I will open the pump and try to get a feeler gauge between the gears this weekend. The hydraulic pump inlet and screen on the 1500 is above the transmission oil level in the sump (topped off and on level ground.) I was having a hard time figuring out how there is so much play between the gears, but the gear to housing still looks nice. I am still having a difficult time figuring that out. There is no play on the gear shafts. All I can think of is that the plugged screen let so little oil pass, that the gear surfaces wore over a number of years. I have been told that these small pumps are very sensitive to deviation from original tolerances.
Hydraulic Pump Woes
- Thread starter samoht
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Jerry/MT
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Ok,samoht, I stand corrected. I found this on the pumpforum.com and is the best explanation I have found on how a gear pump works. Based on this explanatation, I'd have to agree with original poster that if there is a lot of clearence where the gears mesh, then the internal leakge is high and the capacity of the pump will be reduced.
How External Gear Pumps Work
External gear pumps are similar in pumping action to internal gear pumps in that two gears come into and out of mesh to produce flow. However, the external gear pump uses two identical gears rotating against each other -- one gear is driven by a motor and it in turn drives the other gear. Each gear is supported by a shaft with bearings on both sides of the gear.
1. As the gears come out of mesh, they create expanding volume on the inlet side of the pump. Liquid flows into the cavity and is trapped by the gear teeth as they rotate.
2. Liquid travels around the interior of the casing in the pockets between the teeth and the casing -- it does not pass between the gears.
3. Finally, the meshing of the gears forces liquid through the outlet port under pressure.
Because the gears are supported on both sides, external gear pumps are quiet-running and are routinely used for high-pressure applications such as hydraulic applications. With no overhung bearing loads, the rotor shaft can't deflect and cause premature wear.
This is what you were saying.
I'm never to old to learn! Thanks for the lesson.
How External Gear Pumps Work
External gear pumps are similar in pumping action to internal gear pumps in that two gears come into and out of mesh to produce flow. However, the external gear pump uses two identical gears rotating against each other -- one gear is driven by a motor and it in turn drives the other gear. Each gear is supported by a shaft with bearings on both sides of the gear.
1. As the gears come out of mesh, they create expanding volume on the inlet side of the pump. Liquid flows into the cavity and is trapped by the gear teeth as they rotate.
2. Liquid travels around the interior of the casing in the pockets between the teeth and the casing -- it does not pass between the gears.
3. Finally, the meshing of the gears forces liquid through the outlet port under pressure.
Because the gears are supported on both sides, external gear pumps are quiet-running and are routinely used for high-pressure applications such as hydraulic applications. With no overhung bearing loads, the rotor shaft can't deflect and cause premature wear.
This is what you were saying.
I'm never to old to learn! Thanks for the lesson.
Well, I stand corrected as well. I was putting everything back together once more today. I wanted to preprime the pump. There is a screw at the top of the filter housing that allows the oil to flow back to the sump for filter cleaning. I opened this and put a hose on it to try to suck the oil up from the sump into the housing. Guess what I find...A small crack at the braze between the banjo bolt housing and the pipe. ****! So I have some brazing to repair and the old pump might still work.
This is interesting though. It looks like the old pump and the new pump have very close to the same "slop" between the driven and driving gear. I didn't think a gear pump would be able to make pressure without the gears running very closely meshed.
This is interesting though. It looks like the old pump and the new pump have very close to the same "slop" between the driven and driving gear. I didn't think a gear pump would be able to make pressure without the gears running very closely meshed.
JC-jetro
Elite Member
That is exactly what I was saying, the key is no "slop" between gears' tips and the pump case interior. How much did you end up buying the new pump.
JC,
Jerry/MT
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I guess as long as there is line contact on the gear teeth when they are in mesh an it's running it still shouldn't leak much there. They could only leak when they are not touching. Having some slack doesn't mean they are not touching at some point because that slack should be taken up as they are driven to turn in one direction only. I suppose with enough wear, they could get to that point.
The critical leakage path is on the side plates. So if the slop is fore and aft (in and out?) on the shafts then you' ll have a leakage problem.
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The pump was a painful $1600. I opened the package, but didn't install once I saw the crack in the suction line. The old pump sidewalls still look nice. The fact that the new pump has some play between gears makes me think that I might not need the new one. I am going to get the suction line repaired and see if the old pump makes pressure. Its a small crack on the inside of the joint between the suction pipe and its boss for the banjo bolt. Couldn't see it until the line was all the way removed.
Good news is the injectors tested fine. Thats $450 less that I would have to spend on this hole in my pocket.
Good news is the injectors tested fine. Thats $450 less that I would have to spend on this hole in my pocket.
Since there is "slop" in the new pump as well, I am guessing that the critical tolerance between gears is the gap between the end of the tooth and the surface it mates to. Not between the touching surfaces of the gear teeth.
barbqranch
Silver Member
The tip of the gear should not touch the bottom of the other gear, otherwise when things warm up, they would interfere. I expect that since one is driving the other at all times against a fair amount of pressure (ie. hydraulic pressure difference between the input and output) they are always in contact and so minimizing the leakage though that route.
Jerry/MT
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No I think the critical point is the place where the gears contact each other. That should be a straight line across the gear teeth to minimize backflow throught the gears. If you look at JC's pictures of the gear pump on the first page of this thread you can see where the one gear tooth is between two gear teeth. That contact point ( really a line on the face of the gear teeth) on at least on e face of the gear) is the sealing surface of the gears.
The tips of the drive gear teeth are not supposed to touch the bottom of the space between the driven gear teeth.
