diaphram metering pump for Magneasium Hydroxide 1

[jingoluna]

What is the best set up for a diaphram metering pump that pumps magneasium hydroxide? It seems as though we keep losing our prime. As soon as you prime it -the water goes through easily but then the mag gets hung up. Also the mixer does not seem to be mixing the mag very well. The water in the mag tends to seperate out and float on top.
We have not changed our mag type nor the mixer.
Please respond with any help you can.
Thanks

 

[kenvlach]

Re your pump is losing its prime: No inherent reason except solids can sometimes make check balls not seat: clean the foot valve, clean check valves (balls) & make sure your hose connections are tight (not leaking air). Could your outlet hose be draining when pump is off & let air in that could cause drying in outlet check valve?

I used Mg(OH)2 50% slurry from Hill Bros.

http://www.hillbrothers.com/mag50.htm

for some time & the only pump problem was that the solids would settle into lower part of diaphragm chamber & harden somewhat when not used for 3 days.

"Also the mixer does not seem to be mixing the mag very well. The water in the mag tends to seperate out and float on top." -- I'm not sure of your mixing, do you turn it off? If you stop mixing, it will naturally settle. Use a small mixer & keep it running continuously. Position the mixing blade as close as possible to the bottom of the tank.

Are you maybe buying the dry stuff? If yes, try buying some 50% slurry, some brands claim they have additive to prevent settling (I couldn't find out what -- proprietary secret). I tried the dry stuff, hated the dust.

Good luck,
Ken

 

[jingoluna]

Hi Ken and thanks for your reply.

We have checked inside both the suction and discharge valves along with the diaphram itself and no drying or solids appear to be the problem.
I use DOW MHT* 50 S magnesium hydroxide. The pump is set up to turn on automatically if the pH goes below 4 at anytime and this occurs at least 6 times daily-so the pump is never not operating for more than a couple of hours.

The mixer is on contiunually. I was thinking of moving the mixer shaft to between 10 and 15 degrees off the vertical-maybe the mixing will improve.......

If any other ideas pop into your brain please submit.

Once again thanks for your response,
Mary

 

[kenvlach]

Re: "I was thinking of moving the mixer shaft to between 10 and 15 degrees off the vertical-maybe the mixing will improve"
Yes , this is a good idea. A vertical mixer in the center of a round tank creates very little mixing, just concentric laminar flow.
Also, position the blade off center of the tank, and at a height of one propeller diameter from the bottom.

Some of the mixer manufacturers give advice on mounting their equipment, e.g., try

http://www.lightnin-mixers.com/new/ECL_mixers.asp

and click on 'Brochures.'

 

[assco]

What is the NPSHA and NPHSR of your application? Is there any chance of syphoning? Does your metering pump have contour plates on the process side?

 

[jingoluna]

Hi asso,

What is the NPSHA and NPHSR of your application? I do not know what "NPSHA or NPHSR" stand for. Can you please clearify.

No contour plates.

We do not think that syphoning is the problem-we have moved the pump lower to be closer to the suction out point of the mag. vessel.

Thanks for your help,
Mary

 

[glennpan]

Jingoluna,

As KenVlach has already stated, the most probable cause for your problem is the valve balls not seating properly. You may want to consider getting spring loaded check valves which will force the balls to seat.

How is the pump mounted? Does it have flooded suction, or are you drawing out the top of the vessel? Keep in mind that you should be mounting the pump as close to the liquid as possible. Since the specific gravity of your solution is probably close to 1.5, that will de-rate the amount of suction lift that your pump can handle. This could explain why your pump can prime with water but not with your mag solution.

Glenn