Pumping gear profiles

Good answer.Thanks.

Yes, the basics are clear.One is designed for max flow while the other is for efficient transmission of torque (and therefor power).

Different manufacturers use different profiles ; David Brown,UK uses herringbone gears with a high helix angle to achieve phenomenal rate of flow in very compact pump dimensions.Yet the pump runs very quiet at 1450 rpm!

Whether any recommendations/studies are made for pumping gear profile was of interest.

The herringbone gear has two reasons:

- no axial load

- lower flow pulsation

it has nothing to do with the flow optimisation which is only funtion of the inter-teeth area.

Reminds me- the pump i opened the other day (for maintenance) - had the teeth petal shaped ie root thickness reduced as you pointed out . gears anyway I know the roots are always thick to account for the bending stress and the undercuts are avoided. Also the pressure angle is kept on higher side.

Thet means (and it is clear) that the transmission gears are designed with the involute pressure angle (as I remember 25 degress in almost all our gears) to have the strong root and avoid the tooth undercut.

The Pumps must have more flow capacity than the power transmission ,and the root is reduced due to low pressure angle- since here the power transmission os not the prime importance.

I am surprised that you mention 25° as common tangent angle. A bigger angle reduces the overlap and is only used in involute shaft splines profiles where it goes up to 30°. In power transmission the very common angle (standard my I say) is 20°.

Checked up-back, most of our involutes in transmission gearing are 25 deg pressure angle, a few are 20 deg of course . Designers prerogative. Must now research on his intentions

I shall look as well and it will be great to understand his reasons.

I expect an exchange of informations.

What kind of transmissions do you use : power, ratios, speeds ?

If speeds are low and torques important then it could be justified by a stronger root. same if ratios big and small gear with low number of teeth.

power (all combine to same ) - but seriously it is transmission of power from heavy to very heavy at low speed.

May be that is the reason of the high angle (we as usual land up with the high root and thereby the better root strength isn't it ? ) my guess.

being at the low speed means the noise may not matter much.

Of course the higher speed ones I checked up are at 20 deg.

Very high speed (5000+) - i have to trace the data - but they too may be at 20 deg - these are also power transmitter - GT to generator (so from 10s to 100s MW)

For gear pumps you are more likely to find 25 deg Pressure angle than 20 deg as you need low number of teeth in the mesh. In 20 deg PA the minimum number of teeth that can be cut without root under cut is 18 whereas in 25 deg PA it is twelve teeth. Below this you will have to give a profile shift (Long Addendum) to avoid u/cut. With profile shift you can go up to 10 teeth for 20 deg PA, whereas I have designed 6 teeth with 25 deg PA with profile shift. I have seen a gear transmitting power as low as 4 TEEETH!! This was in a Miele Roller Iron. The Germans and Swiss will do the unthinkable but not to be tried by mere mortals