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Author Replies
Happy Feet
02/16/09 05:11 PM  
Slowing Pump Speed
I have added a pump to my brewing set up. It operates at one speed, and I would like to slow it down. It's 115 volts 50/60 hz. I was thinking of a dimmer switch or some other form of rheostat. Has anyone done this? If so, any suggestions? I have been trying to slow the flow rate by restricting with the valve, but the pumps sounds like it labouring.

Thanks!

Baums
02/17/09 11:41 AM  
Re: Slowing Pump Speed
What kind of pump is it?
petec
02/17/09 06:36 PM  
Re: Slowing Pump Speed
Atleast with mag drive pumps, its best to throttle on the output of the pump to keep from starving it.

petec

Tom from Raleigh
02/17/09 10:33 PM  
Re: Slowing Pump Speed
I think you're better off to restrict the flow of wort with a ball valve than futz with the current to the pump. I have a ball valve on the output side of my pump to regulate the flow.

Happy Feet
02/18/09 07:58 PM  
Re: Slowing Pump Speed
To answer Braums question, it a GRI pump and it is not a mag. It was pulled out of a coffee vending machine and I got it for free :) I added a cord and it works just fine. I pulled it a part, cleaned it, made sure the seals were not leaking and tested with hot liquid, all works.

When you mention restricting the flow, I can do this from the kettle (ball valve). Or are you refering to restricting flow on the other side... I guess that would be the output. Why would this be best?

Adrian
02/19/09 06:11 PM  
Re: Slowing Pump Speed
Mr. Feet-

I'd wager you'll want to restrict the output to prevent pump cavitation.

Happy Feet
02/20/09 12:06 AM  
Re: Slowing Pump Speed
What is pump cavitation?
Tom from Raleigh
02/20/09 08:30 AM  
Re: Slowing Pump Speed
Cavitation is turbulence in the flow of the liquid caused by air bubbles, I think. The ball valve for my March pump is on the output side. I have another ball valve on my kettle.

Having a ball valve on the output side gives you the ability to regulate flow which makes it easier to prime the pump.

If you're sufficently handy with electricity, I don't know why you couldn't put a dimmer in the line to regulate the speed, but then I don't know much about the science behind what I'm saying.

Baums
02/21/09 11:10 AM  
Re: Slowing Pump Speed
Sorry, what I was asking is what is the pump design (centrifugal, diaphragm, flex impeller, etc). How to throttle back the pump is hugely dependent on this.

Some positive displacement designs should not be controlled via outlet restriction.

Many AC pumps should NOT be controlled by a dimmer.

Happy Feet
02/21/09 11:43 AM  
Re: Slowing Pump Speed
Hi Braums,

It's a centrifugal pump. I did a search on the make and model number and it confirmed this.

Baums
02/23/09 12:51 PM  
Re: Slowing Pump Speed
> It's a centrifugal pump

A good bet then is restriction of the outlet, and folks have mentioned. (Restricting the inlet may lead to cavitation which can damage the pump.)

A dimmer switch is not a good way to go--this pump is not designed to be controlled by voltage amplitude change. Properly controlling speed electrically would require changing the *frequency* of the incoming electrical current.

Why do you want to slow it down?

Happy Feet
02/23/09 08:20 PM  
Re: Slowing Pump Speed
O.k. restriction of the outlet then. If I restrict on the outlet to slow speed, will it not put back pressure on the pump? Is this o.k.?

Thanks,

Baums
02/25/09 09:39 AM  
Re: Slowing Pump Speed
If it's a centrifugal pump it's probably the best option and should be okay. If you're throttling it WAY back, like 90%, I really don't know for how long that's okay.

One side question I just thought of is whether the pump is rated for continuous duty (especially with hot liquids). Many pumps are rated only for intermittent duty over time/temp and a coffee vending pump could be an ideal candidate for that kind of cost-saving--you might want to see if you can get the manufacturer's sheet.

 
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