Gearpump Suction Side Question

[Dudely7]

Hello all. I've browsed these forums before, never posted until now.

My question is concerning the suction port of external gear pumps. On most, I notice there is a certain degree cut out of the gear wall,lets say 3/4" for a 3/8-1/2" port, thats typically equal on the pressure side and suction side.

Typically the gear tooth makes contact at almost 6 o'clock on the suction, and a tad after 12 o'clock on the pressure.(looking at the left cog) I'm curious how much the amount of wall contact influences the pressure capabilities or other characteristics of the gear? Attatched is an example. I am asking if the left gear will be as powerful and effecient as the left gear? Or does each tooth sealing against the wall surface provide an extra amount of pressure holding power? And before you wonder, yes there is a reason I want to be able to port gears this way!

Sorry for such an immature question. I'm no fluid expert! Any help or insight is greatly appreciated.

 

[MikeHalloran]

One leakage path comprises the clearance between each tooth tip and the outer perimeter wall. ... remembering that there are several such leakage paths in series, one for each tooth tip that's adjacent the wall simultaneously, and there are two such leakage path chains.

Another leakage path comprises the clearance between tooth faces in the central mesh; there is just one such path, but its geometry is constantly changing.

Wait, it gets worse; in parallel with all of that is the clearance between the planar faces of the gears and the planar faces of the housing end caps, i.e. two capillary slots whose major planes are parallel to the paper.

So, you can probably port the gear housings as you describe, but you shouldn't be expecting miracles, and you may not even be able to measure the difference it makes.



Mike Halloran
Pembroke Pines, FL, USA

 

[hydtools]

I think the right hand pump illustration may not fill as well as the typical pump shown on the left. The suction port needs to fill the gears where they begin to separate. The parting gear teeth create an increasing volume that needs to be filled. The right hand pump would have flow going back and forth as the flow tries to fill the separating teeth and then flow must travel back from where it came to continue around the outside of the gears. By the time the tooth spaces get to where you show incoming flow they should be already full of fluid. Looks like an inefficient back and forth flow of fluid.

Tooth tip clearance and end face clearance both play a role in controlling leakage.

Ted

 

[Dudely7]

Thanks for the replies. Gives me somthing extra to think about. The 'island' in between the suction ports could radius up to make contact with the teeth in between the ports if that means anything to anyone.

What we're wanting to accomplish is: having a gear identical or very similar to the left gear in performance characteristics,but to be able to put large,increasing amounts of pressure on the reservoir, without the oil working against the gear. ie: putting 400psi on the oil tank will have the oil pushing against the gear in both directions.I think would push the gear backwards with no load on the pressure side.. If this gives anyone any ideas, don't hold back!

Would just like to have some insight before calling up a manufacturer.

 

[hydtools]

With no pressure on the pump outlet and with pressure on the tank/pump inlet will cause the pump to turn in the pumping direction, not backwards, and act as a motor driving or trying to drive your prime mover whatever it is.

Use the common pump configuration. No sense in reinventing the wheel. This will then not require a special pump with your proposed inlet configuration.

Be aware the pump shaft seal must be able to withstand whatever pressure is on the inlet port in either case. Up to your tank pressure of 400psi. Most pumps have a low pressure shaft seal, 50psi or less, unless you specifically request higher pressure capacity seal.

Ted

 

[Dudely7]

I'm not expert or even a novice,but I know for a fact, if I went and plugged a complete pump to the inlet of the gear, it will shoot fluid straight through it.. BACKWARDS. what other reason would it have to make 2 90* turns, follow the half circles, and make another pair of 90* turns when it could go straight through ,push a couple teeth, and straight out?

In a working system, the pressure works against the gear. The pressure in the tank isnt whats desired, its a bi-product of somthing else. But yes we do need a certain amount of pressure to get rid of the suction and cavitation problems. We are already useing an accumulator on the resevoir,but the pressure still works against the gear over 50psi. There is no pressure leakage, you physically hear the motors bog. We are turning the gear at speeds in excess of 10,000 rpm, at 6-8 cubic cm/revolution, with several thousand pounds of load. With the pump running, as soon as the pressure is put on the return tank, the gear slows CONSIDERABLY.

 

[hydtools]

I guess I don't understand your system. The below references illustrate how fluid pumps and motors work. Flow travels around the gears, not through the center tooth mesh and straight out. Perhaps the increase in tank pressure increases the squeeze on the pump shaft seal, thus increasing the load on the pump shaft and bogs the motor.

A system schematic would be helpful at this pont.

http://www.hydraulicspneumatics.com...ors/Article/True/6427/MotorsActuators#scene_1

http://www.hydraulicspneumatics.com/200/FPE/Pumps/Article/True/6401/Pumps

Ted