Gear Pump 1

[1ton]

Hi, Can someone tell me the advantage between an internal and external gear pump. I am using it to pump diesel for one tank to the other. What would be the selection criteria between a internal gear and external gear pump ? Cost ? Maintenence ?
Thanks

 

[MikeHalloran]

There are many more than two types of gear pumps.

Pick the cheapest one that meets your criteria.



Mike Halloran
Pembroke Pines, FL, USA

 

[hydromech]

External gear pumps are generally better for low viscosity fluid such as diesel. External gear pumps tend to be less efficient.

The better efficiency comes at a cost though...

Do what Mike suggests...

Hydromech

 

[25362]

Hydromech is right. You probably refer to rotary pumps timed with internal or external gears. There are also untimed "screw" pumps in the market.
The Pump Handbook by Karassik et al., McGraw-Hill, has a full chapter on screw pumps. My advice: read it.

 

[ccfowler]

1ton,

I will presume that your question refers to external tooth pumps vs. internal tooth pumps rather than whether external timing gears are involved.

Usually, pumps configured with two meshing external spur gears as the pumping elements offer the lowest initial price, and they are usually reasonably durable. One characteristic of this arrangement is relatively abrupt opening and closing of the void spaces that transport the pumped fluid from the low pressure region to the high pressure region. This can result in significant local accelerations of the fluid and significant noise from the high frequency pressure pulsations.

Pumps configured with a combination of meshing internal and external gear teeth such as "Gerotor" and "cresent" pumps provide less abrupt opening and closing of the void spaces. Because of this, local accelerations of the fluid are more gentle, the NPSHr is lower, and the operating noise level is lower. (I've experienced cases where "Gerotor" pumps replaced "cheaper" external gear pumps and the noise level dropped so dramatically that the pump ceased to be the dominant local noise and the new pumps were functionally silent--their operation simply could not be heard.) These types of pumps are likely to be more sensitive to damage from solid debris in the pumped fluid, and they are more sensitive to the pumped fluid for lubrication.

With reasonable filter protection for the pumps, all types can provide reasonably trouble free service. If noise is a concern, then I would use a "Gerotor" style pump.

 

[1ton]

Yes ccfowler you are right, thanks for the information on gerotor and cresent pumps.

I am sure some of us have not given much thought about gear pumps. I believe the general reason for that, it is cheap , small and insignificant.

Thanks ccfowler, I have learn a new word today, "Gerotor is a study in simple kinematics: the rotation of two conjugately formed profiles, whose centerlines are positioned at a fixed eccentricity" One star for you.

Any other point to consider apart from, which is the cheapest, quietest, efficient? Anybody has anything to contribute?

Thanks
1ton