So you need a new brewery pump, but you don’t know what size, speed and horsepower. Pick a pump that’s too small, and you’re not going to have the pressure you need (maybe even not enough to overcome the hydraulic resistance - aka your system head). Pick one that’s too big can result in cavitation, damaging your pump, lines, and your beer.

First, gather some numbers.

• Flow Rate – How much do you want to move in how much time? For example, let's say you want to transfer 20 barrels of wort in 20 minutes. At 31 gallons per barrel, that’s 620 gallons in 20 minutes or 31 gallons per minute.
• Discharge head (or “lift”) – Simply put, how high do you need to lift the wort? The height of the fermentation tank plus any additional lift. (i.e. Are your tanks elevated on a platform or on the second floor?)
• Back Pressure (also known as pressure drop) – What is stopping that wort from moving? Valves, heat exchangers, and filters all create backpressure. Determining how much can be found in different ways. The nameplates of your heat exchangers should list it. Filter suppliers will have it for different elements. Add all this together and you know your backpressure.

Next, add together your back pressure and discharge head to get your total head. You may need to convert back pressure from PSI to feet/head (which you can do by multiplying it by 2.3). Finally, on your pump curve locate the point corresponding to your flow rate and total head.

In the old day you'd plot that on a pump curve, then choose a pump that suits it (or change/trim the impeller on a pump to suit it). Fortunately, today most of the pumps used are connected to Variable Frequency Drives (VFDs). These curves have one impeller size and multiple speeds.

This curve shows a 6" impeller pump at various speeds.

You can see, you would get the good performance with a full 6" impeller but at 1350 rpm.   

Or you could do the same application with a 4" pump at 2200 rpm

In my opinion, variable frequency drives are the best thing since sliced bread, especially for pumps. If you want we can generate these multiple speed curves for you and find just the right pump for any application.