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  #1  
Old 11-11-2011, 05:44 PM
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Explain hydraulic pump?

Rebuilt the power steering pump in my 94 Landcruiser today. Pump is a vaned pump. Main pump element with movable vanes spins in an elliptical chamber. Vanes move in or out depending on where they are in the ellipse. Can someone explain how this operates and the purpose of the ellipse? I've seen rubber vaned water pumps spinning in a circular chamber before and I think I understand how they work. This ellipse business has me mystified. What's the point? Variable pressure? More pressure? More power?

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Old 11-11-2011, 05:52 PM
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Originally Posted by kerry View Post
Rebuilt the power steering pump in my 94 Landcruiser today. Pump is a vaned pump. Main pump element with movable vanes spins in an elliptical chamber. Vanes move in or out depending on where they are in the ellipse. Can someone explain how this operates and the purpose of the ellipse? I've seen rubber vaned water pumps spinning in a circular chamber before and I think I understand how they work. This ellipse business has me mystified. What's the point? Variable pressure? More pressure? More power?
The PS pump on my F-150 is going bad, are they easy to rebuild?
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Old 11-11-2011, 05:57 PM
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Yes. I really only replaced all the o-rings. It was leaking. There was a DIY on IH8MUD. Took about 5 hrs from start to finish.
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1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
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1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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Old 11-11-2011, 06:00 PM
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Originally Posted by kerry View Post
Yes. I really only replaced all the o-rings. It was leaking. There was a DIY on IH8MUD. Took about 5 hrs from start to finish.
Sounds easy enough, I'll rebuild the F-15 ps pump myself. Thanks Kerry.
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Old 11-11-2011, 06:56 PM
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I tore down a heavy truck PTO hydro pump many years back that had a series of sections. each section was a repeat of the one in front & behind. The vane chambers were kind of elliptical and also angled.
I had figured the shape of the chamber corresponded to where the oil entered & exited, like it exited on the wide side of the chamber with more volume, or vice versa with more pressure? Maybe?
Been quite a while now. I'll ask our heavy equipment mechanic to explain it to me when he comes in a couple days, and report back.
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Old 11-11-2011, 06:57 PM
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I don't have time to go into depth, but I think the main thing you're looking for is that the water pump type pump, with an impellor, is really only good for creating flow. It's a non-positive displacment pump and generally speaking, only good for ~100 PSI. The fluid is drawn in the inlet, and pushed around and out the outlet. But if there is too much resistence at the outlet, say, too much pressure in the system already, the fluid won't go out the outlet, and will just stay circulating in the pump.

The vane pump is a positive displacement pump. turn the shaft while you have it apart and you'll see the "chamber" (the space between the vanes) grow and shrink as the rotor turns. It grows as it passes the inlet, allowing fluid to be drawn in, and then shrinks when passing the outlet FORCING the fluid out. This type of pump can generate much higher pressures, usually several thousand PSI. If perchance the fluid in the system (at the outlet) is already too high a pressure already, there is not option for the fluid to stay in the pump, either the pump stalls (doesn't turn any more) or something gives (think big oily mess). That's why these systems have release valves.

MV
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Old 11-11-2011, 07:22 PM
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Originally Posted by The Clk Man View Post
Sounds easy enough, I'll rebuild the F-15 ps pump myself. Thanks Kerry.
Dont do it...if you think it's bad because it makes some groaning, that's normal for a Ford PS pump. If you change it, the replacement will groan as well.

I'd swap for a Saginaw pump instead...you'll have to change brackets to make it work, but it's the ONLY way to get a quiet pump.
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Old 11-11-2011, 07:31 PM
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sliding vane pump

Here is how it works.
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Old 11-11-2011, 07:53 PM
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Thanks for that link. It got me to this one which looks very similar to the power steering pump although a lot bigger:

Hydraulics_how a vane pump works - YouTube
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1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
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1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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Old 11-11-2011, 08:00 PM
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Originally Posted by jplinville View Post
Dont do it...if you think it's bad because it makes some groaning, that's normal for a Ford PS pump. If you change it, the replacement will groan as well.

I'd swap for a Saginaw pump instead...you'll have to change brackets to make it work, but it's the ONLY way to get a quiet pump.
Thanks, It's been groaning for the 4 years I have owned it.
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Old 11-12-2011, 10:50 AM
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It has to do with where the port is located in the elipse. As the vane comes by the port the volume begins to decrease in the second half of that side of the chamber. The decrease in volume, just as in a piston pump, pressurizes the fluid.
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Old 11-12-2011, 11:09 AM
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Originally Posted by The Clk Man View Post
Thanks, It's been groaning for the 4 years I have owned it.
With F-series trucks, if the fluid level hasn't dropped, then the pump is ok, generally.

I found this out the hard way, by changing the pump three times on my F-250, with no change each time. FTE, a Ford truck site, has great information on the upgrade to a Saginaw pump.
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Old 11-12-2011, 03:22 PM
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Originally Posted by LarryBible View Post
It has to do with where the port is located in the elipse. As the vane comes by the port the volume begins to decrease in the second half of that side of the chamber. The decrease in volume, just as in a piston pump, pressurizes the fluid.

Got it. Now I understand.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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