Metering pumps? 1

[KWTPOP]

I was told about a new style metering pump where the chemical never touches the inside of the pump. A boot style drive compresses or stretches a larger diameter hose inside to create the back pressure to pump the liquid. Anyone have information on this style pump and who manufactures this type?

 

[ccw]

Hi KWTPOP,

I think you are referring to peristalic pumps. Look at

http://www.periflo.com/

and see if that is what you are looking for.

 

[KWTPOP]

Hi CCW.

Great information. Just what I was looking for. The water treatment plant where I work is replacing the metering pumps for lime and polymer next year and going with the peristalic pumps. Any thoughts on these, good or bad?


Thanks,
Rob

 

[ccw]

Hi KWTPOP,

First let me work on my spelling. Is it peristalic or peristaltic? Probably the latter. Google responds to both. There are several mfg and distributers. These pumps work very well provided there is material and flow compatibility between media and the hose, and the units are used within their published limitations.

 

[bulkhandling]

Interested to know what are the current metering pumps and what are the problems with them.

For lime metering, most of the applications have quite a few dosing points, so a centrifugal pump with recirculation line is often used for the pumping and a pulsation valve at each dosing point is used for the metering. The flow of the pump is normally much higher than the required and a pipe normally 2" or 3" is used since scaling on pipe wall is a concern for lime. The pump is normally sealless such as Wilfley dynamic sealless pump.

For polymer metering, progressive cavity (helical rotor?) pump is often used. progressive cavity is also positive displacement pump.

Hose pumps (peristaltic)are often used for metering purpose. A adverse comment on the hose metering pumps is that the volume per revolution does not repeat well enough after the hose is pressed for a period of time. So you may have to calibrate the pump again if your dosing is required to be accurate. Another thing heard from the site is that some hose was cut by some sharp solids in the fluid, but that must be a special case since many people put a strainer at the suction pipe.

 

[moltenmetal]

Peristaltic pumps have one main Achilles' heel: hose life. Neither of your fluids are particularly challenging from a materials selection standpoint, meaning that you can use a very elastomeric hose material like silicone or oil-filled EPDM or natural rubber. But do not assume that these hoses will last forever- they will not. They do burst and they do require periodic maintenance. As required discharge pressure increases, hose life drops.

Progressive cavity pumps as an alternative are not a maintenance-free item unless they're pumping something lubricious like floc polymer.

 

[pumpkind]

If your main objective is dosing - peristaltic pumps are not better than metering pumps at that.
If it is for transfer duty, then they might be considered.
It is probably also a question on when you want to spend the money :
Metering pumps have a large initial cost and relatively reduced life costs.
Peristaltic pumps are just the opposite - initially they seem cheap - until you start ordering spare hoses that is.

 

[KWTPOP]

Thanks for the responses. Right now we are using Wallace & Tiernan Series 44 pumps for lime, polymer and alum. The pumps are 25 plus years old and don't pump at the set rate consistantly enough. The engineer that oversees the mechanical running and upgrades is looking to put in peristaltic pumps. The lime slurry pumps currently have flush cycle systems connected to them. I would be happy with new pumps though. This is the first real upgrade since the plant opened.