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Filter Press

nyoba2in — Tue, 23 Sep 2008 04:00:17 +0000

Filtration

General Considerations

Filtration is the separation of solids from liquids by forcing the liquid to flow through a porous medium and depositing the solids on the medium. A filter aid is a finely divided material which, when added to the liquor to be filtered, helps control flow and solids removal. The septum, usually screen or cloth, serves principally as a support for the cake. The filter aid forms a porous layer on the septum and thus the filter aid is the filtering medium that traps the solids being removed and prevents them from blinding the septum. Filter aid filtration is mechanical, not chemical in nature. Irregularly shaped particles interlace and overlay in a fashion that leaves 85 to 95 % voids or open spaces. These voids form billions of microscopically fine interstices between the filter aid particles. The size of these openings is so minute that the unwanted solids are strained from the liquid. The vast number of openings compensates for their small size resulting in fast flowrates and brilliant clarity.

Good filter aids are light in weight, chemically inert and form high porosity filter cakes to maintain free flow of the liquid. The structure of the particles must be such that they will not pack too closely. This not only permits high initial liquid flow but also provides pore spaces to trap and contain the filterable solids and leave a high percentage of channels remaining open for flow. Particle size distribution must be tailored to permit precoating on coarse wire and yet give the desired flow rate and clarity. Dicalite perlite, diatomite and cellulose filter aids meet these criteria. They are available in a variety of grades to suit the solids removal requirement of any application.

Gear Pump Design

nyoba2in — Thu, 18 Sep 2008 09:55:28 +0000

I got some one asking :Hi. I’ve been asked to design an external Gear Pump from scratch. I’ve found the basic information about how the pumps work, but haven’t found a “plug in the the volume output you want, and out pops the gear sizing” type of information. (I’m rusty on my gear design skills, so it may be my fault…) I’ve been given a flow rate to meet, and have been requested to minimize the volume that the pump takes up. Any help would be appreciated.

And others answered:

t’s probably best if you do this from scratch, and not use a plug and chug. I say this because you need to learn a few things as you go.

We don’t know what your volumes are so I am going to write a generic procedure. You can Email me questions later. I’ve designed many positive displacement pumps from scratch.

1) You need to draw a gear. Start with the easy; Use a solid model CAD to draw an involuted gear tooth. If you need help on how to do this, let me know.

Understand that your volumetric calculations are only going to be ball-park. There are many factors that will determine the actual output. You need to remember during your design, that you may have to make your gear set longer or shorter to hit your target. Be sure to leave room in your housing to lengthen or shorten the gear set.

2) Once you have two gear teeth modeled, measure the surface area with the CAD measurement tools. Measure only one side of each tooth, the area that the fluid will occupy. From the centerline of one tooth to the centerline of the other tooth.

3) Measure the arc length from the centerlines. The tip path.

4) Calculate the volume.

5) Determine the RPMs and see how close you are.

6) Need more? Lengthen the gear set; Need less? Shorten the gear set.

7) Now, if you are way off, select another gear set to model.

It may take you a while to draw your first set of gears, once you get the hang of it, you will have a library of gear sets. You will probably be able to go from 0-3 gpm with one gear set; But, after that you may need to go to larger gears for more volume, lengthening and shortening the gears as you go.

It’s a game of long small diameter gears and short large diameter gears.

Once you have a gear set designed, it’s time to make the housing.

Then we talk about slip, seals, tolerances, material.

Charlie
www.facsco.com

and other gave a formula :You can estimate spur gear pump flow with the following formula. This will allow you to run through some sizing options before starting gear design.

G=(N*W*C*(D-C))/73.48

G=pump flow(gpm)
N=speed (rpm)
W=gear face width (inches)
C=center distance between gears (inches)
D=gear OD (inches).

This is from a very old Design News article. You will need to apply an appropriate volumetric efficiency to account for internal leakage.

That’s all. Hope will contribute something to you

nyoba2in — Mon, 15 Sep 2008 16:09:50 +0000

Loh ko loyo?