In a recent thread documenting results of my project to bench-test electric fuel pumps, I promised to add photos and commentary on the internals of the pumps I tested. When I tried that, it made the opening post too large. Later, I added it as a reply in my own thread but It has received few views, so I thought it worthy of a new thread of its own. I’ve also added a link to a video showing the Walbro gerotor in action and some other commentary that you might find interesting.
Of the three pumps tested, I cut up the Walbro GSL395 and the Delphi supplied to me by Airflow Performance, which are quite different internally. A Walbro tech told me that all of the GSL-series pumps would be very similar inside, with the differences being in gerotor thickness, motor windings, etc., so I decided to keep the winning GSL414 intact as a spare and for demo-ing my test rig at the next EAA chapter 124 meeting here in Santa Rosa, CA.
Major differences between the Walbro and the Delphi, which is OEM on several autos, include an all-steel outer body on the Delphi that is more than 1/10” thick to allow machining in stop-recesses at both ends. It also has plastic inlet and outlet bodies as compared with an integral aluminum inlet and a precision machined cast aluminum outlet of the Walbros. The steel shell contributes to the huge difference in weight (795GM vs. 454GM).
The most significant differences lie within the pump section itself. The first two photos here are from the Delphi pump. On top is a detail of the actual pump section, which is a screwed together sub-assembly as seen in the top photo. With the cover removed you can see the roller vanes captured within a wheel directly driven off a set of five plastic fingers mounted to the end of the motor armature. Centrifugal force keeps the rollers in contact with the fixed, eccentric outer ring, so volume of the cavities between rollers grows and diminshes with each revolution.
The following shots show the Walbro GSL395 outer aluminum housing and thin-walled steel inner housing that carries two permanent magnets inside. The white plastic body to the far left houses a fairly fine-mesh, full cross-section filter screen and a relief valve for internally recirculating pump output back to the pump inlet in the event that output is locked. The Delphi is absent both of these features.This relief valve should never operate in normal operation of a proper installation. The screen is the one thing I don’t like about the Walbro’s because it is NOT SERVICEABLE, suggesting that a low-resistance, large-section, screened pre-filter MUST be used(Walbro recommends 40 microns). The pre-filter installed in my test rig was 120 microns, and the post-filter was 40 microns. One decision I will face is wether to provide each pump in my installation with a pre-filter or let them share one.
The second photo details the gerotor, a marvel of simplicity that has a very reassuring feel when rotated manually, and I’ve included a link to a video of it in action. The inner and outer gear profiles are ingenuously ground so that each lobe maintains precise contact with its neighbor at all times, creating sealed cavities that grow and shrink in volume when rotated. With this design, the inner planetary gear is concentric and also directly driven by four plastic fingers at the end of the armature. The outer ring planetary is driven by the inner gear to rotate within an offset bushing. Notice in the video that the inner gear has eight teeth, and the outer gear nine, so with each rotation the outer ring retreats by one tooth position.
Here is the link to the video, just click on the image below. After viewing, you can slide the white button at the bottom to slow-motion scroll forward and reverse. There is some very elegant geometry going on here!:
Photos of the Chinese-made Airtex pump that I disassembled for an earlier thread, similar in design to the Delphi, can be seen here:
https://media.fotki.com/2v2EcjsWgxBELK5.jpg
And to illustrate just how far off some of the published data are, compare the chart I derived for the GSL395 below with the official version below that!:
My GSL395 chart
Official GSL395 chart:
I’m trying to contact Walbro tech support to discuss this and will report back here.- Otis
Finally, the previous thread in this series can be seen here:
http://www.vansairforce.com/communit...hlight=Anatomy
Fuel pump innards, Anatomy of a pump, part 4-
Linear Mode
