View Full Version : Throttling Flexible Impeller

06-17-2014, 05:06 AM

Im just about to purchase some flexible impeller pumps for the brewery and want to know how I can throttle the flow rate. I know that you can get VSD controlled pumps but was wondering if you can just restrict the suction side (not completely as to maintain lubrication of the impeller), as I have been advised that the discharge side cannot be restricted due to pumps being positive displacement?



06-17-2014, 12:52 PM
You can throttle either side, but it will make the impeller wear faster. VFD is the best way to modulate pump speed on an impeller.

When you slow the output side, the flexible part of the impeller gets slowly torn from the core. When you throttle the input side, the pump cavitates and the sealing edges of the impeller vanes start to chip away and degrade. A magnetic coupling or clutch will prevent this, but adds a lot of cost to the pump. Far easier to buy a VFD from Automation Direct and wire it up, problem solved.

06-17-2014, 12:53 PM
Typically you never throttle the inlet of any pump system.
VFD is likely your best bet but check with a pump specialist.
There are some known on ths forum who deal in pumps.

06-17-2014, 05:54 PM
Never throttle a pump suction. And never throttle the discharge of a positive displacement pump. Buy a VFD if you need variable flow on positive displacement pumps. Why flexible impeller for variable flow rates?

06-18-2014, 07:59 AM
If you want to control the flow use a VFD, especially on a flexible impeller pump.

06-26-2014, 01:29 AM
Thanks for the input. Im having dramas finding flexible impeller pumps rated at wort temperatures here in Australia for a reasonable price (Under US$5500...). The reason I was interested in the flexible impeller style pump was due to the self priming capabilities, though I know you need to provide some lubrication on startup. Either way, it looks like a centrifugal pump is going to be the way to go. Is anyone able to advise me if the following pump is suitable if the viton seals are added:


Im happy to add VSD's to the pumps but even getting data on whether they can be wired in delta is difficult (I only have single phase 220v available).



06-26-2014, 01:53 AM
That looks more like something I'd use for glycol or possibly HLP, not foodstuff. Note how dairy/brewery/food/pharma isn't mentioned as typical applications? Threaded inlet/outlet gives that away. Stay away from threads. Can you not find a pump from a dairy/brewery/food/pharma engineering firm? A quick search shows that Waukesha pumps are available. Or try JEC pumps. Or Alpha Laval or APV. Use a keyword of "sanitary"! Good luck!

06-26-2014, 07:29 AM
The pump we use coming out of the kettle is a Waukesha C-216.
This would be a pump location that could benefit from a carefully applied VFD in my current view.

06-26-2014, 11:27 AM
Hi Filby,

We have shipped quite a few pumps to Australia and for a lot less than $5000 and yes they will run on your 220 volt single phase 50 hz power.

Send us an email and we can give you local references and set you up nicely

07-07-2014, 12:08 PM
Keep in mind that most modern VFDs are capable of converting single-phase to three-phase, so you can still have the convenience of adjustable speed pumps.