Question re sizing gear pump for coolant.

[AlanS]

I’m building a gear pump to circulate coolant on my Seal Major engine model. I wasn’t happy with the centrifugal pump I originally made. I found several formulae on line to calculate the flow rate given the size of the gears and the speed of rotation. Has anyone built a gear pump and measured the flow at a certain speed ? I assume if you built the pump you know the DP size, number of teeth and the thickness of the gears. The calculated flow per rev vary widely with the different formulae.
The picture shows me using the mill as a depthing tool. I didn’t have the correct cutter for 10 teeth so the centre distance has to be measured with no backlash allowance.

 

[petertha]

I'm interested in the same thing. This was discussed on MEM forum where some spreadsheets were shown, some of which had more discreet control of input/output parameters, pump power requirements & such. But information was rather scattered about several individual engine build & pump related posts. Somewhere within that it was identified that there are some erroneous formulas floating around the inter-web, example link below. So rather that backtrack through all that, I'll mention that Terry Mayhugh @mayhugh1 on this forum has posted a few of his pumps on various builds which seems a lot more straightforward & grounded in quantified output pressure & rates. This link is his Offy build.
https://www.homemodelenginemachinist.com/threads/270-offy.31486/page-5

one of the links discussing potential formula aberrations
https://www.insanehydraulics.com/letstalk/gearpumpdisplacement.html

I'm specifically interested in using metric gears so have been working on an equivalent version of Terry's formulas. I've only just collected the gear cutters & such so can't tell you how my story ends, but I do want to make a bench pump just to evaluate. Hope this helps. If you build & test anything. would apreciate seeing your results.

 

[AlanS]

I'm interested in the same thing. This was discussed on MEM forum where some spreadsheets were shown, some of which had more discreet control of input/output parameters, pump power requirements & such. But information was rather scattered about several individual engine build & pump related posts. Somewhere within that it was identified that there are some erroneous formulas floating around the inter-web, example link below. So rather that backtrack through all that, I'll mention that Terry Mayhugh @mayhugh1 on this forum has posted a few of his pumps on various builds which seems a lot more straightforward & grounded in quantified output pressure & rates. This link is his Offy build.
https://www.homemodelenginemachinist.com/threads/270-offy.31486/page-5

one of the links discussing potential formula aberrations
https://www.insanehydraulics.com/letstalk/gearpumpdisplacement.html

I'm specifically interested in using metric gears so have been working on an equivalent version of Terry's formulas. I've only just collected the gear cutters & such so can't tell you how my story ends, but I do want to make a bench pump just to evaluate. Hope this helps. If you build & test anything. would apreciate seeing your results.

Thanks for the info and the links. The formula in the articles about the Offy build was the same as one I'd found on line, which gives me some confidence in the spreadsheet I'd developed. I'll start with a wider gear and then if there's too much flow I can reduce the height within the limitations of the inlet and discharge connection diameters. I intend to do a test with a known speed (probably lathe) and measure the volume pumped per a given time. I'm a ways away as I was just shaping up the three bronze blocks for the body.
I'd made a gear pump before for the engine in my 1831 model locomotive, since known as the Wallaby, design courtesy Edgar T Westbury. One of several ETW designs I've built.

 

[AlanS]

I'm interested in the same thing. This was discussed on MEM forum where some spreadsheets were shown, some of which had more discreet control of input/output parameters, pump power requirements & such. But information was rather scattered about several individual engine build & pump related posts. Somewhere within that it was identified that there are some erroneous formulas floating around the inter-web, example link below. So rather that backtrack through all that, I'll mention that Terry Mayhugh @mayhugh1 on this forum has posted a few of his pumps on various builds which seems a lot more straightforward & grounded in quantified output pressure & rates. This link is his Offy build.
https://www.homemodelenginemachinist.com/threads/270-offy.31486/page-5

one of the links discussing potential formula aberrations
https://www.insanehydraulics.com/letstalk/gearpumpdisplacement.html

I'm specifically interested in using metric gears so have been working on an equivalent version of Terry's formulas. I've only just collected the gear cutters & such so can't tell you how my story ends, but I do want to make a bench pump just to evaluate. Hope this helps. If you build & test anything. would apreciate seeing your results.

You were interested in the performance of the gear pump I’d built. I’ve got it to a point where I can test it and make some delivery rate measurements.

Vital statistics of the pump. Gear DP 20, outside diameter of gears .600” Root diameter of gears .492” Tooth length .375”, Center distance of gears .500”

Pump body and gears are bronze, shafts are stainless steel, hose connections are brass. The pump was run with a cordless drill on max speed 1,500 rpm, pumped water from a pail into a graduated cylinder, timed on my iPhone.

Flowrate measured on two tests 49.8 cubic inches per minute

Calculated flowrate 52.5 cubic inches per minute @ 1,500 rpm using the formula ((D^2-d^2)*gW*pi

Close enough for jazz.

I’ll dismantle the pump and take some images of the innards.

 

[petertha]

Thanks & look forward to your pics. Hard to see, but are your teeth involute or something different? I'm lead to understand both equations show in bold on my spreadsheet assume involute FWIW. What do you figure your annular gear/cavity distance is? Any idea of discharge pressure (even rough estimate like squirts water 12" vertical). I'm just curious for my own purposes which is lubrication oil pump, although I recognize there are differences. I've also heard there is some magic to the inlet & discharge port shape. Maybe this pertains to longer length teeth or specific application, not sure. My teeth will be narrow by comparison so probably of no consequence.

 

[AlanS]

The teeth are involute but because I didn’t have the correct cutter for 10 teeth I’d to use the one which covers the smallest number of teeth. That’s why I was depthing the teeth to measure centre distance. Rather than the standard .500 inches it measured .508 inches and that’s what I made the centres in the three body sections. Radial clearance is about .0005 inches, I wasn’t taking a lot of care making the pump as it’s only splashing cooling water around.
I’ve to do some finishing now, rounding off the corners and mounting it under the distributor. I still haven’t decided whether to use hose or hard pipe the suction. It lifts water well, I was quite surprised how it filled an empty suction line. It will be a flooded suction in the actual installation.
If I get some shop time this evening I’ll take some pictures of the bits.
Alan

 

[AlanS]

Thanks & look forward to your pics. Hard to see, but are your teeth involute or something different? I'm lead to understand both equations show in bold on my spreadsheet assume involute FWIW. What do you figure your annular gear/cavity distance is? Any idea of discharge pressure (even rough estimate like squirts water 12" vertical). I'm just curious for my own purposes which is lubrication oil pump, although I recognize there are differences. I've also heard there is some magic to the inlet & discharge port shape. Maybe this pertains to longer length teeth or specific application, not sure. My teeth will be narrow by comparison so probably of no consequence.

The teeth are involute but because I didn’t have the correct cutter for 10 teeth I’d to use the one which covers the smallest number of teeth. That’s why I was depthing the teeth to measure centre distance. Rather than the standard .500 inches it measured .508 inches and that’s what I made the centres in the three body sections. Radial clearance is about .0005 inches, I wasn’t taking a lot of care making the pump as it’s only splashing cooling water around.
I’ve to do some finishing now, rounding off the corners and mounting it under the distributor. I still haven’t decided whether to use hose or hard pipe the suction. It lifts water well, I was quite surprised how it filled an empty suction line. It will be a flooded suction in the actual installation.
If I get some shop time this evening I’ll take some pictures of the bits.
Alan

Here are the bits of the pump. I’ve still to do some finishing work and complete the mounting to the underside of the distributor as they share a drive. I left the micrometer in for scale.

 

[petertha]

Very nice, pretty much what I was aiming to do eventually. So I assume you reamed the gear ID's for nice fit on the shaft, no need (or probably room) for bearings? I forgot to ask what is clearance between gear thickness & sandwiched pump body housing? When you made the teeth, do you check PD with a dowel pin & micrometer method?

 

[AlanS]

Very nice, pretty much what I was aiming to do eventually. So I assume you reamed the gear ID's for nice fit on the shaft, no need (or probably room) for bearings? I forgot to ask what is clearance between gear thickness & sandwiched pump body housing? When you made the teeth, do you check PD with a dowel pin & micrometer method?

The stainless steel rod was .0005” underside so I started off with a minus .001” reamer for the gears and a dead size reamer for the bearing locations. I use my sets of plus and minus .001” reamers a lot.
There’s about .0005” clearance top and bottom between body and gears.
I didn’t do any checking of the gear teeth as I depthed them using the mill to get the exact centre distance. These are different from power transmission gears, they fit where they touch and no backlash.
The water connections are temporary just for testing, I’ll probably hard pipe the suction.
Alan