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29th May 2021, 11:49 AM #1Golden Member
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Hydraulic question for the brains trust
I need some advice on a hydraulic pump. I mentioned in my project thread about my tractor grapple build, that I was going to have to replace the worn-out pump in the auxilliary PTO-driven hydraulic power pack that I use to power the front-end loader and grapple on my old Ford tractor. The auxilliary power pack came with the tractor when I bought it and is worn out like the rest of the tractor was. I need to know what size pump would provide suitable flow to operate the loader and grapple at a suitable speed. The worn-out pump that is currently in the unit is- according to my measurements and an online calculator- approximately 19cc per rev. I don't know how that converts to LPM or GPH and I have no experience of what a suitable flow rate for the job would be, so would appreciate some guidance on this. Looks like it won't be cheap so I need to make it worthwhile!
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29th May 2021, 12:16 PM #2Most Valued Member
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Hi Pete, where is the old pump worn? If the gears are not pitted and the clearance from the gears to the housing is close enough then check the clearance between the gear and the end plate, you might get away with giving the housing a skim to close that up. Thicker oil might help also.
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29th May 2021, 01:24 PM #3Philomath in training
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Calculate the volume of the cylinders you need to fill, and guess at how quickly you think they should go from extend to retract. That should give you an idea of the flow rate you think is needed. As for the pump, you will need to determine the rpm of the PTO that drives the pump. Divide one by the other, multiply by shoe size etc etc; should give you an estimate of the sort of flow pump you think you need.
Michael
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29th May 2021, 02:36 PM #4Golden Member
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The bores that the pump gears run in have worn oval (gears pushing further apart) which means that the gears have worn into the housing bores also, which, according to my reading, means the pump is not repairable. The bushes in the end housings could be replaced easily enough, but there's apparently nothing that can be done for the clearance around the gears in the main body housing.
I'll do some maths on the required volume / time to move things at a reasonable rate.
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29th May 2021, 03:35 PM #5Golden Member
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I measured the rams (more than half an hour since I bought them so couldn't remember), the curl rams are 2.5" bore x 24" stroke and the grapple rams 2.5" x 6". This makes the volume to extend the curl rams 118 cubic inches, 1.93litres. 2 rams, 3.86 litres. I think a reasonable time to roll the bucket over (it rolls through about 220 degrees) is about 8 seconds, or 0.133 minutes, 3.86 /.133 makes it 29 l/min. That would close the grapple in 2 seconds.
I'm not sure quite where to go from there; the rated PTO speed is 540rpm but the pump is attached to a gearbox inside the tank; I guess I need to figure out what the gear ratio is. If it's 2:1, that would make the existing pump just about right at 540rpm. 19cc x 2 x 540rpm = 20.5 l/min.
Are there other factors to consider that I am missing?
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29th May 2021, 06:32 PM #6Most Valued Member
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That sounds reasonable to me Pete.
What is the current housing made out of?
If it’s cast iron I reckon it would be worth having a crack at building it up with bronze and remachining it.
Steve
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29th May 2021, 07:52 PM #7Golden Member
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The pump is an aluminium double-barrel sandwiched between steel end plates. I don't think there is any point even contemplating repair of the pump, they are considered a throw-away item once the gears have migrated apart like this. Just want to make sure I get an optimum replacement.
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29th May 2021, 07:59 PM #8Most Valued Member
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I think steve is right, it probably could be repaired if you were prepared to put in the effort.
Pete if you can post some photo's of the pump to give some clue to the style and with a few dimensions someone might have one that could work for you even if some mods are required.
I have some pumps, if there is one here that will work for you its yours. Would need a bit more info tho, looks like you want about 5 gals/min, is that right? At what rpm
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30th May 2021, 12:10 AM #9Golden Member
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That's very generous shed, yes 5 gallons per minute looks to be about right but the RPM is a mystery at this stage. I'll have to pull the pump out of the tank and do a bit of investigation of what the gear ratio is on the drive etc. The pump and gearbox arrangement that is inside the tank looks like this
although I think the coupling on the input is female splined iirc. I've seen images of backhoe tractor attachments and similar where these setups are hung straight on the PTO shaft and fed with hoses but on this setup it is immersed in the tank.
hydraulic power pack.jpg
When I get this thing apart and stripped down again I will post up some pics and see what suggestions there are re possible repair of the pump, the online reading I did a few months ago when I took it apart and cleaned it out all stated that they were a throw away item but there's plenty of knowledge and experience on here so I'm very happy to be advised. My hydraulic knowledge is less than very little.
I'm managing to get some unexpected project time at present as we were planning to be camped in the outback right now but covid lockdown stopped that at the eleventh hour. The grapple did some great work yesterday but it would be really nice to get it working at a better speed.
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30th May 2021, 07:04 PM #10Golden Member
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I pulled the pump and gearbox out of the aux hydraulic power pack this afternoon. The gearbox increases RPM by about 3.1:1, the pump is a DIN mount. I'll attach a few pics here, the first one shows the internal wear in the aluminium pump casing. The part of the bore in the housing closest to the camera does not have the gears running in it, it is the part lower down where the gears run and there is a step between the two areas that is easily felt with a finger. I can't see how this could be repaired but I'm prepared to be educated.
hyd pump internal wear.jpg
A few general photos of the pump and gearbox
hyd pump drive gearbox.jpghyd pump disassembled.jpghyd pump and gearbox.jpg
I found this chart on a hydraulic sales website, it gives the DIN mount dimensions and the mounting holes on this pump matches them so at least it will be easy enough to find a replacement when I confirm what displacement to go with.
hydraulic pump DINMOUNTdimensions.jpg
I'm thinking a 25cc pump might be the go; the PTO speed on the tractor is rated at 540RPM but I don't want to be having to run the engine at full noise when using the loader as it is hard on the clutch. 25cc x 540RPM x 3.1 gives close enough to 41LPM, the spool valve is rated to 45LPM so could cope with it at max flow, 20LPM at half revs would be reasonable I think.
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30th May 2021, 07:33 PM #11Golden Member
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It can be repaired, if you really have to, by boring the pockets to clean up the wear and having over sized gears made to bring the clearance back to specifications. A friend of mine had to do exactly that to save the oil pump on a vintage car.
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30th May 2021, 08:58 PM #12Most Valued Member
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This might be close to your pump, i had a bit of a look but could not find or work out its specs, happy to pull it apart and measure the gears and shaft dia tomorrow if you like, or.......if you want a larger pump in the past i have bought hydraulic motors and pumps from this mob, https://www.surpluscenter.com/hydraulics/ postage might be a bit of killer these days, even so some of their stuff is fairly cheap. Its worth a look as they have quite a few types of pumps, heaps of gear pumps and PTO pumps similar to your pic above.
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30th May 2021, 11:44 PM #13Golden Member
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30th May 2021, 11:59 PM #14Golden Member
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If you would be happy to have a look at the internals that would be fantastic, I'll see if I can find the link where I got the formula to measure displacement- it shows what measurements to take. If it's in decent nick and a suitable size I'd be very happy to buy it from you or swap for something you can use. A drive to Healesville would not kill me either- had a family day out at the wildlife sanctuary last weekend in fact.
The surplus centre site doesn't seem to have any DIN mount pumps at all. I found an Oz seller that has heaps of them and the prices are not as bad as I had feared. https://www.berendsen.com.au/product...-2-din-mount-8
Here's a page that shows the measurements needed and the formula https://www.insanehydraulics.com/let...placement.html I think i used the second formula shown, which gave me the 19cc volume of my existing pump.
This page actually has an easier format https://www.flowfitonline.com/blog/f...ulic-gear-pump
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1st Jun 2021, 12:32 PM #15Most Valued Member
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I would be aiming for 15GPM if you could. A Toyota Huski 4SDK8 skid steer or a Bobcat 753 are around that flow and they have good cycle times. Nothing more annoying than slow loader hydraulics. The 15GPM figure is also what Massey Ferguson tractors from the 70's and 80's were running when fitted with the combining valve that combined the linkage pump flow and the auxiliary pump flow.
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