General > General Technical Chat
Why is the curvature of pump rotor blades "backwards"?
IanB:
--- Quote from: NiHaoMike on October 01, 2021, 01:56:21 am ---My application needs a good amount of flow but not much pressure, quite a different case from most oil pumps with relatively low flow but high pressure. The oil is farm grade mineral oil (often used to cool amateur radio dummy loads), not specified for viscosity but much thinner than car engine oil.
--- End quote ---
For a general answer to your question, spinning blade (impeller) pumps fall under two broad categories: axial flow pumps and centrifugal pumps. Axial flow pumps are similar to a fan: they move liquid through from one side to the other like a propeller. Centrifugal pumps work a different way: they take liquid in at the center, spin it round with the blades inside a closed casing and push it out at the edge using centrifugal force (hence the name).
Axial flow pumps generally favor higher flows with lower pressure rise, whereas centrifugal pumps favor lower flows at higher pressures. So for your application, you might be better with an axial flow design, though this is not guaranteed. For example, garden fountain pumps are usually centrifugal, but they circulate water with a reasonable flow and not all that much pressure. You will need some pressure to move the oil through the various heat exchangers in your cooling circuit (this may not be trivial). Selecting a pump requires knowledge of how much flow and how much pressure rise (head) is needed.
Berni:
Impellers and centrifugal pumps are great pumps for when you need lots of flow rate at low pressures. They don't mind there output being blocked and will just keep making a steady pressure. They are easy to make because no tight tolerances are needed, nothing actually rubs and the only seal is around the drive shaft. For 3D printing this is the best design since anything in the right shape will work, having really loose tolerances just means that you will have somewhat reduced pumping performance.
The reason for positive displacement pumps like gear or vane pumps is that they can produce much higher pressures. Once there output is blocked off they will create as much pressure as you can put force into its drive shaft. For pumping lubricating oil this is usually what you want since you need to squeeze the thick oil trough tight passages into small gaps, at the same time the oil itself lubricates all tight tolerance rubbing surfaces in the pump. This makes most of these pumps not very 3D printer friendly.
Pumping mineral oil in cooling should be fine for a centrifugal pump. The stuff is reasonably thin and you typically need mostly flowrate not pressure for cooling. Tho if you had the idea to push mineral oil trough standard PC cooling waterblocks then you might need a bit more pressure (the fins in those are really closely spaced), so for that case you might have to spin your pump at rather high RPM or go for a multistage design that puts 3 or 4 of these pumps in series to build up extra pressure.
beanflying:
You should never dead head (no flow) any pump regardless of type.
If you don't circulate so fluid into and out of the pump body you will see an increase in temperature of that fluid. It is fairly common for example for a water pump left running to turn the casing water into steam vapor and kill impellers and seals.
Re Vane pumps without getting into petrochem grade tolerances are generally going to top out pressure wise at 30-60m maximum head (60-90 psi) and I doubt you will get the tolerances on a small 3DP impeller much over 10m without a lot of work post printing. Even with that said nearly all industrially plumbed options will either have an internal and or an external pressure relief valve. The little domestic and fire service jacking pumps generally don't.
If you make a low tolerance centrifugal impeller then you will be back into the realms of the junk pond pumps and a few M maximum which may or may not be an issue. Still not a fan of unspecified mineral oil and a centrifugal regardless.
jmelson:
My understanding is "forward" facing vanes, meaning concave toward the direction of rotation, are used to impart more energy to the fluid, giving higher pressure differential at lower flow rates. "Backward" facing vanes are for higher flow rates but lower pressure.
Jon
RJSV:
I'm mainly curious (gets me in trouble, fast, often):
?: I've thought, as to wing shape, it was speed, that essentially 'lowers' air pressure, although now I'm not convinced, that the reduction is (?) at rt. angles, to air flow direction?
So, having a wing 'hump' upwards shape, THATs going to produce a volume with lower air pressure,
this regular pressure (underneath) pushes UP, more than the upper surface is getting.
Part of that, is an 'attitude'; that 'vacume' doesn't exist,
(without real 'pressures' elsewhere).
Anyway, no thoughts, about a 'downward directed' air stream, is that real ?
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