump-manual.pdf

MichaelG.

Clearances on this type of pump are fairly tight in order for the pump to be efficient....so you need to ensure the gears mate well and there's the minimum of clearance for the pump body cover plate....

Larger gear pumps have been used on tractors for decades - probably for over a century. Initially as the engine lube pump and later for the hydraulic outlets, too. I expect many power steering pumps are of that type

Many pumps were of the vane type, but I have found the gear pumps to be rather more reliable than the vane type. My experience was that Ford fitted vane oil pumps on some car engines (back in the 50s/60s). Whenever we came across one, we changed it for the gear alternative (after a couple of failures).

Austin Seven (not Mini) engines have this type of pump.The handbooks state that the oil pressure should be 1 or more PSI. A reasonable engine with the correct 30 grade oil usually reads 5 PSI when warm.

Brian

I think cars these days use trochidal pumps.

Mike

The gears need to have some backlash. Rolls Royce Oil Engine Division found that having too close a fit produced short term pressure spikes, (circa 600 psi with a gauge reading of 60 psi ). The result was that external steel oil pipes were splitting.

You could hear the pipes "ring" above the noise of the engine running! The spikes were quite visible on an oscilloscope trace of the signal from a pressure transducer.

The problem seemed to stem from oil being compressed in the space between Tooth crest and the corresponding Tooth root. Increasing clearances by a few thou reduced the spikes to an acceptable level.

To minimise leakage, the gears should be close fit in the casing, (minimal endfloat, circa 0.002" ).

Howard

The size of it (1-1/4" high x 7/8" wide) certainly suggest a model application. Bronze gears rather than the more common steel suggest use for pumping water. But not the usual choice for a boiler feed pump. So probably a cooling water circulating pump? Such as for condensor cooling water, or cooling water on a Stirling engine with water-cooled cool end?

Could be pressed into service as a coolant pump on a lathe etc perhaps?

You used to be able to get similarish pumps but a bit bigger that were designed to be run by an electric pistol drill for transferring liquids from drums to smaller tins etc.

Presumably the fluid flow is round the outside of the gears not between the meshing teeth? I can see that there would be a lot of pressure between the teeth, tending to infinity as the fit becomes perfect.

Ahh, that/those word/words ‘infinite/infinity’. Indeed, the pump could turn infinitely slowly with a perfect fit - but the liquid would have an infinite time to move infinitely slowly out of the way, thereby avoiding the infinite pressure? But, there again, moving infinitely slowly would mean zero speed of movement, so no pressure whatsoever. But infinity is a useful thought, all the same.

Or to put it infinitely more simply : Yes the fluid goes around the outside of the gears, being displaced out through the outlet port when the gears mesh together.

Yes leakage across the teeth is generally considered less of a problem than leakage across the faces of the gears when the end covers get worn over the years. Leakage out around the drive spindle can also be a problem if no seal is fitted. These pumps, being positive displacement, will actually pump at quite high pressures. Typical oil pressure in an older motorcycle engine with a gear type oil pump and plain shell bearings could be 60psi and upward.

Some photos of a geared oil pump for a machine coolant
system.The gears are 1.25 module driven by a 12 volt
dc motor of about 20 watt ,pumps about 2.5 litre minute at zero
pressure through 2 filters to remove micron size particles
from the system.
The smaller gears are from various fuel delivery pumps for a
model gas turbine ,the middle size gears pump about 1 litre a
minute at about 40 psi,end leakage on the small gears is more
of a problem as they are only .050 inch wide and need
careful fitting.

John

This is the third time I've typed this reply, forgotten how un-user friendly this web page is. Anyway it's a standard machine tool coolant pump made in their thousands by companies world wide over the years. Below is a pic of the similar thing in the guts of an original Bulleid pacific. Part of a double pump, two sets of gears on the same shaft. Not for forward and backward but one to pump to each side of the oil bath via a filter each side. Both feeds join in the middle and feed a spray bar going the length of the oil bath. Pumps in forward or reverse by a clever arrangement of non return poppet valves cast in to the pump body. Made by Hamworthy Engineering of Poole and originally designed for reversible marine diesel engines IMHO, although I have never seen this written anywhere.

I made a similar gear pump for circulating cooling water on my Centaur gas engine, it has 1.5 mod x 12 tooth stainless steel gears, driven pulley dia 3/4 " free pulley dia 1/2", The pump body size 1 1/4" wide, 2" high, 1" deep.

Its made by Whitney (City Road) of london. Nice little thing, ive got one too. Works very well. Early 20th C, the premises on City Road in Islington were destroyed in the Blitz. Its now the site of the huge Old Street roundabout. Do a goodle search for whitney city road and in about 5 minutes youll be an expert on them, as there isnt that much known...

i collect Whitney steam engines and accessories, if you ever want to pass it on to someone else then let me know ;c)

cheers!

rich

ps this is my first post- hello everyone!

Hello Richard, I have just caught up with your post. Thanks for that. I had never heard of Whitney steam engines. I shall keep an eye out for them. I have no plan to get rid of it at the moment, but if I do I will contact you. Thanks again,

Maurice

Mines currently being the condenser pump on my latest steam launch build. Seems to work. It’s driven via meccano gears from the crankshaft.

whitney engines are lovely. I’ve got a small vertical in the ‘house colours’ of maroon and a large bottle shaped vertical with reversing gear, a few steam pumps and a few hand pumps. They are mostly maroon, apart from the bottle engine(polished) and the gear pump (same green as yours), but they are all absolutely beautifully built.

They also did kits and casting sets, my large hand pump and bottle engine were both kits I think.

ill post some pics at some point, because there aren’t enough pics of them on the web...

cheers!

rich

Some pictures would be most welcome.

Maurice