Author Topic: Gear Pump  (Read 19870 times)

Offline Brian Rupnow

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Gear Pump
« on: January 08, 2015, 07:33:39 PM »
I may build a gear pump, just for interest sake. I finally bought the last cutter for my 24 DP gear set which will let me cut 12 and 13 tooth gears, and I have never built a gear pump before. The drawing isn't finished yet, so don't shoot me. I haven't put the shafts in, nor the near side cover, but I will get to it. If you are interested, then follow along.---Brian
« Last Edit: January 08, 2015, 10:00:48 PM by Brian Rupnow »

Offline Bearcar1

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Re: Gear Pump
« Reply #1 on: January 08, 2015, 08:08:09 PM »
Looks quite interesting….  :ThumbsUp:  water pump or pressure oiling….. nice! Im definitely watching along this series Brian.


BC1
Jim

Offline rockknocker

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Re: Gear Pump
« Reply #2 on: January 08, 2015, 08:41:57 PM »
I'll be watching as well, micro-pumps like this are very interesting to me, as they have a unique set of challenges. At a previous job we used external gear pumps a bit smaller than this one as fuel pumps for fuel injected engines. To make a long-lasting, efficient, well-sealed high-pressure pump the tolerances *must* *be* *tight*! That said, to make a pump that works for just about everything else it isn't too bad.

I do have a couple questions on the design. What are you using for shaft seals? Shaft seals were one of the biggest problems with the micropumps I've worked with in the past, o-rings didn't seal well enough against pressure in this environment, and u-cup seals were all custom, and still didn't fix the problem entirely. Also, why are both shafts protruding from the pump? Are both shafts being driven, or are the bearings external to the seals?

It looks like a nice design! I can't wait to see some pump-shaped metal!

Offline Brian Rupnow

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Re: Gear Pump
« Reply #3 on: January 08, 2015, 08:48:19 PM »
Rocknocker Read the text in my first post. No shafts shown--right!!! Only one shaft will extend out of the compartment with the gears in it, and it will have a Butyl or nitrile o-ring seal. The near side cover is not shown yet.

Offline Jasonb

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Re: Gear Pump
« Reply #4 on: January 08, 2015, 08:52:18 PM »
I'm sure if you are just using it to lift fuel from a tank to a carb or oil from a sump and  gently move water in a cooling system the seals won't see any significant pressure.

J

Offline Brian Rupnow

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Re: Gear Pump
« Reply #5 on: January 08, 2015, 09:59:42 PM »
This may explain things a bit better.

Offline steamer

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Re: Gear Pump
« Reply #6 on: January 08, 2015, 10:11:40 PM »
Why the check valve Brian?


Dave
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Offline Brian Rupnow

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Re: Gear Pump
« Reply #7 on: January 08, 2015, 10:59:18 PM »
Why the check valve Brian?


Dave
Steamer--I'm just fumbling my way along here, not totally sure what I'm doing. I don't think this gear pump will create enough suction to start dry and pull oil or water up from a sump to "catch" and my thinking is that if it has a check valve in it the pump won't have to be primed every time it is ran. It doesn't cost anything to put a check valve in it, and imagine how awful it would be if someone built it to use as an oil pump for an engine and didn't prime it. They wouldn't know it wasn't working until something burned up.

Offline philjoe5

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Re: Gear Pump
« Reply #8 on: January 08, 2015, 11:20:52 PM »
Brian,
I like it and will use your drawings when you've got them finished.  A gear pump has been on my bucket list forever.

Cheers,
Phil
If you pick up a starving dog and make him prosperous, he will not bite you. This is the principal difference between a dog and a man.  - Mark Twain

Offline steamer

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Re: Gear Pump
« Reply #9 on: January 09, 2015, 12:48:14 AM »
Why the check valve Brian?


Dave
Steamer--I'm just fumbling my way along here, not totally sure what I'm doing. I don't think this gear pump will create enough suction to start dry and pull oil or water up from a sump to "catch" and my thinking is that if it has a check valve in it the pump won't have to be primed every time it is ran. It doesn't cost anything to put a check valve in it, and imagine how awful it would be if someone built it to use as an oil pump for an engine and didn't prime it. They wouldn't know it wasn't working until something burned up.

Gear pumps are terrible with lift...maybe a few inches at best   The Pump needs to be mounted low, in the tank so it doesn't need to lift.  Usually it's best to keep the inlet large and unrestricted.
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline Dave Otto

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Re: Gear Pump
« Reply #10 on: January 09, 2015, 01:20:46 AM »
Interesting project,

Charles Stark one of the NW modelers built this nifty little gear pump to circulate cooling water for his Mery engine. His design incorporates a traditional packing gland for a seal; I'm not sure how well an O-ring will work in this application but it is worth a try.

I believe castings are available for this one.

Dave




Offline Brian Rupnow

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Re: Gear Pump
« Reply #11 on: January 09, 2015, 01:23:44 AM »
 The only difficulty I foresee is end clearance between the end of the gears and the inside of the housing. I have some "real work" thanks to my new Solidworks installation, but I still need a "play project". It may be quite a stunt. If the gears are too long, the cover won't bolt on tightly enough and fluid will leak out the joint between the main pump body and the cover. If I make the gears too short, then fluid will bypass around the ends of the gears, resulting in no pressure. I suppose that if a gear was made a bit short, a round piece of shimstock the outer diameter equal to the gear o.d. and the center hole equal to the gear shaft hole could always be used to remove any end gap. My initial thoughts were to make the gears of brass or bronze so they wouldn't rust if I used them to pump water, (and because brass or bronze is MUCH easier to cut than steel). I was going to make everything else except the steel shaft from aluminum. I believe that brass or bronze is more wear resistant than aluminum, so the gears could actually be made .001" to .002" too long and then have them "wear in" to the cover and main pump body to give an almost "0" gap condition. (If I can actually work to that close a tolerance.)

Offline derekwarner

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Re: Gear Pump
« Reply #12 on: January 09, 2015, 01:38:57 AM »
Guys...after 49+ years in industrial/marine/naval hydraulic systems, it still amazes me that manufacturers still do not strongly recommend  :Director: that gear pumps installation be with flooded or positive head suction

Check valves can weep, anti syphoning devices can fail....pumps can run dry  :Mad:... who benefits?.........who pays   :embarassed:

Gear pumps could be considered the cheapest form of producing say 200 Bar flow in a fluid system, however for longevity of service require careful consideration in the installation design. Gear pumps by design are also one of the greatest contributors of internal contamination within oil fluid systems so also require adequate filtration .... Derek
« Last Edit: January 09, 2015, 01:46:46 AM by derekwarner_decoy »
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Offline steamer

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Re: Gear Pump
« Reply #13 on: January 09, 2015, 01:46:48 AM »
Derek....Relax.   It's a model.


Brian, check out my thread on the Wallaby...I built a gear pump via the Westbury method....worked great, and pumps really well.

It's not as hard as it looks...though it is a challenge.
http://www.modelenginemaker.com/index.php?topic=237.10

Dave

"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline derekwarner

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Re: Gear Pump
« Reply #14 on: January 09, 2015, 02:13:16 AM »
 :old:...thanks steamer.......since retirement I always try to be relaxed......but am haunted by  :LittleDevil: ...when some said ........why doesn't it work.......you never told me that

Well...when we re-read the fine print  :happyreader: we find they missed out a few salient requirements  :slap:

It has been suggested on this forum & others that I cannot escape real world engineering to model engineering.......& so yes I am probably guility here

Derek   :cheers:
Derek L Warner - Honorary Secretary [Retired]
Illawarra Live Steamers Co-op - Australia
www.ils.org.au

 

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